Vegetation of Richards Bay municipal area, wetlands

Vegetation of Richards Bay municipal area, wetlands
Vegetation of Richards Bay municipal area,
KwaZulu-Natal, South Africa, with specific reference to
wetlands
by
Jeanine Burger
Submitted in partial fulfillment of the requirements
for the degree
Magister Scientiae
in the
African Vegetation and Plant Diversity Research Centre
Department of Plant Science
Faculty of Natural and Agricultural Sciences
University of Pretoria
Pretoria
Supervisor: Prof. G.J. Bredenkamp
November 2008
© University of Pretoria
Declaration:
I, Jeanine Burger declare that the thesis/dissertation, which I hereby
submit for the degree Magister Scientiae at the University of
Pretoria, is my own work and has not previously been submitted by
me for a degree at this or any other tertiary institution.
SIGNATURE: ..…………………………..
DATE: 23 January 2009
2
This dissertation is dedicated to my parents Johan and Hester Burger
and my sister, Surette.
“Maybe botanists live so long, I thought, because their own anxieties
leach out and get lost in the intricate details of their subject…”
- Redmond O’Hanlon
3
Table of contents
p 4-10
List of Figures and Tables
p 6-8
List of photos
p 8-10
1 INTRODUCTION
p 11-25
1.1 Basic spatial relationships surrounding Richards Bay
p 11-15
1.2 General introduction to wetlands
p 16-19
1.3 Importance of wetlands
p 20-22
1.4 Threats to wetlands
p 22-24
1.5 Conservation of wetlands
p 24-25
2 LITERATURE REVIEW OF PLANT COMMUNITIES
OF NORTHERN KWAZULU-NATAL
p 26-34
3 RATIONALE AND OBJECTIVES
p 35-41
3.1 What is a MOSS?
p 35
3.2 Aim of MOSS
p 35-36
3.3 Vegetation and the Richards Bay MOSS
p 36-38
3.4 The importance of MOSS for Richards Bay surrounding areas
P 38-39
3.5 The role of the Norwegian Programme for Development, Research and
Higher Education (NUFU).
p 39-40
3.6 Survey analysis of vegetation
p 40-41
3.7 The aims of this research project
p 41
4
4 DISCRIPTION OF THE STUDY AREA
p 42-56
4.1 A brief history of northern KwaZulu-Natal
p 42-44
4.2 Climate
p 44-45
4.3 Topography
p 45-46
4.4 Geology and soils
p 46-49
4.5 Hydro-geological Setting
p 49-56
4.5.1 General
p 49-50
4.5.2 Surface water conditions
p 50
4.5.3 Groundwater recharge
p 51-56
5 METHODOLOGY
p 57-72
5.1 Selection of sites
p 57
5.2 The structural classification method
p 57-62
5.3 The floristic survey
p 62-66
5.4 Plant gathering, pressing, storage and identification
p 66-67
5.5 Data processing
p 67
5.5.1 The TWINSPAN computerized method
p 68-71
5.6 Field mapping and verification of wetland and other vegetation
p 71-72
6. RESULTS: PLANT COMMUNITIES OF THE DUNES P 73-78
7. RESULTS: FOREST COMMUNITIES
P 79-91
8. RESULTS: GRASSLAND AND WETLAND COMMUNITIES
P 92-102
5
9. GENERAL DISCUSSION
p 103-120
10. CONCLUSIONS
p 121-125
11. REFERENCES
p 126-144
Abstract
p 145-146
Acknowledgements
p 147
6
LIST OF TABLES AND FIGURES
Figure 1.1: A map of regional water resources.
P 15
Figure 1.2: A simplified geographical map of the Richards Bay region.
P 17
Figure 1.3: A schematic representation of different wetland types.
P 19
Table 1.1: Number of wetlands and their level of protection.
P 25
Figure 3.1: A schematic representation of wetland functions and values.
P 37
Figure 4.1: Geology of the study area.
P 46-47
Figure 4.2: Weir against saline intrusion between Lake Mzingazi and
Mzingazi River.
P 51
Figure 4.3: A diagrammatic representation of mechanism considered in
Recharge from rainfall.
P 53
Figure 4.4: A map of different land use types in the study area of Richards
Bay.
P 54
Figure 5.1: A spatial representation of suburb open space zones in Richards
Bay Municipal area.
P 58
Figure 5.2: A map indicating outer-lying suburbs of Esikhawini, Nseleni
And Vulindlela in the Richards Bay Municipal area with
drainage channels and water bodies.
P 59
Table 5.1: Tabular key to structural groups and formation classes.
P 61-62
Figure 5.3: An example of a species-area curve.
p 64
Table 5.2: Suggested quadrat sizes for certain vegetation types.
p 65
Table 5.3: The Braun-Blanquet cover scales
p 66
7
Figure 5.4: A flowchart of stages in the subjective classification of
Relevés using Braun-Blanquet method (Adapted from Westhoff
And Van der Maarel).
P 68-69
Table 6.1: Plant Communities of the Dunes.
After P 78
Table 7.1: Forest Plant Communites.
After P 91
Table 8.1: Grassland and Wetland Plant communities.
After P 102
8
LIST OF PHOTOS
Photo 4.1: Weir constructed between Lake Mzingazi and Mzingazi River.
P 52
Photo 6.1: Causerina. equisitifolia one of the diagnostic species of the
Backdune Vegetation Community viewed from the harbour to the south.
P 78
Photo 7.1: Chromolaena ordonata invading riverine, Swamp and Dune
forest vegetation.
P 83
Photo 7.2: Psidium guajava, alien invasive species encroaching in
woodland and Grassland areas.
P 83
Photo 7.3: Barringtonia racemosa Swamp Forest on the banks of Lake
Mzingazi.
P 86
Photo 7.4: Swamp Forest mosaic vegetation invaded by E. grandis.
P 87
Photo 7.5: Clearing of Swamp Forest vegetation for agriculture and building
material on lake shores such as Lake Chubu and Mzingazi.
P 87-88
Photo 7.6: Aerial view of the Mangrove Forest south of Richards Bay
Harbour.
P 89
Photo 7.7: Avicenia marina (White Mangrove) stands of the Mangrove
Swamp Forest vegetation.
P 89
Photo 7.8: A. marina saplings.
P 90
9
Photo 7.9: Aerial roots of A. marina.
P 91
Photo 8.1: Cyperus papyrus beds occring in the back swamps of large water
bodies such as Lake Chubu, Nsezi and Mzingazi.
P 95
Photo 8.2: C. papyus stands with E. grandis invasion at the back of the
Mdibi Swamp area at the northern shores of Lake Mzingazi.
P 96
Photo 8.3: Overgrazed hygrophilous grassland with secondary sand dune
forest at the back.
P 100
Photo 9.1: Phragmites australis - Typha capensis Tall closed Hygrophilous
Grassland community with P. guajava encroachment.
P 112
10
CHAPTER 1: INTRODUCTION
1.1 Basic spatial relationships surrounding Richards Bay
A variety of plant communities with a relatively high diversity of plant
species occur in northern KwaZulu-Natal.
With the moist-subtropical
climate of this coastal area the vegetation has an exuberant appearance. The
communities vary from simple aquatic, wetland and psammophitic
herbaceous communities to complex wetland and dune forests. Currently
though, few of these coastal plant communities still exist in a pristine state.
The coastal vegetation of KwaZulu-Natal is classified by Moll and White
(1978) as comprising part of the Tongaland-Pondoland regional mosaic.
The vegetation consists primarily of woody thicket and forest communities
which Acocks (1988) describes as belonging to the group of Coastal subtropical Forests including Typical Coast-belt Forest, Dune Forest and
Mangrove Forest. Other classifications of the coastal vegetation include
those by Edwards (1967) and Moll (1976).
The coastal forest communities have been most thoroughly documented in
terms of their biogeography (Moll and White, 1978; Tinley, 1985),
phytosociology (Moll, 1969, 1978 and 1980; Macdevette and Walker, 1987;
Guy and Jarman, 1969) and general ecology (Venter, 1972, 1976; Ward,
1980; Weisser et al., 1982).
Other plant communities are less well
described.
The northern KwaZulu-Natal coast forms part of the Mozambique Coastal
Plain.
This area stretches from Mtunzini into the southern region of
11
Mozambique. Maputaland (previously known as Tongoland) is located in
the north-eastern
corner of KwaZulu-Natal, bordered by Mozambique to
the north, the Indian Ocean to the east, the Lebombo Montains and
Swaziland to the west, and the Mkuzi River and Lake St. Lucia to the south
(Moll, 1977 in Lubbe, 1996).
For the size, which is approximately 26 734 km2, the Maputaland Centre is
one of the most remarkable areas of biodiversity in the world. Not only is
the number of endemic species high, but they are spread over virtually the
entire taxonomic spectrum. The total number of vascular plant species is at
least 2500, with 225 or more species or infraspecific taxa endemic or nearendemic to the centre (Lubbe, 1996). The vegetation of Maputaland is
exceptionally diverse. It consists of a mosaic of forest, woodland, grassland
and swamps (Lubbe, 1996).
Moll (1980) classified the vegetation of
Maputaland into fifteen major types, ranging from forest on the Lebombo
Mountain Range through different types of bushveld, sandforest and swamps
down to the coast with coastal grassland and dune forest (Lubbe, 1996).
The diverse vegetation in the study area reflects the topographic and climatic
variability of the region. The dominant primary vegetation is Coastal Forest
but much of this has been destroyed or degraded by agricultural activities or
industrial development. This has resulted in a complex mosaic of different
fragmented communities (Weisser and Müller, 1983). With the exception of
certain coastal dune areas, some wetlands and a few nature reserves, the
greater part of this area has been exploited for agricultural use and forestry
(Venter, 1972). This study broadly comprises a semi-quantitative study of
12
the vegetation on the Richards Bay municipal areas, using the BraunBlanquet method.
The Richards Bay landscape was historically comprised of a wetland
environment, second only to the Greater St. Lucia Wetland Complex in size.
Today the wetland environment is a fraction of its former area, but
notwithstanding its reduction over time, it remains an extensive and
important wetland environment. This area contains many plant and animal
species at the southern limit of their tropical distribution, as well as some
endemic species.
The key feature which maintain these wetlands are the large water bodies
that exist today (Fig. 1.1). The position of, and linkages between these
bodies can be important or useful guides for planning and development
initiatives. Essentially, three large water bodies occur parallel and close to
the coastline. These are Lake Mzingazi, Richards Bay Harbour and the
Sanctuary Nature Reserve, which form part of the uMhlatuze River
catchment (van Wyk and Bailey, 1998). The total catchment area is 4489 to
4258 km2 (Begg, 1978).
These three waterbodies recieve runoff (and
subterranean water) from the immediate drainage catchment of Richards
Bay.
The uMhlatuze River basin area is 3670 to 3936 km2, the main
tributaries being the Nseleni River from the North-East, draining into Lake
Nseze and the Mfule River. The Mthantatheni River drains into Lake Cubhu
on the southern margins of the coastal flood plain. The Mzingazi River
drains Lake Mzingazi on the northern margin of the coastal flood plain and
several small tributaries (Mdibi, Khondweni, Payeni, Amansimyama and the
13
Nkoninga)
discharge
from
the
heavily
urbanised
and
developed
subcatchments surrounding the lake (van Wyk and Bailey, 1998).
These water bodies and their associated drainage systems play a key role in
the functioning of the wetland environment of Richards Bay (Discussion
document 2000). It therefore appears to play a key role in the management
of the town, its open spaces and development areas. It is the open spaces
that encompass the drainage system and the development areas that impact
on the natural system and its ability to sustain itself.
14
15
Figure 1.1: A Map of regional water resources (After Kelbe, Germishuyse, Snyman and Fourie, 2001).
1.2 General introduction to wetlands
“Wetlands” is a relatively new term used to describe the landscape that
many people knew before under different names such as swamp, marsh and
vlei, and indeed is used as a generic term for any ecosystem which has an
aquatic base or hydrological driving force.
Wetlands occur in many
different climatic zones, in many different locations from the upper reaches
of a catchment, down to the river mouths and estuaries and have a wide
range of soil and sediment characteristics (Fig. 1.2). There are a number of
definitions of wetlands in use.
The following definition is a good
description of the wetlands of the Richards Bay area. Areas of marsh, fen,
peatland or water, whether natural or artificial, permanent or temporary, with
water that is static or flowing, fresh, brackish or salt, including areas of
marine water where the depth of which at low tide does not exceed six
meters. These areas may also include adjacent riparian and coastal zones.
This is an intentionally broad definition to stem encroachment on habitats as
diverse as mangrove swamps, peat bogs, water meadows, coastal beaches,
coastal waters, tidal flats, mountain lakes and tropical river systems (Cowan
and van Riet, 1998).
16
Figure 1.2: A simplified geological map of the Richards Bay region (After
Worthington, 1978).
Whatever term used, the distinguishing feature of all wetlands is the
interplay between the land and the water, and the consequent characteristics
which reflect both. The hydrological regime may be a result of a number of
different factors such as the periodic flooding of floodplains, tidal rise and
fall, impeded surface flow due to geological and or geomorphological
processes (such as tilting, uplift or landslip, land subsidence, deposition of
sediments in estuaries or deltas), or the rising of the water table to above
surface level. All these geo-morphological factors contribute to standing
water, or to saturated or waterlogged soils.
17
While hydrology is the most important factor in the formation of wetlands, it
by no means explains their distinctiveness. Wetlands have a distinctive and
characteristic vegetation, and often different to the surrounding vegetation.
These plants (hydrophytes) are adapted to wet conditions, being covered by
water for at least part of the growing cycle and thus temporarily deficient in
oxygen.
The plants decompose slowly and contribute to the process of wetland
formation or maintenance by trapping silt or forming peat. Wetland animals
also have specific adaptations to this environment such as the ability to
breathe under water, or have developed behavioural patterns for making use
of wetlands such as moulting at seasonally high water levels. Wetland soils
are adapted to anoxic biochemical processes. They are physically volatile
and are in constant flux with the decomposition of the vegetation and the
erosion of sediments with river flow, flood and tidal shift.
The interaction between water level, sedimentation and decomposition is
finely balanced, and within the soils there are biochemical processes at work
as energy flows through the ecosystem leading to the transformation and
trapping of nutrients. All of these factors lead to a highly diverse ecosystem
which is one of the most productive in the world (Cowan and van Riet,
1998).
18
19
Figure 1.3: A Schematic presentation of different wetlands types (After Wyatt, 1997)
1.3 Importance of wetlands
Despite being an extremely important distinction, the functions and values of
specific wetland sites often remain undefined. Indeed it has only been in
recent decades that wetlands have been recognized as valuable natural
resources that, in their natural state provide many important economic
benefits to people and their environment.
Wetlands are very important in nature, because they constitute a unique
habitat for certain aquatic plant and animal species, especially large numbers
of waterfowl. Wetlands lessen the devastating effects of floods and are
responsible for cleaner and healthier surface water. They act as a filter for
sediment and other impurities and absorb a lot of water that may be released
over time. Not many plant species grow in wetlands, but the species that do
occur there are often unique (Hey and Phillipi, 1999 in Venter, 2003).
According to Joosten and Clarke (2002) the functions and values of peatland
differ according to the different definitions of the word function and values.
The values can be divided into three different approaches:
idealistic,
naturalistic and preference. The functions of a peatland are divided into five
types: production functions, carrier functions, regulation functions,
information functions and transformation and option functions (Venter,
2003).
The production functions include functions where the peat is
extracted and used for agriculture, horticulture, as a filter, for peat textiles
and as bedding. Drinking water, the use of plants growing on the peatland,
20
the use of wild animals and the uses of the peatland for agriculture are also
included in the production functions (Venter, 2003).
Carrier functions include the use of the site for water reservoirs, as
fishponds, as an area for urban and industrial development and for use in
military exercises and defense.
The regulation functions include the
regulation of global and local climates, catchment hydrology, catchment
hydrochemistry and soil conditions.
The information functions include
functions such as social-amenity and history, recreation and aesthetics
(Venter, 2003).
Certain wetland plants are also used as building material, mostly Typha
species and Phragmites species, or for woven products such as baskets and
mats, mostly Cyperaceae species or Juncus species as well as grasses and
Typha (Venter, 2003). The occurrence of plant species in a certain area is
controlled and influenced by environmental factors (Kent and Coker, 1995).
Species that are tolerant of a similar set of environmental conditions and are
intolerant of another set of conditions would therefore be restricted to
specific habitats and would not occur with species that favour other sets of
conditions (Venter, 2003).
The plant community represents an unique
interaction of a specific plant species composition and a unique set of
environmental variables, to form an ecosystem, which also forms a specific
habitat for animal species (Bredenkamp and Brown, 2001). It is therefore
important to understand that a plant community is not only an indication of
the plant species that occur in an area, but also of the environmental factors
and the vertebrate and invertebrate faunal species (Venter, 2003). Plant
21
communities can therefore be used as the fundamental units for the planning
of Nature Reserves (Bredenkamp and Brown, 2001).
1.4 Threats to wetlands
All classes of wetlands are threatened by organic and inorganic pollutants,
which may reach the wetland either directly or indirectly from point sources
or diffuse sources. With the exception of marine wetlands, all wetland
classes are subject to threats due to changes in their hydrological regimes
through water extraction, impoundments, inter-basin transfer and other water
resource developments and afforestation.
Land-use changes including
afforestation, agriculture, industrial and mining developments, recreational
and urban developments have both direct and indirect threats on many
wetlands.
The 39 freshwater swamp forest sites and 28 peatlands listed in the
Directory of South African Wetlands (Cowan and van Riet 1998), are found
exclusively in the coastal plain region of Northern KwaZulu-Natal.
Peatlands are used for subsistence farming in an area of infertile sandy soils,
and they are important as sources of fresh water, fodder and biomass for
local communities.
Poor catchment management has resulted in nutrient
loading and salinization of the water as well as increased sediment loads.
The introduction and spread of invasive alien biota has had a profound effect
on both the functioning of wetland ecosystems and on many of their species.
This is due to replacement of the indigenous flora, and disappearance of
many animal species of all classes.
22
The vast majority of palustrine wetlands are not found in formally protected
areas. This is true even for the larger wetland systems as shown by Begg
(1989) who indicated that 65% of the priority wetlands of KwaZulu-Natal
are privately owned.
The importance of wetlands in northern KwaZulu-Natal is recognised
(Cowan and van Riet, 1998).
Wetland plant communities and species
composition, and their distribution patterns are still relatively unexplored.
More research is definitely needed to contribute to a better understanding of
these areas. It will assist in the correct management and conservation of
these areas.
