Plantations and biodiversity: A comment on the debate in New Brunswick

Plantations and biodiversity: A comment on the debate in New Brunswick
Plantations and biodiversity:
A comment on the debate in New Brunswick
by Matthew G. Betts1, Antony W. Diamond2, Graham J. Forbes3, Kate Frego4, Judy A. Loo5,
Bruce Matson6, Mark R. Roberts3, Marc-André Villard7, Renee Wissink8 and Lawrence Wuest9
ABSTRACT
The importance of biodiversity has become widely recognized but the best methods for conserving forest biodiversity are
still being debated. Central to this debate is the influence of plantations and managed stands on local and landscape-scale
biodiversity. A recent paper by Erdle and Pollard in The Forestry Chronicle (2002), which concluded that few plantations
are strict monocultures in terms of the total number of tree species, could be interpreted as making the case that plantations have relatively minor consequences for biodiversity. We argue that: (1) it is not only the number of species, but
also the identities and relative abundances of species that are of ecological importance, and (2) defining biodiversity in
terms of tree species alone is of limited applicability. Existing research in New Brunswick on the impact of plantations
on biodiversity at the stand scale reveals potentially significant biodiversity losses, at least in certain taxa. The proposal
that incorporating more structural elements (e.g., snags, coarse woody debris, vertical structure) and retaining greater
tree species diversity to ameliorate negative consequences of plantations remains a hypothesis to be tested in this region.
Scientific information gathered in the following areas will allow better decision making: (1) to what degree are older
plantations used by native species? (2) are productivity and survivorship of vertebrates in intensively managed stands
similar to those in unmanaged forest? (3) are intensively managed stands suitable habitat for non-vertebrates? (4) are
there thresholds in the response of some species to landscape-scale habitat loss caused by intensive forest management?
Key words: plantations, biodiversity, species composition, landscape scale, stand structures
RÉSUMÉ
L’importance de la biodiversité est acceptée de façon générale mais les meilleures méthodes de conservation de la biodiversité forestière font encore l’objet d’un débat. Au cœur de celui-ci, on retrouve l’influence des plantations et des peuplements aménagés sur la biodiversité locale et à l’échelle de l’écosystème. Un article récent publié par Erdle et Pollard dans
Le Forestry Chronicle en 2002 qui concluait que rares sont les plantations qui constituent des monocultures absolues en
terme du nombre total d’espèces d’arbres, pouvait être interprété comme énonçant que les plantations entraînent des
conséquences relativement mineures au niveau de la biodiversité. Nous alléguons que (1) ce n’est pas seulement le nombre
d’espèces, mais également l’identité et l’abondance relative des espèces qui sont d’importance écologique et, (2) la définition de la biodiversité en terme d’espèces d’arbres seulement est d’une applicabilité restreinte. Les recherches en cours au
Nouveau-Brunswick sur les retombées des plantations sur la biodiversité au niveau du peuplement révèlent des pertes de
biodiversité potentiellement significatives, du moins pour certains taxons. La proposition cherchant à incorporer plus
d’éléments structuraux (par ex., les chicots, les débris ligneux grossiers, la structure verticale) et la rétention d’une plus
grande diversité d’espèces d’arbres pour améliorer les retombées négatives associées aux plantations, demeure une
hypothèse qui doit être testée dans cette région. L’information scientifique recueillie dans les domaines suivant permettra
une meilleure prise de décision: (1) à savoir jusqu’à quel niveau les vieilles plantations sont-elles utilisées par les espèces
indigènes ? (2) est-ce que la productivité et la capacité de survie des vertébrés dans les peuplements sous aménagement
intensif sont semblables à celles des forêts non aménagées ? (3) est-ce que les peuplements sous aménagement intensif
constituent un habitat adéquat pour les non vertébrés ? (4) est-ce qu’il existe des seuils de réaction dans le cas de certaines
espèces lors de perte d’habitat au niveau de l’écosystème occasionnée par l’aménagement forestier intensif ?
Mots clés : plantations, biodiversité, composition en espèces, échelle de l’écosystème, structures du peuplement
1Greater Fundy Ecosystem Research Group, Hugh John Flemming Forestry Centre, 1350 Regent St., Fredericton, New Brunswick E3C 2G6.
E-mail: m.betts@unb.ca. Author to whom correspondence should be sent.
