is Enough? How Much Habitat Second Edition A Framework for Guiding

is Enough? How Much Habitat Second Edition A Framework for Guiding
How Much Habitat
A Framework for Guiding
Habitat Rehabilitation in
Great Lakes Areas of Concern
is Enough?
Second Edition
To order printed copies, contact:
Environment Canada
Canadian Wildlife Service
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Tel: (416) 739-5830 Fax: (416) 739-5845 E-mail: [email protected]
This guide is summarized in a fact sheet, How Much Habitat is Enough?
An electronic version is available at www.on.ec.gc.ca/wildlife/publications-e.html.
Canadian Wildlife Service publications are available on-line at the following URL:
www.on.ec.gc.ca/wildlife. All publications are available in both HTML and PDF formats,
for the purposes of accessibility and convenience.
This guide was printed on recycled paper, and printed with vegetable-based inks.
Published by authority of the Minister of the Environment
© Minister of Public Works and Government Services Canada, 2004
Catalogue No. CW66-164/2004E ISBN 0-662-35918-6
Aussi disponible en français sous le titre : Quand l'habitat est-il suffisant?Structure d'orientation
de la revalorisation de l'habitat dans les secteurs préoccupants des Grands Lacs. Deuxième édition.
Funding for How Much Habitat is Enough? A Framework for Guiding Habitat Rehabilitation in
Great Lakes Areas of Concern (Second Edition) was provided by the Great Lakes Sustainability
Fund and Canadian Wildlife Service – Ontario Region.
Photo Credits:
Front cover main picture: John Mitchell
Front cover: Great Blue Heron - Eric Dresser, Grass Pink Orchid - Douglas A. Wilcox, Muskrat - Eric Dresser,
Tulip tree leaf - CWS, Water Lily - Eric Dresser, frog - John Mitchell
About the Canadian Wildlife Service
The Canadian Wildlife Service, part of Environment Canada, manages wildlife matters that
are the responsibility of the federal government. These include protection and management
of migratory birds, nationally-significant habitat and endangered species, as well as work on
other wildlife issues of national and international importance. In addition, the Canadian
Wildlife Service does research in many fields of wildlife biology and provides incentive
programs for land stewardship and donation.
E
Executive Summary
How Much Habitat is Enough?: A Framework for Guiding Habitat Rehabilitation in Great Lakes Areas
of Concern (the Framework) provides science-based information and general guidelines to assist
government and non-government restoration practitioners, planners and others involved in natural
heritage conservation and preservation in ensuring there is adequate wetland, riparian and forest habitat
to sustain minimum viable wildlife populations and help maintain selected ecosystem functions and
attributes. The Framework provides 18 wetland, riparian and forest habitat guidelines and accompanying
rationales. Within Great Lakes Areas of Concern (AOCs), the Framework can be used to assist in the
setting and achievement of delisting criteria concerning fish and wildlife habitat beneficial-use
impairments, and post delisting can provide further guidance on habitat restoration.
A 2002 assessment of the Framework (first edition) showed it was well-used both within and outside
of AOCs. It was used as originally envisioned as a guide to set restoration targets and locate restoration
projects, and also as a science-based reference for agencies protecting habitat and identifying natural
heritage systems. To ensure that the Framework is based on the most current science this second edition
incorporates a review of the relevant new literature that has appeared since the first edition was published
in 1998. Two guidelines, Amount of Natural Vegetation Adjacent to a Wetland and Percent of an Urbanized
Watershed that is Impervious, have changed since the first edition and four guidelines have been modified
to a minor extent – Wetland Size, Wetland Shape, Total Suspended Sediments and Fragmented Landscapes
and the Role of Corridors.
To illustrate application of the Framework within AOCs a summary of its use in the Severn Sound AOC
is provided. An outline is also provided of the Terrestrial Natural Heritage Strategy being developed in
Toronto that moves beyond the general Framework guidelines to consider local conditions and the effect
on habitat of the matrix of land-uses in a landscape. Key to providing adequate wildlife habitat is the
protection of existing habitat and, in acknowledgement, the second edition provides suggestions on use
of the Framework in land-use planning.
The Framework is meant to be built upon and to be adapted according to historical and present local
conditions. The Framework will hopefully continue to serve as a starting point to develop strategies to
conserve habitat, develop natural heritage systems and discuss guidelines regarding other habitat types
such as grasslands.
Acknowledgements for the Second Edition
A Framework for Guiding Habitat Rehabilitation in Great Lakes Areas of Concern (the Framework) has
been the product of many individuals since its beginning in 1995 and publication of the first edition in 1998.
It was guided and championed by the Ontario Ministry of the Environment, the Canadian Wildlife Service
of Environment Canada and the Ontario Ministry of Natural Resources. Al Sandilands and Chris Wren from
Ecological Services for Planning Limited helped in the initial development of the first edition and expertise
was drawn from organizations and agencies within and outside of Areas of Concern (AOCs) which included
conservation authorities, private consultants, Environment Canada, the Department of Fisheries and Oceans,
the Ontario Ministry of Natural Resources, and the Ontario Ministry of the Environment. Environment
Canada’s Great Lakes Cleanup Fund and the Ontario Ministry of the Environment provided funding.
The second edition resulted from a 2002 assessment of the Framework that showed a need to update the
guidelines and science upon which they were based. Brian McHattie, Brian Henshaw, Lionel Normand,
and Keith Sherman made major contributions to the second edition. Valuable review and comments were
provided by Nancy Patterson, Mike Cadman, Angus Norman, the South-Central Ontario Conservation
Authority Natural Heritage Discussion Group, Natalie Iwanycki, Lisa Turnbull, Don Wismer, Janette
Anderson, Sandra George, Rimi Kalinauskas, Carolyn O’Neill, Scott MacKay, John Marsden, Anne
Borgman and Sandra Skog.
Table of Contents
1. INTRODUCTION ______________________________________________________________1
Development background for this guide
2
Guidelines are not targets
2
How to use this guide
3
Setting guidelines for habitat – some considerations
4
2. HABITAT GUIDELINES ________________________________________________________7
2.1 Wetland Habitat Guidelines __________________________________________________7
2.1.1 Percent Wetlands in Watershed and Subwatersheds
8
2.1.2 Wetland Type
9
2.1.3 Amount of Natural Vegetation Adjacent to the Wetland
12
2.1.4 Wetland Location
16
2.1.5 Wetland Size
18
2.1.6 Wetland Shape
20
2.2 Riparian Habitat Guidelines __________________________________________________21
2.2.1 Percent of Stream Naturally Vegetated
21
2.2.2 Amount of Natural Vegetation Adjacent to Streams
24
2.2.3 Total Suspended Sediment Concentrations
25
2.2.4 Percent of an Urbanizing Watershed that is Impervious
27
2.2.5 Establishing Fish Community Targets
28
2.2.6 Additional Riparian Parameters
29
2.3 Forest Habitat Guidelines ____________________________________________________30
2.3.1 Percent Forest Cover
30
2.3.2 Size of Largest Forest Patch
34
2.3.3 Percent of Watershed that is Forest Cover 100 metres and 200 metres from Edge 35
2.3.4 Additional Forest Parameters
37
3. CITED REFERENCES ________________________________________________________42
4. ADDITIONAL SOURCES OF INFORMATION____________________________________49
5. LIST OF ABBREVIATIONS AND ACRONYMS ____________________________________52
6. APPENDICES ________________________________________________________________53
Appendix 1 ____________________________________________________________________53
The Severn Sound AOC: Habitat Identification and Rehabilitation,
Delisting and Use of the Framework
Appendix 2 ____________________________________________________________________63
Toronto and Region Conservation Authority (TRCA) Terrestrial Natural Heritage Strategy
Appendix 3 ____________________________________________________________________66
Applying the Framework to Land-use Planning
Appendix 4 ____________________________________________________________________70
Toronto and Region Conservation Authority (TRCA) Fish Community
Target-setting Framework
Appendix 5 ____________________________________________________________________76
Assessment of Forest Bird Community Integrity: A Draft Methodology
and Field Test in the Severn Sound AOC (Report Highlights)
Photo by CWS
Photo by Douglas A. Wilcox
Introduction
A Framework for Guiding Habitat Rehabilitation in Great Lakes Areas of Concern (Framework) was
published as a first edition in the mid-1990s for Remedial Action Plan (RAP) teams and Public Advisory
Committees (PACs). These groups were working to rehabilitate ecosystems in 17 Canadian Areas of
Concern (AOCs) across the Great Lakes basin. As of 2003, there are 15 AOCs subsequent to the delisting
of Collingwood Harbour and Severn Sound.
In most of these locations, loss of fish and wildlife habitat and related degradation of populations have
been identified as “beneficial-use impairments”. The term was coined by the International Joint Commission
and is used to categorize problems in AOCs. Before an AOC can be considered restored, targets must be
developed to measure progress. Remedial Action Plans guide the remediation of AOCs to the point that
their environmental condition (as defined by the restoration of beneficial-use impairments) is comparable
to regional conditions outside of AOCs.
Primarily, the Framework assists those developing and implementing RAPs to select appropriate fish and
wildlife habitat targets as part of delisting criteria and provide guidance to initiatives which will, post-listing,
help maintain or enhance habitat conditions to support viable fish and wildlife populations. The Framework
can be used on a regional basis throughout the Great Lakes basin to help establish targets for habitat that
will support minimum viable wildlife populations.
Secondly, the Framework provides a method to prioritize locations for wetland, riparian and forest habitat
rehabilitation projects across a watershed or other landscape unit. The guidelines presented here are
based on an understanding of how much habitat is required to provide for the ecological needs of fish
and wildlife species in three types of habitat: wetlands, riparian areas, and forested areas. Note that the
terms rehabilitation and restoration are used synonymously throughout this document.
Beyond the AOCs, the Framework has demonstrated broad applicability in jurisdictions across Ontario
where factors have led to ecological degradation. In a number of locations outside of AOCs, information
from the Framework helped to guide the development of comprehensive habitat rehabilitation plans,
including identifying priority upland and aquatic projects. These plans worked in tandem with protection
plans toward achieving a functioning system of protected natural areas (Canadian Wildlife Service, 2002).
This approach is designed to build on the natural heritage system of protected areas currently implemented
in the province through the municipal land-use planning process.
A natural heritage system identifies the current system of natural areas that is in many cases degraded by
past land-use decisions, such as fragmented and small forest patches or drained wetlands. This second
edition of the Framework provides updated guidance on where and how much habitat to rehabilitate in
order to attain a more fully-functioning natural heritage system (i.e., by expanding and linking forest patches,
re-flooding wetland soils).
How Much Habitat is Enough?
1
Development background for this guide
In response to a need for restoration targets as expressed through the RAP program, Ecological Services
for Planning Limited was hired in early 1995 by Environment Canada (Canadian Wildlife Service), the
Ontario Ministry of the Environment and the Ontario Ministry of Natural Resources to undertake a review
of literature pertaining to natural heritage strategies. The resulting document, Using the Natural Heritage
Strategy Approach to Develop Habitat Rehabilitation and Restoration Targets and Project Priorities,
recommended upland habitat targets derived from landscape ecology concepts, reviewed environmental
mapping approaches, and provided case studies on how the approach could be implemented using two
AOCs as examples: Nipigon Bay and Toronto and Region AOCs.
In January 1996, the document was used to develop a Canada-Ontario Remedial Action Plan Steering
Committee interim report entitled, Identifying Habitat Rehabilitation Targets and Priorities in Great
Lakes Areas of Concern: Upland Systems (Environment Canada, the Ontario Ministry of Natural
Resources and Ontario Ministry of the Environment and Energy, 1996). The report was later refined to
include guidelines for riparian and wetland habitat rehabilitation based on an additional literature search
by Ecological Services for Planning Limited. Pilot applications using a variety of approaches were then
funded by the Great Lakes 2000 Cleanup Fund (now Great Lakes Sustainability Fund) with local partners
in nine AOCs, which served to test and improve early versions of the Framework.
Since its publication in 1998, the first edition of the Framework has been cited and used widely both
within and outside of AOCs. It has gained recognition as a basic overview of current ecosystem principles
applied to rehabilitation within the Great Lakes basin. Within AOCs, the Framework has been used to
establish rehabilitation sites, formulate watershed and natural heritage strategies and, in some cases, help
set delisting criteria.
In 2003, Gartner Lee Limited were contracted by Environment Canada (Canadian Wildlife Service) to
review recent pertinent literature and to present suggested amendments to guidelines and their rationales,
primarily based on new science. Results of the review, which were incorporated in this second edition,
ensure that the Framework maintains currency and applicability in a swiftly evolving area of scientific
investigation and understanding.
Guidelines are not targets
The Framework should be viewed as a means to guide, not dictate, local decisions, providing planners
and rehabilitation teams with the best available information to enable them to make their own decisions
on how much habitat is required to rehabilitate local watersheds and landscapes. The Framework does
not represent policy or legislation – its guidelines are meant to assist and to be used within existing
statutes and policies such as the provincial Planning Act. The Framework is not watershed or landscape
specific. The guidelines provided are not intended as mandatory limits or targets, and it is not intended
that every area must meet the guidelines expressed here.
In terms of AOCs, RAPs tend to focus on the remediation of water quality and the habitats of species which
play a direct role in aquatic ecosystems. The benchmark for terrestrial habitat, which is the focus of
the Framework, is largely defined in the RAP process by conditions in the landscape adjacent to AOCs,
upstream of AOCs or other site-specific considerations. In setting aquatic and terrestrial delisting criteria,
the bounds of RAP objectives have to be primarily considered. The Framework can augment and assist in
2
How Much Habitat is Enough?
setting delisting criteria, bearing in mind RAP objectives, can help set regional targets and benchmarks
for habitat, and can provide a context for the status of habitat in AOCs compared to regional conditions.
An understanding of local conditions is required to set habitat rehabilitation targets that make sense for
local cultural and natural conditions. In this way, the Framework is broadly applicable to both impoverished
and richer landscapes.
The wetland, riparian and forest habitat categories addressed here capture many characteristics of Great
Lakes AOCs. Agencies and/or personnel working in AOCs may also develop their own local strategies to
deal with additional and equally-important habitat categories such as grassland, alvar, and lake habitats.
Indeed, these habitat types may warrant future investigation within the scope of the Framework. In some
AOCs, including St. Clair River, habitats such as grassland may be essential to restore wildlife habitat.
In most AOCs, and across southern Ontario, changes to ecosystems have not been so great as to preclude
rehabilitation of those systems to approach a state of naturalness using pre-settlement conditions for
context. Such rehabilitation has occurred in the former AOCs, Collingwood Harbour and Severn Sound,
where habitat had not been degraded or lost to a degree where ecosystem functions were irreversibly
altered or lost. Local conditions and remaining habitat were considered in rehabilitation efforts that
ultimately restored natural systems to a viable state in a post-settlement landscape. However, changes in
urban areas of some AOCs may have shifted ecosystems to an entirely new state. Providing wildlife habitat
and other ecosystem functions such as maintenance of base flows in streams and local climate moderation
can only partially be provided through restoration and creation of habitat emulating pre-settlement
conditions. New baselines for habitat and functions may have to be set that consider urban areas and their
balance with regional watershed or landscape conditions, and new systems may have to be devised to
remediate lost ecosystem functions and mitigate and balance the impacts of large urban centres beyond
their own borders.
Overall, a review of the ecological literature makes it clear that the habitat guidelines, such as 30 percent
forest cover or 75 percent riparian cover, represent minimum desirable habitat proportions. Landscapes
with habitat exceeding these minimum amounts should be conserved and enhanced whenever possible.
How to use this guide
Guidelines provided here are for three habitat categories: wetlands, riparian areas, and forested areas.
In reality, of course, these habitats overlap and are separated only to provide clearly understood guiding
principles. For instance, the wetland habitat section discusses forested wetland or swamp habitat in
reference to the significant hydrological role it plays; the forest habitat section refers to its key biological
role in providing bird-nesting habitat. Similarly, riparian wetlands are found along vegetated flood plain
zones, which are discussed in the wetland and riparian habitat sections.
Each habitat category contains a background section and a discussion of guidelines and supporting rationale.
Some guidelines lend themselves well to quantification and tables illustrating optimum levels and threshold
values, while other guidelines are more qualitative. In Appendix 1, an example can be found of a natural
heritage strategy that used the guidelines for the former Severn Sound AOC. Appendix 2 is an overview
of the Toronto and Region Conservation Authority’s Terrestrial Natural Heritage Strategy, which considers
the influence of the matrix of surrounding lands when setting rehabilitation or conservation targets.
How Much Habitat is Enough?
3
Appendix 3 describes how Framework thresholds and guidelines can be integrated into Official Plans by
municipal planners in a top-down fashion. Many agencies have used Framework guidelines in creating
watershed strategies and natural heritage strategies with the intention that the documents be considered
and applied by municipalities.
Setting guidelines for habitat – some considerations
The Framework guidelines are intended as minimum ecological requirements. The state of the historic
landscape (pre-settlement) should be used as a base reference point for restoration. AOC watersheds,
municipalities or other land units that contain higher amounts of habitat than outlined here (e.g., 35 percent
forest cover, 15 percent wetlands) should maintain or improve that habitat.
In the case of the Niagara River AOC, wetlands comprised nearly 40 percent of the landscape in presettlement times; whereas, in the Humber River watershed in the Toronto and Region AOC, it is unlikely
that wetlands ever exceeded five percent of the watershed. The establishment of a historic or fundamental
context for ecological function provides one of the reference points required to assist in setting targets.
The second reference point is the existing condition, along with some knowledge of the magnitude of
impacts. Comparison of these two conditions provides a realistic context for the establishment of targets
and identification of rehabilitation activities. The historic condition provides the direction for restoration
while the existing condition indicates how far the system is from being healthy and what needs to be
improved. The knowledge of the magnitude of impacts is also necessary because the establishment of
targets must include an assessment of what might reasonably be achieved with existing restoration
technology and land-use patterns.
Guidelines provided in the Framework represent the best understanding from the current state of
ecological knowledge. They are intended to provide the guidance needed to set local habitat restoration
and protection targets. The state of ecological knowledge is rapidly improving so targets set today may
need to be revised as the understanding of complex, dynamic ecosystems evolves.
Primary importance of habitat protection
For RAPs, the focus is on restoring degraded fish and wildlife habitat in an AOC, and this document is
designed to assist in that pursuit. However, it needs to be emphasized that the protection of existing habitat
must remain the most important planning activity in any jurisdiction. RAP teams and PACs must work
with local planning authorities to ensure that habitats (or natural areas) are identified and protected
within the AOC and the surrounding landscape. The link to the loss of fish and wildlife habitat beneficialuse impairment becomes clear when natural heritage system plans (Riley and Mohr, 1994) identify
gaps in the system, or when existing habitat is determined to be impaired. Protection and rehabilitation
of impaired or missing habitats is integral to a fully-functioning natural heritage system.
4
How Much Habitat is Enough?
Stressors beyond habitat
There are additional stressors that affect fish and wildlife populations beyond the loss of habitat. Poor
water quality due to low oxygen conditions or the presence of toxic substances may explain why fish and
wildlife communities are impaired when other aspects of suitable habitat appear to be present. Some
researchers believe that declines in amphibian populations in apparently pristine habitats may be due to
factors such as viruses, acid rain, concentrations of nitrates, or increased exposure to UVB light. Beyond
habitat issues, restoration practitioners should be aware of any additional stressors from the surrounding
landscape that may impair fish and wildlife populations.
Beyond watershed boundaries
Management of habitats for fish and wildlife may fail if restricted to a watershed. Restoration planners
working on a watershed scale should be prepared to link with planning studies being conducted at other
scales, including ecological units such as an ecodistrict or ecoregion. For example, the Big Picture Project
(Carolinian Canada, 2002) deals with the Carolinian zone. Planning across ecosystems ensures restoration
and protection of a full range of ecosystem types and can help mitigate cumulative impacts. To promote
linkages of habitat between watersheds and across landscapes, surviving habitat corridors and geographic
features should be carefully considered. Valley lands and stream corridors often form the basis for linkages
from the Great Lakes inland and large landscape features such as relict glacial landscapes (e.g., moraines,
dune systems) and unique topographic features (e.g., the Niagara Escarpment, the Frontenac Arch)
provide inter-watershed and greater bioregional linkages. Restoration of, and to, these features may be the
best strategy to efficiently ensure species can disperse and forage between the habitat within the watershed
and the broader landscape.
Landscape matrix
The guidelines and thresholds in the Framework are not landscape or watershed specific. Natural heritage
and watershed strategies can further address ecosystem integrity by considering guidelines in the context
of land-use in a specific watershed. For example, a given percentage of forest cover in a largely urban
watershed may not provide habitat for the same number of forest bird species as it might in a rural
landscape. Natural systems are best considered in the context of the remainder of their watershed, which
may be composed of varying proportions of rural and urban land-uses. This matrix of land cover types in a
landscape can influence the habitat quality, ecological function, and composition of flora and fauna species.
As noted previously, Appendix 2 offers an example of a natural heritage strategy that considers a matrix
of land-uses, the Toronto and Region Conservation Authority’s Terrestrial Natural Heritage Strategy.
Species at Risk
Species context should be considered alongside landscape context. Specific habitat requirements for
species should be considered, especially for those regarded by the federal or provincial government to be
at some risk of extinction or extirpation. Rehabilitation of habitat should consider habitat attributes critical
for such species, and the presence of these species will likely be a factor in prioritizing habitat rehabilitation
and protection projects. Under the federal Species at Risk Act, critical habitat is described as “…the
habitat that is necessary for the recovery of a listed wildlife species and that is identified as the species’
critical habitat in the recovery strategy or in an action plan for the species.” (Canada, 2002).
How Much Habitat is Enough?
5
Table 1. Summary of Wetland, Riparian and Forest Habitat Restoration Guidelines
Wetland Habitat Guidelines
Parameter Guideline
Percent wetlands in
watersheds and
subwatersheds
Amount of natural
vegetation adjacent
to the wetland
Wetland type
Wetland location
Wetland size
Wetland shape
Greater than 10 percent of each major watershed in wetland habitat; greater than six percent of each
subwatershed in wetland habitat; or restore to original percentage of wetlands in the watershed.