Palustrine wetland habitats are found in most of South Africa’s Ramsar sites,
and a number are found in national parks and provincial reserves. Cowardin
et al. (1979) while separating “deep water habitats”, defined wetlands as the
ecosystems which occur between terrestrial and aquatic systems, where an
excess of water is the dominant factor. Assuming a freshwater regime, this
is possibly the best definition of palustrine wetlands, which comprise a wide
range of physical situations, hydrological regimes, chemistries and
vegetation types (Cowan and van Riet, 1998). Included in Dugan’s (1990)
classification of freshwater palustrine habitats are permanent marshes and
swamps, permanent peat-forming swamps, seasonal marshes, peatlands and
fens, alpine and polar wetlands, springs and oases, volcanic fumaroles, shrub
swamps, swamp forest, and forested peatlands. These include both the
forested and herbaceous wetlands of Denny (1996).
23
The main distribution of palustrine wetlands in South Africa almost mirrors
the main distribution of endorheic pans (Cowan and van Riet, 1998).
Generally they are found in the areas with a mean annual rainfall greater that
500 mm. The main exceptions being those found along the main water
courses, and those developed around dolomitic eyes (Skelton et al. 1995).
The knowledge base of palustrine wetlands in South Africa is probably the
poorest of all the wetland types, and given the estimates that approximately
50% of them have already been lost, much work on these wetlands is
required (Cowan and van Riet, 1998).
A relatively high number of
palustrine wetlands occur in northern KwaZulu-Natal and Richards Bay.
Palustrine wetlands occur predominantly as peat-forming swamps, seasonal
marshes and forested peatlands. At present the use of peatlands by local
communities is threefold: drinking water, harvesting naturally occurring
plant material and growing vegetables (Grundling et al. 1998).
Unsustainable harvesting of plant resources and utilizing peat for vegetable
gardens will lead to the degeneration of the wetlands. Consequently not
only will there be a decline in the quantity and quality of potable water in
KwaZulu-Natal, but also the use of wetlands for structural materials, as a
medicinal and subsistence agriculture resource.
1.5 Conservation of wetlands
The conservation of wetlands within a system of protected areas is, by its
very nature, extremely difficult. Being part of the hydrological system, they
form links in normally linear systems, which extend beyond the protected
area boundaries (Cowan and van Riet, 1998). Table 1.1 shows the number
24
of wetlands recorded in the Directory of South African Wetlands, which are
afforded varying levels of on site protection.
Table 1.1: Number of wetlands and their level of protection
Where Total# is the total number of wetlands in that class, 01 is
no information; 02 is no legal protection; 03 is those wetlands
partly or wholly included within a private nature reserve, nonhunting area or similar reserve with low level of protection; 04 is
wetlands protected within a national park, provincial nature reserve,
wildlife sanctuary or equivalent reserve; and 05 wetlands wholly
protected within a national park, provincial nature reserve, wildlife
sanctuary or equivalent reserve (Cowan and van Riet, 1998).
None
Low
Part
Full
01
02
03
04
05
Protection
% Part
% Full
level
Class
Total
#
Marine
11
0
3
4
0
4
36
36
Estuarine
82
24
38
6
10
3
19
5
Lagoonal
204
20
142
10
17
15
13
7
289
220
31
8
6
24
5
8
Riverine
208
155
18
13
9
13
11
6
Lacustrine
69
22
15
7
4
21
16
30
Palustrine
263
56
56
23
13
54
14
21
Man-made
251
187*
20
15
10
19**
10
8
NB * it can be assumed that most of the man-made wetlands for which
there is no information have no legal protection;
** while these wetlands (mainly dams) are located within protected
areas, their management is primarily for water resource development
25
CHAPTER 2: LITERATURE REVIEW OF
PLANT COMMUNITIES OF NORTHERN
KWAZULU-NATAL
A history of vegetation studies in northern KwaZulu-Natal
According to Venter (1972), botanical studies in northern KwaZulu-Natal
are mostly related to research done on the KwaZulu-Natal province as a
whole. In the 19th century a few contributions to the study of vegetation of
KwaZulu-Natal were made by Kraus (1846), Plant (1852), Armitage (1854),
Fourcade (1889) and Wood and Evans (1899-1912). According to Bayer
(1971), J.F. Drege was the first person to collect plants in KwaZulu-Natal
and collected in Zululand as far as Empangeni and Richards Bay. Bayer
(1971) also mentions collectors such as William T. Gerrard and M.J.
McKen and their collection safaris in Zululand in 1856.
Medley Wood though is known as the father of botany in Natal (Bayer,
1971). He collected through the whole of KwaZulu-Natal and developed the
KwaZulu-Natal Herbarium in 1882 in Durban, as a center for taxonomic
work. Various important botanical works, including species lists, keys and a
textbook saw the light out of his work. Thode (1901) divided the vegetation
of KwaZulu-Natal according to altitude into different vegetation regions.
Bolus (1905) drew up a simple vegetation map of South Africa on which
seven vegetation types could be differentiated. From his description of the
vegetation it was clear that the eastern regions of South Africa were very
26
poorly studied. He also noticed an interesting relationship of the vegetation
with tropical vegetation and suggested the probability that the eastern region
representing an extension of the tropical region.
Bews also did various works on KwaZulu-Natal. In 1912 he not only
described the geology, climate and other factors of different regions within
KwaZulu-Natal, but also the plant formations occurring there. In this work
he gave a comprehensive description on the vegetation of the beach, coastal
dunes and estuaries. In 1920 Bews published an article on the plant ecology
of the coastal region of KwaZulu-Natal in which he described the different
communities occurring there.
Most of this description was based on
information gathered in the region north of Durban between Umhloti and
Port Shepstone in southern KwaZulu-Natal with only an occasional
reference to Zululand vegetation. It is important to note that Bews’ analyses
on the vegetation in this work showed that 86% of the genera and 36% of the
species indicated a tropical affinity. He also noted that more temperate,
widely distributed plant types occur in earlier stages of succession, where as
vegetation tends to get more tropical as succession develops further. Also
Aitken and Gale (1921) mentioned the similarity of various plants with
tropical vegetation on their collection and exploration trip to Kosi Bay. .
Henkel et al. (1936) had three short visits to Dukuduku Forest reserve close
to Mtubatuba and the surrounding area. They divided the vegetation into
different communities such as beach- and unestablished dune vegetation,
established dune vegetation, grassveld, mangrove vegetation and stream
bank forest. Pole-Evans’s (1936) vegetation map of South Africa already
showed a clearer concept of the common composition on the vegetation of
27
Zululand. He distinguished between two forest types in the coastal region of
Zululand eg. Continuous “deciduous woodland and subtropical woodland”
as well as discontinuous “temperate indeciduous woodland”. The latter
occurring around Kosi Bay and just south of Lake St. Lucia. Bayer (1938)
described the vegetation of KwaZulu-Natal in detail.
Though no
quantitative studies were done, the descriptions testify were acute and up to
present times, are seen as an important reference source on KwaZulu -Natal
vegetation.
He distinguished between coastal strip- and midlands-
vegetation, and analysed both regions very accurately. The coastal strip
vegetation he divided into coastal dune communities, coastal grassveld,
coastal indeciduous bushland and woodland communities, hygrophyllous,
coastal communities, mangrove vegetation and indeciduous subtropical
forest.
Acocks (1953) described the vegetation of the eastern region of South Africa
as “forest- and thornveld of the coastal region” and he distinguished five
types. Despite the comprehensiveness of this description, it lacks
information on the northern coastal dunes and wetlands, with very little
mentioned of the mangrove vegetation. He admits the need for a better and
more descriptive study of the coastal region, especially north of Isipingo. At
a later stage a remarkable and comprehensive analysis and description of the
northeastern KwaZulu-Natal vegetation was published in four reports by
Tinley. In the first (1958a) he produced a report on the vegetation of Lake
Sibayi. The second (1958b) dealt with the Pongolo- and Mkuze floodplains,
the third (1958c) with the Kosi-lake system and the fourth on the Ndumu
Game Reserve.
28
Huntley (1965) described the vegetation of the Ngoye Forest reserve in the
Mtunzini area of KwaZulu-Natal. The description of the forest is supported
with profile diagrams and histograms. He mentions the presence of common
plants with physical adaptations similar to those found in tropical forest.
Venter (1966 and 1969) analysed and described the vegetation of the
Ubisane valley in the Mtunzini area in a quantitative study. He studied the
influence of the environment on the vegetation and also determined the
productivity of grassveld species occurring in the valley.
The vegetation of the Tugela drainage basin was mapped and described by
Edwards (1967) and a large part of this area he studied stretched into the
borders of KwaZulu-Natal, but only a small strip of the coastal region was
covered north of the Tugela River. He divides the coastal vegetation into
several communities such as pioneer communities, coastal dune – shrubveld
and –forest, with hygrophyllous vegetation at the river mouth. Breen and
Hill (1969) made a quantitative study on the distribution and survival of
mangroves after mass deaths of it occurred in the Kosi Bay estuary. Breen
(1970) did another quantitative survey on the dune forest at Lake Sibayi in
northern KwaZulu-Natal. This data enabled him to describe not only the
composition and density of it, but also the possibility of the composition of
the canopy strata in the future.
Venter (1971a) presented a preliminary overview on the vegetation of
Richards Bay.
In this report he gave a brief review of the different
vegetation communities and dominant species.
A species list of the
grassveld- and wetland communities of Ngoye Forest Reserve was drawn up
29
by Venter (1971b). This list is completive to the quantitative survey and
description of the grassveld of the above mentioned reserve (Venter, 1971c).
In 1972 Venter carried out an in depth study on the plant ecology of
Richards Bay.
The aim of this study was to describe and analyse the
vegetation of Richards Bay and to determine the influence of the
environment on the vegetation and to compare the Richards Bay forests with
those of Mapelane and Sibayi. Basically he distinguished between two
habitat types: dune- and grass veld and swamp veld. A multi-dimensional
ordination of stands according to the method of principal components
analysis showed that there was a distinct difference in the centers of
distribution of the species that were included in the ordination. The floristic
analysis showed that the Poaceae, Asteraceae, Fabaceae and Cyperaceae
were the largest families present at Richards Bay at this time. The above
standing review therefore gives a clear indication of the great variety of
ecological types that are still unknown and undescribed, with a special
emphasis on how little quantitative work has been done.
In studies that followed though, only certain plant communities of specific
areas (usually as part of impact assessments or unpublished reports), were
described. Hemems et al. (1981), made a brief description of the vegetation
surrounding Lake Nseze. They found that Lake Nseze was dominated by the
southern most extensive area of Cyperus papyrus in Africa which continues
into the lower section of the uMhlatuze floodplain. They also observed that
the alien invasive, water hyacinth Eichhornia crassipes was widespread
throughout the system, fringing most of the shoreline of the open water areas
and the whole length of the river channel.
They noted that the forest
30
communities that developed around the lake outlet channel and on sections
of the levees along the course of the river were of particular botanical
interest and that four main forest areas are considered to be among the best
remaining examples of riverine or riparian forest in South Africa.
Walmsley and Grobler (1985) described the vegetation of Lake Mzingazi
briefly as part of an evaluation report. They differentiated the herbaceous
vegetation into Scirpus littoralis communities, Cyperus papyrus swamp,
Phragmites australis reedswamp, Typha capensis reedswamp, and sedge
marsh and hygrophilous grassland. The woody vegetation they divided into
shore-fringing forest, hygrophilous forest along streamlets and swamp
forest. They noted that communities slightly or unaffected by high water
table would be the natural areas with no or little human interference, like
sand forest and areas with conspicuous human interference such as fields,
mixed secondary grasslands and secondary shrubland, secondary grassland,
Acacia
karoo
woodland,
secondary
scrub,
secondary
forest
and
afforestations.
In 1987 Weisser carried out a study on the dune vegetation between
Richards Bay and the Mlalazi Lagoon and its conservation priorities in
relation to dune mining. Six 1: 10 000 vegetation maps based on aerial
photographs (1976) were drawn and used to assess conservation priorities
with special reference to proposed dune mining.
The information was
summarized on three conservation-priority maps (1: 25 000). They revealed
that most of the area was covered by third-priority vegetation and no major
objection to mining would exist if a few areas are excluded from mining.
First-priority areas were found in the Richards Bay area, at the Mlalazi
31
Estuary Peninsula, and some scattered patches mainly along the landward
limit of the study area, and along the coast. Most of these areas were already
excluded from the prospecting lease. The suggestion was also made that a
KwaZulu-Natal Botanical Garden of hygrophilous forest be incorporated
into the Richards Bay Sanctuary area, but to date this has not been
implemented.
Schwabe (1989) carried out a preliminary ecological evaluation of the
vegetation at the site of the proposed Small Craft harbour and marina in
Richards Bay.
His main conclusion arising from the assessment was:
i)
That the swamp forest, dune forest and marshes were threatened
vegetation types and there was justifiable concern that they would have been
adversely affected by development of the marina. He also noted that with
the development of Richards Bay through gradual urbanisation and
increased recreation, the impacts for these vegetation types would be adverse
and inevitable. He realised then that the future of these areas of natural
vegetation systems was uncertain.
A CSIR report 1993 discussed and described the conservation importance
analysis of the Richards Bay Borough vegetation as an aid to assit the
Richards Bay Borough in the planning of the Metropolitan Open Space
System (MOSS).
This study shows that the vegetation of Richards Bay has deteriorated
considerably. Development has imposed greater demands on the land for
32
agriculture, housing and recreational facilities. The natural fire regime has
also been altered and this has resulted in the replacement of Coastal Forest
by Dwarf Shrublands with the associated encroachment of invasive species,
which at this period already started to displace the indigenous flora.
In this report the broad vegetation types occurring within the study area have
been identified and allocated with botanical conservation importance ratings.
Vegetation maps indicated the distribution of vegetation types and were
colour coded to differentiate among different conservation categories.
The study indicates that vegetation types considered to be of high
conservation importance include Mature Coastal Forest, Xeric Transitional
Thicket, Grassland, the Mosiac of Coastal Forest and Swamp Forest, Swamp
Forest and the Mosaics of Reedswamp, Coastal Forest and Swamp Forest
and Swamp Forest and Reedswamp. It is suggested that these vegetation
types should be incorporated as far as possible into the Metropolitan Open
Space System, as it was considered that these vegetation types will be
negatively affected by any disturbance and potential impact on the
vegetation should be avoided.
Strand vegetation, Mangrove, Mosaic of Coastal Forest and Hygrophilous
Grassland, the Mosaic of Coastal Forest and Swamp Forest, Primary
Reedswamp and Hygrophilous Grassland were considered to be of
intermediate conservation priority.
Limited development could be
considered in some of these areas but should be preceded by a
comprehensive study aimed at the retention of as much natural vegetation as
possible.
It is recommended these areas be incorporated into MOSS,
33
especially where the vegetation may adjoin other categories of high
conservation importance.
The least important secondary vegetation types that were included were the
Mosaics of Coastal Forest and Dwarf Shrubland, Acacia karoo woodland,
Dredge Soil Vegetation, the Mosaics of Alien Vegetation, Dwarf Shrubland
and other impacted vegetation types and Plantations, Developed Areas,
Woodlands, Agriculture, Open Sandy areas and Parkland were considered to
be of insignificant importance.
In the newest classification of the vegetation of southern Africa (Mucina and
Rutherford, 2006), the following five vegetation types are found in the
vicinity of Richards Bay:
1. CB1 – Maputaland Coastal Belt, which includes the terrestrial
vegetation of the coastal plain, originally densely forested, but
including dry grassland, palmveld, hygrophilous grassland and
thicket. Now extreme sugar cane fields and timber plantations occur
here.
2.
FO a3 – Mangrove Forest at the coastal lagunes and estuaries.
3.
FO z7 – Northern Coastal Forest which represents the subtropical
coastal forests.
4. AZ d4 - Subtropical seashore vegetation on the seashore dunes.
5. AZ f6 – Subtropical Freshwater Wetlands, including vleis dominated
by reeds, sedges as hygrophilous grasses.
34
CHAPTER 3: RATIONALE AND OBJECTIVES
3.1 What is a MOSS
MOSS is an acronym for Metropolitan (Municipal) Open Space System.
Durban Metropolitan Open Space System (D’MOSS) defines MOSS as:
“network of open spaces made up of important conservation and recreation
areas linked by rivers and beaches” (Discussion document, 1998). D’MOSS
draws attention to the multi-functional role which vegetation plays within a
MOSS.
The interaction between water level, sedimentation and
decomposition is finely balanced, and within the soils there are biochemical
processes at work as energy flows through the ecosystem leading to the
transformation and trapping of nutrients. All of these factors lead to a highly
diverse ecosystem which is one of the most productive in the world (Cowan
and van Riet, 1998).
Functions of open spaces of a MOSS are however, much more diverse than
merely providing opportunities for nature conservation and recreation. They
also play a major role in determining and maintaining the levels of physical
and psychological health of the people and animals that inhabit it
(Discussion document, 1998).
3.2. Aim of MOSS
The aim of the Richards Bay MOSS is to provide all the communities of
Richards Bay and its visitors with the widest choice and diversity of
recreational opportunities and tourist pursuits consistent with the adequate
35
protection of the natural and cultural resources (Richards Bay Structure Plan,
1995).
3.3 Vegetation and the Richards Bay MOSS
Vegetation can contribute to maintenance of a healthy environment through
the removal of harmful substances from air and water at a fraction of the
cost that would be incurred by using man-made alternatives (Discussion
document, 1998).
For example: The social benefit or value of a wetland is a subjective
estimate of the worth, merit, quality or importance of the wetland to
mankind. This implies that a rand value can be ascribed to wetlands (Fig. 4)
in terms of providing habitat for fishing, hunting, game and bird viewing,
plant material harvesting, domestic stock grazing flood damage control and
water cleansing, to name a few (Wyatt 1997).
These values are derived directly from the existing wetland functions. If one
takes the value of a function such as flood attenuation in wetlands, the
question that must be answered is:
“what will it cost to replace the
function?” Likewise to establish the value of the sea fish “nursery” function
of an estuary it would be necessary to establish the economic dependence on
fishing and tourism in the vicinity of the estuary (Wyatt 1997).
36
37
Figure 3.1: A schematic representation of wetland functions and values (After
Wyatt, 1997)
The vegetation units (i.e. physiognomically and floristically distinct
communities which can be distinguished on the 1:5000 scale colour aerial
photographs) recognised in this research project are the major functional
components of the vegetation of the Richards Bay area.