Cooperative Wildlife Ecology Research Network, University of New Brunswick, P.O. Box 45111, Fredericton, New Brunswick
E3B 6E1. E-mail: diamond@unb.ca
3Faculty of Forestry and Environmental Management, University of New Brunswick, P.O. Box 45111, Fredericton, New Brunswick
E3B 6C2. E-mail: forbes@unb.ca, roberts@unb.ca
4Department of Biology, University of New Brunswick Saint John, P.O. Box 5050, Saint John, New Brunswick E2L 4L5. E-mail:
frego@unbsj.ca
5Natural Resources Canada, Canadian Forest Service – Atlantic Forestry Centre, P.O. Box 4000, Fredericton, New Brunswick E3B 5P7.
E-mail: jloo@nrcan.gc.ca
6N.B. Department of Natural Resources, 1045 Main Street, P.O. Box 1063, Hampton, New Brunswick E5N 8H1. E-mail:
bruce.matson@gnb.ca
7Chaire de recherche du Canada en conservation des paysages, Département de biologie, Université de Moncton, Moncton (NouveauBrunswick) E1A 3E9. Courriel : villarm@umoncton.ca
8Fundy National Park, P.O. Box 1001, Alma, New Brunswick E4H 1B4. E-mail: renee.wissink@pc.gc.ca
9P.O. Box 363, Stanley, New Brunswick E6B 2K5. E-mail: wuestl@nbnet.nb.ca
2Atlantic
MARCH/APRIL 2005, VOL. 81, No. 2 — THE FORESTRY CHRONICLE
265
Since the 1992 World Convention on Biological Diversity,
the importance of biodiversity has become widely understood and recognized (CCFM 1995, Chapin et al. 2000,
NBDNR 2000). However, the best methods for conserving
forest biodiversity are still debated (Lindenmayer et al. 2000,
Baskerville 2002). Central to this debate is the influence of
plantations and managed stands on local and landscapescale biodiversity (Binkley 1997, Woodley and Forbes 1997).
In New Brunswick, this debate has become controversial following the release of a consultant’s report, jointly commissioned by the New Brunswick Forest Products Association
and the New Brunswick Department of Natural Resources
(NBDNR), that recommends doubling the wood supply on
Crown land primarily through the implementation of
intensive silviculture (Jaakko Pöyry Management Consulting
2002). If adopted, the recommendations of Jaakko Pöyry
Management Consulting would see 42% of Crown lands
devoted to plantation and 18% in otherwise intensively
managed (largely precommercially thinned) forest. Such a
policy has the potential to act as a precedent for other tenures
within New Brunswick and in other Canadian provinces.
Science has been used to support the positions of both
proponents and detractors of intensive forestry. The Forestry
Chronicle recently published a paper by Erdle and Pollard
(2002) entitled “Are plantations changing the tree species
composition of New Brunswick’s forest?” Their conclusion
that few plantations are strict monocultures could be interpreted as indicating that plantations have relatively minor
consequences for biodiversity. Indeed, the paper has been
cited in several presentations at public hearings as evidence
that plantations may be benign (e.g., Adams 2003, MacLean
2003). However, Erdle and Pollard (2002) also described
important differences between plantations and managed
forests. The purpose of this letter is twofold: (1) to summarize those conclusions of Erdle and Pollard (2002) that do
not support the hypothesis that plantations are benign, and
(2), using recent research from New Brunswick, to highlight
impacts of plantation forestry on components of biodiversity other than tree species.
The main objective of the Erdle and Pollard (2002) study
was to compare the merchantable tree-species composition
of preharvest, unmanaged stands (hereafter, “natural forest”)
with that of plantations. To account for the biased comparison between mature, unmanaged forest and comparatively
young plantations, the authors forecast the species composition and volume of plantations at maturity using the STAMAN growth model (Erdle and MacLean 1999). Erdle and
Pollard (2002) drew two conclusions from their data that
indicate that plantations have negative consequences for biodiversity at the stand level — even at the coarse resolution of
merchantable tree species:
1. They found that the hardwood content in plantations
(10%) is half that of natural forest (20%). Furthermore,
it is important to note that this hardwood component in
plantations is made up primarily of intolerant hardwoods
(white birch (Betula papyrifera Marsh.), largetooth aspen
(Populus grandidentata Michx.), trembling aspen (Populus
tremuloides Michx.), and red maple (Acer rubrum L.)) at
the expense of tolerant hardwoods (beech (Fagus grandifolia L.), sugar maple (Acer saccharum Marsh.), and yellow
birch (Betula alleghaniensis Britt.)), which they replaced
(Erdle and Pollard 2002). Indeed, these species groups
266
are characterized by different silvics (Burns and Honkala
1990), different structural attributes, and different functions as wildlife habitat or microhabitat (Flemming et al.