For key wetland functions and attributes, the identification and maintenance of the Critical Function
Zone and its protection, along with an appropriate Protection Zone, is the primary concern. Where
this is not derived from site-specific characteristics, the following are minimum guidelines:
■ Bog: the total catchment area ■ Fen: 100 m or as determined by hydrogeological study,
whichever is greater
■ Marsh: 100 m
■ Swamp: 100 m
The only two wetland types suitable for widespread rehabilitation are marshes and swamps.
Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be
achieved by rehabilitating wetlands in key locations, such as headwater areas for groundwater
discharge and recharge, flood plains for flood attenuation, and coastal wetlands for fish production.
Special attention should be paid to historic wetland locations or the site and soil conditions.
Wetlands of a variety of sizes, types, and hydroperiods should be maintained across a landscape.
Swamps and marshes of sufficient size to support habitat heterogeneity are particularly important.
As with upland forests, in order to maximize habitat opportunities for edge-intolerant species,
and where the surrounding matrix is not natural habitat, swamps should be regularly shaped with
minimum edge and maximum interior habitat.
Riparian Habitat Guidelines
Parameter Guideline
Percent of stream
naturally vegetated
Amount of natural
vegetation adjacent
to streams
Total suspended
sediments
Percent of an
urbanizing watershed
that is impervious
Fish communities
75 percent of stream length should be naturally vegetated.
Streams should have a minimum 30 m wide naturally vegetated adjacent-lands area on both sides,
greater depending on site-specific conditions.
Where and when possible suspended sediment concentrations should be below 25 milligrams/litre
or be consistent with Canadian Council of Ministers of the Environment (1999) guidelines.
Less than 10 percent imperviousness in an urbanizing watershed should maintain stream water quality
and quantity, and preserve aquatic species density and biodiversity. An upper limit of 30 percent
represents a threshold for degraded systems.
Watershed guidelines for fish communities can be established based on knowledge of underlying
characteristics of a watershed (e.g., drainage area, surficial geology, flow regime), historic and current
fish communities, and factors (and their relative magnitudes) that currently impact the system.
Forest Habitat Guidelines
Parameter Guideline
Percent forest cover
Size of largest
forest patch
Percent of watershed
that is forest cover
100 m and 200 m from
forest edge
Forest shape
Proximity to other
forested patches
Fragmented landscapes
and the role of
corridors
Forest quality – species
composition and age
structure
6
At least 30 percent of the AOC watershed should be in forest cover.
A watershed or other land unit should have at least one 200-ha forest patch that is a minimum 500 m
in width.
The proportion of the watershed that is forest cover 100 m or further from the forest edge should be
greater than 10 percent. The proportion of the watershed that is forest cover 200 m or further from
the forest edge should be greater than five percent.
To be of maximum use to species such as forest-breeding birds that are intolerant of edge habitat,
forest patches should be circular or square in shape.
To be of maximum use to species such as forest-interior birds, forest patches should be within two
km of one another or other supporting habitat features.
Connectivity width will vary depending on the objectives of the project and the attributes of the
nodes that will be connected. Corridors designed to facilitate species movement should be a
minimum of 50 m to 100 m in width. Corridors designed to accommodate breeding habitat for
specialist species need to be designed to meet the habitat requirements of those target species.
Watershed forest cover should be representative of the full diversity of forest types found
at that latitude.
How Much Habitat is Enough?
Habitat Guidelines
2.1 Wetland Habitat Guidelines
Wetlands – a critical part of the landscape
A high proportion of Ontario’s fish and wildlife species inhabit wetlands during part of their life cycle.
Many of the species at risk of extinction in southern Ontario are highly dependent on wetlands.
Wetlands shave off peak flows and impound water, thereby increasing the travel time of water down a
watercourse. This slowing action not only reduces water velocities and peaks immediately downstream,
it also results in an asynchronization of peaks (i.e., peak flows from tributaries reach the main watercourse
at different times). Wetlands provide a significant economic benefit from a flood-control perspective,
and can be more efficient than flood impoundment systems. Wetlands augment low-flow by raising
local water tables, which in turn contribute to stream base flows. Wetlands also perform significant
roles in water-quality improvement.
The following series of wetland habitat guidelines relate to the amount of wetlands in a watershed,
the amount of vegetation adjacent to a wetland, wetland type and location, and shape and size.
Table 2. Summary of Wetland Habitat Guidelines
Parameter
Percent wetlands in
watershed and
subwatersheds
Amount of natural
vegetation adjacent
to the wetland
Wetland type
Wetland location
Wetland size
Wetland shape
Guideline
Greater than 10 percent of each major watershed in wetland habitat; greater than six percent
of each subwatershed in wetland habitat; or restore to original percentage of wetlands in the
watershed.
For key wetland functions and attributes, the identification and maintenance of the Critical Function
Zone and its protection, along with an appropriate Protection Zone, is the primary concern. Where
this is not derived from site-specific characteristics, the following are minimum guidelines:
■ Bog: the total catchment area
■ Fen: 100 m or as determined by hydrogeological study, whichever is greater
■ Marsh: 100 m
■ Swamp: 100 m.
The only two wetland types suitable for widespread rehabilitation are marshes and swamps.
Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be
achieved by rehabilitating wetlands in key locations such as headwater areas for groundwater
discharge and recharge, flood plains for flood attenuation, and coastal wetlands for fish production.
Special attention should be paid to historic wetland locations or the site and soil conditions.
Wetlands of a variety of sizes, types, and hydroperiods should be maintained across a landscape.
Swamps and marshes of sufficient size to support habitat heterogeneity are particularly important.
As with upland forests, in order to maximize habitat opportunities for edge-intolerant species,
and where the surrounding matrix is not natural habitat, swamps should be regularly shaped
with minimum edge and maximum interior habitat.
How Much Habitat is Enough?
7
2.1.1 Percent Wetlands in Watershed and Subwatersheds
> Guideline
Greater than 10 percent of each major watershed in wetland habitat; greater than six percent of each
subwatershed in wetland habitat; or restore to original percentage of wetlands in the watershed.
> Rationale
Critical ratios of wetland area to watershed area
will vary according to channel slope, as well
as land-use or land cover within a watershed
(Detenbeck et al., 1999). In addition, the
interaction of riparian buffer zones, soil types
and other factors (e.g., forest cover) will affect
hydrologic effects of wetland loss or gain within a
watershed. When considering wetland restoration
opportunities or guidelines, it is also important
to consider the location and type of wetlands
that might be appropriate within a landscape.
This assessment can be based on historical and
current patterns of wetlands in the landscape
(Bedford, 1999; Detenbeck et al., 1999).
This condition was found to be particularly true
for flood control and suspended solids loadings.
The guideline of six percent wetland cover for
subwatersheds helps to ensure that wetlands are
distributed around the watershed basin, while
retaining a realistic wetland-cover percentage that
can result in tangible hydrological and ecological
benefits on a subwatershed basis. This guideline
will also be influenced by historic wetland extent,
topography, and soils in a specific watershed
or AOC.
Historically, wetland coverage within the Great
Lakes Basin exceeded 10 percent (Detenbeck et
al., 1999). In Wisconsin, Hey and Wickencamp
(1996) examined nine watersheds and found that
increasing the amount of wetland in a watershed
resulted in reduced watershed yield of water,
reduced flooding, higher base flows, and reduced
occurrence of high flows. However, these responses
flattened very rapidly above 10 percent of wetland
cover. A study in Saginaw Bay estimated that
having 15 percent of a watershed in wetlands
would reduce phosphorus loadings by 66 percent
(Wang and Mitsch, 1995), and other studies have
determined that having five percent wetland
cover greatly helped water quality.
A study conducted by Carol Johnson at the
University of Minnesota (Johnson et al., 1990)
found that watersheds in the southern United
States containing less than 10 percent wetlands
were more susceptible to incremental losses of
wetlands than watersheds with more wetlands.
8
How Much Habitat is Enough?
Photo by Graham Bryan
2.1.2 Wetland Type
> Guideline
The only two wetland types suitable for widespread rehabilitation are marshes and swamps.
> Rationale
There are four general wetland types in Ontario: bogs, fens, marshes, and swamps.
Bogs and Fens
Bogs are highly specialized environments and true
bogs are rare in the southern part of the Great
Lakes Basin. They receive almost all of their water
and nutrients from precipitation. They are acidic
and have very low productivity. Plants inhabiting
bogs must be adapted to these low nutrient levels.
There are few trees in bogs (by most definitions six
metres tall) – generally less than 25 percent cover
and usually consisting only of Black Spruce. The
dominant vegetation is usually ericaceous shrubs
and sphagnum mosses. Bogs are also characterized
by their relative lack of vascular plant species,
although they may be rich in other life forms.
Fens receive most of their water and nutrients
from groundwater. Depending on the source of
the groundwater, they may be either nutrient-rich
or nutrient-poor. Nutrient-rich fens are often
dominated by sedges. Calcareous fens can support
a wide variety of plant species and may be treed with
White Cedar (although with less than 25 percent
cover). Nutrient-poor fens may be very similar in
their character to bogs, with subtle differences
in the sedge and moss species that dominate and
the presence in fens of so-called “fen indicators”
that are typical of higher-nutrient environments.
Because carnivorous plants (e.g., various sundews
and Pitcher Plants) frequently occur in fens, they
are not useful indicators of true bogs.
Bogs and some fens have a substrate of peat
covered with mosses. Due to microdrainage
patterns, bogs and fens may co-exist, particularly
in large wetlands. Occasionally, the edge of
a wetland may be a fen as it is exposed to
groundwater; however, the accumulations of
peat prevent groundwater from reaching the
centre where it may be more bog-like. Over
centuries, fens may evolve into bogs and vice
versa, as a result of how peat forms and changes
water flow patterns.
Fens and especially bogs are rare habitats in
southern Ontario, off the Canadian Shield.
Together, they constitute only one percent of the
wetlands remaining in the south. However, in the
north and particularly in the Hudson Bay Lowlands,
poor fens cover extensive areas. Bogs and fens are
highly susceptible to changes in nutrient and water
inputs. Even small variations may alter them into
other wetland types or even into upland habitat.
Limited information is available on the science of
rehabilitating bogs and fens. The best management
strategy for these wetland types is to protect them.
It is also essential to protect their water sources
and not alter their watersheds.
Swamps
As the most abundant wetland type in southern
Ontario, swamps comprise 89 percent of
remaining wetland area.
Swamps perform many important biological
functions. They may be dominated by a variety of
coniferous and deciduous shrub and tree species.
Swamps also tend to be hummocky and may
support upland plant species in these microhabitats.
Swamps support higher diversities of plant and
wildlife species than other wetland or forest
communities. They also provide critical habitat
for many species. For example:
How Much Habitat is Enough?
9
■
most deer and moose-wintering areas
are in coniferous swamps
■
a high proportion of cold-water streams
originate in swamps (most Brook Trout
streams originate in swamps)
■
in southern Ontario, forest-interior or areasensitive species are often found in swamps,
as these frequently comprise the largest
remaining forested tracts on the landscape
■
many of Ontario’s wildlife species primarily
occur in swamps, including: Wood Frog,
Northern Ringneck Snake, Wood Duck,
Common Goldeneye, Hooded Merganser,
Olive-sided Flycatcher, Cerulean Warbler,
Northern Waterthrush, Louisiana Waterthrush,
Snowshoe Hare, Woodland Jumping Mouse,
and Common Gray Fox.
Swamps also contribute significantly to the amount
of forested habitat in southern Ontario. A high
proportion of the remaining forests are swamps,
as the lands they occupy often have limited
capabilities for supporting agricultural crops
or other land-uses if they are cleared.
Depending upon the terrain, swamps may perform
important hydrological functions. They are
frequently in areas of groundwater discharge,
thus protecting headwaters of streams. In these
situations, swamps maintain the cold-water nature
of watercourses through the interception or
reflection of heat energy. They also contribute
critical nutrients to these small streams through
leaves and other detritus. These provide food for
grazing species of aquatic invertebrates, which are
a basis of the food chain in small streams. Tree
limbs and logs are important in-stream cover for
aquatic invertebrates and fish.
Swamps along larger watercourses provide storage
for floodwaters, thereby reducing peak flows and
downstream flooding. This natural inundation
within the forest supplies essential nutrients to
plant communities and habitat for certain wildlife
species. These types of swamps are also important
10
How Much Habitat is Enough?
in improving stream water quality. Plant
communities in some swamps are very dynamic,
with the understory being dominated with wetland
species early in the growing season, and species
adapted to drier conditions later in the year. Spring
flooding provides ephemeral ponds that are used
for breeding by frogs, toads, and salamanders.
These same pools are also important breeding
areas for invertebrates such as some caddisflies
and midges, and these, in turn, are important food
for bats and many bird species.
Marshes
Marshes are the other type of wetland in southern
Ontario. Although the term wetland usually means
a cattail marsh to most people, marshes represent
only about 10 percent of the area of wetlands in
southern Ontario and 5.4 percent of all of the
province’s wetlands (Riley, 1989).
Marshes perform many important biological
functions. Today, extensive marshes relative to
historic conditions are rare in the landscape, so
species that require this habitat are also restricted
in their distribution. Several fish and wildlife
species are totally dependent on marshes, and a
high proportion of these are of provincial and
federal significance. Some examples of obligate
marsh species are: Spotted Gar, Spotted Sucker,
Banded Killifish, Bullfrog, Map Turtle, Fox Snake,
Pied-billed Grebe, Red-necked Grebe, Least
Bittern, Ruddy Duck, King Rail, Virginia Rail,
Sora, Common Moorhen, American Coot, Forster’s
Tern, Black Tern, Marsh Wren, Yellow-headed
Blackbird, and Muskrat.
Marshes are used by a high proportion of other
fish and wildlife species for some period of their
life cycle, frequently for critical functions such
as breeding, nursery areas, or for feeding. Jude
and Pappas (1992) found that of 113 fish species
occurring in the Great Lakes, 41.6 percent were
coastal marsh species and 31 percent used coastal
marshes for nursery habitat or feeding. In Lake
Ontario marshes, 63.9 percent of species present
used marshes for spawning and 86 percent of
species used marshes as nursery habitat. The
importance of marshes to the fish of the Great
Lakes and also inland water bodies cannot be
overemphasized. Approximately 90 percent
of the fish biomass in Lake Erie is forage fish,
and most of this is produced in wetlands (Keast
et al., 1978; Stephenson, 1988; 1990).
One of the most important hydrological functions
of wetlands is uptake of nutrients, heavy metals
and other contaminants. The efficiency of marshes
in improving water quality varies considerably,
depending on factors such as the location of the
marsh in relation to overland flows, substrate types,
dominant plant species, contact time with the water
that flows through, and climate. As an example, the
marshes at the mouth of Old Woman Creek in Ohio
have been estimated to remove 12 to 60 percent
of the metals passing through the system and 35
to 80 percent of the biologically active nutrients
(Herdendorf, 1992).
Types of Wetlands Suitable
for Restoration
The two wetland types that are practical for
widespread rehabilitation are marshes and swamps.
Currently, limited information is available on the
science of rehabilitating fens and bogs. The best
management strategy for bogs and fens (and for
all wetlands) is to protect them by protecting their
water sources and not altering their watersheds. In
some cases, abandoned pits and quarries that are
connected to the water table may offer unique
opportunities for fen creation (Hough Woodland
Naylor Dance, and Gore and Storrie Ltd., 1995).
Marshes are easier to rehabilitate and a newlycreated marsh will be at least partially functional
within a few years. It may take longer before a
rehabilitated swamp becomes functional, and a
few decades before it is fully-functional, as it takes
more time for trees and tall shrubs to grow.
Inland marshes are important in flood control.
Isolated marshes store water and prevent a certain
proportion of precipitation runoff from reaching
watercourses. Marshes on watercourses also store
water and reduce flow velocity, thereby reducing
peak flows.
Marsh vegetation stabilizes shorelines and reduces
the risk of erosion. This is a particularly important
function in watercourses and on lakes where there
is a long fetch. By helping to maintain shorelines,
marshes prevent loss of property, reduce sediment
delivery to water bodies, and help maintain the
character of stream channels.
Photo by John Mitchell
How Much Habitat is Enough?
11
2.1.3 Amount of Natural Vegetation Adjacent to the Wetland
> Guideline
For key wetland functions and attributes, the identification and maintenance of the Critical Function
Zone, and the protection of it, along with an appropriate Protection Zone, is the primary concern.
Where this is not derived from site-specific characteristics, the following are minimum guidelines:
■
Bog – the total catchment area
■
Fen – 100 m or as determined by hydrogeological study, whichever is greater
■
Marsh – 100 m
■
Swamp – 100 m.
> Rationale
The amount of natural habitat that is located adjacent to wetlands can be particularly important to the
maintenance of wetland functions and attributes. These adjacent lands are often referred to as “buffers”.
However, in many cases they form an intrinsic part of the wetland ecosystem, providing a variety of
habitat functions for wetland-associated fauna that extend beyond the wetland limit and therefore could
better be described as Critical Function Zones (CFZs).
Critical Function Zones defined
The term Critical Function Zone (CFZ) describes non-wetland areas within which biophysical functions
or attributes directly related to the wetland of interest occur. This could, for example, be adjacent
upland grassland nesting habitat for waterfowl (that use the wetland to raise their broods). It could
also be upland turtle nesting habitat for turtles that otherwise occupy the wetland, foraging areas
for Leopard Frogs, dragonflies or nesting habitat for birds that often straddle the wetland-upland
ecozone (e.g., Yellow Warbler). A groundwater recharge area that is important for the function of
an adjacent wetland could also be considered a CFZ.
Effectively, the CFZ is a functional extension of the wetland into the upland. Once identified, the
CFZ (with the wetland itself) needs to be protected from adverse effects that originate from outside
the wetland and its CFZ, by a Protection Zone (PZ). This could range in scope from a simple fence
(for example to dissuade human access) to a vegetated area for intercepting storm water run-off or
providing physical separation from a stressor. Effectively, the Protection Zone is aimed at reducing
impacts on wetland functions that originate from the upland side.
The combined CFZ and its Protection Zone may range in total width from a few metres to hundreds
of metres.
Other “buffer” functions such as providing a filtering function to reduce nutrients or contaminants,
decrease indirect effects such as noise or visual disturbance, or reduce direct human-associated intrusions
into the wetland from the outside, are better addressed through a PZ, which is analogous to a barrier
or filter strip. The PZ can also be integrated into urban design, offering opportunities for the focussing
of pedestrian traffic, recreation, aesthetics, interpretation, and integration of urban infrastructure
(e.g., storm water management facilities as barriers).
12
How Much Habitat is Enough?
These two layers on the outside of the wetland – the CFZ (that encapsulates functions that extend out
from the wetland) and the PZ that seeks to protect the CFZ from outside influences – together make
up the total adjacent-lands area (i.e., the wetland buffer).
Differentiating between CFZs and PZs within the overall adjacent lands, the Framework encourages a
shift towards the development of Multicriteria Evaluation for buffers (van der Merwe et al., 2001). This
approach encourages the identification and prioritization of various criteria that are selected on a site
specific basis. This could result, for example, in the encouragement of some land-uses or activities within
the PZs, but not within the CFZs. The use of these “bands” within the adjacent-lands area could help
resolve some difficult land-use questions when urban development is proposed close to wetlands.
The overall adjacent-lands width needs to be responsive to the ecological setting (e.g., the complementary
effect of adjacent habitats [Pope et al., 2000; Guerry and Hunter, 2002]) and its inter-relationships with
potential stressors (Gartner Lee Limited, 1992). Management objectives, individual characteristics of
the wetland, ecological interactions with upland areas, the source, magnitude and frequency of potential
stressors and engineering options, all contribute to the design of effective adjacent-lands areas.
Table 3. Critical Function Zones
Function or Attribute
(when present)
Nesting Painted
Turtles
Spotted Turtle and
Blanding’s Turtle
Spotted Turtle
Freshwater turtles
Green Frog foraging
forays
Ambystoma
salamanders
Tiger Salamander
(an Ambystoma)
Nesting waterfowl
Extent of attribute
into uplands (CFZ)
1 m to 620 m, mean 90 m
Reference
Christens and Bider,
1987.
Joyal et al., 2001.
(Distances are mean plus
standard deviation.) Spotted
Turtle 85 m for nesting, 54 m
for dormancy; Blanding’s
Turtle 380 m for nesting,
18 m for basking and 114 m
for dormancy
Milam and Melvin,
Nesting 75 m to 312 m;
2001.
dormancy up to 412 m
73 m for 90 percent of nests Burke and Gibbons.
1995.
Lamoureux et al.,
Mean 36 m, standard
2002.
deviation 25 m
Means: 125 m for adults,
70 m for juveniles; 164 m
(90 percent)
173 m
Semlitsch, 1998.
0 m to more than 400 m;
90 percent were within
200 m
Henshaw and
Leadbeater, 1998.
Trenham, 2001.
Notes
Used radio-tracking in Maine.
Used radio-tracking of 26 animals in
Massachusetts.
Used radio-tracking.
Used radio-tracking in New York. Terrestrial
feeding areas may be critical (based on frog
mass changes).
Recommends corridors be integrated
into adjacent land determination.
Study may have under-estimated adjacentland requirements.
Based empirical data over two years and
102 nests at coastal marshes. About 20
percent of nests were inside or within 25 m
of wetlands. May be applicable where
suitable waterfowl nesting habitat is present.
How Much Habitat is Enough?
13
Table 4. Protection Zones
Stressor
Suggested extent of
protective zone (PZ)
Herbicide drift from Strip at edge of cultivated fields
agricultural lands (data indicate >6 m to 9 m)
Nitrate 16 m to 104 m
Non-point source 16.3 m grass/woody strip
agricultural pollutants (riparian)
Residential stormwater 15 m; 23 m to 30 m on slopes
greater than 12 percent
Urban cats 190 m
Lawn-related (e.g., 19 m to 38 m
wood piles,
composting)
Recreation-related 67 m to 130 m
(e.g., camping, hacked
trees)
Human disturbance Flush distances (proximity of
by watercraft disturbance that will cause bird to
leave a nest) (mean plus standard
deviation) approximately 45 m
to 80 m for Great Lakes species
(no waterfowl). Recommended
distances are greater.