3.4 The importance of MOSS for Richards Bay and the surrounding
areas
Although the Richards Bay Municipality has formalised the importance of
creating a MOSS system, such a system has long been recognised by itself
and environmental organisations such as the Wildlife Society of Southern
Africa and the Zululand Society for the Protection and Care of the
Environment (Richards Bay MOSS Report, 1994).
Richards Bay has an abundance of natural areas. Consequently, it has a
tremendous advantage over many other cities in South Africa in the rich
diversity of its natural areas. By harnessing these areas into a MOSS plan,
opportunities, usually scarce (if not absent) in most urban context, can be
created for the people of Richards Bay to benefit from a broad-based open
space system offering educational and recreational outlets to these
community (Richards Bay MOSS Report, 1994).
Urban growth in Richards Bay and fringe areas has resulted in increased
pressure on the remaining natural or open space areas, many of which may
be lost through indiscriminate development.
There is, thus, a need to
identify natural and particularly sensitive, areas to ensure their conservation
as well as to reserve open space for future needs. Richards Bay at present
38
lacks a linked system of open space that combines all the town’s natural
assets and recreational opportunities (Richards Bay MOSS Report, 1994).
Over a thirty-year period, Richards Bay’s population increased dramatically,
from 237 in 1960 to 28 405 in 1992. Furthermore, as people’s standard of
living improves, they (generally) have more leisure time at their disposal
with the result that the demand for recreation facilities has grown and will
continue to grow in the future, particularly with respect to outdoor recreation
on the coast, the lakes, rivers and wetland areas. Richards Bay, with its
outstanding scenic and natural assets, has a unique opportunity to make use
of tourism as a major contributor to its economic base.
3.5 The Role of the Norwegian Programme for Development, Research
and Higher Education (NUFU)
The NUFU programme’s goal is to focus on the development of sustainable
capacity as well as competence for research based, higher education in
developing countries such as southern Africa, in terms of national
development and reduction in poverty (NUFU 2007 Online).
This study formed part of a large scale project of NUFU, namely the
“Biodiversity in coastal Maputaland (northern KwaZulu-Natal and southern
part
of
Mozambique):
links
between
geology
and
ecology.
1999 – 2002.” The main objective of this project was to build expertise able
to address intricate environmental tasks of importance to the area’s
management.
This project initiated capacity building directed towards
interdisciplinary studies in geoscience and ecology (NUFU 2007 Online).
This included training programmes, staff visits to the relevant regions and
39
countries and student participation.
Master degree students from the
Eduardo Mondlane University, Mozambique along with South African
students were encouraged to conduct their research studies along this coastal
area, supervised by scientists from the University of Natal, KwaZulu-Natal
Conservation Services, the Council for Geoscience (NUFU 2007 Online).
The participating institutions were the Agricultural University of Norway,
the University of Natal, Eduardo Mondlane University, Mozambique, and
University of Zululand, KwaZulu-Natal Nature Conservation Service, the
Council for Geoscience, South Africa and the National Directorate of
Geology, Mozambique.
This programme focused on the conservation of coastal areas along the coast
of Maputaland in northern KwaZulu-Natal and southern Mozambique
because of the endemism of Maputaland and the well established
relationship between geology and ecology in this region.
Other
characteristics also contributing to the selection of this specific study area
are the role of the dunes and the threats to this dunes posed by development
(NUFU 2007 Online).
3.6 Survey analysis of the vegetation
In this study each mapped plant community was classified according to its
structure and floristic composition. The Braun-Blanquet classification
system was used, that includes a number of variables such as abundance or
extent of occurrence, and apparent species richness. This data can then be
used to establish an importance hierarchy to identify areas of high botanical
40
value. This strategy can indicate which plant community should receive
special attention in the process of Metropolitan Open Space System (MOSS)
planning.
Plant communities of high botanical importance are considered to be those
that are relatively rare. Usually they include one or more threatened species,
they are species rich. Wetlands are often not rich in plant species but the
species that occur here, occur only here, and these habitats are rare, resulting
in a rare composition of species. Therefore they are in particular need of
protection from disturbance such as development.
The priority for conserving the plant communities therefore varies according
to their perceived value, their ecological importance and the degree of
development threat already imposed on them.
3.7 The aims of this research project are as follows;
i)
The primary aim for this project was therefore to describe the
different plant communities and vegetation types recognised within
the area under the jurisdiction of the City of uMhlatuze Municipality.
ii)
To provide an indication of the conservation importance of the
vegetation types within the study area.
41
CHAPTER 4: DESCRIPTION OF THE STUDY
AREA
4.1 A Brief history or northern KwaZulu-Natal
Humans have been a constant factor in the ecosystems of KwaZulu-Natal
province for a relatively long period. Archaeological records from the last
quarter of the nineteenth century provided for the earliest discoveries of
stone
implements
in
South
Africa
(Duminy
and
Guest,
1989).
Archaeological fieldwork conducted by Goodwin and Van Riet Lowe lead to
the publication of the first comprehensive study of the South African Stone
Age in the late 1920s (Duminy and Guest, 1989). The Stone Age preceded
the Iron Age which was not only characterized by the introduction of
metallurgy but with the introduction of agriculture, with a settled, village
way of life in comparison to the nomadic patterns of the Stone Age (Duminy
and Guest, 1989).
Specific environments of site escavations in southern
Mozambique gave specific clues of these Iron Age communities.
The
majority of these sites occurred on ancient dunes which have been covered
by coastal forest at the time. In the St. Lucia area, sites are concentrated at
the inland foot of the dunes, where these meet seasonly flooded grassland
(Duminy and Guest, 1989). The sandy soils which occurred in this area are
poor and leached but the accumulated forest humus would have ensured
good crops for the first 2 years after it has been cleared (Duminy and Guest,
1989).
42
The invasion of more nations to KwaZulu-Natal caused the total
disappearance of the San people, with only their rock art as memory of their
presence (Venter, 1972). The Nguni people, from whom the Zulus and
Xhosa people originated, apparently appeared in KwaZulu-Natal by 1400 or
even earlier. The Nguni had a higher standard of civilisation than the San
people and farmed with cattle, goats and sheep. Besides other food items,
they also farmed with crops like sorghum and mealies (Brooks and Webb,
1967). In the early 19th century the population of northern KwaZulu-Natal
was more or less 78 000 individuals (Bryant, 1929).
After the incorporation of northern KwaZulu-Natal area into the former
Natal province in 1897, white people also began to settle in this region.
During the late 1800s visible evidence of economical growth in KwaZuluNatal was observed together with the changing of the physical environment
(Duminy and Guest, 1989). Whole herds of animals were hunted for their
skins and during the mid-1870s it was commented that no herds of game
could be seen anymore, in spite of the introduction of the Colony’s first
game law in 1866 (Duminy and Guest, 1989). The excessive hunting of
game was followed by the destruction of the natural forest and by the
clearing of the land for cultivated fields. Destruction of vegetation and
habitats was extensive with the effect being most noticeable in the river
estuaries. Estuaries were silted up and polluted by the 1870s (Duminy and
Guest, 1989).
The coastal lowlands were found to be suitable for the cultivation of sugarcane, tea, coffee and arrowroot but sugar farming was soon to become
KwaZulu-Natal’s largest agricultural industry (Duminy and Guest, 1989). In
43
1905 the area was available for sugar-cane cultivation and after 1904 for
forestry plantations (McCrystal and Moore, 1967). The sugar-cane industry
expanded rapidly and by 1913 it had reached as far north as the Umfolozi
River.
Sugar-cane and timber plantations had the greatest impact on the
vegetation of northern KwaZulu-Natal. The increase in African population
from 113 000 to 169 800 in the locations from 1850s to 1881, lead to a
higher demand in food, exhausting existing agricultural lands and forced
encroachment onto grazing lands (Duminy and Guest, 1989). This forced
indigenous vegetation to be cleared and to be altered habitats.
The draining of wetland areas is an example, as it is an important component
of the ecosystem of the coastal lakes and it has many important functions.
Richards Bay is named after Admiral Sir Frederick William Richards, who
carried out a marine survey in 1878 along the coast of KwaZulu-Natal.
Richards Bay and the surrounding area, the major wetland area, were
proclaimed as public land in 1902. According to this the land could not be
inhabited or cultivated and it was left undisturbed to a large extend, but this
soon changed on 10th December 1969, when a local town council was
established for the development of this area into a future harbour city.
4.2 Climate
Richards Bay is situated in the transition zone between subtropical and
tropical climatic conditions (Weisser and Müller, 1983). The climate is
humid and warm to hot with a high year-round rainfall (Schulze, 1984). The
mean annual temperature at the Cape St Lucia Weather Station is 21.5ºC and
the mean annual rainfall is 1 292 mm (Weisser, 1979). Most of the rainfall
occurs in summer with winter being generally less humid. The region falls
44
within the 20ºC isotherm, which is accepted as the limit for tropical
vegetation (Aubert de la Rue et al., 1958, in Venter, 1972).
4.3 Topography
Richards Bay is located at the seaward margin of the Mozambique Coastal
Plain at an altitude of less than 100 m. The Coastal Plain is characterised by
an undulating surface of old dune ridges supporting shrubland and forest,
swampy drainage courses and lake systems. The dune ridges were formed in
an alternating sequence parallel to the present coastline by a receding
Pleistocene sea with the onset of the Würm glaciation (Tinley, 1985).
Richards Bay is located at the seaward margin of the Mozambique Coastal
Plain at an altitude of less than 100 m. The Coastal Plain is characterised by
an undulating surface of old dune ridges supporting shrubland and forest,
swampy drainage courses and lake systems. The dune ridges were formed in
an alternating sequence parallel to the present coastline by a receding
Pleistocene sea with the onset of the Würm glaciation (Tinley, 1985).
Both the shore and foreland are eroding (Tinley, 1985) and massive dune
slumping occurs continually along the seaward edge. The red dune sands
overlie a thick layer of clay material which influences in situ water drainage.
The wetting of the clay by water percolation and the seaward drainage which
occurs through lateral piping at the point of contact between the dune sand
and clay zones creates unstable conditions along the dune front.
This
resulted in cavitational dune slumping and the formation of steep basinshaped scars or cirques with flat floors of deep, steep-sided ravines.
Because the water table becomes exposed at the cirque floor surface, these
45
areas are usually stabilised with hygrophilous vegetation.
The cirque
formation is unique in that it is found at only a few localised places in South
Africa (Tinley, 1985)
4.4 Geology and Soils
The geological history of the Zululand coastal plain follows the rise and fall
of the sea levels.
The geological sequence shown in Figure 4.1 is as
follows.
During the Cretaceous era, marine deposits formed the Cretaceous system
some 50 million years ago. The Cretaceous shore-line underlies the entire
coastal plain and consists mostly of uniform siltstone with occasional thin
clay lenses and thin bands of hardy limestone. It is believed that the fine silt
stones make up the impermeable layer of the aquifer bottom.
W
E
Port Dunford Formation
Berea Red Sands
100
Recent Sands
Recent Sands
Indian Ocean
0
Miocene
Siltstone
-100
Hornblendic granitegneiss (Precambian)
Cretaceous
-200
46
Figure 4.1 Geology of the study area (After Worthington, 1978)
In the Miocene Epoch the Cretaceous system was overlain by relatively thin
Miocene deposits which are highly permeable, but not continuous. The Port
Durnford system is more widespread than the Miocene deposits and is
present below most of the coastal barrier complex. The Port Durnford
formation is not a homogenous layer and consists of poorly consolidated fine
grain sands, clays, silts and lignite. A discontinuous lignite (peat) band
subdivides it into two layers.
Within the Recent Sands, the whole area is covered in a layer of
unconsolidated, fluvial and aeolian sands. Geologically, the sand dunes are
generally composed of beach derived sand that is blown inland. Initially a
low sand dune forms a foredune which may be colonised by pioneer
vegetation. This vegetation aids in the accumulation of additional sand by
trapping the wind blown sand. Normally the foredunes mature, become
larger and develop mature vegetation if the dunes are stable and receive
adequate inputs of water as is the case along the coastline of the study area.
The high coastal dunes in the study area are believed to be very young, in
some places still being formed and only stable because of the vegetation
cover (Germishuyse et al. 1998).
The more recent red, brown and grey sands that have covered the Port
Durnford formation as a result of wind action have given rise to the plateau
features that characterise the coastal plain. The plateau areas consist of a
series of ridges approximately aligned in a north-south direction. Some of
47
the inter-dune hollows contain accumulations of peat up to a few metres
thick (Worthington, 1978).
The coastal dune barrier complex, which frequently attains heights in excess
of 100 metres, is made up of sands that range in colour from creamy-white
and yellow to light grey, brown and red. These sands are mainly quartzitic,
fine grained, well sorted and contain rich deposits of heavy minerals such as
ilemite, rutile and zircon which are being extracted commercially
(Worthington, 1978). Except in the case of the older more clayey dunes, the
soils are generally low to very low in natural fertility because of their high
permeability and rapid leaching of nutrients (Maud, 1991).
The uMhlatuze River flood plain and channels through which the river
flowed at different times contain alluvial and estuarine sediments which
range in texture from sands to clays. Soft unconsolidated dark grey clays
characterise the lower course of the uMhlatuze River including the harbour
and the broader areas of the flood plain (Worthington, 1978). The depth to
suitable foundation material is very deep in large sections of these areas with
significant implications for construction costs. These areas also have an
abnormally high water table with significant implications for the provision
of engineering services, waste water and sewerage disposal systems.
The study area is richly endowed with building sand and stone. Course sand
for concrete is mainly confined to the bed of the uMhlatuze River, while
mortar sand and binder material are rare, confined to isolated deposits in the
Berea Red sand and shale deposits near Mtunzini and Empangeni. Limited
48
clay deposits, suitable for brick making, are also confined to the Empangeni
area.
The narrow beach extent and local wind characteristics render the beach and
dune sands highly susceptible to scour by the sea and wind erosion,
emphasising the extreme sensitivity, conservation importance and need for
controlled recreational use and development of the dune area.
4.5 Hydro-Geological Setting
4.5.1 General
The general groundwater flow pattern in the Zululand coastal plain is
directed towards the sea. In the vicinity of the larger inland lakes, the flow
deviates towards the lakes (Meyer and Godfrey, 1995). The lakes in the
coastal plain play a significant role in the geo-hydrology of the area since the
water levels in these lakes are an expression of the local groundwater
system.
The local groundwater movement in the study area is strongly related to the
topography, which is considered to be a consequence of the relatively low
permeability of the Pleistocene succession (Worthington, 1978) and of
relative shallow groundwater tables. The Pleistocene succession is overlain
by more permeable Holocene deposits. Infiltrated water flowing towards the
streams through the Pleistocene succession, having lower permeabilities,
will encounter higher drainage resistance than water that flows directly from
the top layers of the Holocene deposits towards the streams.
49
Since 1975 water level measurements in the study area show a decrease in
hydraulic heads of the deep aquifereous units in east and south-east
direction. This is caused by infiltration of rainfall in the higher elevated
Plateau areas and discharge in the lower surface water dominated areas.
Based on the description of the geological and geo-morphological setting
and the relationship with the surface water conditions, three principally
different hydrological reacting regions are distinguished within the study
area. These are the uMhlatuze flood plain, Lake Mzingazi and the Plateau
area and are more or less the same as the geo-morphological units.
4.5.2 Surface water conditions
The higher elevated plateau area north of the lake mostly acts as a recharge
area, meaning that in these areas rainwater will infiltrate into the subsurface
causing replenishment of the aquifers. Lake Mzingazi and the surrounding
wetlands act as a discharge area, into which the water from the Plateau areas
is drained. The south western edge of the lake is part of the uMhlaluze
Flood plain and acts as a discharge area for the lake. Both groundwater and
surface water from the lake drain into the Mzingazi Canal (Krikken and van
Nieuwkerk, 1997).
Lake Mzingazi is the main water resource of Richards Bay. The lake is
threatened by possible saline intrusion from the Mzingazi Canal, which is in
open contact with the sea and is in fact itself saline. In the past a weir has
been built between the outflow of the lake and the Mzingazi River (Fig. 4.2
and Photo 4.1), which artificially maintains Lake Mzingazi as a freshwater
zone at or above the water level in the Mzingazi Canal.
50
4.5.3 Groundwater recharge
In the Zululand Coastal Plain area the only major source of groundwater
recharge is rainfall. The groundwater recharge is considered to represent the
portion of the rainfall that reaches an aquifer after percolation through the
unsaturated zone (Fig. 4.3). The net charge is defined as the total recharge
minus the losses caused by evapo-transpiration from the saturated zone.
Figure 4.2:
Weir against saline intrusion between Lake Mzingazi and
Mzingazi River (After Krikken and van Nieuwkerk, 1997).
51
Photo 4.1: Weir constructed between Lake Mzingazi and Mzingazi River
(February 2001).
52
Figure 4.3: A diagrammatic representation of mechanism considered in
recharge from rainfall (After Krikken and van Nieuwkerk, 1997).
The main processes which govern the losses from the total rainfall are
interception by vegetation, evaporation from the unsaturated zone, soil
moisture storage replenishment and evapo-transpiration from the saturated
zone.
These processes are assumed to be primarily controlled by the
different land use types. For example a larger part of the precipitation will
be lost by evapo-transpiration in a forest area than in grasslands, because of
the difference in interception characteristics and rooting depth of both land
use types.
Four land use types with fundamentally different recharge
characteristics are distinguished in Fig. 4.4.
53
Figure 4.4: A map of different land use types in the study area of Richards
Bay (After Krikken and van Nieuwkerk, 1997).
Eucalyptus plantations:
Throughout the region large forests of Eucalyptus tree species have been
planted for commercial purposes. Each plot of trees is harvested every
seven years and young eucalyptus trees are put in place. Therefore, this
alien plant community has the highest growth rate in the study area (Krikken
and van Nieuwkerk, 1997). The rooting depth is also relatively high. Both
factors account for large evapo-transpiration rates and the deep canopy of
the eucalyptus trees causes large interception of rainfall.
54
Indigenous forest:
This land use type covered large areas of the region before humans
interfered with landscape. Indigenous forest comprises trees and shrubs
(indigenous plants), which have variable root depth. Indigenous trees that
are old can have very deep roots (Krikken and van Nieuwkerk, 1997). The
growth rate of these trees is much slower than that of eucalyptus, since these
forests are not cut for commercial purposes, causing them to have a lower
evapo-transpiration rate (Rawlins, Kelbe and Germishuyse, 1997).