1999). The abundance of red spruce (Picea rubens Sarg.)
is greatly reduced in plantations (it is about 1.5–7 times
more common in natural forest, Erdle and Pollard 2002).
As this species is considered a key component of the
Acadian forest (Mosseler et al. 2003), such large differences
are striking and should be cause for concern. The key
point here, in our opinion, is that not only the number of
species, but also the identities and relative abundances of
species are of ecological importance (Balmford et al. 2003).
2. They also found that the same volume proportion made
up by the four most abundant species in natural forest is
restricted to two or three species in plantations. The
authors conclude that this suggests reduced diversity
evenness at the landscape level. Using data extrapolated
from Fig. 7 (Erdle and Pollard 2002), we calculated an
average decline in diversity of ~30% (Normalized
Simpson index, natural forest = 0.58, plantation = 0.40)1.
These conclusions indicate that plantations lead to a
reduction in diversity, even when measured in terms of merchantable tree species.
There is also some evidence to suggest that Erdle and
Pollard (2002) underestimated the negative impacts of plantations on biodiversity. First, they have used as a baseline
condition a forest that has been substantially altered from its
natural condition in pre-Colonial times. Therefore, the negative effects of plantations on biodiversity have been overlaid
on a forest that was already negatively affected by high grading (Betts and Loo 2002). Second, data used for natural
(pre-harvest) stand types were from the period 1984–1990.
During and subsequent to this period, the harvest of hardwood and mixedwood stands has increased in proportion to
softwood harvest. Volume of hardwood harvested in 2003
was nearly five times greater than the amount harvested in
1983, and approximately twice the harvest in 1989 (NBDNR
1983, 1989, 2003). If harvested mixedwood and hardwood
areas have been planted in New Brunswick with conifers
(research on the degree to which this has occurred is scant),
we predict that differences in tree-species diversity would
have been more pronounced had Erdle and Pollard (2002)
used more recent data.
Erdle and Pollard (2002) stated that defining biodiversity in terms of tree species alone is of limited applicability.
We strongly concur. Existing New Brunswick studies on
structural attributes (e.g., snags, coarse woody debris;
Freedman et al. 1994), birds (Parker et al. 1994), amphibians
(Waldick et al. 1999), herbaceous plants (Ramovs and
Roberts 2003), and bryophytes (Ross-Davis and Frego 2002)
report reduced stand-level diversity as a result of softwood
plantation in southern New Brunswick.
Indeed, even to examine species diversity alone is potentially misleading. Diversity in community types and structural diversity are also central to the definition of biodiversity (Noss and Cooperrider 1994). Estimates of the number
of softwood community groups in New Brunswick range
1The
Normalized Simpson Index of Diversity, sometimes referred
to as the index of equitability or evenness E is given by: E = 1
/i pi2 . 1/N, where pi is the proportion of the population in class i
and N is the total number of classes (Magurran 1988).
MARS/AVRIL 2005, VOL. 81, No. 2 — THE FORESTRY CHRONICLE
from six to 22 (NBDNR 2000, Basquill et al. submitted).
It would theoretically be possible to eradicate a large proportion of these community types through planting with
only small decreases in species diversity. This theoretical
possibility becomes more probable if about 96% New
Brunswick’s Crown softwood is managed intensively for fibre
production, as recommended by Jaakko Pöyry Management
Consulting (2002).
Furthermore, the structure of softwood plantations is
simplified compared with post-budworm, naturally regenerated stands (Fleming and Freedman 1998). Research in
northwestern New Brunswick indicates that reductions
in structural heterogeneity, combined with short-rotation
harvesting, would be detrimental to at least 12 species of
passerine birds (Guénette and Villard 2005). This does not
account for species that occurred too infrequently to conduct statistical analyses (e.g., Black-backed Woodpecker,
Picoides arcticus, and American Three-toed Woodpecker,
Picoides dorsalis). Reductions in the density of snags and
coarse woody material have been demonstrated to have negative effects on birds and on many other organisms in
Fennoscandia (Esseen et al. 1997, Siitonen 2001).