Human disturbance on 100 m
nesting Great Blue
Herons
Reference
Boutin and Jobin, 1998.
Basnyat et al., 1999.
Lee et al., 2003.
Notes
Cites other studies suggesting
5 m to 10 m.
Objective was >90 percent nitrate
removal.
Removed >97 percent of sediment,
narrower (7 m) grass provided some
benefits.
Groundcover type also very important.
Woodard and Rock,
1995.
Haspel and Calhoon, 1991. Predation rates on wildlife variable.
Matlack, 1993.
Fencing may achieve same results
in less width.
Matlack, 1993.
Rodgers and Schwikert,
2001.
Empirical data, based on a Florida
study of personal watercraft and
outboard-powered boats.
Rodgers and Smith, 1995. Flush distance was 32 m plus 5.5 m
standard deviation, plus 40 m to
Erwin, 1989.
mitigate antagonistic behaviour.
Table 5. Selected Reviews or Guidelines that Consider Adjacent Lands Areas
Citation
Adjacent lands
Brown, M.T., J. Schaefer and Groundwater mostly 30 m to 168 m
K. Brandt. 1990. (range 6 m to 168 m). Sedimentation
PZ 23 m to 114 m. Wildlife CFZ 98 m
to 223 m.
Castelle, A.J., A.W. Johnson Minimum of 15 m to 30 m under
and C. Conolly. 1994. most circumstances, but site-specific.
Gabor, T.S., A.K. North,
L.C.M. Ross, H.R. Murkin,
J.S. Anderson, and M.A.
Turner, 2001.
Lowrance, R., S. Dabney
and R. Schultz. 2002.
No conclusions are offered regarding
minimum or maximum adjacent lands
areas.
Presents 10 U.S. adjacent-lands
practices (USDA-NRCS). Range from
1 m to 30 m.
Norman, A. J., 1996. Baseline adjacent lands area of 50 m,
then subject to site-specific
considerations (e.g., waterfowl
production, sensitive hydrology).
14
How Much Habitat is Enough?
Notes
Provided PZ minimum and maximums based on
landscape associations. Average conditions used,
based on literature review.
Provides review of literature pertaining to sediment
removal, nutrient removal, stormwater runoff,
moderation of temperature, habitat diversity, wildlife
and human impacts (i.e., CFZs and PZs).
Presents literature regarding PZs for sedimentation
and erosion, nutrient management, pathogens and
pesticides.
Generally providing PZ for erosion control, reduced
contamination transport or other agricultural benefits.
Recommend caution regarding very narrow strips.
PZ and CFZ literature reviewed, mostly pre-1989
literature. Includes citations for wildlife.
(e.g., nesting waterfowl).
Table 6. Adjacent-Lands Guidelines
For key wetland functions and attributes, the identification and maintenance of the Critical Function Zone (CFZ), and
the protection of it, along with an appropriate Protection Zone (PZ), is the primary concern. Where this is not derived
from site-specific characteristics, the following are minimum guidelines:
Wetland Type*
Habitat Guidelines
Bog
Fen (poor fens and rich fens)
Marsh
Swamp
Catchment
100 m or as determined by hydrogeological study, whichever is greater
100 m
100 m
* There are varying definitions of wetland types, particularly bogs. This guideline is based on the definition of wetland types provided by OMNR (1994).
Determining a guide for the appropriate delineation of adjacent-lands areas requires knowledge of the
attributes of the area of interest, an understanding of the existing or future stressors, the use of up-to-date
science to help determine both the likely extent of attributes (including their CFZs), and the type and
extent of PZs that may be required. In the following tables (Tables 3, 4 and 5) some examples are provided.
A review of these tables demonstrates that appropriate adjacent-lands areas cannot be determined based
on a one-size-fits-all approach. A scientifically supportable CFZ/PZ combination might be 170 metres
in one location and 50 metres in another even though both locations may be part of the same wetland
system. Determination must be based on functions, attributes, site characteristics, stressors, design, and,
not least, management objectives and expectations for the adjacent-lands area.
Based on current knowledge, the literature increasingly indicates that the greatest CFZ requirements
tend to be associated with wildlife attributes, especially those around marshes. Much of this new
information is coming from studies that are making use of new miniature tracking technologies. It is
critical that rehabilitation efforts focus on the CFZ of key existing or anticipated species.
Most wetlands around the Great Lakes Basin are likely to support at least some wildlife attributes that
also include the upland areas as seasonal habitat. Therefore, minimum wetland adjacent-lands areas based
on water quality parameters alone (i.e., 15 metres to 30 metres on slopes of less than 12 percent with
good ground cover) are unlikely to be sufficient. Based on this review, the CFZ for attributes associated
with wetlands can only be determined based on site-specific knowledge of those attributes and their
sensitivities, and on management objectives.
Based on the current level of scientific support for adjacent-lands areas, reasonable minimum guidelines
are provided in Table 6.
How Much Habitat is Enough?
15
2.1.4 Wetland Location
> Guideline
Wetlands can provide benefits anywhere in a watershed, but particular wetland functions can be
achieved by rehabilitating wetlands in key locations such as headwater areas for groundwater
discharge and recharge, flood plains for flood attenuation, and coastal wetlands for fish production.
Special attention should be paid to historic wetland locations or the site and soil conditions.
> Rationale
Wetlands rehabilitated anywhere within a watershed
will provide an array of benefits including regulation
of peak water flows and increases in biodiversity,
provided that they are sites suitable for creating
or restoring wetland habitat.
Increasingly, there is scientific guidance available
regarding the “best” location for wetlands within
a watershed (e.g., Griener and Hershner, 1998;
DeLaney, 1995). This will depend in part on the
characteristics of a watershed (Norton and Fisher,
2000). However, there is little doubt that landscape
setting is important for wetland function (Mitsch
and Gosselink, 2000) or that the correct landscape
placement is also important for wetland creation
projects (Babb et al., 1997).
Wetlands can provide benefits that address specific
objectives, problems or research needs when they
are strategically-located. Guidance on determining
the strategic location of, and approach to, wetland
restoration projects is becoming increasingly
available. Almendinger (1999) describes a method
to prioritize restoration sites for water quality
improvement, while Bedford (1999) suggests an
approach that relies on the a priori establishment
of cumulative effects to help determine past and
present wetland profiles.
In headwater areas, wetlands can provide critical
functions. For swamps, these include protection
of the quality of groundwater discharge (and/or
recharge), introduction of leaves and woody debris
that are essential to the diversity of fish and
macroinvertebrates downstream (Gurnell et al.,
1995 cited in Detenbeck et al., 1999), and reducing
the warming of streams at the source. In turn,
16
How Much Habitat is Enough?
good water-quality conditions in higher portions
of watersheds are likely to benefit downstream
coastal wetland ecosystems (Crosbie and ChowFraser, 1999).
Further downstream, palustrine and riverine
wetlands are important in reducing and
asynchronizing peak flows, improving water
quality, and providing habitat for aquatic
invertebrates, fish and other wildlife.
In lakes, marshes are critical habitat for fish, and
it has been demonstrated that wetland habitat in
lakes supports about 60 percent more fish biomass
than unvegetated areas (Petzold, 1996). These
wetlands may be critical to the fisheries of an
entire lake. For example, changes in the amount
and type of wetlands at Long Point have affected
the fish assemblages populating all of Lake Erie
(T. Whillans, pers. comm.).
Existing land-uses, complementary habitat types
(e.g., upland forest for amphibians), hydrology,
water depths, substrate types, and fetch should
be examined to determine the area suitable for
rehabilitation. Ideally, all potential areas should
be restored to wetland vegetation.
A second priority is to expand existing marshland.
The larger a marsh, the better protection it provides
zooplankton and fish from predators, and the higher
the species richness in terms of birds. It has been
demonstrated that fragmentation of marshes
within lakes can result in depletion of zooplankton
and the fish species that depend on them. Even
in systems where zooplankton is not a concern,
small marsh patches may be ecological traps.
They attract fry of many fish species as nursery
habitat, but predation rates by common piscivores
(fish that eat other fish) such as Rock Bass may be
very high. However, small marshes – especially
a high concentration of marshes in a landscape –
can be beneficial in terms of waterfowl production.
If a new marsh is to be created within a lake, select
the site where the largest marsh can be established,
for the reasons mentioned above. Although even
a tiny patch of wetland will increase biomass of
invertebrates and fish, areas of at least 0.4 hectares
should be the goal. Wetlands situated within
100 metres of another are more likely to have
movement of fish among them, and the two patches
are likely to collectively support more species than
they would if they were isolated from each other.
Nonetheless, opportunities for establishing a new
wetland that is isolated from other marshes should
definitely not be ignored. New marshes can create
new nodes of fish production, can increase fish
biomass in the lake, and can be important for other
species such as waterfowl, amphibians and reptiles.
The following, in no particular order, are
recommended locations for restoring wetlands
in AOCs:
■
headwater wetlands, particularly swamps,
should be restored where they previously
existed
■
on-line or flood plain marshes and swamps
should be rehabilitated or restored on second
and third-order streams
■
rehabilitation of wetlands in lakes is a very
high priority because of their extreme
importance to fish as well as other wildlife
species
■
rehabilitation of wetlands in known historic
locations is encouraged, where still feasible
■
any wetland, no matter where it is in a
watershed or how large it is, will provide
some benefits.
Photo by CWS
How Much Habitat is Enough?
17
2.1.5 Wetland Size
> Guideline
Wetlands of a variety of sizes, types and hydroperiods should be maintained across a landscape.
Swamps and marshes of sufficient size to support habitat heterogeneity are particularly important.
> Rationale
Treed swamps are a type of forest and they have the potential to support area-sensitive wildlife species
(those that require larger areas of continuous habitat in which to be productive) or edge-intolerant
species (those that prefer to use habitat away from the influence of habitat edges, also often referred to
as “interior” habitat species). In AOCs, swamp forests may be the only remaining significant contributors
to interior-forest habitat, so the discussion on forest size and species that may be expected in forests of
different size applies here also. However, swamp forests provide interior habitat for a different suite
of specialist area-sensitive forest species compared to large patches of upland forest.
Wetlands of a wide range of sizes can be important for local or regional biodiversity. For example, a small
(<0.5 hectare) salamander breeding pond within an upland forest may be a critical habitat feature. These
temporary wetlands are also likely to support a unique group of species (Snodgrass et al., 2000), hence
increasing the diversity of assemblages of species in an area. These animals and invertebrates often respond
to the short hydroperiod (length of time the wetland has standing water) and the absence of predatory or
competing fish. Snodgrass et al. (2000) also found that in the southeast U.S. at least, there was no relationship
between wetland size and amphibian diversity.
For marshes, even small units (e.g., 0.01 hectare) may be important for breeding amphibians or as waterfowl
habitat, in the latter case especially for springtime pairing and feeding where a series of small wetlands
exist in an area. In addition, some species of wildlife have adapted to exploit a complex of wetlands in the
landscape and will readily move between them to forage (e.g., Northern Harriers, herons, dabbling ducks).
This is the reason that the Ontario Wetland Evaluation System recognizes the concept of wetland complexes
(OMNR, 1994).
Independent of whether or not large forest units are important (see discussion under forest cover) large
swamps tend to have greater habitat heterogeneity (that is, the habitat is more varied within them), which in
turn tends to support more species of wildlife (Golet et al., 2001). This effect can also be seen in marshes,
and is often termed “interspersion” or the juxtaposition of different marsh communities (e.g., submerged
versus emergent vegetation); although the mechanisms for maintaining heterogeneity in marshes are very
different from swamps (e.g., bathymetry, water depths and hydroperiod).
High levels of habitat interspersion (i.e., open water/submerged vegetation, emergent vegetation and in
some cases shrubs) within a marsh provide higher quality-habitat for a wider variety of species than, for
example, a narrow band of cattails around the shoreline. It must be emphasized that marshes are very
dynamic systems, so the ratio of open water/submerged vegetation to emergent vegetation (the optimum
“hemi-marsh” for some species is around 1:1) and the interspersion pattern, may vary considerably from year
to year. However, size remains a key factor: there is less chance that smaller wetlands will have sufficient
areas of different marsh habitat types regularly available to be used as productive habitat by wildlife.
18
How Much Habitat is Enough?
There is limited evidence to suggest that not all wildlife species benefit from high interspersion; some
may require extensive stands of emergents with few or no openings (i.e., Northern Harrier), while others
seem to prefer areas dominated by emergents, but with small, isolated openings (i.e., Least Bittern).
Like other wetland types, larger marshes and wetland complexes also have the ability to attract areasensitive wildlife species. Area-sensitive birds may include species such as Marsh Wren (10 hectare),
Black Tern (30 hectare) and Forster’s Tern (larger coastal systems). The Black Tern will nest in smaller
wetland units if larger feeding areas are located nearby. There are also a number of other species, such
as Least Bittern and King Rail, which occasionally occur in smaller wetlands, but long-term viable
populations are associated with extensive wetlands.
Table 7. Wildlife Use of Various Sized Habitats
Area Forest/Treed Swamp
1 ha
■
■
■
4 ha
■
■
10 ha
■
30 ha
■
■
50 to
75 ha
■
■
■
100 to
400 ha
■
■
■
1,000 ha
■
■
10 000
ha
■
Marsh
Edge tolerant mammals (Gray Squirrel)
Common edge-tolerant birds (Blue Jay, American Crow)
A few birds may be associated with mature trees (Black-capped
Chickadee, Eastern Wood-Pewee)
■
A very few common edge-tolerant birds (Downy Woodpecker,
Great Crested Flycatcher)
Eastern Chipmunk may be present
Still dominated by edge-tolerant species may have very small
areas of interior habitat supporting low numbers of modestly areasensitive species (Hairy Woodpecker, White-breasted Nuthatch)
May be large enough to support some species of salamander
Small populations of edge-intolerant species (Winter Wren,
Brown Creeper, Black-and-White Warbler)
A variety of area-sensitive species may be present; some will
be absent if there is no nearby suitable habitat
Still predominantly edge influenced, but will support small
populations of most forest bird species
Some will be absent if there is no nearby suitable habitat
All forest-dependent bird species
Many will still be in low numbers and may be absent if there
is no nearby suitable habitat
Woodland Jumping Mouse may be present
Suitable for almost all forest birds
Some forest-dependent mammals present, but most still absent
Almost fully functional ecosystem, but may be inadequate
for a few mammals such as Gray Wolf and Bobcat (100 000 ha
has been suggested as a minimum)
■
■
■
Small populations of Muskrat
Edge-tolerant birds (Red-winged
Blackbird, Canada Goose, Mallard)
Persistent and common herpetofauna
(such as Green Frog and Midland
Painted Turtle)
Similar species as above, but may
also support Bullfrog
■
May support Marsh Wren, other
waterfowl species
■
Similar marsh bird species as above,
plus possibly Black Tern
■
Least Bittern may be present in
marshes of this size
■
Small numbers of diving ducks possible
(e.g., Redhead, Canvasback,
Ruddy Duck)
■
All marsh species, although some may
still have small populations
■
Fully-functional ecosystem
How Much Habitat is Enough?
19
2.1.6 Wetland Shape
> Guideline
As with upland forests, in order to maximize habitat opportunities for edge-intolerant species, and
where the surrounding matrix is not natural habitat, swamps should be regularly shaped with
minimum edge and maximum interior habitat.
> Rationale
The optimum shape of a wetland also varies by wetland type. Treed swamps are a type of forest, and
the discussion on forest shape applies: they can be most useful to edge-intolerant species when they are
regularly-shaped (e.g., a circle). The less edge-to-area ratio a swamp has, the better it will support wildlife
species that are adapted to interior habitat conditions (see Figure 1).
There has been little investigation on the effects of wetland shape with respect to other wetland types,
such as marsh. It is known that biodiversity responds to internal variation in communities (i.e., emergent
versus submerged plant communities within a marsh), and this effect is addressed under Wetland Size.
The shape of a marsh may be important if water quality improvements are an objective. Long, narrow
marshes and those that maximize water contact with vegetation and residence time within the wetland
are likely to be most effective in improving water quality.
Photo by Eric Dresser
20
How Much Habitat is Enough?
2.2 Riparian Habitat Guidelines
Guidelines for riparian habitats (Table 8) relate to the amount of natural vegetation adjacent to a stream,
the width of the vegetated buffer, total suspended solids concentrations, percent imperviousness in
urbanizing watersheds, and fish communities.
Table 8. Summary of Riparian Habitat Guidelines
Parameter
Percent of stream naturally
vegetated
Amount of natural vegetation
adjacent to streams
Total suspended sediments
Percent of an urbanizing
watershed that is impervious
Fish communities
Guideline
Seventy-five percent of stream length should be naturally vegetated.
Streams should have a minimum 30 m wide naturally vegetated adjacent-lands areas
on both sides, greater depending on site-specific conditions.
Where and when possible, suspended-sediment concentrations should be below 25 mg/l
or be consistent with Canadian Council of Ministers of the Environment (1999) guidelines.
Less than 10 percent imperviousness in an urbanizing watershed should maintain stream
water quality and quantity, and preserve aquatic species density and biodiversity. An
upper limit of 30 percent represents a threshold for degraded systems.
Watershed guidelines for fish communities can be established based on knowledge of
underlying characteristics of a watershed (e.g., drainage area, surficial geology, flow
regime), historic and current fish communities, and factors (and their relative magnitudes)
that presently impact the system.
2.2.1 Percent of Stream Naturally Vegetated
> Guideline
Seventy-five percent of stream length should be naturally vegetated.
> Rationale
In a Toronto area study, stream degradation occurred when riparian vegetation amounted to less than
75 percent cover along first to third-order streams (Steedman, 1987). This is consistent with the target
of 75 percent that was selected for the Rouge River watershed in the Toronto and Region AOC.
In the Toronto and Region/Humber River field test of this guideline, the Toronto and Region Conservation
Authority (TRCA) commented that there are many cold-water streams that have less than 75 percent, or even
less than 50 percent vegetated riparian habitats. TRCA felt that the level of achievement gained by stream
buffers was more related to stream integrity as measured by fish community targets than by warm or cold-water.
Related comments were provided by Gartner Lee Limited (1997b) in the Severn Sound/Hogg Creek field
test. In Hogg Creek, only 43 percent of the first to third-order streams are vegetated; however, several
tributaries of the main branch of Hogg Creek exhibit cold-water characteristics, which seem to relate to
a high ratio of baseflow (46.9 percent) as a percentage of average annual discharge per square kilometre.
Gartner Lee Limited (1997a) also note that the presence of cold-water streams is heavily dependent
on the geological characteristics of the area. They suggested that the guideline may be best viewed as
the percentage of riparian habitat that is vegetated along first to third-order streams in permeable soils
(i.e., smaller headwater streams in clay soils are more likely seasonally dry and therefore the riparian
cover holds less significance). This discussion highlights the need to consider a number of factors in
stream corridors along with the readily measurable percentage of riparian cover.
How Much Habitat is Enough?
21
The Importance of Stream Orders
Stream order is a measure of the position of a stream or river in the hierarchy of the tributaries which
make up the watershed. First-order streams are headwater streams that do not have any tributaries.
Second-order streams are those with only first-order streams as tributaries. Third-order streams start
below the confluence of second-order tributaries, and so on. In general, the higher the order, the larger
the stream or river. In Ontario, most drainage systems rarely have in excess of a fifth-order stream prior
to emptying into one of the Great Lakes.
As the order of a stream increases, the flow and width increases. Small headwater streams are generally of
orders one through three. These streams are highly dependent upon vegetative cover for stream temperature
moderation and the input of organic matter from adjacent vegetation (e.g., falling leaves and insects) for
production. Stream gradient is generally greater in lower-order (one through three) streams, which often
indicates higher erosion potential if riparian vegetation is removed. As stream order increases there is
greater in-stream productivity and there is a transition from a stream dominated by terrestrial vegetation
to one dominated by internal production. Higher order streams generally have a lower gradient with
correspondingly deeper, slower-moving flows. Deposition of suspended sediments may be significant
in some locations.
The characteristics of lower-order streams (one through three) make them much more dependent upon
riparian vegetation and buffer strips for protection of natural ecological functions. From a watershed
perspective, planting vegetation along streams of orders one through three will produce greater benefits
than planting along higher-order rivers. Woody vegetation along a smaller stream has better potential to
provide sufficient cover to lower summer maximum stream temperatures than along the banks of a large
river, but deep-rooted vegetation is important in maintaining bank stabilization along larger river systems.
A recent study in a heavily-forested environment found an overall decrease in fish abundance as the
length of non-forest riparian patch increased and suggested that downstream fish habitat impairment may
follow if forested riparian buffers are disrupted over much more than one kilometre to three kilometres in
length (Jones et al., 1999). Others have suggested that upstream processes (such as those found in largely
deforested watersheds) may overwhelm the ability of riparian vegetation to support stable in-stream
habitat (Roth et al., 1996 as cited in Jones et al. 1999). Guidelines for maximum lengths of disrupted
riparian buffer and their location within the watershed could be generated on a watershed basis, thus
taking account of the conditions encountered.
The percent of natural vegetation along first to third-order streams is readily measured through the use of
remotely-sensed data and Geographic Information Systems (GIS). However, it is often difficult to measure
grassy vegetation remotely, so percent vegetated often refers to percent woody vegetation. In some cases,
grassy vegetation may be preferable to woody vegetation (i.e., adjacent to first-order headwater streams
that are small and often arise from cool groundwater). These cool, narrow streams (less than 2.5 metres)
often do not require thermal protection or leafy material from a shrub or tree, as grasses will suffice (Blann
et al., 2002). Therefore, it is important to note that although it is difficult to measure using remote sensing
techniques, grassy riparian vegetation may be just as important to the stream system as woody vegetation.