Grasslands:
This incorporates the areas covered with grass. These areas have the lowest
root depth, lowest evapo-transpiration rates and lowest interception rates of
the plant communities in the study area. The land use of grasslands also
comprises the wetlands surrounding the lakes. Though these land use types
are not the same, the rooting depth and evapo-transpiration rate is assumed
to be equal in the study area (Krikken and van Nieuwkerk, 1997).
Urban areas:
Urban areas mainly consist of buildings, roads and gardens. Most of the rain
water in the study area, which falls on roads and buildings will be drained
artificially, almost no water will percolate to the water table.
Only in
gardens and parks can rainwater infiltrate and percolate to the groundwater
table.
There are, however, additional recharge sources in urban areas.
Krikken and van Nieuwkerk, (1997) distinguished three additional recharge
sources in urban areas. Recharge can occur from leaking water mains. This
can cause up to 45% of total urban recharge, though 30% is more common.
55
Leakage from sewers might be a source of pollution (Krikken and van
Nieuwkerk, 1997).
Since the urban areas in the study area were developed very recently, using
modern techniques for constructing sewers and water mains, it is assumed
that these additions to the recharge are of minor importance. The third
source of extra recharge is over-irrigation of gardens and parks, which
contribute 20 to 40% of the urban recharge in (semi) arid areas (Krikken and
van Nieuwkerk, 1997). However this factor does not apply to the study area,
due to high average rainfall amounts and irrigation on a very low scale in the
urban areas.
56
CHAPTER 5: METHODOLOGY
5.1 Selection of sites
Wetland categories such as hygrophyllis grasslands, riverine forest, swamp
forest and mangrove forest as well as vegetation occurring in the dune plant
communities and disturbed open spaces in the City of uMhlatuze
Municipalities area (Fig. 5.1), were selected for floristic analysis and
description of the recognised structural vegetation types occurring within the
municipal area of Richards Bay. These areas included the main open spaces
of the City of uMhlatuze Municipality area (Fig. 5.1) and the outer-lying
suburbs of Esikhawini, Nseleni and Vulindlela (Fig. 5.2). In most instances
these areas were also characterised by urban and industrial development.
Therefore sites were randomly selected in open space areas where urban and
industrial development have a relatively high environmental impact as well
as in open space areas where urban and industrial impacts were less
prominent.
5.2 The structural classification method
In this study each structural vegetation type was described using the
structural classification according to Edwards (1983).
57
58
Figure 5.1: A spatial representation of Suburban Open Space Zones in the Richards Bay
Municipal area (After Discussion document, 2000).
59
Figure 5.2: Map indicating the outer-lying suburbs of Nseleni and Vulindlela in the Richards Bay
Municipal area with drainage channels and water bodies (After Discussion document, 2000).
For the broad structural classification of the vegetation in the study area, the
method used in Edwards (1983) was applied. As derived from combinations
of the sets of growth form, cover and height attributes, with a limited use of
substratum growth form to define Thicket and Bushland and of total plant
cover to define desert vegetation classes (Edwards, 1983).
The Table in Edwards (1983), being essentially a multiple entry key to the
nine structural groups A to I, which are Forest and Woodland, Thicket and
Bushland, Shrubland, Grassland, Herbland, Desert Woodland, Desert
shrubland, Desert grassland and Desert herbland. Each structural group is
then subdivided on the basis of the height of the dominant height class
(Edwards, 1983). According to Edwards (1983), in terms of the criteria for
classification as given by Whittaker (1980), the structural classification
given here is:
i)
highly accessible in that the community attributes used are simple and
readily observable on the ground and from the air.
ii)
the criteria are significant at the broad classificatory level in
distinguishing the broad structures of vegetation and in covering
the continuum from forest to desert in all combinations of primary
growth form type, cover and height; and
iii)
effectively at the broad scale of resolution, but also, as field trails have
shown, remarkably sensitive to structural differences in vegetation at
the local scale.
60
Table 5.1: Tabular key to structural groups and formation classes (Edwards.
1983).
Total plant cover > 0.1%
Total plant cover
Dominant height
Total tree cover > 10% if >1m high
≤ 0.1%
class
A. Forest & Woodlandf
F. Desert woodland
Total tree cover
Trees dominant
100-75%
0-0.1Ø
75-10%
10-1%
0-0.2Ø
1-01%
2-8.5 Ø
8.5-30 Ø
Trees > 20 m
1. High forest
5. High close
9.High open
13. High sparse
woodland
woodland
woodland
Tees 10-20 m
2. Tall forest
6. Tall closed
10. Tall open
14. Talls sparse
woodland
woodland
woodland
Trees 5-10 m
3. Short forest
7. Short closed
11. Short open
15. Short sparse
woodland
woodland
woodland
8. Low closed
12. Low open
16. Low sparse
woodland
woodland
woodland
Trees 2-5 m
4. Low forest
57. High desert woodland
58. Tall desert woodland
59. Short desert woodland
60. Low desert woodland
Total tree cover >1% shrub cover >10% & >1 m high
B. Thicket & Bushland
Total tree & shrub cover
100-10% 0-2 Ø
Trees 5-10 m &
0-1% 2-8 Ø
17. Short thicket
19. Short bushland
18. Low thicket
20. Low bushland
Shrubs 2-5 m
Trees 2-5 m &
Shrubs
1-5 m
Total tree cover <0.1% shrub cover >0.1%
G. Desert
Or tree cover up to 1% & shrub cover >1 m high (closed
Shrubland
shrublands)
Shrubs dominant
C. Shrubland
Total shrub cover
100-10% 0-2 Ø
Shrubs 2-5 m
21. High closed
10-1% 2-8 Ø
25. High open shrubland
1-0.1% 8.5-30 Ø
29. High sparse shrubland
61. High desert shrubland
30. Tall sparse shrubland
62. Tall desert shrubland
27. Short open shrubland
31. Short sparse shrubland
63. Short desert shrubland
28. Low open shrubland
32. Low sparse shrubland
64. Low desert shrubland
shrubland
Shrubs 1-2 m
22. Tall closed
26. Tall open shrubland
shrubland
Shrubs 0.5-1 m
23. Short closed
shrubland
Shrubs <0.5 m
24. Low closed
61
shrubland
Total tree cover < 0.1% shrub cover <0.1% grass cover
H. Desert grassland
dominant and >0.1%
Grasses dominant
D. Grassland
Total grass cover
Grasses >2 m
Grasses 1-2 m
Grasses 0.5-1m
Grasses <.05 m
100-10% 0-2 Ø
10-1% 2-8.5 Ø
33. High closed
37. High open
grassland
grassland
34. Tall closed
38. Tall open
grassland
grassland
35. Short closed
39. Short open
grassland
grassland
36. Low closed
40. Low open
grassland
grassland
1-0.1% 8.5-30 Ø
41. High sparse grassland
65. High desert grassland
42. Tall sparse grassland
66. Tall desert grassland
43. Short sparse grassland
67. Short desert grassland
44. Low sparse grassland
68. Low desert grassland
Total tree cover <0.1% shrub cover <0.1% herb cover
dominant and >0.1%
I.
Desert
herbland
Herbs dominant
E. Herbland
Total herb cover
Herbs >2 m
Herbs 1-2 m
Herbs 0.5-1 m
Herbs <0.5 m
100-10%
10-1%
0-1 Ø
2-8.5 Ø
45. High closed
49. High open
herbland
herbland
46. Tall closed
50. Tall open
herbland
herbland
47. Short closed
51. Short open
herbland
herbland
48. Low closed
52. Low open
herbland
herbland
1-0.1%
8.5-30 Ø
53. High sparse herbland
69. High desert herbland
54. Tall sparse herbland
70. Tall desert herbland
55. Short sparse herbland
71. Short desert herbland
56 Low sparse herbland
72. Low desert herbland
5.3 The Floristic survey
For sampling to be done efficiently, the continuum of vegetation occurring
in the study area must be divided into describable communities of vegetation
types (Kent and Coker, 1995). A concept of particular vegetation types is
formed within the study area. Representative stands of that type are found in
the field, and one or more sampling plots are placed so that each sampling
plot enclosed the essence of that stand. Although positioning of sampling
62
plots is traditional non-randon in the Braun-Blanquet method, plots were
placed randomly within the stratified structural units already identified. The
site of vegetation description should however be a representative area of a
particular vegetation type (Kent and Coker, 1995). It is also prerequisite that
the relevé or sample should be uniform and homogenous in terms of floristic
composition and structure. This means that the particular assemblage of
species which are believed to be representative of the community type being
described, should exist over a sizable local area without any detailed
variations within it (Kent and Coker, 1995).
The minimal area may be determined by using the species-area curve
method (Mueller-Dombois and Ellenberg, 1974). The species-area curve is
compiled by placing larger and larger sampling quadrats on the ground in
such a way that each larger quadrat encompasses all the smaller ones, an
arrangement called nested quadrats (Fig. 5.3). As each larger quadrat is
located, a list is kept of additional species encountered.
A point of
diminishing return is eventually reached, beyond which increasing the
quadrat area results in the addition of only a very few more species
(Mueller-Dombois and Ellenberg, 1974). The point on the curve where the
slope most rapidly approaches the horizontal is called the minimal area (Fig.
5.3).
63
Figure 5.3 The species-area curve.
determining minimal area.
(a) A system of nested plots for
(b) Minimal area for dune grassland.
(c) Minimal area for English woodland is about a 100 m2. (d) Minimal area
for two stands of tropical rain forest in Brunei are 1000 m2 (a ridge) and 20
000 m2 (valley bottom) (Mueller-Dombois and Ellenberg, 1974).
Sampling plot size, shape and area are very important and will vary form
one type of vegetation to another. Methods have been devised to estimate
the optimum size of quadrats for a particular community type and are based
on the concepts of minimal area and species-area curve. The reason is that
64
the method is really only suitable as part of the overall Braun-Blanquet
approach to subjective vegetation classification, where a vegetation sample
or relevé, as it is known, is deliberately chosen as being a uniform and
representative sample of the plant community being described.
Table 5.2: Suggested quadrat sizes for certain vegetation types (MuellerDombois and Ellenberg, 1974).
VEGETATION TYPE
QUADRAT SIZE
Bryophyte and lichen communities
0.5m × 0.5m
Grasslands, dwarf heaths
1m × 1m to 2m × 2m
Shrubby heaths, tall herbs and 2m × 2m to 4m × 4m
grassland communities
Scrub, woodland shrubs
10m × 10m
Woodland canopies
20m × 20m to 50m × 50m
(or use
plotless sampling)
In this study sampling plot size for grassland and bushveld vegetation types
was 100 m2 (10 m x 10 m) as often used for South African vegetation types
(Mueller-Dombois and Ellenberg, 1974).
Cover is defined as the area of ground within a quadrat which is occupied by
the above-ground parts of each species when viewed from above. Cover is
usually estimated visually as a percentage, but stratification of multiple
layering of vegetation will often result in total cover values of well over
100%.
65
Table
5.3:
The Braun-Blanquet cover scales (Mueller-Dombois and
Ellenberg, 1974).
VALUE
BRAUN-BLANQUET
R
One individual with small cover
+
Less then 1 % cover
1
1 –5 % cover
2a
5 – 12 % cover
2b
12 – 25 % cover
2m
Less then 1 % cover
but
abundant in number
3
25 – 50 % cover
4
50 – 75 % cover
5
75 – 100 % cover
Sampling was undertaken during the growing season of 2001/2002.
5.4 Plant gathering, pressing, storage and identification
Plant species which could not be identified in the field during the survey
were collected and identified afterwards with the use of field guides and
other books (Burrows, 1990, Gibson, 1975, Tainton, 1976, Gibson, 1978,
Palgrave, 1983, Pooley, 1993, Pooley, 1998, van Oudtshoorn, 1999 and
Henderson, 2001). Gordon-Grey, 1995 was used to assist in identification of
Cyperaceae species.
66
Species of uncertainty were verified through comparison with herbaria
prototypes of the herbarium of the University of Zululand, the University of
KwaZulu-Natal and the South African National Biodiversity Institute
(SANBI) in Durban. Specimens taken to herbaria for confirmation were
prepared according to SANBI standards.
5.5 Data processing
The aim of classification is to group together a set of individuals (quadrats of
vegetation samples) on basis of their floristic composition. The end product
of a classification should be a set of groups derived from the individuals
where, ideally, every individual within each group is more similar to other
individuals in that group than to any individual in any other group.
The purpose of the methodology of Braun-Blanquet is to construct a global
classification of plant communities (Kent and Coker, 1995). The method is
based on several fundamental concepts and assumptions.
The association is the basic unit of the classification system, the plant
community. An association is therefore a plant community type, found by
grouping together various sample relevés that have a number of species in
common (Kent and Coker, 1995).
The final associations, which represent groups of similar relevés, are derived
by a subjective process of tabular sorting and rearrangement of both relevés
and species. Generally, sorting involves the following stages of the whole
process (Fig. 5.4).
67
5.5.1 The TWINSPAN computerised method
The subjective nature of the process of tabular rearrangement has been
reduced over the past 30 years by the writing of various computer programs
to carry out tabular arrangement. Some of these programs are related to the
more objective methods of numerical classification, particularly similarity
analysis (Kent and Coker, 1995).
Most techniques devised over the past 25 years have been hierarchical in
nature. This means that the results can be portrayed as a dendrogram. The
reason why hierarchical method are more common is that such a dendrogram
shows different levels of similarity or dissimilarity very clearly and the
different levels displayed in a dendrogram are often very helpful when it
comes to making ecological interpretations (Kent and Coker, 1995).
Methods of classification may be applied to either quantitative or qualitative
data. Most methods will accept either type of data (except association
analysis), and the decision on whether to use quantitative data depends on
the type of problem being analysed (Kent and Coker, 1995).
Figure 5.4: A Flowchart of stages in the subjective classification of relevés
using the Braun-Blanquet method (Adapted from Westhoff and Van der
Maarel, 1978 in Kent and Coker, 1995).
68
Field Description
Tabular rearrangement and
sorting
Floristic description
Relevés – typical, minimal area,
homogeneous
Environmental description
Raw data table
Partial table
Ordered partial table
Differentiated table
Synoptic table
Syntaxonomy
Association table
(phytocoenon)
Synoptic association table
Comparison with other
literature (Syntaxonomy)
Environmental characterisation of
associations (Synecology)
Syntaxon table
(Higher orders)
Field checking
69
More recent methods, notably two way indicator species analysis
(TWINSPAN), employ the idea of the pseudospecies, whereby the presence
of a species at different predetermined levels of abundance is used. In
TWINSPAN the percentage cover scale is often divided into six using five
levels. Thus the first pseudospecies may be 1 – 2 per cent cover of the
species, 3 – 5 per cent the second pseudospecies, 6 – 10 per cent the third, 11
– 20 per cent the fourth, 21 – 50 per cent the fifth and over 50 per cent the
sixth.
These six levels of abundance of a species are then used in
presence/absence form to make the classification (Kent and Coker, 1995).
The complete Richards Bay vegetation database (320 relevés stored in
TURBOVEG) was exported as a Cornell Condensed species file (cc-file) to
a working directory in MEGATAB (Hennekens, 1996b). The option in
TURBOVEG to distinguish between different vegetation layers a single
species occupy was made inapplicable by combining all layers into one layer
(no layer) (Du Plessis, 2001).
A Twinspan classification (Hill, 1979b), incorporated in MEGATAB, was
used to obtain a first approximation of the plant communities occurring in
the area. This classification was used to compile a table using the BraunBlanquet method (Werger 1974, Westhoff and Van der Maarel 1978) in the
data editor program MEGATAB (Hennekens 1996b). These results showed
three major plant communities, which were then separated into three
different tables. The data in each of the parts were classified separately,
using TURBOVEG (Hennekens 1996), TWINSPAN (Hill, 1979b) and
MEGATAB, to clearly indicate the different communities and the
differences between the sub-communities within the major communities.
70
The communities and their sub-communities were then described, according
to their diagnostic species, dominant species and associated species. The
final three phytosociological tables indicate the different plant communities,
as well as the floristic variation within each community and the relationship
between communities (Venter, 2003).
The classification of vegetation types in terms of their floristic composition
using the Braun-Blanquet classification technique with the use of the two
way indicator species analysis (TWINSPAN) computerised method for
numerical classification as well as the hierachical technique where the
results are potrayed as a dendrogram, also known as a tree of linkage
diagram (Kent and Koker, 1995).
To facilitate the task of refining a phytosociological table containing more
than 300 relevés and almost 500 species, a synoptic table was constructed
directly from the TWINSPAN table as an option in MEGATAB (Du Plessis,
2001).
5.6 Field mapping and verification of wetlands and other vegetation
One of the aims of this study was to establish the occurrence and distribution
of the Richards Bay plant communities.
Information on the plant
communities was obtained from colour aerial photographs, taken in May
1998. The plant communities were identified principally on the basis of
colour and structural variation portrayed by the aerial photographs. Where
identification was uncertain because of poor photographic resolution,
identification was on the basis of apparent similarity to other clearly
recognised vegetation types.
71
The potential and limitations of aerial photo interpretation for vegetation
studies are discussed in the literature (For example, Edwards, 1972; Weisser,
1979 and Jarman et al., 1983). While mapping, the aerial photos were
realigned as soon as a deviation of corresponding points and areas could be
observed.
Inaccuracies owing to distortions and mapping difficulties
though, are at a level that will not impair main conclusions.
Ground truthing of the vegetation was carried out in the growing season of
2001/2002, during which the general species composition, apparent species
diversity and overall condition of plant communities, within their
communities was assessed over their distribution ranges.
72
CHAPTER 6: RESULTS:
PLANT COMMUNITIES OF THE DUNES
The result of the floristic analysis of the vegetation of the dunes is given
in Table 6.1. All references to species groups in this Chapter refer to this
Table. Four communities were recognised, but these may be grouped into
two major communities. The classification of these communities is as
follows:
6.1 Classification
1. Carprobotus dimidiatus – Gazania rigens Dune vegetation.
1.1 Gazania rigens – Scaevola plumieri Foredune community.
1.2 Cynanchum natalitium – Carprobotus dimidiatus Mid-dune community.
2. Chrysanthemoides monilifera – Casaurina equisetifolia Dune Scrub
2.1 Chrysanthemoides monilifera – Carpobrotus dimidiatus Dune Scrub
2.2 Chrysanthemoides monilifera – Brachylaena discolor Backdune Scrub
Thicket.
73
Description of Dune vegetation
1. Carprobotus dimidiatus – Gazania rigens Dune vegetation
This vegetation is characterised by species group C. The diagnostic species
are the succulent creepers Carprobotus dimidiatus and Ipomoea pes-caprae,
the shrub Helichrysum kraussii and the herbaceous creepers or forbs
Gazania rigens, Arctotheca populifolia and Launaea sarmentosa.