It is also critical to consider the potential landscape-scale
impact of plantations on the biodiversity of New Brunswick. Under the scenario recommended by Jaakko Pöyry
Management Consulting (2002), 42% of Crown land will be
occupied by plantations (compared with 17% in the current
planning scenario). Although knowledge of landscape-scale
impacts of intensive forestry/silviculture is scant, a number
of studies suggest that the relationship between habitat loss
and population size is not proportional (Andrén 1999,
Radford and Bennett 2004). As landscape mosaics are converted into a patchwork of plantations, managed and
unmanaged second- and third-growth stands, not all habitat that is suitable at the stand scale may be occupied by certain species (Lichstein et al. 2002, Betts et al. submitted,
Guénette and Villard unpublished data). This probably
reflects disruptions in processes taking place over larger
scales (e.g., dispersal, predator–prey dynamics) (Krawchuk
and Taylor 2003). In addition, area-demanding species simply may not be able to combine scattered resource patches
into a home range (Chapin et al. 1998). These landscapescale impacts are of greater concern in the context of the
rapid decline in unmanaged forest due to the Allowable Cut
Effect (ACE), whereby unmanaged forest is harvested more
rapidly (the allowable cut is increased) in anticipation of
future plantation yields.
If plantations are to be used as a way of decreasing harvest pressure on unmanaged forest, it is critical that: (1) the
mix of planted species be broadened, (2) natural regeneration be encouraged in patches within plantations, (3) biogeographical site conditions be considered in plantation
species choice, and (4) plantation establishment be concentrated in ecological zones that are naturally most similar to
plantations (Erdle and Pollard 2002). We emphasize that
existing research in New Brunswick on the impact of plantations on biodiversity at the stand scale reveals potentially
significant biodiversity losses, at least in certain taxa
(Freedman et al. 1994, Waldick et al. 1999, Ross-Davis and
Frego 2002, Veinotte et al. 2003, Ramovs and Roberts 2003,
Guénette and Villard 2005). We recognize that much of the
MARCH/APRIL 2005, VOL. 81, No. 2 — THE FORESTRY CHRONICLE
previous research was conducted on young (< 20 years old)
plantations and that research is continuing on older (> 50
years old) plantations. However, results from a study of
plantations aged 19–64 years (Ross-Davis and Frego 2002,
Ramovs and Roberts 2003) indicated that differences in
species composition remain in these older plantations, at
least for vascular plants. The proposal that incorporating
more structural elements (e.g., snags, coarse woody debris,
vertical structure) and retaining greater tree species diversity
will ameliorate negative consequences of plantations
remains a hypothesis to be tested in this region (Seymour
and Hunter 1999). Indeed, in Fennoscandian countries,
where intensive silviculture has occurred for over 80 years,
about 50% of red-listed species are threatened as a result of
intensive forestry (Berg et al. 1994, Nilsson and Ericson
1997). Many of these species are lesser known and rare
species, including fungi (polypores), bryophytes, and
lichens (Finnish Environment Institute 2000).
Scientific information gathered in the following areas
will allow better decision making:
1. To what degree are older (> 50 years old) plantations used
by native species? Most plantation-based research in
New Brunswick during the 1990s was in the context of
large-scale, post-budworm salvage. Planting converted a
landscape composed of mature, mixed forest to young,
planted forest characterized by short-rotation harvesting
(Freedman et al. 1994). Recent trends to treat planted sites
with two- to three-pass harvests will increase plantation
age, and will potentially decrease structural differences
between plantations and mature, unmanaged forest
(Freedman et al. 1994). For example, older plantations are
more likely to contain larger trees (> 30 cm dbh), which
are important structural components for a range of forest
bird species (Guénette and Villard 2005).
2. Are productivity and survivorship of vertebrates in intensively managed stands similar to those in unmanaged
forest? Reliance on presence–absence or density data does
not recognize the possibility that plantations may serve as
sinks or ecological traps if net productivity is less than zero
(Pulliam and Danielson 1991, Kristan 2003). For example,
a reliance on presence–absence data does not recognize
bias from processes such as sub-optimal habitat use by
juvenile individuals, or that singing, territorial male birds
may not indicate successful reproduction (Hagan et al.
1996). Under certain conditions, density does not necessarily reflect productivity (van Horne 1983).
3. Are intensively managed stands suitable habitat for
non-vertebrates? There is a tendency to monitor several
vertebrate species and extrapolate results to biodiversity
in general. Because of their energy requirements and
mobility, large vertebrates are less likely than bryophytes,
vascular plants, insects, and soil biota to respond directly
to stand structures.
4. Are there thresholds in the response of some species to
landscape-scale habitat loss caused by forest management?
For species, or populations, that use areas larger than single stands, what is the impact of the matrix becoming less
usable? At present, most research is conducted at the stand
scale, ignoring the influences of landscape context.
Until research in these areas is conducted, we advocate a
precautionary approach to plantation establishment.
267
Acknowledgements
We wish to thank Caroline Simpson (Canadian Forest
Service) for providing thorough editorial review and Vince
Zelazny for thoughtful comments on earlier drafts of this
manuscript.
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