22
How Much Habitat is Enough?
The Rouge River example: Applying the 75 percent rule
The TRCA completed a study of the Rouge River drainage system, called the Forested Watersheds Study,
which analyzed watercourses by order and amount of riparian vegetation. This information is used to
guide habitat restoration and reforestation efforts (Strus et al., 1995). Summarized below are the amounts
of stream/river by order with riparian vegetation on either side of the stream.
The habitat targets for the Rouge River watershed include a 30-metre buffer strip along 75 percent of
stream length. A threshold of fish community degradation in Toronto area streams was defined when less
than 75 percent vegetated cover remained in riparian lands. From the table above, it is apparent that none
of the stream groups examined has 75 percent forest cover. To achieve the best benefit for rehabilitation
effort, priority will be given to first-order streams.
Non-Forested Streams
Stream Order Forested
1st
2nd
3rd
Other
Total
Area (ha)
1,216.0
483.0
211.0
691.0
2,601.0
Length (km)
202.0
80.0
35.0
115.0
432.0
Percent
18.0
33.0
41.0
40.0
40.5
Source:
Modified from Strus et al., 1995
Photo by Eric Dresser
How Much Habitat is Enough?
23
2.2.2 Amount of Natural Vegetation Adjacent to Streams
> Guideline
Streams should have a minimum 30-metre wide naturally vegetated adjacent lands area on both
sides, greater depending on site-specific conditions.
> Rationale
It is difficult to generalize about the effectiveness
of natural vegetative adjacent lands (buffers) in
riparian situations as so much depends on the
nature of the watercourse, soil types, vegetation
cover types, slopes, and adjacent-land uses. In
addition, the possibility of solutions that incorporate
remedial bioengineering techniques to attenuate
adjacent-land width requirements is a developing
field that will play an increasing role in the future.
A review of adjacent-land requirements for the
attenuation of sediments and nutrients was provided
in the section of this report that addresses the
amount of wetland vegetation adjacent to wetlands.
However, riparian zones possess an unusually
diverse array of species and environmental processes
(Naiman and Decamps, 1997), and in many
respects, the science is necessarily more complex
than that which applies to wetlands.
A review of riparian adjacent lands (Knutson and
Naef, 1997) presented a variety of sources that
varied in the typical range of three to 200 metres,
but with a preponderance in the 23 to 60-metre
range (all these are applied to both sides of the
stream). They concluded by recommending
that fish-bearing streams have either 46 or 61metre buffers depending on their classification,
extending to 76 metres for shorelines or streams
of state-wide significance.
In reviews by Castelle et al. (1994) and O’Laughlin
and Belt (1995), and based on a variety of sitespecific conditions, adjacent-lands widths of three
to 200 metres were found to be effective for
different functions in riparian zones. The Castelle
et al. (1994) review looked at the effectiveness
of different-sized areas in sediment removal. The
relationship between width and sediment removal
24
How Much Habitat is Enough?
was non-linear, with disproportionately wider areas
required for relatively small improvements in
sediment removal. For example in one test case,
widths of 30.5 metres removed 90 percent of
sediments on a two percent slope, but a width of
61 metres was necessary to remove 95 percent
of sediments. In another study, a 24-metre width
removed 92 percent of sediment in runoff from
a feedlot; two other studies found that widths of
60 metres were effective in removing 80 percent
or more of sediments even on steep slopes.
Relatively narrow adjacent-lands areas may be
adequate when the area is in good condition
(i.e., dense, native vegetation on undisturbed
soils), and the adjacent-land use has a low impact
potential (i.e., parkland, low density residential,
shallow slopes, or non-erosive soils). Larger
adjacent lands areas are required for high value
resources, where the area is in poor condition,
where soils are less permeable or highly erodible,
slopes are steep, or where the adjacent-land use
is intense (e.g., intensive agriculture). Widths
may also be influenced by the sensitivity of the
receiving watercourse and its ability to assimilate
any stressors.
Established vegetated adjacent-lands areas are
fairly efficient at removing excess nutrients from
water. In some studies, areas as narrow as 4.6
metres wide have been 90 percent effective in
removing nitrogen and phosphorus, but most areas
require a minimum of 10 to 15 metres. A 30-metre
wide adjacent-lands area along a stream adjacent
to logging operations greatly reduced nutrient
levels to below drinking-water standards. Wooded
riparian adjacent land areas in Maryland removed
80 percent of excess phosphorus and 89 percent
of excess nitrogen, mostly within the first 19 metres.
A recent study (Lee et al., 2003) found that >97
percent of sediment and 80 to 90 percent of key
nutrients could be removed with a 16.3-metre
mature grass/woody riparian adjacent-lands area.
The Draft Chesapeake Bay Program (2001)
recommends buffers of 7.6 to 76 metres.
The range of appropriate adjacent-lands area
widths based on function is great; for most
functions, the published range in the literature
varies from a few metres to over 100 metres.
In addition, the total width of the riparian zone
is indicated as the feature of interest in some
literature (e.g., as wildlife corridors or habitat).
However, riparian adjacent lands areas are usually
described for application to each side of the
watercourse and this has created some confusion.
In conclusion, the recommended guideline is
a minimum 30-metre wide naturally vegetated
adjacent-lands area on each side of the watercourse.
This minimum is strongly supported in the
literature for riparian systems, but depending on
site-specific parameters it may need to be greater
to attain the desired level of function. It is also worth
noting that there is increasing scientific support
for this guideline to be expanded to 50 metres and
this is one guideline that may change in the future
as more information becomes available.
2.2.3 Total Suspended Sediment Concentrations
> Guideline
Where and when possible suspended sediment concentrations should be below 25 milligrams/litre
or be consistent with Canadian Council of Ministers of the Environment (1999) guidelines.
> Rationale
Suspended sediments may adversely affect aquatic
habitat by filling in interstices of coarse substrate,
thereby limiting habitat for aquatic invertebrates.
As amounts increase and material settles, coarse
substrate may be covered with finer sediments,
fish eggs may be smothered, and under extreme
conditions, fish that feed by sight may have difficulty
in finding prey, gills may become clogged, and
disease may occur. Suspended sediments may also
adversely affect plant communities by reducing
light penetration into the water column, reducing
the extent of submergent vegetation, and
smothering plants. Increased abrasion of stream
channels may occur from an oversupply of
suspended sediments. For a concise overview
of the problem of sediment in water for fish see
OMNR (1992); more detailed information is
available in the Canadian Environmental Quality
Guidelines (CCME, 1999).
Alabaster and Lloyd (1982) presented the quality
of fishery that may be expected with different
levels of suspended sediments:
■
normally less than 25 milligrams/litre:
no harmful effects
■
normally between 25 and 80 milligrams/litre:
good fishery maintainable
■
normally between 80 and 400 milligrams/litre:
moderate to poor fishery maintainable
■
normally greater than 400 milligrams/litre:
poor quality fishery maintainable.
In an evaluation of this guideline on the urbanized
Don River, the TRCA found that suspended
sediment levels varied dramatically with flow
conditions where the dry weather flows tended
to have much less suspended material than high
flows. In response to this, the Don Watershed
Report Card (Don Watershed Regeneration
How Much Habitat is Enough?
25
Council and TRCA, 1997) suggested the target
for suspended sediment to be achieved by 2030
should be less than 80 milligrams/litre more
than 75 percent of the time, incorporating the
understanding that management activities will
only be effective in reducing suspended sediments
for the intermediate and small flow events in
an urbanized watershed. Suspended sediments
will not consistently be within the 25 to 80
milligrams/litre threshold.
Gartner Lee Limited (1997b) found a similar
pattern in Severn Sound’s Hogg Creek, a rural
agricultural watershed. Peak values of suspended
sediments reached 234 and 459 milligrams/litre
during short-term runoff events; however, the
median amounts of suspended sediments were
found to be in the order of 10 milligrams/litre,
suggesting that a good fishery is maintainable in
the creek. Gartner Lee Limited note that peak
concentrations indicated that there are periodic
problems associated with runoff that meant that
the stream did not remain below the suspended
sediment guidelines all of the time. Of importance
to the guidelines presented in this Framework,
Gartner Lee Limited recommended that the high
levels of suspended sediments associated with
runoff events should be addressed through
measures such as developing vegetated adjacentland strips used to filter runoff from adjacent
agricultural land-uses.
In a review of relevant data, Newcombe and
MacDonald (1991) found that aquatic biota
respond to both the concentration of suspended
sediments and the duration of the exposure. They
developed a stress index ranking the severity of
effects of suspended sediments on fish and aquatic
life ranging from lethal (outright mortality),
sublethal (reduction in growth rates, moderate
habitat degradation, injured tissues), and
behavioural effects (reduction in feeding rates,
avoidance response, abandonment of cover). They
reviewed species-specific effects based on length
of exposure, physical effect, and ranking of the
effect based on the stress index. From their review
of a range of values from different studies they
found that the data were too variable to formulate
generalizations about the effects of suspended
sediments. However, they argued that high
concentrations over even a short duration of time
(i.e., the spring freshet period discussed earlier in
the Toronto and Severn Sound examples) can have
extreme effects on biota. This indicates a need to
measure and remediate high event-associated
concentrations of suspended sediments, not just
concentrations calculated by averaging readings
taken over a year.
When evaluating the effects of suspended
sediments, the concentration, duration, and timing
of suspended-sediment values should be taken into
account. Large volumes of suspended sediments
in urbanized and agricultural watersheds may cause
severe but lethal short-term effects on stream biota.
Average annual suspended-sediment concentrations
in isolation do not tell the complete story. This is
why the new CCME (1999) guidelines incorporate
various parameters.
Table 9. Total Suspended Sediment Concentrations
A site-specific condition that is based on background levels, not low flow.
For Clear Flow
For High Flow
■ short-term exposure (e.g., over 24 hours)
– no anthropogenic-induced increase more than 25 milligrams/litre
■ no increase more than 25 milligrams/litre
when background levels are between 25
and 250 milligrams/litre
■ no increase over 10 percent of background
level when background levels exceed
250 milligrams/litre
■ long-term exposure (e.g., over 30 days)
– average suspended sediment should not increase by more
than 5 milligrams/litre over background
26
How Much Habitat is Enough?
2.2.4 Percent of an Urbanizing Watershed that is Impervious
> Guideline
Less than 10 percent imperviousness in an urbanizing watershed should maintain stream-water
quality and quantity, and preserve aquatic species density and biodiversity. An upper limit of
30 percent represents a threshold for degraded systems.
> Rationale
The replacement of natural vegetation with
impervious surfaces contributes to disturbed
runoff processes within urban watersheds (Booth,
1991; Booth et al., 1997; Booth, 2000; Knutson
and Naef, 1997). The loss of fish and wildlife
habitat, along with channel erosion and
downstream flooding, are the primary components
of stream-system decline that result from
imperviousness within a watershed (Booth 1997;
Booth 2000; Knutson and Naef, 1997). The effects
of natural vegetation loss to impervious surfaces
are often permanent (Booth, 1991), and in this
regard implementing mitigation efforts after
impervious surfaces are established is largely
unsuccessful (Booth, 1997).
The debate on identifying reasonable thresholds
for impervious surfaces within a watershed began
in 1979. In his pivotal paper, Klein (1979) reported
that impairment of stream quality is first noted at
10 to 12 percent impervious cover and becomes
severely impaired at 30 percent watershed
imperviousness. From a review of the recent
literature regarding the effects of urbanization on
aquatic systems, the Stormwater Manager’s
Resource Center proposed that two thresholds
exist within urbanized watersheds: at 10 percent
imperviousness, certain stream-quality parameters
will be affected and at 25 to 30 percent impervious
cover, stream quality will consistently shift to a
degraded condition (www.stormwatercenter.net).
Booth (1991) found that after 10 percent of a
watershed was covered with impervious surfaces,
there was a rapid decline in fish habitat and
channel stability of riparian zones. In addition,
Booth (1991) stated that urban development both
magnifies peak discharges and creates new peak
runoff events. In a later study, Booth and Jackson
(1994) demonstrated that unstable stream banks
and channels occurred when watershed
imperviousness surpassed 10 percent. Snodgrass
(1992) reported that water quality became
degraded when hard surfaces from development
(e.g., housing, roads) reached 15 to 25 percent
of the watershed. State-of-the-art stormwatermanagement could not prevent stream-quality
impairment in the study provided by Snodgrass
(1992). Schueler (1994) reports on a number of
studies that relate imperviousness to runoff
characteristics, the shape of streams, water quality,
pollutant loading, stream warming, as well as
stream biodiversity. In his review, he suggests that
impervious land-use should remain below 10
percent as a guideline to protect stressed streams.
Various indicators of aquatic macroinvertebrate
community health are widely used as relationship
indicators between watershed imperviousness and
aquatic systems. The thresholds presented below
are taken from the Stormwater Manager’s Resource
Center review (www.stormwatercenter.net). As
impervious cover increased to eight to nine percent
within a watershed, there was a significant decline
in wetland aquatic macroinvertebrate health (Hicks
and Larson, 1997). When the percentage of total
impervious surfaces surpassed five to 10 percent of
a watershed landscape, there was a rapid decline in
biological stream indicators (May et al., 1997). At a
study conducted in Washington, D.C., a significant
decline in the diversity of aquatic insects was noted
at 10 percent impervious cover (MWCOG, 1992).
Further, the density and diversity of wetland plants,
amphibians, and fish are also impaired as watershed
How Much Habitat is Enough?
27
imperviousness exceeds 10 percent (Limburg
and Schmidt, 1990; Taylor, 1993; Weaver, 1991).
The most commonly-chosen threshold for
impervious surfaces is 10 percent of the land cover
within a watershed (Booth, 2000). Although not every
watershed will respond uniformly or as anticipated to
proposed impervious-surface thresholds, a guideline
of 10 percent or less will do much to preserve the
health of aquatic systems. Further, a second
threshold of 30 percent or less impervious surfaces
is suggested for urban watersheds that have, to date,
exceeded the proposed 10 percent impervioussurface guideline. In addition, implementing and
defending stormwater best-management practices in
watersheds that are near or exceeding the 10 percent
guideline will aid in maintaining aquatic systems.
In relatively undeveloped rural watersheds,
stream baseflow is dictated by underlying soils
and geologic conditions that influence the amount
of groundwater discharge. Within urbanizing
watersheds, however, careful planning must ensue
to mitigate the effects of impervious surfaces.
Extreme peak flows typical of urban environments
can be reduced through minimizing hard surfaces.
Booth et al. (1997) suggests that by reducing the
surface area covered by constructed surfaces
(rooftops, pavement, compacted soils), these
necessary impervious areas can be generated using
new products, such as permeable pavements that
allow for infiltration of water.
2.2.5 Establishing Fish Community Targets
> Guideline
Watershed guidelines for fish communities can be established based on knowledge of underlying
characteristics of a watershed (e.g., drainage area, surficial geology, flow regime), historic and current
fish communities, and factors (and their relative magnitudes) that presently impact the system.
> Rationale
The TRCA has developed a guide for use in
establishing fish community targets and measuring
the health of aquatic habitats in Toronto area
watersheds. The guide, or Framework, can be
used to assist in restoring both fish and wildlife
habitat and populations. Municipalities and other
users of the guide will likely wish to request advice
from fishery biologists at the Ontario Ministry of
Natural Resources and/or the local Conservation
Authority prior to application.
The general Framework is derived from TRCA’s
work in establishing fish management plans for
the Rouge River, Don River, and Humber River
watersheds in the Toronto and Region AOC. The
approach is based on three types of information:
28
How Much Habitat is Enough?
■
knowledge of the fundamental or underlying
characteristics of the watershed or
subwatershed (e.g., drainage area, surficial
geology, flow regime) and the makeup of
historical fish communities
■
knowledge of what the system is presently
supporting (i.e., the existing fish community)
and some idea of its condition
■
knowledge of the factors that presently
impact the system and their relative
magnitudes.
The establishment of a historical context for
function provides the fundamental reference point
required to assist in setting targets; the second
reference point is the existing condition along with
some knowledge of the magnitude of impacts.
Comparison of these two conditions provides a
realistic context for the establishment of targets
and identification of rehabilitation activities.
The historic condition provides the direction for
rehabilitation while the existing condition indicates
how far the system is from being healthy and what
needs to be improved. The knowledge of the
magnitude of impacts is also necessary because
the establishment of targets must include an
assessment of what might reasonably be achieved
with existing technology and land-use patterns.
Based on available literature and work in the
Rouge, Don and Humber River watersheds, the
Framework for setting fish-community targets
provides a general guide to assist habitat
rehabilitation practitioners in the development
of fish-community expectations and targets for
watercourses in their area. The Framework is
based on information available for streams in
southern Ontario, and therefore, may not be
directly applicable to other areas (see Appendix 4
for a full discussion of its application in Toronto
area watersheds).
2.2.6 Additional Riparian Parameters
The Framework largely focuses on terrestrial habitat and its relation to the health of streams and
waterbodies. The emphasis is on the reduction of terrestrial impacts upon watercourses that can be
achieved through protection and restoration of vegetation. There is also a large and growing body of
knowledge on in-stream habitat and hydraulic parameters. Factors such as baseflow contributions, a
stream’s pool-to-riffle ratio, and channel sinuosity should be considered when assessing stream health
while conducting a stream rehabilitation program across a watershed.
Photo by CWS
How Much Habitat is Enough?
29
2.3 Forest Habitat Guidelines
The following series of guidelines for forest habitat (Table 9) relate to overall forest cover, size of forest
patch, percent of interior forest, shape and proximity of a forest patch to other patches, corridors, and
forest quality.
Table 10. Summary of Forest Habitat Guidelines
Parameter Guideline
Percent forest cover
Size of largest forest patch
Percent of watershed that is
forest cover 100 m and
200 m from forest edge
Forest shape
Proximity to other forested
patches
Fragmented landscapes and
the role of corridors
Forest quality — species
composition and age
structure
At least 30 percent of the AOC watershed should be in forest cover.
A watershed or other land unit should have at least one 200 ha forest patch which is a minimum
500 m in width.
The proportion of the watershed that is forest cover 100 m or further from the forest edge
should be greater than 10 percent.
The proportion of the watershed that is forest cover 200 m or further from the forest edge
should be greater than five percent.
To be of maximum use to species such as forest breeding birds that are intolerant of edge
habitat, forest patches should be circular or square in shape.
To be of maximum use to species such as forest-interior birds, forest patches should be within
two km of one another or other supporting habitat features.
Connectivity width will vary depending on the objectives of the project and the attributes of the
nodes that will be connected. Corridors designed to facilitate species movement should be a
minimum of 50 m to 100 m in width. Corridors designed to accommodate breeding habitat for
specialist species need to be designed to meet the habitat requirements of those target species.
Watershed forest cover should be representative of the full diversity of forest types found
at that latitude.
2.3.1 Percent Forest Cover
> Guideline
At least 30 percent of the Area of Concern watershed should be in forest cover.
> Rationale
The amount of forest cover in a landscape
determines its ability to support wildlife species.
This is particularly noticeable for mammals that
require extensive forests. Species such as Gray
Wolf, Lynx, Elk, and Wolverine disappeared from
southern Ontario shortly after forest clearing
was initiated.
Recent literature indicates that a complex
relationship exists between the relative importance
of overall forest cover versus forest patch size and
the ultimate response of individual wildlife species
(Lee et al., 2002). On balance, the axiom “the
bigger, the better” appears to be in the process
30
How Much Habitat is Enough?
of replacement by “the greater amount of habitat
within the landscape mosaic, the better” (see
Austen et al., 2001; Golet, 2001; Fahrig, 2002;
Lindenmayer et al., 2002; Trzcinski et al., 1999;
Friesen et al., 1998; Friesen et al., 1999; Rosenburg
et al., 1999). These studies and reviews have shown
or suggested that forest patch size and shape may
play a lesser role in maintaining biodiversity than
the total amount of forest cover, although the
three metrics are to some extent interrelated.
Empirical studies that have examined the
independent effects of habitat loss versus habitat
fragmentation suggest that habitat loss has a much
larger effect than habitat fragmentation on the
distribution and abundance of birds (Fahrig,
2002). This is supported by other studies that
found forest size and edges effects did not
significantly affect either nesting success or the
productivity of neotropical songbirds (e.g., Friesen
et al., 1998). Golet (2001) found that bird relative
abundance was not predictable from swamp size
and found that the pattern of distribution was
consistent with total forest availability. Lee et al.
(2002) found that the relative importance of patch
characteristics, patch size and landscape forest
cover varied for different bird species.
A further consideration is that landscape-scale
effects (i.e., total forest cover) may be different in
largely-forested environments compared to largely
fragmented environments. It is possible that in large
forested areas (e.g., Quebec’s boreal forest) birds
respond primarily to local habitat effects (Lichstein
et al., 2002) whereas in fragmented landscapes,
landscape-scale forest cover may be critical
(Trzcinski et al., 1999). It is also possible that within
a landscape matrix that includes a significant urban
component, the negative influences originating from
the urban matrix will have different implications for
these landscape-scale effects. However, analysis is
currently lacking on the relative effects on wildlife
productivity of forest cover versus forest patch size
in these types of systems.
The overall effect of a decrease in forest cover on
birds is that certain species disappear and many
of the remaining ones become rare, or fail to
reproduce, while non-forest and edge species
prosper as artificially-inflated populations. Species
with specialized-habitat requirements are most
likely to be affected adversely. Although little data
exist for other wildlife, the reduction of forest
habitat likely affects other forest dependent
species such as Mole Salamanders, Wood Frogs,
and many mammals. In the future, we can expect
more empirical data on the effect of forest loss
for non-bird species.
In one study area near Ottawa, several species of
forest birds disappeared as breeders when forest
cover declined to below 30 percent (Freemark,
1988). In Essex County, with only about three
percent forest cover, many wildlife species that
are common to abundant elsewhere in Ontario
are rare (e.g., Black-capped Chickadee and Whitebreasted Nuthatch [Oldham, 1983]) and 80 percent
of the forest-interior species have disappeared.