Few other species may be present, including Chrysantehmoides monilifera,
Eugenia capensis and the alien tree/shrub Casuarina equisetifolia.
The dune and strand vegetation occurs on unconsolidated loose sand of the
sand dunes north and south of Richards Bay harbour. Analysis on the sand
indicated that the sand’s water holding capacity is generally low and that it is
almost uniformly alkaline with a pH as high as 8.7 (Venter, 1972). This
vegetation on the frontal dunes is subjected to high concentrations salt spray
and consequently only species tolerant to these conditions establish in this
habitat (Venter, 1972).
Carprobotus dimidiatus is a perennial, trailing succulent. It grows in sand
on the coastal strip and will grow down as far to the high tide mark on
beaches (Pooley, 1998). This species generally forms large mats on open
sand as observed in the study area. C. dimidiatus forms a good ground cover
as well as a sand stabilizer and is tolerant to salt spray conditions (Pooley,
1998).
74
Gazania rigens is a creeping perennial herb which is a common sand
coloniser, which is distributed from southern Cape to Mozambique (Pooley,
1998).
Two communities were recognised under the Carprobotus dimidiatus –
Gazania rigens Dune vegetation:
1.1 Gazania rigens – Scaevola plumieri Foredune community.
This vegetation is characterised by species group A. The only diagnostic
species is Scaevola plumieri, however the diagnostic species of the
Carprobotus dimidiatus – Gazania rigens Dune vegetation (species group
C) are also present, and especially Gazania rigens is prominent. Dense
stands of Scaevola plumieri and Gazania rigens were very common on sand
dunes north of the bay mouth and Richards Bay harbour.
Scaevola plumieri is an evergreen succulent shrublet and form large colonies
on coastal sand dunes (Pooley, 1998).
Gazania rigens is more widely
distributed as a pioneer species throughout the front dunes and backdunes
which are exposed to wind and salt spray. S. plumieri is however more
restricted and forms more dense stands on the frontdunes than the back
dunes.
75
1.2
Cynanchum
natalitium
–
Carprobotus dimidiatus Mid-dune
community.
This vegetation is characterised by species group B. The diagnostic species
include the scrambling vine Cynanchum natalitium, the shrub Maytenus
procumbens, the forbs Canavalia bonariensis, Senecio macroglossoides and
Hibiscus trionum and the sedge Mariscus solidus.
Cynanchum natalitium is a vine occurring in dune forest or scrub. The
stems are woody and bark corky (Pooley, 1998).
This vegetation occurs on the mid-dune areas, and is transitional between the
foredunes and the backdunes. This is indicated by the presence of species
from species group C, and especially species group E.
2. Chrysanthemoides monilifera – Casaurina equisetifolia Dune Scrub
This major dune scrub community is characterised by species group E.
Diagnostic species are the shrubby Chrysanthemoides monilifera and the
alien tree Casaurina equisetifolia.
Chrysanthemoides monilifera grows in the form of a shrub or small tree
which can reach heights between 1 to 6 meters and can be found from
coastal dunes to the Drakensberg escarpment in KwaZulu-Natal and
Transkei (Pooley, 1993). Maximum heights of 3.5 meters were observed for
this species on the back dunes of the northern shores area of Richards Bay as
76
well as in the open spaces of the Meerensee suburb of Richards Bay where
soils were still sandy.
Casaurina equisetifolia is an alien tree species used to stabilise shifting
sands at the coast, now naturalised in Transkei, KwaZulu-Natal and
Mozambique (Pooley, 1993). This alien species forms part of a community
occurring in dense stands on the northern and southern bounderies of the bay
mouth. Littoral drift sands that originated on the beach formed tongues into
the vegetated dunes (Weisser and Muller, 1983). Many drift sands were too
small to be mapped, however, the position of the drift sand along the coast
was reasonably constant through the years (Weisser et al., 1983).
By comparing 1937 and 1976 maps, a reduction in size and number of
coastal drift sands was found. This was most probably a consequence of the
protective management (e.g. reduction of grazing and fire) carried out by
the Department of Forestry and of their drift sand rehabilitation programme
using Casaurina equisetifolia (Weisser et al., 1983). Three main inland drift
sands were found on the 1937 photographs. On the 1976 photos they were
found to have stabilized mainly through the plantings of Casaurina
equisetifolia (Weisser et al., 1983).
Less frequent species occurring in the back dune communities include:
Imperata
cylindrica,
Carissa
macrocarpa,
Helichrysum
areum,
Cymbopogon validus, Phoenix reclinata, Momordica foetida and Rhus
chirindensis.
77
Photo 6.1: C. equisetifolia one of the diagnostic species of the Backdune
Vegetation Community viewed from the harbour to the south (March 2002).
78
Table 6.1: Plant communities of the dunes
|
|
|2 2 2 2 2 2 2 2 |2
Releve number
|6 7 6 6 6 6 6 6 |5
|9 0 3 4 5 6 7 8 |7
|
|
-------------------------- - - - - - - - - Species Group A
Scaevola plumieri
| m1 b b 1 b b b | .
. |. . . . . . |. . . . . . . . . . . . . . . . . |
Species Group B
Cynanchum natalitium
Maytenus procumbens
Canavalia bonariensis
Senecio macroglossoides
Hibiscus trionum
Mariscus solidus
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Species Group C
Ipomoea pes-caprae
Gazania rigens
Carpobrotus dimidiatus
Helichrysum kraussii
Arctotheca populifolia
Launaea sarmentosa
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Species Group D
Brachylaena discolor
Eugenia capensis
Strelitzia nicolai
Sideroxylon inerme
Microsorium scolopendrum
Chromolaena odorata
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Species Group E
|. + . r . . . . |r + |. 1 r b 1 3 |4 4 . . . r . 3 . 1 . 4 3 b 5 5 5
Casuarina equisetifolia
Chrysanthemoides monilifera | . . 1 r . . . . | b 1 | 3 3 + 4 b b | . . 3 1 . b . 1 + 1 b . 1 m. . . |
Infrequent Species
Imperata cylindrica
Carissa macrocarpa
Helichrysum aureum
Cymbopogon validus
Rhus nebulosa
Phoenix reclinata
Abrus precatorius
Isoglossa woodii
Tagetes minuta
Passiflora subpeltata
Allophylus africanus
Momordica foetida
Smilax anceps
Rhus chirindensis
Acacia karroo
Cyperus rupestris
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Helinus integrifolius
Acacia robusta
Cryptocarya myrtifolia
Blechnum australe
Eulophia horsfallii
Acalypha sonderiana
Catunaregam spinosa
Lablab purpureus
Tricalysia lanceolata
Erythrina lysistemon
Syzygium guineense
Chironia baccifera
Echinochloa pyramidalis
Asparagus falcatus
Lantana camara
Halleria lucida
Allophylus natalensis
Oplismenus hirtellus
Digitaria eriantha
Aristida junciformis
Dactyloctenium australe
Pinus elliottii
Senecio tamoides
Cissampelos mucronata
Trichilia dregeana
Zehneria parvifolia
Maytenus nemorosa
Grewia pondoensis
Ipomoea cairica
Panicum repens
Commelina erecta
Senecio madagascariensis
Helichrysum aureonitens
Bulbostylis hispidula
Canavalia rosea
Indigofera spicata
Pycreus macranthus
Hydrocotyle bonariensis
Helichrysum auriceps
Paspalum distichum
Vigna unguiculata
Diospyros natalensis
Rubia cordifolia
Zehneria scabra
Trema orientalis
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CHAPTER 7: RESULTS:
FOREST COMMUNITIES
The results of the floristic analysis of the forest vegetation are given in Table
7.1. All references to species groups in this Chapter refer to this Table. Four
communities were recognised. The classification of these communities is as
follows:
1. Isoglossa woodii – Macaranga capensis Tall Closed Forest
2. Chromolaena ordonata – Melia azedarach Short Woodland and Forest
3. Barringtonia racemosa – Ficus tricopoda Tall Swamp Forest
4. Avicia marina Short Mangrove Forest
Description of Forest Communities
1. Isoglossa woodii – Macaranga capensis Tall Closed Forest.
This forest community occurs north and south of the bay mouth and forms
an extensive part of the coastal forest vegetation (Venter, 1972).
This vegetation is characterised by species group A. Species considered to
be diagnostic include the trees Macaranga capensis, Trichillia emetica,
hibiscus tiliaceus, Mimusops caffra, Psychortria capensis and Strelitzia
reginae, the shrub Isoglossa woodii, the lianas Asparagus falcatus, Senecia
tamoides and the alien invasive Ipomoea purpurea, the geophyte Scadoxis
multiflorus subsp. katharinae and the fern Cheilanthes viridis.
79
Macaranga capensis is a tall deciduous tree, found in low altitude forests,
usually in wet areas (Pooley, 1993). It is mainly distributed along lake
banks and also occurred frequently on river and stream banks. Most trees
observed were mature trees differing in height from 9 to 20 meters. Isoglosa
woodii is a shrub which can grow up to 4 meters and usually grow in
colonies in forest understoreys (Pooley, 1998). It appears to be the dominant
species occurring within the understorey of the forest community within the
study area. Asparagus falcatus is a robust climber also associated with forest
margins and thickets and has a wide distribution from Eastern Cape to
tropical Africa (Pooley, 1993)
Species that are often found in these forests (species group C) include the
trees Strelitzia nicolai, Acacia karroo, Trema orientalis, Rhus nebulosa and
Brachylaena discolor and the prominent forb Asystacia gangetica, while the
alien invader tree Psidium guajava and alien liana Passiflora subpeltata may
also be present.
Other species encountered include (species group F) the trees Tricalysia
capensis, Albizia adianthifolia and Phoenix reclinata, the lianas Smilax
anceps and Cissampelos torulosa and the climbing fern Stenochlaena
tenuifolia.
Strelitzia nicolai occurred scattered through out the open grassveld and
became more evident in denser stands with higher cover abundance in closed
forest areas. Strelitzia nicolai rarely reached heights above 3 meters and
formed part of the sub-crown stratum of coastal dune and sand forest. Trema
80
orientalis is a common pioneer tree or shrub (5 to 15 meters) high and is
usually found on forest margins, disturbed soils, water courses in warm,
fairly high rainfall areas (Pooley, 1993). Asystacia gangetica is a spreading
herb and is commonly found growing in woodland and forest where it
occurs predominantly in shady areas as groundcover (Pooley, 1998). The
species has preference to shady and moister conditions within the forests of
Richards Bay area. Within the more open grassveld patches with more
direct exposure to sunlight, Asystacia gangetica occurs less prominently.
As mentioned, this community also has the alien invasive species Psidium
guajava. This species is a small tree, found in the scrub forest, riverine
vegetation and on roadsides and although an exotic from tropical America, it
is now naturalised along the KwaZulu-Natal coastal areas (Pooley, 1993).
Results (7.1) indicate that P. guajava and L. camara has invaded the greater
parts of the Richards Bay municipal area. It was also observed during this
study that erosion was visible in this study area and that open eroded patches
were colonised by Psidium guajava and Lantana camara.
As observed by Venter (1972) Acacia karroo may form a community on the
outer bounderies of the forest communities where it separates the grassveld
from the rest of the forest community. This species may occur in loose
standing stands within other forest communities, as shown in species group
C (Table 7.1). Previous observations of active A. karroo encroachment into
adjacent grassveld and dune wetland areas, where sufficient moisture
conditions exists (Venter, 1972 and Matsau, 1999) could be supported with
observations of this study.
81
2. Chromolaena ordonata – Melia azedarach Short Woodland and Forest
This vegetation is degraded woodland or more open degraded forest where
alien species invaded and became very prominent. The community is
characterised by species group B. Diagnostic species are often alien invader
species, e.g. the woody Chromolaena ordonata, Melia azedarach, Lantana
camara and Eucalyptus grandis. Other diagnostic species include the tree
Rhus chirindensis, the grasses Oplismenus hirtellus and Paspalum distichum
and the reed Phragmites australis.
Other species that are often encountered include (species group C) the trees
Strelitzia nicolae, Acacia karroo, Trema orientalis, Rhus nebulosa and
Brachylaena discolor and the prominent forb Asystacia gangetica, while the
alien invader tree Psidium guajava and alien liana Passiflora subpeltata may
also be present. Other species present include (species group F) the trees
Albizia adianthifolia and Phoenix reclinata, the lianas Smilax anceps and
Cissampelos torulosa and the climbing fern Stenochlaena tenuifolia.
Chromolaena ordonata is a scrambling, sparsely hairy shrub up to 4 metres
or higher, often forming dense thickets. This species originally cultivated as
an ornamental plant, is now found as an invader of forest margins, savanna,
plantations as well as along water courses and roadsides (Henderson, 2001).
The species is usually associated with growing in disturbed places and is
regarded as a serious threat to South Africa’s natural vegetation (Pooley,
1998).
82
Melia azedarach is a deciduous, spreading tree up to 23 meters high. It was
cultivated for ornamental, shade providing trees, but now invades savanna,
roadsides, urban open spaces, wasteland and riverbanks (Henderson, 2001).
This species appears to be distributed mainly along riverbanks and the man
made drainage channels as well as roadsides in the study area of Richards
Bay municipal area. This species was declared as a category 3 invader,
which is not allowed to occur within 30 meters of a 1:50 year flood line of a
river, stream, spring, natural channel in which water flows regularly or
intermittently, lake, dam or wetland (Henderson, 2001).
Photo 7.1: Chromolaena ordonata invading
Photo 7.2: Psidium guajava, alien invasive
riverine, Swamp and Dune forest
species encroaching in woodland and
Vegetation (February 2002).
Grassland areas (June 2002).
83
Lantana camara is another alien invasive species observed in this
community and was first introduced as an ornamental plant from central and
South America, which now became a noxious invasive weed in southern
Africa and also known to be poisonous to cattle (Pooley, 1998).
Eucalyptus grandis is a tall evergreen tree which was originally cultivated
for timber, shelter, firewood and a honey source (Henderson, 2001). This
species invades forest gaps, plantations, watercourses and roadsides. It is a
declared category 2 invader. This species are only allowed to grow in areas
demonstrated to primarily serve a commercial purpose, use as a woodlot,
shelter belt, building material, animal fodder, soil stabilisation, medicinal or
other beneficial function (Henderson, 2001).
The presence of the species listed in species group C occur in both the
Isoglossa woodii – Macaranga capensis Tall Closed Forest and the
Chromolaena ordonata – Melia azedarach Short Woodland and Forest. This
may indicate a floristic and ecological relationship between these two
communities. It may also indicate that the Chromolaena ordonata – Melia
azedarach Short Woodland and Forest is a degraded form of the Isoglossa
woodii – Macaranga capensis Tall Closed Forest, totally invaded by alien
species. This could indicate that pristine coastal forest will change to a
degraded forest type dominated by alien species if not protected against
human caused impacts.
84
1.
Barringtonia racemosa – Ficus tricopoda Swamp Forest
Freshwater Swamp Forests grow along the coast of northern KwaZuluNatal.
These small communities of Barringtonia racemosa – Ficus
tricopoda Swamp Forests grow mainly in localised groups on the shores of
Lake Mzingazi along drainage lines. In some areas, especially towards the
Mdibi River in the north of the lake, Barringtonia racemosa is extensively
harvested for building material by locals and several other species uses as
traditional medicines by the Zulu community (Reavell, Maseko and Matsau,
1998). Barringtonia racemosa is one of some trees having a broad tolerance
to a range of hydroperiods and soil moisture, whereas Ficus tricopoda is
more confined to wetter areas (Reavell, et al. 1998).
This Swamp Forest is characterised by species group D and the diagnostic
species are Barringtonia racemosa, Ficus tricopoda and Ficinia trichodes.
Other species that may be present (species group F) include the tree Phoenix
reclinata, the liana Smilax anceps and the fern Stenochlaena tenuifolia.
Barringtonia racemosa is a small to medium sized tree, found fringing
coastal swamp forest, estuaries and rivers from the KwaZulu-Natal south
coast to Mozambique (Pooley, 1993). This species previously formed large
continuous communities as indicated by Venter (1972). However, in the
study area Barringtonia racemosa and Ficus tricopoda dominated swamp
forests have been reduced to relatively small patches occurring within the
Richards Bay municipal area. These trees usually occur in association with
each other and are restricted to the back swamps of Lake Mzingazi, Lake
Nzeze and on the river banks of the Mzingazi river and other streamlets and
85
drainage channels. A possible decline in Barringtonia racemosa over the
years could be a result of the harvesting of this species by local people in the
areas of Lake Mzingazi for fence and hut building and those areas where
trees are removed are usually invaded by species like Chromolaena odorata
(Maseko, 1996).
Photo 7.3: Barringtonia racemosa Swamp Forest on the banks of Lake
Mzingazi. Dead B. racemosa trees in the front (May 2002).
86
Photo 7.4: Swamp Forest mosaic vegetation invaded by Eucalyptus grandis
(May 2002).
87
Photo 7.5: Clearing of Swamp Forest vegetation for agriculture and
building material on lake shores such as Lake Chubu and Mzingazi (June
2002).
2.
Avicenia marina Mangrove Forest
Avicenia marina occurred as the only species within this mangrove
community (species group E) and formed dense stands on the northern
banks of the bay and as far to the west as the Mhlatuze River. Dense
stands with cover abundance scales of 3 to 5 were often observed,
especially closer to or on the banks of the estuary and in areas that are
more protected to direct wave action than those stands occurring in more
open waters.
Avicenia marina is a small to medium sized and pioneer mangrove,
found in estuaries and intertidal area in KwaZulu-Natal and Eastern Cape
coastlines (Pooley, 1998). The largest trees were observed in the dense
stands where the species reached heights of up to 9 – 10 meters.
Although Avicenia marina is usually associated with Brugeuiera
gymnorrhiza, the only species recognised in the sub-crown stratum of
this community, was Avicenia marina. Brugeuiera gymnorrhiza was not
recorded in the sample plots in the mangrove forest community of
Richards Bay area. If Brugeuiera gymnorrhiza still occurs it is to a much
lesser that was observed by Venter (1972).
Other studies indicated that different age groups were recognised in the
mangrove forest that developed after the construction of a harbour in the
88
Umhlatuze Estuary in 1976 (Bedin, 2001). The rate of progress was high
during the first period, varying until 1982. Thereafter there was a small
decrease in the total area, and progress has been 5.4 ha per year over 13
years. The difference in stem densities was also observed and higher
densities were found in youngest stands (Bedin, 2001). Stem densities
became significantly lower in older stands.