In Ottawa-Carleton, Hairy Woodpeckers may be
found in woodlands 10 hectares or even smaller;
whereas in the Town of Markham (five percent
forest cover) none were found, although some
woodlands approached 100 hectares in area.
Table 10 summarizes the number of forestassociated breeding birds in five areas with varying
amounts of forest cover. The total number of
species present is compared to the number
of species that could occur, based on broad
geographic ranges. As the top third of the table
indicates, 100 percent of the species that should
occur are present in Ottawa-Carleton, which is
approximately 30 percent forested. In contrast,
Essex (at three percent forest cover) has lost
almost 40 percent of its forest birds. The Ontario
Breeding Bird Atlas (Atlas) results (Cadman
et al., 1987) were used to determine the number
of forest-dependent bird species in municipalities
with varying amounts of forest cover (an explanation
of how to use the Atlas for local study areas follows
in a subsequent section). A new Atlas is being
compiled and updates are available on-line:
www.birdsontario.org/atlas/atlasmain.html.
How Much Habitat is Enough?
31
Table 11. Number of Forest-Associated Bird Species in Five Areas of Southern Ontario with Differing
Percentages of Forest Cover (Adjusted for Potential Breeding Ranges Based on Pre-settlement Habitat)
OttawaCarleton
Percent forest cover
Total number of species within range
Number of species occurring
Percent of total number of species within range present
Number of FIE and FI species within range
Number of FIE and FI species present
Percent of FIE and FI species within range present
Number of FI species within range
Total FI species present
Percent of FI species within range present
FIE Forest-interior/Edge (moderately edge-intolerant)
29.4
94.0
94.0
100.0
60.0
60.0
100.0
18.0
18.0
100.0
Haldimand- Waterloo and
Middlesex
Norfolk
Wellington
16.2
102.0
98.0
96.1
66.0
2.0
93.9
20.0
19.0
95.0
14.8/18.2
100.0
88.0
88.0
64.0
54.0
84.4
20.0
15.0
75.0
13.5
102.0
83.0
81.5
61.0
50.0
82.0
20.0
16.0
80.0
Essex
3.0
102.0
63.0
61.7
66.0
36.0
54.5
20.0
4.0
20.0
FI Forest-interior (highly edge-intolerant)
Source: Cadman et al. (1987); Riley and Mohr (1994)
Other studies have supported a 20 to 30 percent threshold beyond which persistence of bird species was
virtually ensured or that habitat configuration had little or no affect on species richness or abundance
((Fahrig, 1997; Andrén, 1994; both cited in Villard et al., 1999). Data collected by Tate (1998) also
suggests that bird species favouring interior habitat conditions continue to increase in number from
20 percent to at least 35 percent forest cover depending on the scale of the analysis.
Photo by John Mitchell
32
How Much Habitat is Enough?
Effects of Forest Cover Loss and Fragmentation
Forest habitat guidelines are designed to address habitat loss and fragmentation as two of the key
factors in the decline of wildlife species. The loss of forest cover not only directly results in habitat
loss, but it also contributes to increased water run-off quantity (Bosch and Hewlett, 1982) and
associated water-quality concerns. Forest birds are often used as indicators of the quality of the
landscape because they are more easily surveyed, and more is known about their habitat requirements
and distribution than any other group of wildlife. Much less is known about the sensitivity of
invertebrates, amphibians, reptiles, plants, and small mammals to forest fragmentation.
One of the key factors that contributes to an understanding of the loss of birds from a fragmented
landscape is the concept of metapopulations (semi-isolated populations in a region, linked by dispersion)
(Merriam, 1988; Opdam, 1991). Local extirpations of populations occur naturally within forests due to
failed reproductive efforts because of factors such as predation, parasitism, adverse weather conditions,
natural catastrophes (e.g., fire, floods), and insufficient food. Under normal circumstances, forest
patches become recolonized by individuals from adjacent areas (so-called source-sink dynamics [Howe
et al., 1991]). However, as overall natural area declines, there may be no source of colonists due to other
local extinctions as a result of lack of connectivity, and extirpations may become permanent. Recent
studies suggest that the same factors may regulate amphibian populations (e.g., Knutson et al., 2000).
The metapopulations concept can be used to explain the fact that the breeding bird assemblage in
forests changes annually (Villard et al., 1992). Common species are always present, but the more
specialized species are sporadic in occurrence. It has been demonstrated that the number of breeding
pairs in a region remains almost constant, but that the areas used for breeding vary. Thus, a woodland
may support a given species as infrequently as once every four or five years, yet this woodland is still
critical to the overall maintenance of the regional populations. The disappearance of apparently
insignificant woodlands may cause declines in the size of wildlife populations.
Factors such as overall forest cover, forest size, shape and degree of fragmentation all affect the
viability of habitat for wildlife species. However, for forest-dependent fauna, the overall forest cover
in the environment may be the single most important habitat metric. The negative effects of forest loss
may not be countered by careful consideration of the spatial pattern of remaining forest (Trzcinski
et al., 1999). This may be particularly important to consider in light of the fact that a review of
134 fragmentation studies showed evidence that the ecological mechanisms and effects of habitat
fragmentation are poorly understood (McGarigal and Cushman, 2002).
How Much Habitat is Enough?
33
2.3.2 Size of Largest Forest Patch
> Guideline
A watershed or other land unit should have at least one 200 hectare forest patch that is a minimum
500 metres in width.
> Rationale
In the forest-cover guideline, the relative importance
of overall forest cover and the pattern of forest cover
were discussed. Despite increasing support in the
literature indicating the significant contribution of
forest cover, it remains clear that forest patch size can
be important to many wildlife species. Some studies
have suggested that as the relative importance of
patch size, patch characteristics and landscape cover
varies for different species and these multiple factors
should be considered in conservation planning (Lee
et al., 2002; Mortberg, 2001; Villard et al., 1999;
Andren, 1996). By way of examples, some recent
studies have identified only large (500 hectare) or
continuous forests as sources for Ovenbirds (Burke
and Nol, 2000; Mancke and Gavin, 2000); while
others have demonstrated productivity in Wood
Thrushes that appeared to be independent of forest
size (Friesen et al., 1999).
Larger patches of forest tend to have a greater
diversity of habitat niches and therefore are more
likely to support a greater richness and/or diversity
of wildlife species. Very large patch sizes are
also associated with total forest cover as these
phenomena tend to occur simultaneously in
real-world landscapes (Villard et al., 1999).
Robbins et al. (1989) determined habitat area
requirements for forest birds in the mid-Atlantic
states. Almost all of the bird species documented
occurred at least occasionally in forests 100 hectares
or smaller; the few species not found in forests this
small have been confirmed breeding in southern
Ontario forests 100 hectares or smaller. However,
100 hectares is considered an absolute minimum
guideline for forest patch size. Many of the most
area-sensitive or edge-intolerant species are rare in
forests this small; the probability of detecting some
34
How Much Habitat is Enough?
of these species in 100-hectare forests is as low
as 20 to 30 percent (Robbins et al., 1989).
In the Illinois Department of Conservation
management guidelines for forest and grassland
birds, Herkert et al. (1993) suggest that a 400hectare forest patch was required to support 75 to
80 percent of the highly sensitive regional forest
bird species pool. They predicted that a 100-hectare
forest patch should contain about 60 percent of
the highly-sensitive species. Forest bird species
preferring interior habitat conditions, as discussed
here, incorporate all of the highly-sensitive species
identified by Herkert et al. (1993).
In the summer of 1997, Tate (1998) evaluated the
forest patch size guideline outlined in this guide by
surveying four large forest patches ranging in size
from 140 to 201 hectares in the Severn Sound
AOC. Tate found over 70 percent of the regional
pool of forest bird species in the four forest tracts
collectively, and 79 to 87 percent of the expected
forest-interior species in individual tracts between
100 and 200 hectares in size. From this work, it
was determined that a single tract of 100 hectares
was too small to support the regional forest bird
community. Instead, a forest patch of 200 hectares
was recommended, which will be more likely to
provide suitable habitat for species that prefer
interior habitat conditions, and over 80 percent of
all expected species may occur. Several large tracts
of forest are recommended as they will support
90 to 100 percent of all expected species (see
Appendix 5 for details).
Table 7 summarized some of the relationships
between wildlife and size of forest, marsh and
grassland habitat, and the following table
summarizes data from Tate (1998) and others.
Table 12. Anticipated Response by Forest Birds to Size of Largest Forest Patch
Size of Largest Forest Patch
200 ha
100 ha
50 - 75 ha
20 - 50 ha
<20 ha
Response by Forest Associated
Will support 80 percent of edge-intolerant species including most area-sensitive species.
Will support approximately 60 percent of edge-intolerant species including most
area-sensitive species.
Will support some edge-intolerant species, but several will be absent and edge-tolerant
species will dominate.
May support a few area-sensitive species but few that are intolerant of edge habitat.
Dominated by edge-tolerant species only.
2.3.3 Percent of Watershed that is Forest Cover 100 metres
and 200 metres from Edge
> Guideline
The proportion of the watershed that is forest cover 100 metres or further from the forest edge should
be greater than 10 percent. The proportion of the watershed that is forest cover 200 metres or further
from the forest edge should be greater than five percent.
> Rationale
In a southern Ontario study, Sandilands and
Hounsell (1994) determined that certain bird
species avoided forest edges in small forests when
they were breeding. In larger forests, one guild (or
group) of species typically nested 100 metres or
further from the edge, while a second guild nested
200 metres or further from the edge. More recent
work has at least partly confirmed these findings.
For example, Austen et al. (2001) found that edge
intolerant (“forest-interior”) species increased
and edge-tolerant species decreased with both
increasing woodlot size and core area, and Burke
and Nol (2000) concluded that Ovenbirds required
90 hectares of interior forest to be successful.
Other studies have also found that predator
intrusions have the potential to induce patch size
effects (Cantrell, 2001); that avian predators can
be more abundant in forest edges (Chalfoun et al.,
2002), and that depth or distance to edge affects
forest-breeding birds (Mancke and Gavin, 2000).
As forest area alone cannot account for edge
effects within a forest patch (as this is dependent
on variables such as shape), guideline thresholds
that address distance from an edge or “depth”
need to be developed. This concept of forestinterior habitat therefore takes into account the
effects of both patch size and patch shape.
Tate (1998) suggests that the amount of interior
forest habitat is more critical to improving
conditions for edge-intolerant bird species when
planning across larger land units (i.e., 1,600 square
kilometres) versus smaller subwatersheds (i.e., 100
square kilometres). See Appendix 5 for details.
Table 7 summarizes how forest-associated bird
species are affected by differing percentages
of intolerant forest cover. In this table, species
designated as forest-interior/edge-species are
those that tend to nest inside forests, and a high
proportion of them nest 100 metres or further
from the forest edge. Forest-interior species are
those that are most sensitive to habitat edges and
are usually found nesting 200 metres or further
from the edge. Note that when forest cover
declines to around 15 percent (in combination
with fragmentation into smaller forest patches),
20 to 25 percent of edge-intolerant species
disappear. An exception is Haldimand-Norfolk,
How Much Habitat is Enough?
35
which continues to support a high percentage of forest-breeding birds.
This is partly because it contains several large (1,000 hectare) forests
in relatively close proximity, and several areas within the county
contain over 30 percent forest cover.
Deep forest habitat is also a contributor to landscape richness. This is
a concept that considers the spatial distribution, quality, and diversity
of habitats. A rich landscape has representation of all natural habitats
that occurred historically, which are well connected to adjacent habitat
types. Not only should a wide range of habitats be represented in a
landscape or study area, a range of successional stages of each habitat
should be present. Each habitat and each age class of habitat has
the potential to support different plant and wildlife species. Rich
landscapes enhance biodiversity, and ameliorate the effects of natural
catastrophes such as diseases or insect infestations.
Photo by CWS
36
How Much Habitat is Enough?
Using the Forest Cover and Interior Forest Cover Guidelines:
Effects of Scale
In order to test the efficacy of the forest habitat guidelines (i.e., 30 percent forest cover, five percent
200-metre interior forest cover), the Canadian Wildlife Service (Tate 1998) used Geographic
Information System (GIS) to overlay forest bird species occurrence from the Atlas and forest cover
from the Ontario Hydro satellite image database of forest cover for southern Ontario. The presence
of forest bird species in relation to percent forest cover, and percent forest-interior cover was analyzed
at four different scales: 10 000 hectares (100 square kilometres, or a single Atlas square); 40 000
hectares (400 square kilometres, or four Atlas squares); 90 000 hectares (900 square kilometres,
or nine Atlas squares); and 160 000 hectares (1,600 square kilometres, or 16 Atlas squares).
The applicability of each guideline and the response by forest birds varied considerably with the scale
at which statistical analysis was conducted. This work identifies the importance of setting different
targets for critical amounts of forest habitat rehabilitation at different scales from subwatersheds up
to regional landscapes. Please refer to Appendix 5 for tables demonstrating how the number of forestinterior birds changes with varying amounts of forest cover at different scales.
2.3.4 Additional Forest Parameters
The guidelines outlined above (percent forest cover, size of forest patch, and percent of forest-interior
habitat), are readily measured through the use of remotely sensed data and Geographic Information
Systems (GIS). Additional guidelines that can be important but more difficult to measure follow.
Forest Shape
> Guideline
To be of maximum use to species such as fores- breeding birds that are intolerant of edge habitat,
forest patches should be circular or square in shape.
> Rationale
Figure 1 demonstrates how habitat shape
influences the amount of interior habitat. Square
or circular habitats provide the greatest amounts
of interior habitat compared to the area of habitat
that is influenced by edge. Similarly-sized linear
or irregularly-shaped habitats may contain little
or no interior.
How Much Habitat is Enough?
37
Figure 1. Forest Shape Determines Amount of Forest-interior (Ecological Services for Planning Limited, 1995)
There is conflicting evidence in the literature regarding the response of birds to edge habitats. Some
studies have found evidence that linear habitats may have higher densities or that edge-use avoidance
is linked to overall density of the species within the patch (Bollinger and Switzer, 2002). However, the
literature appears relatively consistent, for example, on the increased negative effects of Cowbird nest
parasitism and avian predators on edge-nesting birds (Chalfoun et al., 2002). Although the same authors
caution strongly against generalization about nest predators and edges, they found that there were no
differences in small and medium-sized mammalian predators between edge and interior.
Areas with high edge-to-interior ratios tend to favour edge specialists and generalist species as opposed
to those species that are usually considered to be interior specialists or are at least edge-intolerant.
Various edge effects (e.g., predation, disturbance, changes in food supply) may be important in some
circumstances for some species. These effects likely extend from birds to other groups such as plants
(Bowles, 1999) and bryophytes (Hylander et al., 2002).
Some of the confusion regarding the role of patch shape may be due to the use of presence-absence
data (which are relatively easy to collect) compared to the detailed investigations needed to determine
productivity of various wildlife species in linear versus circular habitat patches. Nevertheless, it is clear
that in terms of restoration opportunities, the “infilling” of irregular forest patches can offer considerable
benefits in terms of increasing interior habitat conditions (and decreasing the influence of edge) for a
relatively small investment.
38
How Much Habitat is Enough?
Proximity to Other Forested Patches
> Guideline
To be of maximum use to species such as forest-interior birds, forest patches should be within two
kilometres of one another or other supporting habitat features.
> Rationale
Habitats in close proximity to other natural areas support more species than isolated habitats of the same
size. Recolonization of habitat patches by Scarlet Tanagers (a forest-interior species) was found to decrease
as the isolation of patches increased (Hames et al., 2001). Interpatch distance was suggested as a critical
factor for a study that investigated patch colonization by the Common Buckeye butterfly (for a non-forest
habitat) (Haddad, 2000). It is likely that recent improvement in radio-tracking technology will produce
some interesting and relevant research on this topic in the future; in one study, male Hooded Warblers
were recorded travelling up to 0.5 kilometre over open fields, primarily to solicit extra-pair matings
(mating with individuals other than breeding partner) (Norris and Stutchbury, 2001).
Abundant forest cover within two kilometres of a particular forest patch was found to be a significant
predictor for the presence of bird species that prefer interior forest habitat in Norfolk County (Austen
and Bradstreet, 1996).
Some species with large home ranges may use several patches instead of one large area. Close proximity
of habitats also facilitates wildlife movements among them. When rehabilitating habitats, improving the
shape of existing habitats and focussing on areas that are near other natural areas will be most effective.
Fragmented Landscapes and the Role of Corridors
> Guideline
Connectivity width will vary depending on the objectives of the project and the attributes of the nodes
that will be connected. Corridors designed to facilitate species movement should be a minimum of
50 metres to 100 metres in width. Corridors designed to accommodate breeding habitat for specialist
species need to be designed to meet the habitat requirements of those target species.
> Rationale
Riley and Mohr (1994) presented the arguments
for and against the role of corridors as movement
corridors and cited Noss and Harris (1986) who
proposed a conservation strategy that considers
the pattern of existing high-quality nodes relative
to actual and potential corridors.
Arguments regarding the utility of corridors
continue in the literature (e.g., Hannon and
Schmiegelow, 2002; Whitfield, 2001). It is clear
that the development of a corridor strategy needs
to consider landscape features and attributes
(such as natural cover and the composition of
surrounding matrix: i.e., to what are we
connecting?), matching habitat for target species,
corridor opportunities and constraints, as well as a
balanced view of potential ecological effects both
positive and negative.
The determination of optimum corridor widths for
wildlife movement is difficult. This topic is further
complicated by the difference between the
intrinsic habitat values that may be found within
linear habitat patches (e.g., breeding habitat for
area-sensitive breeding birds), and the narrower
function of movement by plants (through
How Much Habitat is Enough?
39
pollination and seed dispersal) or animals along a
pathway that facilitates movement from one node
to another. An area of only one metre in width
will be used as a travel corridor by some wildlife
species, while other species that must breed within
corridors (e.g., some salamanders, small mammals,
or insects) may require much wider features
that will support productive breeding habitat.
The long-term stability of the corridor within the
surrounding existing or future landscape matrix
might also be factored into the determination
of an appropriate width.
would require knowledge of patch size requirement
and an analysis of the potential for edge effects.
In rural landscapes, it has been suggested that
corridors should be as wide as 500 metres for
specialist species, although this approach begins
to overlap corridor function with other functions
such as habitat patch size and shape. Intuitively,
in urban environments it might be supposed that
wider corridors would be required to provide the
same level of function in the face of urban effects,
assuming that target attributes might persist at all
in an urban matrix.
To complicate matters, some species, such as Red
Fox and Coyote, often move through open habitat.
Others, such as White-tailed Deer, are indifferent to
corridors; they tend to go directly from one place to
the next and will either travel through open habitat
or along a corridor if it happens to be leading in
the direction that they want to go. Some species
are obligate users of corridors, either being totally
dependent upon them to get from one natural
patch to another or highly-preferring to use them
to get across the landscape.
Corridors for wildlife must provide suitable habitat
for the species that are expected to move along
them. Vegetation composition in the corridor
should be similar to that in the nodes that it is
connecting (or reflect soil/historic conditions).
The corridor should be continuous between nodes
and a minimum width along its entire length,
although stepping stones of habitat do have
connectivity value, if no other approach is
feasible. (See also the discussion on riparian
habitat guidelines.)
Corridors 50 metres in width can facilitate
movement for common generalist species while
stream corridor widths of 75 metres to 175 metres
have been suggested for breeding bird species
(Spackman et al., 1995). These latter researchers
also found that 10 to 30 metres was sufficient to
include habitat for 90 percent of streamside plant
species. Many studies have demonstrated that
the wider a corridor is, the more effective it is
(Dawson, 1994).
Like wetland adjacent-land areas, corridor widths
must be determined based on a functional
assessment of what the corridor is expected to
achieve. Considering only movement, a minimum
guideline of 50 metres to 100 metres is supportable.
The provision of breeding habitat for target species
40
How Much Habitat is Enough?
Forest Quality: Species Composition and Age Structure
> Guideline
Watershed forest cover should be representative of the full diversity of forest types found at that latitude.
> Rationale
Using remote sensing and GIS, quantitative
measures such as percent forest cover can be
readily measured. However, measuring qualitative
information such as species composition and age
structure of a forest is more difficult, requiring a
higher degree of effort through ground-truthing.
Although forest cover may be plentiful in a
particular watershed, it may consist of early to
mid-successional plant communities, mostly
conifer plantations, or a variety of non-native
species. Now increasingly available (e.g., through
Conservation Authorities), Ecological Land
Classification is a useful source of information
in many locations.
in the Niagara River AOC, Environment Canada
(Snell et al., 1998) used soil drainage categories
to determine the original proportion of upland to
lowland forest present. Due to drastic losses of
upland forest, they recommended that restoration
focus on drier vegetation communities. Deciding
which forest types are priorities for restoration
requires a sense of the pre-settlement landscape
as guidance in the same manner in which a
cumulative impact analysis was recommended
for wetlands prior to decisions being made on
wetland restoration projects (Bedford, 1999).
Austen and Bradstreet (1996) found differences
in forest composition, as defined by proportion
of deciduous-to-coniferous and swamp to upland
forest, were important for individual bird species.
For example, Veery and American Redstart were
found in areas with more deciduous cover, while
Blackburnian Warbler, Pine Warbler, and Ovenbird
were found more often in woodlands with more
coniferous forest.
Working in the Severn Sound AOC, Tate (1998)
suggested that in areas where coniferous and
deciduous forest are both naturally occurring,
at least one forest patch of 200 hectares is
recommended for each forest type to support
all or most edge-intolerant bird species.
Photo by CWS
Site conditions, such as soil and topography,
should play important roles in determining which
habitat types to restore in a particular area. In
order to guide forest and wetland restoration
How Much Habitat is Enough?
41
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Changes in the geometry and the sediment budget of a 3rd-order stream caused by urbanization. Geological Society of America,
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Effects of habitat fragmentation on birds and mammals in landscapes with different proportions of suitable habitat: A review.
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Andren, H. 1996.
Population responses to habitat fragmentation: statistical power and the random sample hypothesis. Oikos, Vol. 76, pp. 235-242.