This suggests that the
mangrove progression has slowed down and that the system was settling
down (Bedin, 2001).
Photo 7.6: Aerial view of the A. marina Forest south of Richards Bay
Harbour (March 2002).
89
Photo 7.7: Avicenia marina (White Mangrove) stands of the
Mangrove Swamp Forest vegetation (March 2002).
Photo 7.8: A. marina saplings (March 2002).
90
Photo 7.9: Aerial roots of A. marina (March 2002).
91
Table 7.1: Forest plant communities
Relevé nr
|
|
|
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 |
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 1 2 | 2 2 2
1 1 1 1 1 1|
| 3 4 7 7 8 8 2 2 2 3 4 5 5 6 7 7 7 7 7 7 7 7 8 8 8 2 2 2 3 4 4 4 4 | 5 5 5 7 7 7 8 8 9 9 9 9 2 4 4 4 4 5 5 5 6 6 6 6 6 8 8 8 9 9 9 9 0 1 1 2 2 3 4 4 5 5 | 1 2 2 8 9 9 3 4 5 6 7 7|
| 4 9 1 2 5 6 3 4 9 1 0 4 5 8 0 1 4 5 6 7 8 9 3 4 5 5 6 8 9 0 5 6 7 | 2 7 8 3 5 7 7 8 1 2 4 6 5 2 7 8 9 2 8 9 0 2 3 5 6 2 6 7 4 0 1 4 2 0 7 2 4 8 1 8 9 3 | 4 0 7 9 0 5 0 4 3 7 2 3|
|
------------------------Species Group A
Isoglossa woodii
Macaranga capensis
Asparagus falcatus
Trichilia emetica
Ipomoea purpurea
Hibiscus tiliaceus
Mimusops caffra
Psychotria capensis
Scadoxis multiflorus katharinae
Senecio tamoides
Cheilanthes viridis
Strelitzia reginae
Species Group B
Chromolaena odorata
Melia azedarach
Lantana camara
Rhus chirindensis
Oplismenus hirtellus
Eucalyptus grandis
Paspalum distichum
Phragmites australis
Species Group C
Asystasia gangetica
Strelitzia nicolai
Acacia karroo
Commelina africana
Psidium guajava
Trema orientalis
Rhus nebulosa
Passiflora subpeltata
Commelina erecta
Brachylaena discolor
Centella asiatica
Microsorium scolopendrum
Ficus sur
Species Group D
Barringtonia racemosa
Ficus trichopoda
Ficinia trichodes
|
|
|
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | . . + . . + + . 1. . 1. . mb 1. b 3m 1 4 3 3+ + + mm 3 3m | . . . . + . . . . . . . . . . . . . . . . . . . 1. 3. . . . . . . . 1. . 1 1. .
| . . . . . . . . . . . . |
| . . . . . . . . b . . 4b . . 3. m 3 4b b . . . . mb . + . . .
| . . . . . . . . . . . . . . . . . . . . . 3. . 1. . . . . . . . . . . . r . . . .
| . . 1. . . . . . . . . |
| . + . . . . . . + . . + + . + + + . + . . + + . + + + + . + . . .
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + . . . . . + . . . . .
| + . . . . . . . . . . + |
| . . 1. . . 1 1 3. 4. . . . + b 3 4. . . . . . . . . . . 1. 1 | . . . 1. + . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
| . + . . . . . . . . . . . . . + . . . + . + + + . . + . . . . . .
| . . . . . . b . . . . . . . . . . + . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . + . . . . . + . |
| . . . . . . . b . . . . . . . . m 3b . 1. . . . . . . 1. . . .
| . . . . . . m. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
| . . . . . m. . . . . b . . . . . . 1. . . . . . 1 1. . . . . .
| . . . . . . . . . . . . + . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| 1. . . . . . . . . . . |
| . . . . . . . . . . . m. . . . . . . . . . . 3b . m. . . . . m | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . 1. . . . . . . . . |
| . . . . . . . . . + + . + . . + + . . . . . . . . . . . . . . . .
| . . . r . + . . . . . . |
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . + . . . . . . . . . + . . . . . . . . . . . . . . . . + + | . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + | . . . . . . . . . . . . |
| . . . + . . . . . 1. + . . . . . 1. . . . . . . . . . . . . . m | . . . . . . . . . . . . . . . . . . . . . . . . . . . + . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
| . . + . . . . . . + . . . . . + r . . . . . . . r . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
| . . + . . . . . . . . . . . . . . . . . . . . . . b 3. + . + . .
| . . . . . 1. . . . b . . . . . m 1. . . . b . 3m 3b b 4b b . 4b 4mb b 3. 1 | 3+ . . . . . . . . . . |
| . . . . . . . . . 1. . . . . . . . . . . . . . . . . . . . . . .
| . . . . . 4 4 4mm. . b . . . b 3 1 3 1 3. 1m. 1. . . r . . . . . 1. . . 3.
| . . . 1 4. . . . . . . |
| . . + . . . . . . . . . 1. . . . . . . . . . . . . . . . . . . .
|
| . . . . . . . . . . . . |
4 1. + b b 3 1. . . 3. . . r . + . . . . r . . . + 1+ . 1+ . . . 3. . . . .
| . . . . . . 1. . . . . . . . . . . . . . . . . . . . . . . . . 1 | + . . . . . mm 1. . . 4 1b + . m. . . . . . . 1+ . . . . . . . + . + . 1+ . m | . . + . . . . . . . . . |
| . . . . . . . . . . . . . . . . . . . . + . . + + . . . + . . . .
| . . . b m 1+ . . . . . + . . . . . . + . . . + + . . . + . . + . . + . . . + . + .
| . . . . . . . . . . . . |
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . 4 3. . . 4. . . b 4. + . . . m. . m. . 1. . . . . . 3. . . .
| . . . . . . . . . . . . |
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + + | . . . . . . . . . . . . . . . . + . . . . . . . . . . . . a a . a . . . . a . + . + | . . . . . . . . . . . . |
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + | . . . . . . 1. . . . . . . b . . . + . . . . . . . . . + . 1+ . + . . . . . . . .
| . + . . . . . + . . . . |
|
| . . . . . . . . . + . . |
. . + . . . . . m. + . . . m+ 1. 1 1 1m 1m+ . . + 1+ . + | . r + . . . . . . . . . . . . . . . . . . . . . . . + 1m 1 3m+ . . + + 3. . . .
| . . . + . . . . 1+ . . 4. . . . . . . . b 1. . . . . . + . 1.
|
| . + + + + . . . b + . 1. + . . . . 4 3. b 3. 3. . . . . . . . . 3+ 1. + . 3.
| . . . + . . . . . . . . |
. . . . . . . b . . . 1. . . . . . + . . 1. 3. . + . m 1. 4 | . . . . 1. . . 1. 4. . . b 1 3. . . . b . m. . 1+ . 1. . b 1 1. . 1. . . .
| + + . . . . . . . . . . |
| . . . . . . . . 1. . 1 1b 1. . . . 1. . 1b . . . 1+ + . . 1 | . . . . + . . . . . 1+ 1. . . . 1. . . . b 1+ . + . . . . . . . 1. . r . + . .
| . . . . . . . . . . . . |
| . b . . 3. 4m. . . . . . . . . . . . . . b . . . . . 1 3m 4.
| m+ . . . . . b . . . b . . . . . . . . . . . . . b 4+ 1+ . 1. 1. 4 1. 4. . 4 | . . . . . . . . . . . . |
| . . . . . . . . . + . + + + . + . . . . . . . + . . . . . + . . + | . . . 1b . . . + . . . . . . . + + + + + . + . + . . . . . . . . . . . + . . + + .
| . . . . . . . . . . . . |
| . . + . . 1. . . . . . . . + + . . . . . . . . 1. + . . . . . .
| . . . . . . . . . . . . |
| + . . . . . . . . . . . b . + . . . . . + 1. 1. + . 1. . . . r . . + . . . 1. .
| . . . . . . . . 1. . . . . . . . . . . 3 4 3b b . . . 4. . . 1 | . . . . . . 3mb . . . 1b . . . . . 3. . . . 1. . . . . . . . . . . . . . b 3.
| . . . . m. . . . . . . |
| . . . . . . . . . . 1. . . . . m. . . 3. . . . . 1 1+ + . . b | . . . . . . . b + . . . . 1. . . . . . . . . . . . . . mmr m. . 1. . . . . . .
| . 1. . . . . . . . . . |
| . . 1+ . . . 1. 1. m. . . . . . . . . 1. + . . . . . . . m.
| . . . . . . . . . . . 1. m+ b . + . . . . . . . . . + . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
| . . + . . . . . + + . + . . . . . . . . . . . . + . . . . . . + .
| + . . + . + + + . + + . . . . . . . . . . . + . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
. . . . . . . . + . . . . . + 1. . . . . + . . . . . . . . . + .
| . . . + . . . . . . . + . . . . + . + . + . . + . . . . . + . . . . + + . . . . . .
| . . . . . . . . . . + . |
. . . . . 3 1. . . b . . . . . . . . . + 1. . 1. . . . + . . .
| . . . . . . . . . . . b 1. . . . . . . . . m. . . . . . . . . . . . . . + b . . 1 | . . . . . . . . . . . . |
| . . . . . . . . . + . . . . . . . . . . . + . + . . + . + + . . .
| . . . . + . . . . . . . . . . . . . . . . . . . . . . + + . . + + . . . . + . . . .
| . . . . . . . . . . . . |
| . . . . . . . . . . . 1. . . . . . . . . . . . . 1b . . . . . r
| . r . . . . . . . . m. . . . . b . . . m. . . . . . . . . r . . . . . . . . . . .
| . r . . . . . . . . . . |
| . . . . . . . . 3m. b . . 1 1. . 1. . . . . . m. m. . . . .
| . . . . . . . . . + m. . . 3. . b . . 1b . . . . . . . . . . . b . . . . . . . .
| 3 3 4 4 4 5 5 4 5 4. 4|
| . . . . . . . . . m. b . . . . . . . . . . . . . . . . . . . . .
| . . r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . b 4b . . . . . b |
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . 3 3. |
Species Group E
Avicenia marina
Species Group F
Smilax anceps
Phoenix reclinata
Stenochlaena tenuifolia
Albizia adianthifolia
Cissampelos torulosa
Senecio macroglossoides
Cissampelos mucronata
Tricalysia capensis
Ipomoea alba
Dalbergia armata
Dichrostachys cinerea
Pisonia aculeata
Abrus laevigatus
Solanum panduriforme
Zanthoxylum davyi
| . . + . . . . . + b + + . . . . + . + + . . + . . + + + . + . . + | . + . + + . . . . . + . . + + + . + . arinam
. . + + . . . . + + + + + + + + . + + + . .
| . + + . . . . + . . . + |
| + + + 1m. b + mb b + b + + + . 1 1+ 1+ . . . . . . . + + . .
| . . . . . . . . . . . . . . . . . . . . . 1. r + + . . . . . . 3. 1. . + . 1. .
| + b + . . . . . . . + . |
| . . . . . . . . . 1. . . . 1. m. . m. . . . . . . . . . . . .
| . + + . . . . . + b . . . . . . . . . . . + . . + 4. . . . . . . . . . . . . . . .
| . . . 3b + . . . + 1+ |
| . . 1. . . . . 1+ . . . . . + 3. . + . + . . . . m. . . . . .
| . . . . . . . . . . . . . 1. . . . . . . . m. m. . . . b . . . . 1. . . . . . .
| . . . . + . . 1. . . . |
| . . . . . . . . . + + . + . . . + . . . . + + . + + . . . . . . .
| . . . . . . . . . . . . . . . . . . + . + . . . . + . . + . . + . . . . . . . . . .
| . . . + . . . . . . + . |
| . . . . . . . . + . + . . . . + . . . . . + . . . . . . . . . . .
| . . . . . . . . . + + . . + . . . . . . . . . . + . . . . . . . . . . . . . . + . + | . . . + . . . . . . + + |
| . . . . . . . . . . . + . . + . . . . . . . . . . . + . . + + . .
| . . . . . . . . + . + + . . . . + . . . . . . . . . + . . . . . . . . . . . . + . .
| . . . . . . . . . . . + |
| . . . . . . b . . b . 1. . 1. . . . . . . . . . . . . . . . . .
| . . . . . + . . . . . . . 1. . + . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . 3|
| . . . . . . . . . . . . . . . . + . . . . . . . . . . . . . + . .
| . . . . . . . . . . . . . . . . . . + . 1. . . . . . . . . . . . . + + . . . . . .
| . . + . . . . . . . + . |
| . . . . . . . . . 1. . . . mb . . . . . . . . . + . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . m 1. m. . . . . . . . . .
| . . . . . . . . . . . . |
| . . . . b . . . . . . . . + + . . . . . . . . . . . . . . . . . .
| . . . + . . . . . . . . . + . . . . . . . . . . . . . . . 1. . . . r . . . . . . .
| . . . . . . . . . . . . |
| . . . . . . . + . . . . . . . . . . . . . . . . . . . . . . 1 1r
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1. . 1. . . . . . . 1. .
| . . . . . . . . . . . . |
| . . . . . . . . . . . . . . . . . . . . . . . . . . + + . + . + .
| . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + + . . . . . . . . . . .
| . . . . . . . . . . . . |
| . . . . . . . . . . . . . . . . . . . . . . . . . . + . . . . . .
| . . . . + + . . . . . . . . . . . . . . . . . . . . . . . r r . . + . . . . . . . .
| . . . . . . . . . . . . |
| . . 1. . . . . . . . 1. . . 1. . . 3. 3. . . . . . . . . . .
| . . . r . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . |
CHAPTER 8
RESULTS: GRASSLAND AND WETLAND
COMMUNITIES
The results of the floristic analysis of the forest vegetation are given in Table
8.1. All references to species groups in this Chapter refer to this Table. Five
communities were recognised. The classification of these communities is as
follows:
1. Phragmites australis – Typha capensis Tall Closed Hygrophilous
Grassland
2. Pycreus polystachyos – Schoenoplectus senegalensis Short open
Hygrophilous Sedgeland
3. Pycreus polystachyos – Cyperus rotundus Short Open Hygrophilous
Sedgeland
4. Imperata cylindrica – Sporobolus fimbriatus Temporary Hygrophilous
Grassland
5. Paspalum distichum – Eragrostis chloromelas Temporary Hygrophilous
Grassland
92
Description of Grassland and Wetland Communities
1. Phragmites australis – Typha capensis Tall Closed Hygrophilous
Grassland
This community dominated by the diagnostic reed Phragmites australis is
characterised by species group A. Typha capensis is a further diagnostic
species. The widespread species of species groups F, G and H are however
mostly absent in this community.
Very few other species occur, though some species (species group H) may
be found scattered in this community. The alien woody invader Psidium
guajava is often found in these reed communities, while species such as
Ipomoea cairica and Microsorium scolopendrum can also be present.
This community usually grows in or close to water sources like rivers or
wetlands where it forms dense stands. Although it has very little grazing
value it does play an important ecological role. It protects soil from flooding
and acts as a water purifier by filtration. It also provides habitat for various
animals and birds (Van Oudtshoorn, 1999).
In comparison to findings of a predominant importance value of 66.1 %
(Venter, 1972), Phragmites australis occurs to a much lesser extend during
2001. Although widely distributed throughout the Richards Bay area it only
occurred locally in dense stands. Although another reed species, Phragmites
mauritianus was recorded in previous studies (Venter, 1972), as a species
93
occurring in wet sand beds, none were encountered in sampling plots of this
study.
This was verified according to specified differences between
Phragmites australis and Phragmites mauritianus (Gordon-Gray and Ward,
1970).
The disappearance or decreased occurrence of Phragmites mauritianus
surrounding Lake Mzingazi was linked to an abrupt rise in lake level in 1984
(Weisser et al. 1985).
Furthermore, the pond weeds Potamageton
schweinforthii and Potamageton pectinatus disappeared from Lake Bhangazi
South (Hart and Appleton, 1997), the wilderness Lakes and Swartvlei in the
Eastern Cape (Taylor 1983, Whitfield, 1984). This was attributed to severe
lake level fluctuations (Weisser et al. 1985).
Phragmites australis was widely spread throughout the area of Richards Bay
and covered almost all of the wetland and marsh areas around the bay and
the wetlands between the dunes (Venter, 1972). The species’ habitat was
almost constantly covered with standing or at least slow flowing water. It
survived in areas of salt water on the banks of the bay and in clay and saline
in comparison to stands growing in sandy and alkaline soils between the
dunes (Venter, 1972). For this species to decrease to the extent it did from
1972 to 2001, it can be assumed that a drastic change in habitat must have
occurred. The possibility of extensive drainage for development of the
Richards Bay municipal area over the years might have lowered the water
table to such an extent that Phragmites australis no longer had optimal
conditions for growing.
94
Phragmites australis forms part of the dominant vegetation on the periphery
of most perennial water bodies and in some swamp areas. These swamps
includes the extensive Papyrus stands that fringe onto open-water and
Phragmites reed-beds, which often occur adjacent to Swamp Forest.
Reedswamps consist of dense, often monospecific Cyperus papyrus
communities up to 3 metres tall. No sample plots were placed in Cyperus
papyrus communities.
Photo 8.1: Cyperus papyrus beds occurring in the back swamps of large
water bodies such as Lake Chubu, Nsezi and Mzingazi (April 2002).
95
Photo 8.2: C. papyus stands with E. grandis invasion at the back
Of the Mdibi Swamp area at the northern shores of Lake Mzingazi (April
2002).
Typha capensis is a perennial herb which is wide spread along water courses
in marshy areas and can reach heights up to 2.5 meters (Pooley, 1998).
Phragmites australis and Typha capensis seldom grow together, but they
form more or less monospecific stands (Table 8.1). In wetland areas the two
species will frequently occur in separate stands next to each other, but
seldom mixed. This was also noted by Venter (1972).
Cyperus prolifer is a perennial herb which also occurs in colonies along the
KwaZulu-Natal coast as well as in well aerated water of streams and
marshes (Pooley, 1998). No sample plots were placed in this community,
described by Venter (2003), from Mfabeni swamp at St Lucia.
96
2. Pycreus polystachyos – Schoenoplectus senegalensis Short open
Hygrophilous Sedgeland
This wetland community is found scattered throughout the study area,
mainly in bottomland situations adjacent to small streams. It is characterised
by species group B, which is rather poorly defined. The widespread species
of species group F are however mostly absent in this community. Diagnostic
species include the sedges Schoenoplectus senegalensis and Bulbostylis
hispidula and the grass Andropogon eucomis.
The sedges Cyperus rotundus and Pycreus polystacyous and the grass
Digitaria eriantha (species groups G and H) are also present in this wetland
community.
Cyperus rotundus is a perennial sedge growing between 60 to 150 mm. The
species grows in moist and usually disturbed places. The species is also
widely used as traditional medicine around the world. This species as well
as Cyperus esculentus, is reputed to be one of the most formidable weeds in
KwaZulu-Natal and most of the world, spreading rapidly by means of small
tubers (Pooley, 1998).
Pycreus polystachyos is a perennial sedge ranging from 0.6 to 1 metre in
height. This species is common in moist areas including slightly saline
conditions and warm temperate regions throughout the world (Pooley,
1998).
97
Schoenoplectus senegalensis is distributed through Maputaland. The species
is tufted, glabrous annual sedge (Gordon-Grey, 1995).
3. Pycreus polystachyos – Cyperus rotundus Short Open Hygrophilous
Sedgeland
This wetland community also occurs scattered thoughout the study area in
bottomland situations where water accumilate during the rainy season. The
community is characterised by species group C. Several diagnostic species
were recognised, including the tree Syzygium cordatum, the shrubby
Chrysanthemoides monilifera and Helichrysum kraussii, the grass Setaria
sphacelata, the sedge Carex zuluensis, the fern Cheilanthes viridis and the
forb Hydrocotylebonariensis.
Several other more widespread species from species groups F, G and H may
also be present in this community. The most frequently found species
include the grasses Imperata cylindrica and Paspalum distichum, the sedges
Cyperus rotundus and Pycreus polystachyos, the forbs Ludwigia octovalvis
and Commelina erecta and the woody alien invader Psidium guajava.
Imperata cylindrica usually grows in poorly drained soil such as wetlands
and river banks where it can form dense stands. It does grow in other habitat
types in regions with high rainfall (Van Oudtshoorn, 1999). It is poorly
utilized by animals due to the general hardness of the leaves. It is however
an important soil stabiliser in many tropical regions of the world (Van
Oudtshoorn, 1999). Imperata cylindrica may form the predominant plant
98
species in some area (Table 8.1). Venter (1972) indicated that Imperata
cylindrica may form communities which may invade moist grassland.
Syzygium cordatum is a medium sized evergreen tree species occurring in
wooded grassland, forest and along watercourses in KwaZulu-Natal and
Eastern Cape, and sometimes found in groves (Pooley, 1993). Syzygium
cordatum is distributed throughout this wetland community. This species
starts occurring more frequently in wetter grassland areas of Richards Bay.
Localities where Syzygium cordatum was recorded were all in the vicinity of
Lake Nzeze and Lake Mzingazi, where various man-made drainage channels
and natural streamlets were observed.
Helichrysum kraussii is an aromatic shrublet which occur in colonies of the
coastal grassland and open woodland (Pooley, 1998).
H. kraussii was
observed in drier and elevated grassland open spaces where soil water
content was lower due to water leaching out to lower laying grasslands
suppressions in Richards Bay area.
Old lands, Secondary Mixed Dune Grassland and Dwarf Shrubland covered
the largest area of Richards Bay in 1937 (Weisser and Müller, 1983). This
was the result of destruction of the original forest by humans, through fire,
clearing of forest for cultivation and grazing (Weisser and Müller, 1983). In
these areas grasslands were dominated by grasses such as Imperata
cylindrica and dwarf shrubland with species such as Chrysanthemoides
monilifera and Helichrysum kraussii (Weisser and Müller, 1983).
99
Table 8.1: Grassland and Wetland Communities
|
Community nr
|
Releve nr
Species Group A
Phragmites australis
Typha capensis
Species Group B
Schoenoplectus senegalensis
Bulbostylis hispidula
Andropogon eucomus
Species Group C
Cheilanthes viridis
Hydrocotyle bonariensis
Setaria sphacelata
Syzygium cordatum
Chrysanthemoides monilifera
Carex zuluensis
Helichrysum kraussii
Species Group D
Sporobolus fimbriatus
Chromolaena odorata
Centella asiatica
Lantana camara
Bridelia micrantha
Panicum repens
Aristida junciformis
Schinus terebinthifolius
Crotalaria natalitia
Abildgaardia ovata
Schistostephium rotundifolium
1
|
2
|
1 1 1 1 2 |
3
|
4
|
5
1 1 | 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 | 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 | 2 2 2
|
4 4 4 4 4 6 0 1 2 6 0 | 2 3 4 5 6 6 6 7 7 0 0 | 0 0 0 0 0 1 1 1 1 2 3 3 4 4 5 5 5 6 8 8 | 8 8 9 9 9 9 9 0 0 0 0 0 0 0 1 1 1 1 1 2 2 3 3 3 | 3 3 3
|
0 2 4 5 6 7 8 9 8 1 6 | 7 0 3 0 1 5 9 0 6 2 3 | 4 5 6 7 9 0 2 3 8 7 3 4 5 6 1 6 7 9 0 1 | 8 9 5 6 7 8 9 0 1 3 4 5 8 9 1 2 3 5 6 3 9 0 1 2 | 3 4 5
|
3 5+ + 5+ 4a a 4b | . . . . . + .
| + .
5 5+ + . + a . .
| . . . . .
3. . .
| a a b a a . . . + . . . . . + . . . . .
| . . . . . .
1. . . . . . . . . . . . + . . + .
| . . .
1. . . . .
| . . . . . . . . . a . . . . . . . . . .
| . . . . . . . . . . r . . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . .
1a . + .
| . . . . . . . a . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| + a . . . + . . . . .
| . . . . + . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| . . b . . . + + . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| + + . . r + . . + + . . .
| . . + . . . + . . . . . . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| + . . . .
1. . . . .
| . . . + + . . . . . . . + + . . . . . + | . . . . . . . . . + . + . . . . . + . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . + a + . . . . . + + | . . . . . . . + . . . . . . . . . . . . . . . .
| . . .
| . . . . . . . . b . .
| . . . . . . . . . . .
| 1. . . . .
| . b .
| . . . . . . . . . . .
| . . . . . . . . . . .
| + m 1. . + . . . . . . . . . . . . . .
| . . . . . . . . . . . .
1. . . . . . . . . . .
| . . .
1. . . .
| . . . . . . . + . + . . . a . a . . . .
| . . . + . . . . . . . . . . . . . . + . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . b . . . . . b . . + . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . .
3. .
| . . .
| . . . . . . . . . . .
| . . . . . . + . . + .
| . . . . . . . . . . . . . . . . . . . .
| + . + + + . . + . + . + . . + + + + . . + + . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| 1+ + b + b . . b r
3 4. m . + . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . b . . . . . .
| . . . . . . . . . . . . . + . . . . . .
| . + + + + . . + + + . + . . + . + . . . + + . .
| . . .
| . . . . . . . . . . .
| . . . . . . . .
| . . . . . . . . . . a | . . . . . .
1. . .
1+ .
1 5. .
1 1. . . . . b . .
| . . + . . . . . . . . . . . . . . . . . . .
4.
3.
1. .
| 1. . . . . . . . . . . . . . . . . + .
| + + . . . + 3. . . . + + m . . . . . . . . . + | . . .
| . . . . . . . . . . + | . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . r . . . + . . + . r . . . . . . r . . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . + . . . . . . . . . .
| . . . . . . . . . + . + . . . . . . + a + . . .
| . . .
| . . . . . . . . . . .
| . + . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . + . + . . . . . . . + . . + . . . . + . . .
| . . +
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| .
1m 1. . . . . . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . + . + + . . + + . .
| . . +
| . . . . . . . . . . .
| . . . . . .
1+ . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . + . . + . . . + a . . + .
| . . .
| . . . . . + . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . + . + . . . . . . . + . . . . .
| . . .
3+ .
1 1 | . . .
Species Group E
Dissotis canescens
Eragrostis chloromelas
Chloris gayana
Pycnostachys reticulat
Species Group F
Imperata cylindrica
Ludwigia octovalvis
Paspalum distichum
Species Group G
Cyperus rotundus
Digitaria eriantha
Species Group H
Pycreus polystachyos
Psidium guajava
Commelina erecta
Microsorium scolopendrum
Ipomoea cairica
Rare Species
Cyperus prolifer
Commelina africana
Dactylocteni australe
Smilax anceps
Tagetes minuta
Panicum maximum
Cymbopogon validus
Rhus chirindensis
Hibiscus surattensis
Fimbristylis obtusifol
Melinis repens
Asystasia gangetica
Pycreus macranthus
| . . . . . + . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| + + .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| . . a
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| . . +
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . . . . . . . . . . . . . . .
| + . .
| . . . . . . . . . . .
| . . . . . . . . . + a | . + a 1. + + 1+ . . . . . + . . . . .
| . a . + . . + . a . . a . . . . . . . . . . . .
| m 1. . . . . . . b . . . . . b 1+ . b | . . . . + .
1. . . . . . + . . . . + .
| . . .
| . . . . . . . . . . .
| . . . . + . . . . . .
| . . . . . . . . . . . . . . a . . + a a | a . . . . a . . . a . . . . . . . . . . . . . .
| a a a
| . . . . . . . . + . .
| . .
| . + + + . . + . + + . + . a + + + + + + | . . . . . a . . . . . + . a + . + . + a + + + + | a 1+
| . . . . . . . . . . .
| . + . . . + + . . + + | . . . . . . + . . . . . . . . . . . . .
| + . . + + . . + . . . . . . . . + . . . . . . .
| . . .
| . . . . . + . + + . .
| a b . . a 1b 1+ a + | + . + + + . . . + . + + + a . + + + + + | . . . + . . . + . + a + + . + . + . . . + + a .
| + + .
| + . . . . . . b . . .
| . . . . . . . . . . .
| 1 1 1. .
| . . . . . . + . + . .
| . . . . . . + + . + .
| . + . + + + . . + + + . . . . + . + . .
| . + . . + 1. .
3+ . .
1. . + .
3. b | . . + . . . . . . . .
1+ . .
1 1. + r + + + .
1.
3. . . + r . + | . . r
| + . . . + + . . . . + . . + . . . . . + . . . + | . . .
1 | . + + . b + . . . . . . . . . . . . + . . . . .
| + . .
| . . . . + . . . . . . . . . . + + + . + | + . . . . . . . . . . + . . . . . . . . . + . .
| . . +
| . . . . . . . . . . .
| + 1. . . . . + . . .
| + . . . . . . . . + . . . . . . . . . .
| . + . . . . . . . + . . . . . . . . + . . . . .
| . . .
| + . . + . . . . + . .
| . . . . . + . . . + .
| . . . . . . . . . . . . . . . . . . + .
| . . . . . . + . . . . . . . . . . . . . . . . + | . . .
| . . . . . . . . . . .
| . . + . . . + . . . .
| . . . . . . . . . . . . . . . . + . . .
| . . + . . . . . . + . + . . . . . . . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . b . .
| . . . . . . . . . . + . . . + . . . + .
| . . . . . . . . + . . . . . . . . . + . . . . .
| . . .
| . . . . . . . . . . .
| . . . . r . + . . . .
| + . . . . . . . . . . . . . . . . . . .
| . . . . . . . . . . + . . . . + . . . . . . . .
| . . .
| . . . . . . . . . . .
| . . . . . . . . . . .
| . . . . . . + . . . + . . . . . . . . .
| . . . . + + + . . . . . . . . . . . . . . . . .
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1b . . + b . . .
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1. . .
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1. . . . . . . . . .
1. . .
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1. . .
Cyperus papyrus
Conostomium natalense
Sida cordifolia
Phoenix reclinata
Eucalyptus grandis
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3. b . . . . . . . . . . . . . . . . .
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Rhus nebulosa
Fimbristylis complanat
Helichrysum aureum
Lactuca indica
Indigofera spicata
Helichrysum auriceps
Rubus fruticosus
Carex cognata
Desmodium incanum
Alinula paradoxa
Hypoxis angustifolia
Eriosema psoraleoides
Persicaria serrulata
Eragrostis ciliaris
Bidens biternata
Cuscuta campestris
Chamaecrista mimosoide
Melia azedarach
Ipomoea purpurea
Hibiscus tiliaceus
Asplenium monanthes
Senecio deltoideus
Diheteropogo amplecten
Gomphocarpus physocarp
Helichrysum aureoniten
Trema orientalis
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1. m . . . . . . . . . . . . . r . . .
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4. m . . . . . . . . . . . . . . . . . . .
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3. . . . . b . . . . .
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1. . .
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1. . . . . . . . . . . . + | . . .
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Acacia karroo
TRIHANN0
Ipomoea obscura
Crotalaria natalensis
Hewittia species
Dicliptera clinopodia
Zantedeschia aethiopic
Crotalaria macrocarpa
Oxalis corniculata
Sutera floribunda
Barleria meyeriana
Cyanotis speciosa
Brachylaena ilicifolia
Pteridium aquilinum
Oxygonum dregeanum
Ethulia conyzoides
Eragrostis gummiflua
Dumasia villosa
Desmodium dregeanum
Desmodium setigerum
Ischaemum fasciculatum
Oldenlandia herbacea
Gnidia kraussiana
Nidorella undulata
Lycopodium cernuum
Eleocharis limosa
Juncus kraussii
Themeda triandra
Lobelia coronopifolia
Strelitzia nicolai
Ficus sur
Pinus elliottii
Ficus trichopoda
Pergularia daemia
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1 3 | . . . . . . . . . . . . . . . . . . . . . . . .
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1a . . . . . . . . . . . . . . .
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1.
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Passiflora subpeltata
Crocosmia aurea
Tricalysia capensis
Senecio tamoides
Cissampelos mucronata
Strychnos spinosa
Pisonia aculeata
Rubus flagellaris
Laportea peduncularis
Ipomoea congesta
Pleurostylia capensis
Eugenia natalitia
Ipomoea alba
Senecio madagascarie
Scleria poiformis
Thelypteris dentata
Canthium inerme
Cyperus dives
Uvaria caffra
Xymalos monospora
Pinus species
Eucalyptus camaldulens
Cnestis polyphylla
Asparagus setaceus
Strychnos madagascarie
Justicia campylostemon
Ranunculus multifidus
Pavetta lanceolata
Rumex sagittatus
Pavonia burchellii
Manilkara discolor
Myrica serrata
Scleria angusta
Abutilon grantii
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| . . . . . . . . . . . . b . . . . . . . . . . .
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Vangueria infausta
Coleotrype natalensis
Acacia nilotica
Senecio polyanthemoi
TRIHPIL0
Rhoicissus tridentata
Hibiscus vitifolius
Solanum retroflexum
Scleria dregeana
Indigofera micrantha
Ursinia tenuifolia
Euclea crispa
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Lotononis corymbosa
Lagynias lasiantha
Acacia niloti s. kraus
Asclepias albens
Argemone mexicana
Strychnos henningsii
Rhynchosia caribaea
Solanum nodiflorum
Becium obovatum
Rhynchosia monophylla
Rabdosiella calycina
Hibiscus pusillus
Berkheya setifera
Pennisetum clandestinu
Senecio napifolius
Schinus molle
Cyathea dregei
Canthium setiflorum
Arundo donax
Helictotrich turgidulu
Melanthera scandens
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1. . . . . . . . . . .
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| . . . m . . . . . . . . . . . . . . . . . . . .
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1.
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Hibiscus calyphyllus
Cycnium racemosum
Ficinia laciniata
Nidorella auriculata
Cynanchum obtusifolium
Indigofera dimidiata
Scabiosa columbaria
Monocymbium ceresiifor
Gnidia calocephala
Teucrium kraussii
Schoenoplect scirpoide
Paspalum scrobiculatum
Ipomoea ficifolia
Aristea juncifolia
Indigofera velutina
Tephrosia grandiflora
Strychnos decussata
Premna mooiensis
Canthium kuntzeanum
Canna indica
Cyperus obtusiflorus
Justicia flava
Chamaecrista plumosa
Agrost barbul v. barbu
Rhinacanthus gracilis
Ornith tenuif s. tenui
Justicia protracta
Eragrostis cilianensis
Leersia hexandra
Eragrostis superba
Pycreus pelophilus
Miscanthus capensis
Catharanthus roseus
Bidens pilosa
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1. . . . . . . . .
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| . . . . . . . . . r .
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Lippia javanica
Hyparrhenia cymbaria
Berkheya speciosa
Buchnera species
Pavetta bowkeri
Monopsis stellarioides
Andropogon appendicula
Pentanisia prunelloide
Urochloa panicoides
Senecio inornatus
Androcymbium eucomoide
Hibiscus aethiopicus
Utricularia livida
Panicum ecklonii
Mariscus dubius
Chironia purpurascens
Gnidia burchellii
Helichrysum decorum
Wahlenbergia grandiflo
Rhus discolor
Verbena bonariensis
Setari sphace v. seric
Senecio macroglossoi
Mariscus solidus
Brachylaena discolor
Casuarina equisetifoli
Isoglossa woodii
Halleria lucida
Oplismenus hirtellus
Stenochlaena tenuifoli
Rubia cordifolia
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CHAPTER 9: GENERAL DISCUSSION
The study area of the Coastal Forest or Thornveld (Low and Rebelo, 1998),
was observed as a mosaic of vegetation types, which occur from just above
sea level to about 300 meters in altitude. This mosaic of vegetation types
was also mentioned in previous publications (Low, and Rebelo, 1998). The
area is more or less flat to gently undulating terrain with slope gradients
rarely steeper then 8 degrees. However, the region is also deeply dissected
by the many rivers and streams which drain eastwards across KwaZuluNatal.
The primary aim of this research project was to delimit and describe the
different plant commuities recognised within the area under the jurisdiction
of the Richards Bay Municipality and providing an indication of the relative
conservation importance of these plant communities.
The study identified three major vegetation types which comprised 3
floristically distinct plant communities.
1. The Dune or Strand vegetation containing four plant communities
2. The Forest vegetation containing four plant communities
3. Grassland and Wetland vegetation containing five communities.
103
Dune vegetation
The Dune vegetation was classified into four plant communities (Table 6.1).
The Carprobotus dimidiatus – Gazania rigens Dune vegetation, also known
as the Strand Community, although many authors refer to it as the Dune
Pioneer community (Donnely and Pammenter 1983; Weisser and Backer
1983).
Breen (1979) however, differs in opinion and notes that this
community represents a stage of succession of dune forest.
Barbour, Burk and Pitts (1980) states that the dune pioneer community
forms part of a toposequence, where different distances from a stress, in this
case salt spray, influence the topographical distribution of plants. Strong
winds causes salt spray and form new dunes, which expose or cover beach
pioneer plants. The beach sand of northern Kwazulu-Natal consists of silica
quartz and has a high salt content (Tinley 1985). The sand also has a high
infiltration rate and rapidly dries out after rain and due to full sun exposure
also experiences high extremes of temperatures.