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50
How Much Habitat is Enough?
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How Much Habitat is Enough?
51
List of Abbreviations and Acronyms
AOC: Area of Concern
CFZ: Critical Function Zone
CCME: Canadian Council of Ministers of the Environment
FI: Forest-interior
FIE: Forest-interior/Edge
Framework: A Framework for Guiding Rehabilitationin Great Lakes Areas of Concern
GIS: Geographic Information System
mg/L: milligrams per Litre
PZ: Protection Zone
PAC: Public Advisory Committee
RAP: Remedial Action Plan
TRCA: Toronto and Region Conservation Authority
UVB: Ultra-Violet radiation of relatively short wavelengths
Photo by Eric Dresser
52
How Much Habitat is Enough?
Appendix 1
The Severn Sound AOC: Habitat Identification and Rehabilitation, Delisting and Use of the Habitat Framework
The Severn Sound Remedial Action Plan Stage Two Report (SSRAP Stage 2) was developed and submitted
in 1993. Stage Two reports are intended to set goals and identify remedial and preventative actions to restore
beneficial uses. (Stage One reports describe environmental conditions and basic problems and issues.)
Wherever possible in the RAP process, delisting objectives were developed that were specific, reproducible
and defensible measures to respond to each of the use impairments in the Severn Sound AOC. The SSRAP
Stage 2 identified that littoral, tributary and watershed habitats were important to the ecosystem health of
Severn Sound and that these habitats were degraded in several areas (SSRAP Stage 3). The objectives set out
in the SSRAP Stage 2 reflected the best indicators available at the time of writing. The delisting objectives for
the use impairment, degradation of fish and wildlife habitat, for the Severn Sound RAP were as follows:
■
To implement the Severn Sound Fish Habitat Management Plan and other policies to enhance
and prevent the loss of fish and wildlife habitat.
■
To encourage the restoration of fish habitat in target areas by proponents of new shoreline development.
■
To develop plans for rehabilitation or development of new coastal wetland areas as opportunities arise.
■
As part of the Matchedash Bay project (North American Waterfowl Management Plan 1991), to:
i) secure and manage 1,715 hectares of wildlife habitat
ii) restore and develop 1,427 hectares of habitat for waterfowl and other wetland -dependent wildlife
iii) maintain and enhance 442 hectares of habitat for staging waterfowl.
■
To rehabilitate tributaries and riparian areas for fish and wildlife habitats.
■
To maintain existing colonial waterbird nesting sites within and near Severn Sound.
■
To maintain and increase Osprey nesting sites within Severn Sound.
(Source: SSRAP Stage 2)
In some cases, knowing that methods were under development, the indicators used to assess the objectives
were left “to be determined”. Since implementation of remedial actions did not occur all at once or by a
certain date, the rigorous measurement of change in ecosystem health is difficult. This has been especially
true in the case of habitat restoration since the planting of trees and shrubs and the rehabilitation of riparian
habitat still continues. The full benefit of each individual project will be realized as rehabilitated areas mature.
Substantial implementation of remedial actions, such as habitat restoration, took place between the late
1980s and 2002. At the end of that period, the third stage of the RAP process commenced. This stage
involved documenting completed actions and the status of each use impairment. During the period between
the release of the SSRAP Stage 2 and the SSRAP Stage 3, additional indicators had been developed to
assess use impairments as well as improved methods to measure ecosystem responses. In terms of habitat,
some indicators were based on Framework guidelines.
The principles followed in assessing the status of the delisting objectives included:
■
selecting a variety of indicators wherever possible that best reflected the status of the delisting objective
■
selecting a measurable end point or threshold for each indicator
■
having indicators that should show measurable changes in time and in space.
How Much Habitat is Enough?
53
Indicators used to evaluate delisting objectives in Severn Sound
The first edition of the Framework was evaluated to be applied on a subwatershed basis in the AOC
and considered as indicators for the assessment of RAP delisting objectives (Gartner Lee Limited, 1997a;
Gartner Lee Limited, 1997b; Tate, 1998, Sherman and McPhail, in prep.).
The following guidelines were selected for use as indicators in Severn Sound.
Upland Habitat
a. percent forest cover >30 percent of watershed
b. interior forest with 100 metre buffer >10 percent
c. interior forest with 200 metre buffer >five percent
d. size of largest forest patch: at least one patch with a minimum of 200 hectares,
minimum of 500 metres across
e. shape and proximity considerations for forest patches and corridors
f. forest cover should represent full diversity of species composition and age structure
found in ecoregion
Riparian Habitat
a. percent of stream naturally vegetated: at least 75 percent of first to third-order streams
b. amount of natural vegetation adjacent to streams at least 75 percent of a 30-metre buffer
of natural vegetation on both sides of the streams
c. suspended solids concentrations <25 milligrams/litre for the majority of the year
d. percent urbanized: <15 percent imperviousness in an urbanized watershed
e. fish communities based on fish-community survey and temperature
Wetland Habitat
a. percent wetlands in watershed and subwatersheds: >10 percent of each major watershed,
>six percent of each subwatershed or restore to original percent wetlands
b. amount of natural vegetation adjacent to each wetland: >240 metres width of adjacent
natural vegetation (using adjacent forest cover in Severn Sound)
c. wetland type: marshes and swamps suitable for rehabilitation
d. wetland size and shape: swamps as large and regular as possible to maximize interior forest,
marshes of various sizes and shape to maximize interspersion
In addition to the literature review carried out to support the Framework, a review of local conditions and
other studies was used to evaluate and augment the guidelines as indicators for use in Severn Sound. Interior
forest habitat guidelines were evaluated in the Severn Sound area using interior forest bird species as
indicators (Tate, 1998), which allowed the health of the Severn Sound interior bird populations to be directly
assessed as well as the habitat metrics (forest cover, 100 metre and 200 metre interior forest, patch size).
54
How Much Habitat is Enough?
Identifying habitat in the Severn Sound AOC
Severn Sound forest habitat, riparian habitat and wetland habitat was examined using the Framework. The
watershed was divided into 16 subwatersheds, which range from 24 to 121 square kilometres. A Geographic
Information System (GIS) analysis was conducted on each subwatershed to determine the status of habitat
targets and to refine the habitat strategy for the Severn Sound AOC (see Appendix 1 – Figure 1; McPhail,
1999). Changes in forest cover and riparian cover were also examined between 1982 (the year documented
in the Ontario Base Map, or OBM, for the area) and 1998, using a forest layer developed from 1998 Ontario
Ministry of Natural Resources infrared air photos (see Appendix 1 – Figure 2; Hudolin, 1999). Using the
same interpretive techniques and Geographic Information System (GIS) methods, it was also possible to use
other available air photo coverage to document longer-term and more detailed time steps in the changes in
forest cover for selected subwatersheds.
The value of comparing the Framework guidelines among two or more dates is illustrated by Appendix 1 –
Figure 1A, where interior forest patch size increases with time over three air photo coverages (1953, 1982
and 1998). Appendix 1 – Figure 2 shows the differences in forest cover between 1982 and 1998 for the entire
subwatershed and illustrates the importance of sustaining a net increase in forest cover over time.
Appendix 1 – Table 1 shows that the size of the largest forest patch in Hogg Creek has increased due to
strategic planting. This was not the case in all subwatersheds where some form of securement of large
forest patches is needed despite a general net gain in percent forest cover.
The assessment of riparian habitat is illustrated in Appendix 1 – Figure 1B. A restoration project was
carried out in 1991; the figure shows increases in habitat between 1981 and 1998 in terms of percentage
of vegetated stream length and percentage of stream with a 30-metre buffer. The hydrogeology within
subwatersheds in Severn Sound (Singer et al., 1999) suggests that headwater areas of some streams may
not contribute as much to the groundwater recharge/discharge as some of the mid-sections of subwatersheds
where groundwater recharge was known to occur. Many of the headwater areas of Hogg Creek are
intermittent or warm-water marshes while areas downstream (even fourth or fifth-order streams) have
observed groundwater input and maintain continuous cool water flows, suggesting that efforts to restore
headwaters may not be as beneficial as efforts on downstream reaches. Despite these local differences,
the indicator for Severn Sound streams was that 75 percent of the length of first to third-order streams
be vegetated.
In addition to the 75 percent guideline, the threshold value of 50 percent from the narrative portion of the
Framework was used to evaluate riparian habitat in each subwatershed. The stream segments intersecting
wetlands but without forest cover at the bank were also considered as vegetated in the estimate of length
of stream with “natural vegetation” for Severn Sound subwatersheds.
As stated in the Framework, a number of factors need to be considered in relation to streams and stream
corridors in addition to percent riparian cover. For example, the suspended solids guideline for riparian
habitat was interpreted for Severn Sound streams to apply to the baseflow period of the year, which
usually extends over at least 90 percent of the year. During spring freshet and increased runoff events
(usually <10 percent of the year), the suspended solids and the total phosphorus concentrations were
found to be significantly related to flow.
How Much Habitat is Enough?
55
The importance of being aware of local conditions in combination with Framework guidelines was
illustrated along some stream reaches where forest cover was not established along stream banks due to
natural meander belts and marsh vegetation. These reaches, however, support cool and cold-water habitat
conditions that would be expected on a forested reach. The use of relatively inexpensive temperature
loggers to characterize the stream temperature regime was used in Severn Sound tributaries to further
characterize stream habitat conditions.
The wetlands evaluated for adjacent natural vegetation consisted of Provincially Significant Wetlands in
the Severn Sound watershed (with upland “islands” removed) combined with the smaller unclassified
wetlands from the OBM wetland layer. Appendix 1 – Figure 1C shows the status of wetland habitat in
1982 and 1998 with the changes resulting from restoration as well as from natural succession. The percent
wetland area guideline of 10 percent of watershed was not met with the exception of Sturgeon River and
Wye River watersheds. The percent wetland area guideline of six percent for subwatersheds was generally
met, with the exception of Coldwater River (SSRAP Stage 3). Note that no change with time comparison
was made for wetlands because no historical layer for wetlands was available other than the Classified –
OBM wetland layer.
Other guides and references were used in addition to the Framework and field data. Habitat issues such
as nearshore fish habitat and waterbird habitat were addressed through other methods developed for the
Great Lakes AOCs. A Defensible Methods approach was developed (Minns et al., 1999) that combines
a physical habitat inventory with a model to classify most of the littoral zone fish habitat suitability for
different groupings and life stages of fish in Severn Sound (see also Randall et al.,1993; 1998). Surveys
of waterbirds and important bird species in Severn Sound also revealed valuable habitat areas within the
AOC (Weseloh et al., 1997; Wilson and Cheskey, 2001a; 2001b; 2001c).
Site specific initiatives within the Severn Sound area also provide an indication of the restoration status
of habitat within the AOC. The Eastern Habitat Joint Venture, part of the North American Waterfowl
Management Plan, is conducting a large scale habitat protection and improvement project in Matchedash
Bay (Tymoshuk and Martin-Downs, 1990, North American Waterfowl Management Plan, 1991). The
Severn Sound RAP Tributary Rehabilitation Project and the Penetanguishene Shoreline and Wetland
Restoration Projects are examples of restoration projects that were evaluated on a site specific basis as
well as on a subwatershed basis.
56
How Much Habitat is Enough?
Appendix 1 – Figure 1. Habitat Cover Over Time
Examples of measurable changes in upland forest, riparian and wetland habitat conditions
for the Hogg Creek watershed.
Illustration by Severn Sound Environmental Association
How Much Habitat is Enough?
57
Appendix 1 – Figure 2. Hogg Creek – 1982/98 Difference in Forest Cover
Illustration by Severn Sound Environmental Association
58
How Much Habitat is Enough?
Habitat status in Severn Sound at RAP Stage 3
Upland Habitat
Although there were significant reductions in the size of the largest forest patches, there has been little
net change in forest cover across Severn Sound. The 1998 analysis shows that upland habitat targets are
generally being met for the Severn Sound watershed with the exception of interior forest targets in Hogg
Creek, and some subwatersheds on the Wye River and the North River. These areas will be the subject
of further targeting for remediation where feasible.
It would appear from planned or proposed development in some subwatersheds that the reduction in
percent forest cover will continue. It should also be recognized that the net increase results from forest
planting and natural succession exceed forest removal. In order to sustain forest cover, planting programs
should be sustained. Mechanisms to secure large interior forest patches should also be pursued.
Riparian Habitat
Riparian vegetation along first to third-order streams in Severn Sound has increased between 1982 and
1998, with the exception of Silver Creek (North River) and McDonald Creek (Wye River). This increase
is evidence of improved awareness of the value of vegetation in stabilizing stream banks and is directly
attributable to the Severn Sound RAP Tributary Rehabilitation Project. The longer-term changes in
riparian buffers for Hogg Creek show a gradual increase from 1953 to 1998.
The projected future riparian cover will result from changes to livestock-watering practices at traditional
farms and expected growth of areas planted during recent Severn Sound RAP Tributary Rehabilitation
Project efforts. Since 1991, a total of 133 projects were completed through the project. Some 127 kilometres
of stream banks have been fenced and/or remediated, restricting the access of more than 2,700 livestock
units. The riparian projects have resulted in more than 470 hectares of fragile valley lands being retired
from agriculture. Also, some 154,000 trees and shrubs have been planted.
Appendix 1 – Table 1. Severn Sound RAP – Habitat Restoration Strategy – Hogg Creek Subwatershed.
Summary of Forest, Riparian and Wetland Habitat Targets for First to Third-order Streams
Guidelines
Forest Habitat Guidelines
% Forest cover
Size of largest patch (Ha)
% Forest > 100 m from edge
% Forest > 200 m from edge
Riparian Habitat Targets
% first to third-order streams with natural veg.
% first to third-order streams with > 30m natural veg.
% first to third-order steams with natural veg. plus wetlands
% first to third-order streams with > 30m natural veg. plus wetlands
Wetland Habitat Targets
% Wetlands in watershed
Amount of vegetation mean width (m)
Target
1982
1998
Difference
>30
> 100 Ha
>10%
>5%
32%
163 Ha
6%
1%
38%
199 Ha
11%
3%
6%
36 Ha
5%
2%
>75%
>75%
>75%
>75%
47%
29%
57%
36%
57%
40%
64%
44%
10%
11%
7%
8%
>10%
(sub>6%)
>240 m
7%
7%
0%
71 m
122 m
51 m
How Much Habitat is Enough?
59
The promotion of the riparian program has been systematic and has resulted in generally increased awareness
of the need for restricting cattle access to streams. However, landowners took advantage of the program
on a case-by-case basis, which resulted in a gradual and sometimes uneven distribution of projects along
the streams. Despite the voluntary nature of the participation, extensive habitat corridors have been
realized on several streams in the Severn Sound area. The projects have not been restricted to first to
third-order streams.
Wetland Habitat
There was a general increase in mean width of vegetation adjacent to wetlands between 1982 and 1998.
Significant decreases were noted in the Bass Lake and Silver Creek subwatersheds due to increasing
urbanization and in the Purbrook Creek subwatershed due to an increase of pasture area. Coastal wetland
habitat has been rehabilitated in Penetang Bay, Midland Bay and Hogg’s Bay. The trend in loss of coastal
wetland habitat described by Cairns (SSRAP Stage 2) was greatly reduced through the 1990s. However,
increasing pressure to develop shoreline areas, especially during current low water levels (1999 to 2001),
have led to destruction of some areas of Provincially Significant Wetlands.
On private lands, rehabilitation projects have resulted in 10 hectares of created wetlands, 36 hectares of
enhanced wetlands, and more than 170 hectares of wetlands protected by planning designation or conservation
agreement. Classified wetlands and associated complexed wetlands are being systematically reviewed and
reclassified, resulting in updated wetland boundaries for better planning protection and enhancements.
How were Framework guidelines used to contribute to delisting
the Severn Sound AOC and sustaining the local ecosystem?
Once the status of Severn Sound habitat had been determined, the Framework guidelines provided
valuable benchmarks to aid the direction of further restoration efforts and protection of habitat areas.
The forest-cover mapping and habitat assessment allowed systematic targeting of properties that would
provide the greatest benefit to planting programs. The use of this information continues to help focus
efforts in ongoing landowner contacts.
Municipalities were provided with habitat assessments for use in Natural Heritage Strategies, Official
Plan designations and zoning bylaws, as well as planning decisions on individual land-use proposals.
As a result of the RAP analysis based on the first edition of the Framework, the extent of habitat on a
subwatershed basis could be summarized in a defensible fashion and presented for expert review. The status
of restoration and the rationale for delisting of the Severn Sound RAP for the habitat-use impairment was
in part determined based on the analysis. The SSRAP Stage 3 concluded that restoration had been achieved
conditional to ongoing assessment and implementation of habitat restoration. This is not surprising considering
that the sustainability of habitat in Severn Sound requires ongoing assessment and management.
60
How Much Habitat is Enough?
References
Craig, R.E. and Black, R. M. 1986.
Nursery habitat of muskellunge in southern Georgian Bay, Lake Huron, Canada. Am. Fish. Soc. Spec. Publ. No. 15: pp. 79-86.
Environment Canada, Ontario Ministry of Natural Resources and Ontario Ministry of the Environment. 1998.
A Framework for Guiding Habitat Rehabilitation in Great Lakes Areas of Concern. Canada-Ontario Remedial Action Plan
Steering Committee. ISBN 0-662-26577-7.
Gartner Lee Limited. 1997a.
Severn Sound Habitat Restoration Strategy: Final Report. Prepared for the corporation of the Township of Tay. 42 pp.
Gartner Lee Limited. 1997b.
Wetland and Riparian Targets Pilot Application – Hogg Creek watershed. 46 pp.
Hudolin, G. 1999.
Image Rectification & Vegetation Layer Updating Method, Severn Sound Remedial Action Plan Technical Report.
Long Point Bird Observatory. 1997.
Marsh bird and amphibian communities in the Severn Sound AOC, 1995-1996. Marsh Monitoring Program Newsletter Supplement.
McPhail, A. 1999.
Habitat restoration strategy for Severn Sound: Automated Arcview 3.1 habitat analysis method. Severn Sound Environmental
Association Technical Report.
Minns, C.K., Brunette, P., Stoneman, M., Sherman, K., Craig, R., Portt, C. and Randall, R.G. 1999.
Development of a fish habitat classification model for littoral areas of Severn Sound, Georgian Bay, a Great Lakes Area of Concern.
Can. MS Rep. Fish Aquat. Sci. 2490,ix+86p.
Randall, R.G., Minns, C.K., Cairns, V.W. and Moore, J.E. 1993
Effect of habitat degradation on the species composition and biomass of fish in Great Lakes Areas of Concern. Can. Tech.
Rept. Fish. Aquat. Sci. No. 1941.
Randall, R.G., Minns, C.K., Cairns, V.W., Moore, J.E. and Valere, B. 1998.
Habitat predictors of fish species occurrence and abundance in nearshore areas of Severn Sound. Canadian Manuscript
Report of Fisheries and Aquatic Sciences No. 2440.
Severn Sound Remedial Action Plan (SSRAP). 1993.
Stage 2 Report: A strategy for restoring the Severn Sound ecosystem and delisting Severn Sound as an Area of Concern.
Toronto. ISBN: 0-7778-1168-5
Severn Sound Remedial Action Plan (SSRAP). 2002.
Stage 3 Report: The status of restoration and delisting of Severn Sound as an Area of Concern. Prepared by Severn Sound
Environmental Association for Environment Canada and the Ontario Ministry of the Environment.
Sherman, R.K. and McPhail, A. In preparation.
Status of habitat conditions and restoration strategies for the Severn Sound Area of Concern. Severn Sound Environmental
Association Technical Report.
Singer, S., Cheng, T., Scafe, M., Sherman, K., Shiekh, G. and Zaia, W. 1999.
The groundwater resources of the Severn Sound Remedial Action Plan Area. Severn Sound Remedial Action Plan
and the Ontario Ministry of the Environment.
Tate, D.P. 1998.
Assessment of the biological integrity of forest bird communities - a Draft Methodology and Field Test in the
Severn Sound Area of Concern. Severn Sound RAP Technical Report. Canadian Wildlife Service - Ontario Region.
Tymoshuk, S.J. and Martin-Downs, D. (Gartner Lee Limited). 1990.
A biological inventory and evaluation of the Matchedash Bay Provincial Wildlife Area. OMNR, Huronia District and Parks
and Recreational Areas Section, Central Region, Aurora. Open File Ecological Report 9003. 117 pp.
How Much Habitat is Enough?
61
Weseloh, D.V., Ryckman, D.P., Pettit, K., Koster, M.D., Ewins, P.J., and Hamr, P. 1997.
Distribution and abundance of waterbirds in summer in Severn Sound (Georgian Bay), Lake Huron: an IJC Area of Concern.
J. Great Lakes Rs. 23(1): pp. 27-35.
Wilson, W.G. and Cheskey, E.D. 2001a.
Wye Marsh Important Bird Area Conservation Plan. Canadian Nature Federation, Bird Studies Canada and Federation
of Ontario Naturalists.
Wilson, W.G. and Cheskey, E.D. 2001b.
Matchedash Bay Important Bird Area Conservation Plan. Canadian Nature Federation, Bird Studies Canada, Federation
of Ontario Naturalists.
Wilson, W.G. and Cheskey, E.D. 2001c.
Tiny Marsh Important Bird Area Conservation Plan. Canadian Nature Federation, Bird Studies Canada and Federation
of Ontario Naturalists.
Photo by Eric Dresser
62
How Much Habitat is Enough?
Appendix 2
Toronto and Region Conservation Authority (TRCA) Terrestrial Natural
Heritage Strategy
The Toronto and Region Conservation Authority (TRCA) has an approach to terrestrial natural heritage
that considers all the natural cover in a region (all forest, wetland and native meadow) as one “organism”
functioning in the landscape rather than as a collection of individual sites, some of which may be considered
“significant”. The approach uses the following criteria:
■
quantity (the percent natural cover in a region)
■
quality (the average habitat patch size, shape and matrix influence)
■
distribution (the distribution of that quantity and quality of natural cover).
Calibration
The approach to evaluating the condition of natural systems works in a kind of nested fashion among
all scales, for two reasons:
■
the basic unit used for assessing quality (size, shape and matrix influence) is the individual
habitat patch
■
every patch in the TRCA’s area of jurisdiction is scored individually but within one range
calibrated to the entire jurisdiction’s collection of patches.
This allows one to calculate an average-quality value for a natural system at any scale within the broad
region (such as the TRCA jurisdiction or Toronto and Region AOC) down to an individual watershed,
municipality, subwatershed and individual site. Using the patch as a basic unit within the entire regional
patch data set enables one to show how strategies and actions can work together with relevance to smaller
or larger scales.
Furthermore, the quality measures can be used to determine a quantifiable target for a desired average
quality at any scale or, as in the case of AOCs, a delisting target. Thus, improving natural system quality
(average patch size, shape and matrix influence) in the Centreville Creek subwatershed would have a
positive influence on the Toronto and Region AOC, for example, and can be portrayed as a quantified
contribution toward a targeted quality for delisting the AOC.
This methodology was developed at a time when the RAP guidelines were emerging. The guidelines
provided support and inspiration in pursuing this landscape-scale, target-setting exercise. One main point
of expansion, however, is the matrix-influence criterion mentioned above, which is discussed further below.
The TRCA is in the process of writing a Terrestrial Natural Heritage Strategy to work with its partners
and stakeholders, and assist in associated projects. The Toronto and Region AOC covers most of the
TRCA jurisdiction and the collaborative exercise of setting delisting targets is an important objective
of the Strategy.
How Much Habitat is Enough?
63
Matrix influence
The most important characteristic of a habitat patch for biodiversity is its size (Kilgour, 2003), which
relates to the amount of space required for species to find resources and remain in viable populations.
The second factor is matrix influence. (Shape, to a lesser degree, is also a factor in determining the
quality of a habitat patch.)
Matrix influence is a measure of the positive or negative influence which a patch receives from its
surroundings. Land-uses, especially urbanization, adjacent to a patch can exert pressure or impacts with
a profound effect on its biodiversity (Lindenmayer and Franklin, 2002). Conversely, a patch can have a
synergistic and beneficial relationship with other natural cover in its surrounding area and, to a lesser degree,
with agricultural lands. In other words, a patch’s score for matrix influence reflects the degree to which the
surrounding land cover and land-uses threaten or contribute to its biological integrity and diversity.
The TRCA measures the character of the matrix within a two-kilometre radius out from the outside edge
of each habitat patch. The two-kilometre radius of influence will extend beyond the limit of a study area
(a watershed or an AOC, for example) if the patch is near the limit of that study area. The radius length
was chosen because:
■
it is considered to be a reasonable foraging circuit for predatory species associated with edge
effects, such as raccoons, foxes, feral cats and cowbirds (negative influence)
■
it is the distance within which most genetic exchange and species dispersal can be expected
from most flora and fauna species (positive influence)
■
it is a distance that could be considered reasonable by people to regularly visit a natural area
for recreational purposes, by walking, cycling or driving (negative influence).
Scoring patch matrix influence
In scoring for matrix influence, the land-cover types are calculated as a percentage of the total area within
the two-kilometre radius from the edge of each habitat patch. For the purposes of this calculation, there
are three categories of land cover (natural, agricultural and urban); each receives a base value of negative
one, zero or one on the gradient of influence.
Natural cover surrounding a patch is considered to have a positive influence and receive a value of one.
Included in this category are patches of the major habitat types such as forest, wetland and meadow,
as well as open water in the form of lakes, rivers and ponds.
Agricultural lands can have negative impacts such as pesticide runoff, but they also allow for the
movement of many species between patches and across the landscape, in particular for amphibian
movements between forests and wetlands. As a result, they score zero points as the mid-point on
a continuum.
This connectivity function is not provided for many species by urban land-uses. In fact, due to pollution,
refuse, recreational pressures, the presence of dogs and cats, invasive species and other negative influences,
urban areas in general can be considered harmful to natural habitats. Therefore, they receive a base point
of negative one.
64
How Much Habitat is Enough?
The percent of each of the land-cover types is measured for within the two-kilometre matrix, and each is
multiplied by the base point value. The three resulting values add up to the matrix influence score for the
patch, as in the following example:
Land Cover Type
Natural
Agricultural
Urban
Percent of Matrix
40
30
30
Cover Type Value
+1
0
-1
Patch Score
Total
40
0
-30
10
From a biodiversity-conservation perspective, the perfect patch surroundings would be totally natural
(e.g., wetland within an extensive forest patch, measuring at least two kilometres out from the wetland
edge) and would receive a matrix score of 100, while the lowest possible score is negative 100 for a natural
habitat patch immersed within an expanse of urban (residential or industrial) land.
Natural systems matrix influence
The patch scores give a localized measure based on single patches that, when averaged for a study area,
can give a sense of the overall matrix influence on a natural system as a whole and, when graphed, can
show the amount of hectares that fall within a range of matrix influence values for the natural system.
It must be remembered that the value is not only a measure of the urban and agricultural influence on the
natural system, but that it also encompasses the internal positive value of the natural cover in toward itself.
This natural matrix influence speaks to the concept of patches benefiting from each other and to natural
system connectivity at the landscape scale. The combination of all natural, agricultural and urban land-uses
in this measure also speaks to land-use planning as a determinant of biodiversity in the landscape.
Matrix values in context
An important consideration is that the TRCA approach is based on three equal attributes. These quality
measures (size, shape and matrix) are useful strictly in consideration of the quantity and distribution of
natural cover in the landscape. For example, a natural system that in total covers 20 percent of a primarily
agricultural watershed could conceivably obtain a good average matrix influence value, especially if its
patches are clumped in one area of the watershed. However, that natural cover would not be of sufficient
quantity and appropriate distribution necessary to attain the desired biodiversity and ecosystem function
in that watershed.
For more information on the TRCA’s Terrestrial Natural Heritage Strategy and its matrix influence
measure, please contact the TRCA at (416) 661-6600.
References:
Kilgour. 2003.
Landscape and patch character as a determinant of occurrence of eighty selected bird species in the Toronto area. Unpublished.
Lindenmayer, David B. and Jerry F. Franklin. 2002.
Conserving forest biodiversity: A comprehensive multiscaled approach. Washington, DC. Island Press. 351 pp.
How Much Habitat is Enough?
65
Appendix 3
Applying the Framework to Land-use Planning
The Framework was originally designed to provide guidance on how to restore (or delist) AOCs throughout
the Great Lakes basin. A 2002 review of Framework implementation revealed that the approach has been
applied in nine AOCs and several others have considered the guidelines in developing delisting criteria.
In practice, Geographic Information System (GIS) mapping of current habitat conditions is undertaken
to compare against preferred Framework target conditions, and the resulting maps are used to pinpoint
“best bet” restoration opportunities (see the Severn Sound AOC approach in Appendix 1).
Interest has been expressed in using the Framework guidelines for habitat protection and for restoration
through the municipal land-use planning process. The purpose of this appendix is to provide discussion on
how the Framework can advance habitat protection in land-use planning within, and possibly beyond, AOCs.
The ecological concepts important in conserving the fragmented natural landscapes of southern Ontario
can be expressed around the themes of landscape retention, landscape restoration and ecosystem
replacement (Riley and Mohr, 1994). Beginning in the 1970s, Ontario municipalities have attempted
to protect natural areas by designating environmentally significant areas (ESAs) in Official Plans. In
addition, many such plans include specific policies protecting Provincially Significant Wetlands, flood
plains and Niagara Escarpment lands. Work introduced by the Ontario Ministry of Natural Resources
in the mid-1990s (Riley and Mohr, 1994) advanced natural heritage system planning through identifying
a system of core areas with linking corridors and identifying the need for restoration.
This evolution in natural areas protection occurred through recognition that protecting ESAs is
problematic as they are often isolated “islands of green” that are too small to support viable wildlife
populations. Frequently, these areas were designated as significant because they contained rare species;
however, focussing primarily on rare species resulted in population declines of more common species
being overlooked until they too were designated rare. The rare-species approach also failed to account
for the interdependence of all native species as integral components of a healthy ecosystem.
In many parts of Ontario, habitat loss has been significant. The identification and designation of natural
heritage systems in Official Plans still only seeks to protect what exists without consideration for what
could or should exist. The focus of this appendix is linking habitat protection with restoration towards
protecting long-term, sustainable natural heritage systems that function with ecological integrity.
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How Much Habitat is Enough?
How can the Framework be incorporated into land-use planning?
Proposed applications are discussed below, drawing upon land-use planning practice examples where applicable.
Ways that the Framework can be incorporated into land-use planning applications in Ontario include:
■
combining protection and restoration philosophy for Official Plans
■
developing specific Official Plan policy language
■
developing an approach for enhancing natural heritage systems
■
scientific grounding for specific policies on protecting significant woodlands and wetlands,
and other landscape features.
Combining protection and restoration philosophy for Official Plans
Many Official Plans contain introductory paragraphs that set the tone for the actual policies in a particular
section. For example, the Region of Hamilton-Wentworth’s 1995 Official Plan (Regional Municipality of
Hamilton-Wentworth, 1998) contains a preamble to the section called Natural Setting that reflects the
vision developed by their Task Force on Sustainable Development:
There exists in Hamilton-Wentworth a system of natural areas of varying significance as well as
locations where degraded natural habitat has the potential to be ecologically enhanced or restored…
Such a preamble, influenced by the Framework guidelines, could speak to the current state of the
Natural Heritage Strategy, introduce the Framework guidelines, and then express a policy interest in not
losing any additional habitat while undertaking ecological restoration towards locally-established habitat
targets. Habitat protection policies could follow, along with policies stating restoration goals. A table
outlining current habitat conditions, local habitat targets, and anticipated end points for habitat restoration
could be included.
Policy-making is an art as much as a science and creativity demonstrated by municipal planners often
leads to innovative policy initiatives. While the wording would be more local and precise in actual
application, the following paragraph illustrates this concept:
The current municipal Natural Heritage Strategy incorporates the best of the remaining habitat in
the municipality, including core areas and linking corridors. The Framework for Guiding Habitat
Rehabilitation outlines desired quantities of habitat suitable to maintain ecological integrity. Based
on community input, the Municipal Biodiversity Strategy has been developed, which outlines current
habitat conditions in the Natural Heritage Strategy, compares those levels against ecologically-desired
habitat levels outlined in the Framework and, using guidelines contained in the Framework, establishes
local specific targets for habitat protection and restoration. The policies contained in this section
express community interest in protecting and restoring the municipality’s biodiversity, using targets
derived from the Framework. Map 1 (Appendix A) outlines the most desirable locations for restoration
of the municipality’s natural heritage system.”
How Much Habitat is Enough?
67
Developing specific Official Plan policy language
Opportunities may arise for extracting guidelines from the Framework and building them into Official
Plan policies. For instance, the City of Windsor sought to develop a greenway along the St. Clair River
and developed policy to minimize impervious-surface treatments for the Central Riverfront Park Lands –
no more than 15 percent coverage of the total, reflecting Framework guidelines of the time (City of
Windsor, undated).
Developing an approach for enhancing natural heritage systems
In Ontario, the Planning Act, the Provincial Policy Statements (PPS), and accompanying implementation
guidelines provide the primary requirements for development of municipal Official Plans. It is important
to note that they are also considered as minimum policies and municipalities are invited to go beyond the
PPS in development of their Official Plans (see cautionary note below).
Policy 2.3 of the PPS contains natural heritage policies related to significant woodlands, wildlife habitat,
wetlands, valleylands, Areas of Natural and Scientific Interest, fish habitat, and significant portions of
the habitat of endangered and threatened species. The Ontario Ministry of Natural Resources Natural
Heritage Reference Manual introduces the Natural Heritage Strategy approach that supports section
2.3.3 of the PPS, which states that “the diversity of natural features in an area and the natural connections
between them should be maintained, and improved where possible”.
Most municipalities have designed, or are in the process of designing, a Natural Heritage Strategy based
on existing habitat that is in most cases below optimum Framework guidelines (i.e., less than 30 percent
forest cover, small amounts of interior forest, small forest patch sizes, less than 10 percent wetlands, low
levels of riparian vegetation). As AOCs have done, municipalities can be encouraged to compare existing
levels of habitat with a future desired strategy that meets locally-derived habitat targets drawn from the
Framework guidelines. One example of building the Framework guidelines into policy would be insertion
of a Natural Heritage Strategy restoration policy in the Official Plan, with reference to a future-oriented
map depicting potential restoration sites.
Scientific grounding for specific policies on protecting significant woodlands and wetlands,
and other landscape features
The Framework has been used as a key guidance document in criteria development for protection
of significant woodlands in the Regional Municipality of Halton (Gartner Lee Limited, 2002).
Criteria chosen from the Framework include woodland patch size, distance from perimeter, and
landscape connectivity.
The Framework has also been used to guide habitat protection planning in the community of Willoughby
within Langley Township, British Columbia (Astley, 2003). Willoughby is an area faced with increasing
housing development. The Framework guidelines were used to ensure that wildlife values were incorporated
into neighbourhood plans. Due to the fragmented nature of local habitat, the authors used the guidelines
to suggest retaining the largest remaining habitat patches and the small number of wetlands present.
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How Much Habitat is Enough?
Possible Limitations
A recent comparison of the PPS Natural Heritage Guidelines, the Oak Ridges Moraine Protection Act
regulations, and the Framework guidelines found that, in general, the Framework guidelines were more
protective than the others (Rowe 2002). However, both provincial policies are enshrined in legislation and form
a de facto mandatory planning approach for municipalities. To date, the Framework guidelines do not carry
legislative or substantive authority, although they have been used in this way as the examples above indicate.
Although municipalities are invited to treat the PPS as minimum planning guidelines when establishing policy,
planners must consider the potential of an Ontario Municipal Board challenge to policies that stray beyond
provincial norms. This concern may serve to limit the use of the Framework guidelines in Official Plans.
References
Astley, Caroline. 2003.
Willoughby Habitat Status Report. Langley Environmental Partners Society.
City of Windsor. Undated.
City of Windsor Official Plan, Vol. II Special Policy Areas, Policy 1.13.13 (e).
Gartner Lee Limited. 2002.
Rationale and Methodology for Determining Significant Woodlands in the Regional Municipality of Halton: Technical
Background Paper #6. Regional Municipality of Halton.
Ontario Ministry of Natural Resources. 1999.
Natural Heritage Reference Manual For Policy 2.3 of the Provincial Policy Statement. Ontario Ministry of Natural Resources.
Peterborough. 127 pp.
Regional Municipality of Hamilton-Wentworth. 1998.
Towards a Sustainable Region: Hamilton-Wentworth Official Plan.
Riley, J.L. and P. Mohr. 1994.
The natural heritage of southern Ontario’s settled landscapes. A review of conservation and restoration ecology for land-use
and landscape planning. Science and Technology Transfer, Technical Report TR-001. Ontario Ministry of Natural Resources,
Southern Region. Aurora. 78 pp.
Rowe, Steven. 2002.
Relating the Habitat Framework Approach to the Provincial Policy Statement and the Oak Ridges Moraine Conservation Plan.
A presentation at the December 2002 Great Lakes Sustainability Fund Sharing Experiences workshop.
Photo by Graham Bryan
How Much Habitat is Enough?
69
Appendix 4
Toronto and Region Conservation Authority (TRCA)
Fish Community Target-Setting Framework
Management direction for watercourses or subwatersheds often has been based on the existing condition of
a fish community. In some situations where the aquatic system has not been severely impacted, the existing
fish community is likely a reflection of the historic community and establishing a management direction
based on this information would be appropriate. However, in many situations the existing fish community
has been impacted by historic or present land-use practices and may not reflect what was historically
present, nor the potential fish community that could be present based on the existing physical conditions.
For example, in the Rouge River watershed most of the fish communities are dominated by warm-water
species with some cool-water species also present. However, the fundamental characteristics of the
watershed such as surficial geology and baseflow indicate that migratory salmonids should be supported
although none are present. Through transfers of adult trout into habitats deemed appropriate for
spawning, successful reproduction was achieved. In this example the major factors impacting the potential
of the fish community were the inability of salmonids to get to appropriate habitat due to migration
barriers and, secondarily, water temperature.
This reach is now being managed for cold-water species with planting of riparian vegetation to shade the
stream as one of the rehabilitation recommendations. Had the assessment of this watershed not included
an analysis of fundamental characteristics, the fish community might have been managed strictly for a
warm-water community and it might never have achieved its historic potential.
This general Framework is derived from the TRCA fish-management planning approach for the Rouge,
Don and Humber River watersheds. Rather than basing planning on existing, often degraded, fish
communities, the TRCA establishes targets based on setting an expectation for a fish community. The
approach is based on three types of information:
■
knowledge of the fundamental or underlying characteristics of the watershed or subwatershed
(drainage area, surficial geology, flow regime) and what fish communities have historically
been present
■
knowledge of what the system is presently supporting (existing fish community) and some idea
of its condition
■
knowledge of the factors presently impacting the system and their relative magnitudes.
It is important that management targets for fish communities be based in part on an assessment
of historic conditions by examining historic fish communities and fundamental characteristics of the
watershed such as surficial geology. These factors provide an indication of what a healthy system would
support. Without this reference, management decisions would be made relative to an existing condition
that may already be impacted. The closer the present condition is to the historic condition, the less
impacted and the healthier the system; alternately, a system that deviates significantly from the historic
condition is less healthy. Where a system is slowly being degraded, the reference point to determine
what might be supported would change over time and perception of health would change. The historic
reference point is critical in order to maintain continuity in perceptions of the health of ecosystems.
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How Much Habitat is Enough?
In some severely-impacted systems, returning to a historic condition may seem unachievable, while in other
less degraded systems the historic condition might reasonably be achieved. For example, Taylor/Massey
Creek is a highly degraded tributary in the Don River watershed that would have historically supported trout
and salmon. Approximately 25 percent of this subwatershed consists of coarse soils, conducive to infiltration.
The middle and lower reaches of this tributary would have supported Brook Trout and Atlantic Salmon but
presently support only four fish species: Creek Chub, White Sucker, Blacknose Dace, and Fathead Minnow.
These conditions are due to extensive urbanization and the absence of stormwater controls (due to the age
of the housing development).
The target set for these reaches is to improve conditions so that species such as Johnny Darter and
Mottled Sculpin would be supported. In the headwaters where no fish are present, the short-term target
is to have a pollution-tolerant fish community present. In the long term, as rehabilitation occurs, the fish
community targets could be shifted to more sensitive species. In this situation, the historic condition
provided a context and the direction for management while the existing conditions were used to temper
expectation of what might reasonably be achieved.
Based on available literature and work in the Rouge, Don and Humber River watersheds, a Framework for
setting fish community targets has been prepared (see Appendix 4 – Table 1). The Framework provides a
general guide to assist managers in the development of fish-community targets. It is based on information
available for streams in southern Ontario and therefore may not be applicable to other areas due to lack of
information. Drainage area is used as a measure of the size and habitat diversity of a watercourse. Based
on river theory, the habitat complexity of a watercourse increases with size, resulting in an increase in the
number of fish species that can be supported.
Steedman (1988) quantified the relationship between the number of native species present and drainage
area for streams in southern Ontario. Steedman also identified species-richness expectations for trophic
composition. The expected number of native species in Appendix 4 – Table 1, the categories for the size
of drainage basins, and the expected trophic composition were derived from Steedman’s work.
The percentage of coarse soils by drainage area is a surrogate for the flow regime in a watercourse. Soils
are one of the major determinants of runoff potential, infiltration and groundwater discharge. The coarser
the soils, the lower the runoff potential and the greater the potential for infiltration and groundwater
discharge to local watercourses. Watercourses with a drainage basin consisting of a high percentage of
coarse soils will tend to have a high baseflow and exhibit less fluctuation in flow from storm events. Portt
and King (1989) indicated in their literature review that physiographic features and associated geology
have distinctive characteristics that influence stream characteristics and the presence or absence of trout
species. Nelson et al. (1992) found that the presence or absence of trout species related to an area’s
geologic history.
Surficial geology and soils are important measures of the fundamental characteristics of a drainage basin.
Although these features can be covered by pavement or other development, they are not readily eliminated.
Knowledge of the geology and soils provides a look past the existing conditions to identify how a basin would
have functioned. However, soils and geology are themselves surrogates for the actual flow regime in a
watercourse and in some situations may be misleading.
How Much Habitat is Enough?
71
For example, Robinson Creek is a small cold-water tributary of the Rouge River watershed. Robinson
Creek originates from the clay soils of the Peel Plain and should exhibit characteristics of a warm-water
stream. However, where the creek valley cuts into the surrounding till to join with the main Rouge, it
intersects a zone of upwardly moving groundwater. The amount of groundwater encountered is sufficient
to moderate temperatures and stabilize stream flows to the extent that the creek is able to support a small
run of migratory salmonids. Therefore, soils and geology should not be used in isolation, but rather in
conjunction with other stream measures such as baseflow and historic fish communities.
The baseflow ratio is an index derived from the Habitat Suitability Indices (HSI) developed in the United
States (Raleigh, 1982; Raleigh et al., 1986). The index is the result of average baseflow divided by the
average annual daily flow. The index provides a measure of the quantity of baseflow relative to the annual
flow and an indication of the stability of the flow regime. A watercourse with a high baseflow ratio will
show little fluctuation in flow from storm events. Baseflow will occupy a large amount of the channel and
the water temperatures will tend to be low. Watercourses with these characteristics would support coldwater fish communities.
A watercourse with a low baseflow ratio will tend to fluctuate with storm events. Baseflow will occupy
only a small amount of the channel and water temperatures will tend to be high. Watercourses with these
characteristics would support a warm-water fish community. In the middle are watercourses with a
moderate baseflow ratio, where local conditions may determine whether they can support cold or warmwater fish communities.
Some caution should be used in applying the baseflow ratio on its own since flow can in fact be altered
by land-use practices. Furthermore, differences can also arise between watercourses depending on where
in the drainage area the groundwater input occurs. For instance, in a creek where the majority of the
groundwater input occurs far up in the headwaters, the lower reaches may still have a high baseflow ratio
and thus not exhibit a large fluctuation in flow. However, water temperatures may be high because of
the distance the groundwater traveled in the creek and the resulting heating that would have occurred.
One example is West Duffins Creek where the baseflow ratio for the lower part of the creek is 23 percent.
This would put the creek on the high end of cool water habitat but marginal for trout and salmon. However,
the lower part of the creek intercepts groundwater discharge. Enough groundwater enters the watercourse
at this point to cool the water and provide summer refugia for Rainbow Trout that spawn in these reaches.
The baseflow ratio is a useful tool that should be used in conjunction with the soils and geology.
When fish indicator species are used in conjunction with physical parameters of drainage area, baseflow
ratio and soils/geology, insight can be provided as to the historic function of a river system. Using the suite
of parameters outlined above, the riverine habitat in a watershed can be categorized into reaches of similar
characteristics with an associated fish community. These parameters provide an expectation as to the type
of fish community that should be present, the number of native species that should be present, and the
trophic composition as per the following table.
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How Much Habitat is Enough?
Appendix 4 – Table 1. Framework for Setting Fish Community Targets
Size of
Drainage Basin
Percentage coarse
soils by drainage
area
Baseflow ratio
Historic fish
community
Small <10 km2
Medium 10 to 200 km2
High
>25%
Moderate Low
10 to 25% 0 to 10%
>20%
Trout,
salmon,
present
10 to 20%
Trout,
salmon
may have
been
present
0 to 10%
No trout
or salmon,
or
migration
only
Coldwater
>18
Coolwater
>18
Warmwater
>18
3 to 7
>7
>7
>7
3 to 5
3 to 5
>5
>5
>5
2 to 4
2 to 4
>4
>4
>4
High
>25%
Moderate Low
10 to 25% 0 to 10%
>20%
Trout,
salmon,
present
10 to 20%
Trout,
salmon
may have
been
present
0 to 10%
No trout
or salmon,
or
migration
only
Coldwater
8 to 18
Coolwater
8 to 18
Warmwater
8 to 18
3*
3 to 7
3 to 7
2*
2*
3 to 5
2*
2*
2 to 4
High
>25%
Moderate Low
10 to 25% 0 to 10%
>20%
Trout,
salmon,
present
10 to 20%
Trout,
salmon
may have
been
present
0 to 10%
No trout
or salmon,
or
migration
only
Coldwater
<8
Coolwater
<8
Warmwater
<8
3*
3*
2*
2*
Large>200 km2
Expectation
Habitat category
Total number of
native species
Number of Darter/
Sculpin species
Number of Sunfish/
Trout species
Number of Sucker/
Catfish species
* Number of species present should be up to this value
Applying the Framework
In developing the Humber River fish plan, seven habitat categories were defined using the Framework
approach (see Appendix 4 – Table 2). Each category defines an expectation of function that relates to the
physical characteristics of the stream and the fish community that would be present. These categories
provide the baseline against which to compare the existing fish community in order to identify impacts that
have occurred or are occurring, to identify rehabilitation requirements and establish fish community targets.
In order to provide a better picture of the present health of the fish communities in the individual habitat
categories, the Index of Biotic Integrity (IBI) was used. The IBI is a broad measure of health that was
adapted for southern Ontario by Steedman (1988). The IBI integrates 10 measures of the fish community
at a site and provides a score that can be compared between sites or to a generic scale of integrity. The
fish community at a site is scored based on the sum of five sub-indices that measure species richness,
local indicator species, and other sub-indices, ranging from a low of 10 to a maximum score of 50.
For the Humber, the IBI ranges from nine to 45, with ranges of nine to 20 being poor; 21 to 27 being
fair; 28 to 37 being good; and 38 to 45 being very good. (For the Humber River watershed, Steedman’s
IBI had to be adapted for the data that was available and one sub-index was removed.) The data for
the Humber watershed indicates that 57 percent of the stations sampled scored poor or fair, while the
remainder (43 percent) were good or very good. Only one station scored in the very good range. Although
the Humber watershed is considered to be in better condition than other watersheds in the Toronto and
Region AOC, it remains highly impacted.
How Much Habitat is Enough?
73
Appendix 4 – Table 2. Characteristics of Habitat Categories used in the Humber River Fisheries
Management Plan
Habitat Category
Small riverine
cold-water
Small riverine
warm water
Intermediate
riverine cold-water
Intermediate
riverine warm
water
Large riverine
Estuarine
Lacustrine
Description
Drainage areas <10 km2; mainly first and second-order tributaries; most streams are permanent, some
are intermittent in their upper reaches; originate primarily on the Niagara Escarpment and Oak Ridges
Moraine; most slopes >one percent; coarse soils in drainage area; stable flows and continually low water
temperatures due to groundwater inputs
Drainage areas <10 km2; mainly first and second-order tributaries; high proportion are intermittent;
originate primarily on the Peel Plain; most slopes are 0.3 to 10 percent; clay soils with little groundwater
discharge; fluctuating water temperatures and flows
Drainage areas range from 10 to 300 km2; mainly third and fourth-order streams; drain the Oak Ridges
Moraine and Niagara Escarpment; slopes of 0 to 0.3 percent; permanent flow; variety of soil types;
relatively stable flows and water temperatures due to inputs from upstream cold-water tributaries
Drainage areas between 10 to 300 km2; mainly third and fourth-order watercourses; drain the Peel
Plain; slopes of 0 to 0.3 percent; some streams dry up or become standing pools in summer; fluctuating
flow regime and water temperatures due to low baseflow
Drainage area >300 km2; fifth and sixth-order watercourses; permanent flow; fluctuating flow regime
and water temperatures
Extends from the mouth upstream a distance of 3 km; very low slope (0.03 percent); slow-moving,
turbid water, influenced by water level in Lake Ontario
Low slope, low-gradient areas that may be eutrophic, and in some of the kettle lakes, anoxic near the
bottom; on-line or off-line; pond; kettle lake; impoundment; or reservoir
Toward Delisting
The system of habitat categories and the approach presented provides a framework for managers to
establish an expected fish community against which to assess the present conditions, establish fish
community targets and identify the general health of the system. However, the use of species richness
and the presence or absence of a few specific indicator species is not enough of a measure of health to
use as the basis for delisting watercourses from the AOC. A broader measure of health such as the Index
of Biotic Integrity (IBI), when used in conjunction with the habitat categories outlined above and the
riparian guidelines, may provide an appropriate tool for delisting.
The habitat categories provide an expectation for function of the watercourse and composition of the
fish community while the IBI provides a measure of health. Targets for delisting could be set based
on achieving a certain degree of function, a specific level of IBI and meeting the riparian targets. For
example, a watercourse that meets its expected function and general fish community composition
would also have to achieve a specific level of IBI and riparian habitat condition before it would be
considered delisted.
For the Humber watershed, it may be appropriate to establish targets of: fish communities appropriate
for the habitat categories; 75 percent of all stations scoring IBI of good to very good, no stations scoring
poor; 75 percent of stream length (first to third-order) with woody riparian vegetation, and; 30 metre
riparian buffer along 75 percent of stream lengths (first to third-order). These targets are tangible and
can be related to people through the species that are being managed. These types of targets are also
adaptable to more impacted systems where a high level of function cannot be achieved.
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How Much Habitat is Enough?
References
Nelson, R.L., W.S. Platts, D.P. Larsen, and S.E. Jensen. 1992.
Trout distribution and habitat in relation to geology and geomorphology in the North Fork Humbolt River Drainage, Northeastern Nevada.
Transactions of the American Fisheries Society. 121: pp. 405-426.
Portt, C. and S.W. King. 1989.
A review and evaluation of stream habitat classification systems and recommendations for the development of a system for use in Southern Ontario.
Ontario Ministry of Natural Resources. 80 pp.
Raleigh, R.F. 1982.
Habitat suitability index models: Brook trout. US Department of Interior, Fish and Wildlife Service FWS/OBS-82/10.24. 42pp.
Raleigh, R.F. L.D. Zuckerman, and P. Nelson. 1986.
Habitat suitability index models and instream flow suitability curves: Brown trout, revised. US Fish and Wildlife Service Biological Report 82
(10.124). 65 pp.
Steedman, R.J. 1988.
Modification and assessment of an index of biotic integrity to quantify stream quality in Southern Ontario. Can. J. Fish. Aquatic. Sci. 45: pp. 492-500.
Appendix 4 – Table 3. Fish Species Historically and Presently Found in the Habitat Categories
in the Humber River Watershed
Habitat
Category *
Species
Species Found in
Found in
Two Categories
One Category
Species Found in Three
Categories
Species Found in
Four Categories
All habitat
categories
Species Found
in All Categories
American Brook Lamprey,
White Sucker, Northern
HoggSucker, Redside
Dace, Brassy Minnow,
Common Shiner, Blackchin
Shiner, Blacknose Shiner,
Bluntnose Minnow,
Fathead Minnow,
Blacknose Dace, Creek
Chub, Brown Bullhead,
Brook Stickleback, Rock
Bass, Pumpkinseed,
Smallmouth Bass,
Largemouth Bass, Yellow
Perch, Rainbow Darter,
Iowa Darter, Fantail
Darter, Johnny Darter
Small riverine
cold-water
Northern Brook Lamprey,
Atlantic Salmon,
Rainbow Trout, Brook Trout, Central Mudminnow
Goldfish, Pearl Dace
Brown Trout, Northern
Redbelly Dace, Banded
Killifish, Mottled Sculpin
Small riverine Three Spine
warm-water
Stickleback
Northern Pike
Central Mudminnow,
Golden Shiner, Emerald
Shiner, Sand Shiner
Northern Redbelly Dace,
River Chub, Rosyface Shiner,
Longnose Dace, Banded
Killifish, Yellow Bullhead,
Mottled Sculpin
Intermediate
riverine
cold-water
Bluegill
Rainbow Trout, Brook
Trout, Pearl Dace,
Mimic Shiner
Atlantic Salmon, Central
Mudminnow, Golden Shiner,
Spottail Shiner, Hornyhead
Chub, Stonecat
Brown Trout, Northern
Redbelly Dace, River Chub,
Rosyface Shiner, Longnose
Dace, Yellow Bullhead,
Mottled Sculpin
Intermediate
riverine
warm-water
Bluegill
Emerald Shiner, Spottail
Shiner, Sand Shiner,
Hornyhead Chub, Stonecat
Brown Trout, Northern
Redbelly Dace, River Chub,
Rosyface Shiner, Longnose
Dace, Banded Killifish, Yellow
Bullhead, Mottled Sculpin
Large
riverine
Fallfish,
Blackside
Darter
Atlantic Salmon, Golden
Shiner, Emerald Shiner,
Spottail Shiner, Sand Shiner,
Hornyhead Chub, Stonecat
Brown Trout, River Chub,
Rosyface Shiner, Longnose
Dace, Banded Killifish,
Yellow Bullhead
Northern Brook Lamprey,
CommonCarp, Goldfish,
Mimic Shiner
Northern Pike,
Common Carp
* Table does not include estuarine and lacustrine habitats.
How Much Habitat is Enough?
75
Appendix 5
Assessment of Forest Bird Community Integrity: A Draft Methodology
and Field Test in the Severn Sound AOC (Report Highlights)
During the summer of 1997, the Canadian Wildlife Service conducted breeding bird surveys in the
Severn Sound AOC (Tate, 1998). The purpose of the study was to:
■
assess habitat guidelines (percent forest cover and largest forest block) contained in the Framework
in terms of forest bird species composition, and make recommendations on their utility
■
determine the response of the forest bird community to reforestation efforts
■
develop criteria for delisting the forest bird community of an AOC
■
assess the current status (integrity) of the forest bird community in Severn Sound, and its potential
for delisting
■
suggest methodology for forest bird community assessment in other areas.
Highlights of this work, combined with Geographic Information System (GIS) and statistical analysis
on Ontario Breeding Bird Atlas (Atlas) data are provided here. The information serves to validate and
expand upon the forest habitat guidelines.
Assessing Forest Habitat Guidelines
Forest Cover Guidelines
> Methods
Forest bird data from the Atlas database were combined with the Ontario Hydro satellite-image
database of forest cover for southern Ontario to test the forest cover guidelines. Relationships
between species and forest cover were determined using regression analyses at three different scales
(10 000 hectares; 40 000 hectares; 90 000 to 160 000 hectares). Iterative regression analyses were
used to determine thresholds of forest cover, beyond which any increase in species richness (slope)
was not significant.
> Results
On a scale of a single Atlas square, or 10 000 hectares, analyses indicate a strong increase in the number
of forest bird species as forest cover within a square increases. Forest-interior bird species exhibit the
steepest slope and the best fit for the model.
Forest-interior bird species continue to increase in number to at least 35 percent forest cover. The
proportion of forest cover greater than 100 metres from forest edge was also found to have a slight but
significant effect when combined with forest cover. Deep forest-interior (greater than 200 metres) was not
found to make a significant contribution to interior species richness. Therefore, total forest cover appears
to be the most important feature influencing forest-interior species richness and the most critical of the
habitat guidelines at the scale of single squares.
On a scale of four adjacent Atlas squares, or 40 000 hectares, the number of forest-interior species
encountered continues to increase with increasing forest cover to approximately 24 percent forest cover.
76
How Much Habitat is Enough?
At this scale, total forest cover is the primary factor determining the number of interior species expected
to occur, and the proportion of 200-metre interior forest is also a significant contributing factor.
Interpretation of the scales of nine adjacent squares, or 90 000 hectares, and 16 adjacent squares, or
160 000 hectares were combined as they demonstrated similar patterns. The observed pattern of increasing
numbers of forest-interior bird species with increased forest cover continues to hold at these scales. An
increase in number of interior species continues up to 20 percent forest cover. Although total forest cover
and 100-metre forest-interior were important independently, neither made a significant contribution
to predicting species richness when included in multiple regression models with 200-metre deep interior
forest. The important factor in predicting interior species richness at these scales is the amount of 200-metre
interior forest in a block.
The following series of tables summarizes the response of two groups of birds, all forest birds and forestinterior birds, to changes in forest cover at four scales. Note which scale best applies to the planning unit
being assessed (i.e., a small subwatershed or a larger watershed).
Regional numbers of expected forest birds are 120 species in south-western Ontario, 127 species in southcentral Ontario, and 117 species in south-eastern Ontario. A mean value of 121 species was used for the
analysis of proportion of expected forest bird species. Numbers of forest-interior birds expected by region,
according to Atlas breeding ranges, are 31 species in south-western Ontario, 37 species in south-central
Ontario, and 36 species in south-eastern Ontario. A mean value of 34 species was used for the analysis of
proportion of expected forest-interior bird species.
Regional Patterns
Performing similar analyses on a regional basis for south-western, south-central and south-eastern Ontario
suggested some regional differences. Central and eastern regions had much higher average forest cover.
The western region showed the steepest increase in numbers of all forest birds and interior species with
amount of forest cover. This relationship suggests that even some of the most heavily-forested squares
in the south-west (Carolinian zone) may not be supporting as many forest species as they could if more
forest habitat were available. These patterns suggest that additional forest cover is most urgently required
in the Carolinian zone, and reforestation efforts in that region would likely yield the greatest benefit in
terms of increasing forest bird diversity. Both central and eastern regions displayed an increasing number
of interior species to 34 percent cover, nearly identical to the overall Ontario estimate of a 35 percent
threshold (at a scale of a single square).
The difference in landscape patterns is interesting by comparison with other work. Freemark and Collins
(1992) in a study of forest birds in four landscapes of varying forest cover in Ontario, Missouri and Illinois
found that the greatest increase in species with forest area (steepest slope) occurred in the landscape of
greatest total forest cover. This study, on the other hand, has determined that the total number of species
occurring in an area shows the greatest increase with forest cover in the landscape with the least total
forest. This result highlights the value of considering diversity on a broad regional scale, rather than on
an individual patch basis.
How Much Habitat is Enough?
77
Patch Size Guidelines
> Methods
Four large forest tracts were censused for breeding evidence of all forest bird species and breedingbird community composition (relative abundance). Sites included two natural primarily deciduous
tracts, one pine plantation and one pine plantation/natural deciduous forest mixed tract. Due to
logistical constraints, the plantation site was not an isolated forest block, but was continuous with
additional plantation and forested swamp for a total of over 400 hectares.
> Results
The two natural forest sites had higher forest bird species richness. The number of forest-interior species
was slightly higher in the red pine plantation than in other sites. Note that there are more forest-interior
species associated with coniferous (19 species) than deciduous (15 species) forest habitat in the Severn
Sound region.
None of the forest tracts supported all forest-interior birds possible in the region. These findings suggest
that to support the full complement of forest birds, one forest tract of 100 hectares is not sufficient.
The study suggests that a tract of 200 hectares provides habitat for over 80 percent of expected forestinterior birds in a natural deciduous habitat. Several large tracts of forest are recommended to support
90 to 100 percent of expected species. In areas where coniferous and deciduous forest are both naturally
occurring, forest tracts of 200 hectares are recommended for each forest type to support all or most
native interior species.
The Effects of Reforestation (Plantations)
> Methods
Five survey sites were set up at conifer plantations in the Severn Sound AOC. Plantations ranged
in age from one year to 66 years of age. Selected sites were adjacent to remnant natural deciduous
forest, typically Sugar Maple. At each site, three survey stations were aligned perpendicular to
existing adjacent forest edge: one in natural forest-interior; one at the forest/plantation edge; and,
one in the plantation (or recently planted) interior. Point-count surveys were completed at each
of the three stations per site.
> Results
The strongest relationship occurs in the plantation interior stations where the number of edge species
decreased from five in the one year site to zero in the 66 year-old plantation. Conversely, forest-interior
species increased from zero to three at the same stations.
References
Freemark, K. and B. Collins. 1992.
Landscape ecology of birds breeding in temperate forest fragments. In D. Finch and P. Stangel, eds. Status and management
of neotropical migratory birds. USDA-FS Ge. Tech. Rep. RM-229, 422 pp.
Tate, D.P. 1998.
Assessment of the Biological Integrity of Forest Bird Communities: A Draft Methodology and Field Test in the Severn Sound
Area of Concern. Canadian Wildlife Service – Ontario Region.
78
How Much Habitat is Enough?
Appendix 5 – Table 1. Predicted Response of All Forest Bird Species to Percent Forest Cover
Percent Forest
Cover
<5
5-10
10-20
20-30
30-40
>40
Percent of Expected Forest Bird Species Occurring at Selected Scales
1,600 km2
82
82-86
86-89
89-91
91-93
>93
900 km2
<72
72-77
77-81
81-84
84-86
>86
400 km2
<65
65-70
70-75
75-78
78-80
>80
100 km2
<53
53-57
57-61
61-63
63-65
>65
Appendix 5 – Table 2. Predicted Response of Forest-interior (FI) Bird Species to Percent Forest Cover
Percent Forest
Cover
<5
5-10
10-20
20-30
30-40
>40
Percent of Expected Forest-interior Species Occurring at Selected Scales
1,600 km2
60
60-72
72-85
85-92
92-97
>97
900 km2
<44
44-57
57-70
64-77
77-82
>82
400 km2
<40
40-50
50-61
61-67
67-71
>71
100 km2
<26
26-34
34-41
41-45
45-49
>49
Photo by John Mitchell
How Much Habitat is Enough?
79
Appendix 5 – Table 3. Predicted Response of All Forest Bird Species to Percent 100 m Forest-interior
(greater than 100 metres from edge)
Percent Interior
<1.0
1.0-2.0
2.0-5.0
5.0-7.5
7.5-10.0
>10.0
Percent of Expected Forest Bird Species Occurring at Selected Scales
1,600 km2
up to 85
85-87
87-89
89-90
90-91
>91
900 km2
up to 75
75-78
78-82
82-84
84-85
>85
400 km2
up to 69
69-72
72-75
75-77
77-78
>78
100 km2
up to 56
56-59
59-61
61-62
62-63
>63
Appendix 5 – Table 4. Predicted Response of Forest-interior (FI) Bird Species to Percent 100 metre
Forest-interior (greater than 100 metres from edge)
Percent Interior
<1.0
1.0-2.0
2.0-5.0
5.0-7.5
7.5-10.0
>10.0
Percent of Expected Forest-interior Bird Species Occurring at Selected Scales
1,600 km2
up to 67
67-75
75-85
85-89
89-93
>93
900 km2
up to 53
53-61
61-71
71-76
76-79
>79
400 km2
up to 48
48-54
54-62
62-65
65-68
>68
100 km2
up to 32
32-36
36-42
42-45
45-46
>46
Table 5. Predicted Response of All Forest Bird Species to Percent Deep Forest-interior (DFI)
(greater than 200 metres from edge)
Percent DFI
<0.5
0.5-1.0
1.0-2.0
2.0-3.0
3.0-4.0
>5.0
Percent of Expected Forest Bird Species Occurring at Selected Scales
1,600 km2
900 km2
400 km2
100 km2
up to 87
up to 79
up to 73
up to 59
87-88
79-81
73-75
59-61
88-90
81-83
75-76
61-62
90-91
83-84
76-77
62-63
91-92
84-85
77-78
63-64
>92
>86
>79
>64
Table 6. Predicted Response of Forest-interior (FI) Bird Species to Percent Deep Forest-interior (DFI)
(greater than 200 metres from edge)
Percent DFI
<0.5
0.5-1.0
1.0-2.0
2.0-3.0
3.0-4.0
>5.0
80
Percent of Expected Forest-interior Bird Species Occurring at Selected Scales
1,600 km2
900 km2
400 km2
100 km2
up to 75
up to 64
up to 56
up to 38
75-80
64-69
56-60
38-41
80-86
69-74
60-64
41-44
86-89
74-77
64-66
44-46
89-92
77-79
66-68
46-47
>94
>80
>69
>48
How Much Habitat is Enough?
Photo by CWS
Photo by Eric Dresser
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