It is reasoned that the pioneers do not extend further into the more sheltered
areas of the back dune communities and adjacent shrub thickets because of
their adaptation to extreme environmental conditions or that they are unable
to compete with species occurring in these communities (Lubbe 1996).
The species composition of the Dune vegetation shows many similarities
with those found in previous studies (e.g. Weisser 1978, Weisser and
Marques 1979, Weisser et al. 1982), especially with the vegetation occurring
on the foredunes.
104
The species composition recorded in the study area is, for example, similar
to that found in studies done on beach pioneer communities in the Mhlalazi
– Richards Bay and Mtunzini areas to the south (Weisser and Müller, 1983)
and studies done to the north (Lubbe 1996).
Scaevola plumieri is the main colonizer on the foredunes. This species is
also said to be the most efficient sand binder in these communities, but its
efficiency and ability to colonize the beachfront seems to be declining south
of the Fish River Mouth in the Eastern Cape (Weisser and Müller, 1983)
indicating a more tropical affinity.
The dune pioneer community does not have high species diversity, but
fulfils a very important function in the stabilizing and formation of dunes. It
acts as a barrier providing some protection to the dune scrub community.
Behind the foredune and dune pioneer community, the salt spray and sand
deposition decreases and it is in this area where a change in vegetation can
be observed on the mid-dune areas where dune scrub community becomes
more prominent (Donnelly and Pammenter, 1983). In this study this
vegetation is represented by the Cynanchum natalitium –Carprobotus
dimidiatus Mid-dune community and even the Chrysanthemoides monilifera
– Carpobrotus dimidiatus Dune Scrub
Behind these foredunes, on the backdunes, dune scrub communities occur.
These are described as Chrysanthemoides monilifera – Casaurina
equisetifolia Dune Scrub.
105
These results compare well with results found by Weisser and Backer (1983)
in the Mtunzini area. However, the Passerina sp. Scrub zone, which occurs
between the coastal scrub thicket and the dune pioneer communities in the
Mtunzini and Mhlalazi – Richards Bay area (Weisser and Müller, 1983; and
Weisser and Cooper, 1993), seems to be absent within the current study area.
This trend was also observed by Lubbe (1996), who noted that the coastal
scrub thicket in the Kosi Bay Forest reserve, bordered directly on the pioneer
community. The absence of the Passerina sp. Scrub community might be
attributed to a lack of space or suitable habitat (Lubbe, 1996).
In the case of the Chrysanthemoides monilifera – Casaurina equisetifolia
Dune Scrub, Casuarina equisitifolia an alien a pine-like angiosperm, which
dispersed seeds and occurs naturally on Indo-Pacific Islands, became
established. It is not an aggressive invader, but dense growth, shade and
heavy leaf litter inhibits succession of natural forest (Tinley, 1985). Few
other plants grow in Casuarina stands (Table 6.1). The reason that this
species was planted in the study area was to bind the sand as to prevent local
destruction of coastal dune forest by being covered with sand (Lubbe, 1996).
Management of these stands can include the felling of these trees in order for
drift sands to re-assume its natural geomorphic functions and to allow
natural vegetation to re-establish in the study area.
Forest
The second vegetation type occurring within the study area is Forest. Four
forest communities were identified.
106
Swamp and riparian forest are widespread in the Zambezian region, but
limited to specific habitats, while in the eastern half of Africa, afromontane
and coastal forests have a localised and fragmented distribution (White,
1980).
The Isoglossa woodii – Macaranga capensis Tall Closed Forest is the best
example of primary coastal forest within the study area. Many fine examples
of forest trees occur here, though a degree of degradation resulted in the
presence of alien invader species, notably Psidium guajava.
A severely degraded form of the coastal forest is represented by the
Chromolaena ordonata – Melia azedarach Short Forest, where several alien
species invaded, e.g. Chromolaena odorata,Melia azedarach, Lantana
camara and Eucalyptus grandis. This could indicate that pristine coastal
forest will change to a degraded forest type dominated by alien species if not
protected against human caused impacts.
The natural climax grasslands of the areas within which the three outlying
suburbs occur, would, according to Acocks (1953), have formed part of the
Coastal Forest and Thornveld One variation of this veld type, Typical Coastveld Forest would have occurred in the study area (Discussion document,
1998). Acocks also stated that when this forest is removed, it becomes
replaced with Thornveld. The dominant species of thorn tree is Acacia
karroo while the grass component includes species such as Aristida
junciformis, Eragrostic spp., Sporobolus spp., Hyperrhenia spp., and
occasionally Themeda triandra.
107
As observed by Venter (1972) Acacia karroo may form a community on the
outer bounderies of the forest communities where it separates the grassveld
of the blowsand from the rest of the forest community. This species may
occur in loose standing stands within other forest communities, as shown in
species group C (Table 7.1). Previous observations of active A. karroo
encroachment into adjacent grassveld and dune wetland areas, where
sufficient moisture conditions exists (Venter, 1972 and Matsau, 1999) could
be supported with observations of this study.
Fires in these vegetation types are rare and restricted to occasional extreme
fire weather conditions (Van Wilgen et al., 1997). Dry or deciduous forests
have a canopy, which is near – continuous and multi – layered, dominated
by deciduous trees. These types of forests occur in areas where there is a
two to three month dry period in the year. Dry forest would be more prone
to fire than evergreen forests, and would therefore burn periodically because
of the accumulation of fuel in the form of dry leaf and twig litter (Van
Wilgen, et al., 1997).
Swamp Forest
Another Forest community is Barringtonia racemosa – Ficus tricopoda Tall
Swamp forest community which forms small dense stands along rivers,
drainage channels and on the shores bordering Lake Mzingazi.
This
community is severy impacted on by urban development in the Richards Bay
and surrounding area. Some human settlements that have been developed on
the borders of the small remaining stands of this community caused a
decrease of the species, especially due to slash and burn cultivation, which
also increased the size of canopy gaps. This enabled other woody species to
108
invade and regenerate, increasing the numbers and density of climbing
plants (Reavell, et.al., 1998).
Alien invasive species like Chromolaena
odorata also invaded into these open gaps.
Reavell et al. (1998) identified the environmental impact of urban and rural
development on Richards Bay Swamp Forest. It was noted that 24 species of
angiosperms were removed for use in traditional medicine, by slash and burn
cultivation practices and for building material.
This could lead to the
disappearance of this plant community and the habitat for its associated
animals. This also led to an increase of alien invader plants such as
Chromolaena odorata.
The drainage and dessication of the hydromorphic peat due vegetable
gardening also had an impact on turbidity levels in Lake Mzingazi. From
June to July 1996 there was evidence of an eight fold increase in turbidity
and a fifty fold increase in soluble reactive phosporus in the Mdibi River
channel after heavy rainfall (Reavell, et.al., 1998). If this process continues
it could smother submerged macrophytes in Lake Mzingazi.
Excess
nutrients, such as phosphorus, being washed into the lake will also cause
eutrophication of the lake water, which may cause increases in water
treatment and associated costs.
Mangrove Forest
The fourth forest vegetation type recognised is the Avicennia marina Short
Mangrove Forest with stands dominated by a single mangrove species,
namely Avicennia marina, which is restricted to areas south of Richards Bay
harbour.
109
Mangrove forests with more than one mangrove species have been described
in very few areas in South Africa. The Kosi Bay Forest Reserve to the north
of Kwazulu-Natal coast has six mangrove species (Lubbe, 1996). These
species included Acrostichum areum, Avicennia marina, Bruguiera
gymnorrhiza, Ceriops tagal, Lumnitzera racemosa and Rhizophora
mucronata (Steinke, 1995, Lubbe, 1996). In the current study of Richards
Bay only Avicennia marina was recorded in the sample plots.
Mangroves fulfill important functions as breeding and feeding grounds for
marine fauna species and also protect shorelines against erosion and
flooding. Mangroves also provide a source of reduced carbon in the form of
leaves, wood and other litter that falls from the trees and contributes to
detritus-based food chains in estuaries (Steinke, 1995). Management of the
mangrove community would therefore include controlled utilization as well
as the maintenance of the natural hydrolocical processes occurring in the
study area.
The ecological importance of mangrove swamps in the tropics and subtropics has not been widely recognised. Roughly one-fourth of the world’s
coastline is dominated by mangroves. Evidence indicates that mangroves
are highly productive ecosystems and are responsible for the production of
large quantities of organic matter, the export of this organic matter and
particularly fallen leaf material, from under the mangroves into surrounding
deeper water (Hasler, 1975). Mangrove communities are also responsible
for the transformation, as it decays, of the leaf material into detritus particles
covered with bacteria, micro-algae and protozoans and permeated with
110
fungi. The utilization of mangrove detritus particles as food by a large
group of consumer organisms contribute to mangrove communities’
ecological functionality (Halser, 1975).
The importances of Swamp Forest are set out in unpublished report (1998)
as follows:
- This vegetation type provides deep-rooted stabilization to hydromorphic
soil.
- Together with other wetland plants, assists in removing nutrients such as
nitrates and phosphates from runoff, preventing eutrophication of
freshwater sources.
- Contributes to the filtering properties of wetland systems, which are able
to reduce levels of micro-organisms such as the bacteria, E. coli.
- Contributes to the maintenance of very scarce habitats which is required
by various species of fauna, such as amphibians and birds.
- Although Swamp Forest plant species are mostly intolerant of fire, it does
create an effective firebreak.
Wetlands
The third vegetation main type is the Grassland and Wetland vegetation.
Five communities were recognised, the first three being wetlands and the
last two represent moist grasslands.
The mosaic of Coastal Forest and Hygrophilous Grassland still occurs where
the water table is raised in the proximity of coastal forest, which creates an
environment that is suitable for hygrophilous grass species to establish and
occupy the herbaceous layer within the vegetation mosaic (CSIR report,
111
1993). These communities are influenced by the topography of the study
area, which plays a major role in the origin and the maintenance of these
grassland communities. With topography, slope and water table depth being
some of the most important environmental factors by which grassland was
differentiated.
The absence of trees and shrubs and the dominance of
grasses distinguish the grasslands from the forests, thickets and woodlands.
A low water table depth differentiates the coastal grasslands from the
hygrophilous grasslands, which has a high water table (Lubbe, 1996).
Photo 9.1: Phragmites australis - Typha capensis Tall closed Hygrophilous
Grassland community with P. guajava encroachment fringing (June 2002).
112
The Phragmites australis – Typha capensis Tall Closed Hygrophilous
Grassland is quite unique with either Phragmites australis or Typha capensis
dominant and very few other species present.
The large Reedswamp community occurs along water courses and the
backswamps of the fresh water lakes. Reedbeds can also play an important
role in the successional development of Swamp Forest by impeding the flow
of flood waters and causing the deposition of silt (Moll, 1976). Once the
ground surface has risen above the permanent water level, Swamp Forest is
able to develop. Swamp Forest trees are found growing on the periphery of
most of the reedbeds in the study area and within major drainage channels.
Reedswamps are important in that it is a unique vegetation type and create a
buffer between open water and the terrestrial environment (Unpublish
report, 1993).
The Pycreus polystachyos – Schoenoplectus senegalensis Short open
Hygrophilous Sedgeland and the Pycreus polystachyos – Cyperus rotundus
Short Open Hygrophilous Sedgeland are both wetland communities within
the study area, dominated by the sedges Pycreus polystachyos and Cyperus
rotundus.
Permanent wetlands (excluding the seasonally – wetted hydromorphic
grasslands) make up a small fraction of the southern hemisphere African
landscape.
Phragmites – dominated reedbeds are associated with most
rivers and burn frequently (two to five years), whereas the peat – producing
Papyrus swamps burn once every century or more (Van Wilgen et al.,
1997).
113
Marshes and other wetlands in which there is a profuse growth of aquatic
plants are common in many parts of the Richards Bay Municipal area.
There is a certain flux of nutrients to the marsh from groundwaters, surface
flow, and direct precipitation and gas exchange.
Wetlands are often
considered low – value land since in their normal condition they cannot be
used for most agricultural activities or urban development, and increasing
pressure exists to drain marshes to provide higher – value land for suburban
development (Hasler, 1975).
Hygrophilous grassland communities composed of hygrophilous grass
species also occur within depressions in the study area, where the water table
is relatively near to the soil surface.
These depressions are seasonaly
flooded after heavy rains and may occasionally become waterlogged. The
community growth appears to be maintained by fire, but due to the moist
environment, fires burn at lower temperatures than the surrounding
Shrublands. Here the state of the water table inhibits succession towards a
woody community.
The importance of wetlands are set out as follows (Unpublished report,
1998):
- Wetland communities attenuate high velocity runoff.
- These communities retain large quantities of nitrates and phosphates.
- By retarding runoff wetland communities cause deposition of silt, thereby
enhancing the life of rivers and other large water bodies.
114
- Wetlands are habitats for economically important plants such as Juncus
kraussii (Ncema grass), which is used for the making of baskets and
mats.
- Wetlands are habitats for a variety of birds and other fauna playing vital
roles on the ecology of the system.
Grassland
The Imperata cylindrica – Sporobolus fimbriatus Temporary Hygrophilous
Grassland and the Paspalum distichum – Eragrostis chloromelas Temporary
Hygrophilous Grassland are both moist grassland types.
The latter community is severely encroached by alien woody species,
indicating a degraded form of grassland in the area.
Moll and White (1978) and White (1983) distinguished two broad types of
grassland in the Tongaland-Pondoland Regional Mosaic, namely edaphically
controlled grassland associated with scattered palms on poorly drained soil
and secondary fire-maintained grassland that has replace anthropogenically
destroyed coastal dune forest. There is a rather abrupt change from coastal
dune forest to coastal grassland. No obvious environmental changes occur
in this area and it is therefore difficult to explain this abrupt transition from
forest to grassland (Lubbe, 1996), except for clearing by man. Tinley (1982)
described the grasslands of the Mozambique plain as sour, occurring on
leached sands, in contrast to the calcicole trees and shrubs found in the
coastal dune forest on calcareous sands.
The differences in the sand are probably caused by the different impact that
grassland and forest has on the soil. The grasslands of the dune systems of
115
REFERENCES
Acocks, J.P.H. 1953. Veld Types of South Africa. Mem. Bot. Surv. S.
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Abstract
The vegetation of Richards Bay municipal area, KwaZulu-Natal,
South Africa, with specific reference to wetlands
by
Jeanine Burger
Supervisor: Prof. G.J. Bredenkamp
Submitted in partial fulfillment of the requirements for the degree
Magister Scientiae
A vegetation survey was conducted at plant community level within the
boundaries of Richards Bay Municipal area during 2001 to 2002.
Relevés was randomly selected and floristic information was recorded for
310 sample plots and was referenced by GPS. The data were captured in
TURBOVEG data base, for vegetation data and classified using the
TWINSPAN numerical classification algorithm.
Phytosociological
tables were compiled using the MAGATAB computerized table
management program.
Thirteen plant communities were identified,
described and characterized by diagnostic and dominant species
occurring in them. The study in general showed that vegetation in the
Richards Bay Municipal area has deteriorated considerably over the last
30 years.
The study indicated that wetland communities occupy a
relatively small area and has become relatively degraded within the study
area.
It is recommended that Richards Bay Town Council plan the
Metropolitan Open Space System (MOSS) bringing the ecological areas
145
of importance into consideration and that all new developments in the
Richards Bay area be subjected to proper ecological investigation as part
of the Environmental Impact Assessment process.
146
Acknowledgements
I would like to thank the following people and institutions for their
assistance in the project:
Prof George Bredenkamp for advice and assistance with the
fieldwork, data analysis and compilation of this thesis.
Dr Ed Granger for his assistance.
My field assistant Mr Simon Khumalo from the University of
Zululand.
Norwegian Programme for Development, Research and Higher
Education (NUFU).
NUFU for funding part of this project.
Mr Patrick Reavell for his advice, literature and proofreading of my
thesis.
Mrs Ann Hutchings of the department of Botany, University of
Zululand for her assistance in plant identification.
Department of Botany, University of Zululand for the use of their
herbarium for plant identification.
The Richards Bay Municipality, department of Town Planning for
their assistance in providing maps, aerial photos and literature.
147
Kwazulu-Natal were classified as secondary grasslands created by the
clearing of coastal forest and maintained by regular fires and grazing
(Conlong and Van Wyk, 1991). Grasslands occurring on dunes between
Richards Bay and the Mfolozi River also seem to be secondary, originating
from forest clearing by local inhabitants (Weisser, 1978).
Although more than one factor was probably involved in the formation of
coastal grasslands, fire has certainly played a major role (Lubbe, 1996). It
was also suggested that before Early Iron Age settlement, the extent of
marshlands and alluvial flats were less extensive, with larger expanses of
open water (Hall, 1981).
This could therefore made it possible that
grasslands or woodlands formed after the water table dropped and were
maintained by fires either induced by man or lightning (Lubbe, 1996).
Edwards (1967) states that it is unlikely that fire was a major limiting factors
on the vegetation, due to the high rainfall and humid climate of the area,
which lacks a pronounces dry season and large fuel load accumulation. If
this is correct it would be difficult to explain the adaptations to fire that are
displayed by the vegetation (Lubbe, 1996).
Syzygium cordatum, one very common woody species occurring in the
grasslands of the Richards Bay study area as well as in the Kosi Bay Forest
Reserve is very resistant to fire (Lubbe, 1996). Other common species like
Phoenix reclinata also occurring in the grasslands of the Richards Bay study
area shows quick recovery after fire in the Kosi Bay Forest Reserve (Lubbe,
1996). Other fire-maintained woody plants include Brachylaena discolor,
116
Strychnos spinosa, Strychnos madagscariensis and Garcinia livingstonei
(Lubbe, 1996).
The high occurrence of geoxylic suffrutices or dwarf shrubs in the coastal
grassland, also suggests a long period of exposure to fire. Suffrutices seem
to be most abundant in areas with a high frequency of less intense fires.
Further evidence indicates that fires must have had a long history of
occurrence in the coastal grasslands, is the presence of 5 endemic suffrutice
species in the coastal grasslands of the Kosi Bay Forest Reserve (Lubbe,
1996).
This therefore suggests that the grasslands of this study area have been
subjected to frequent fires over a long period of time, enabling the
development of taxa with suffrutex habit (Lubbe, 1996).
The grasslands in the study area of Richards Bay Municipal area however
are not maintained by fire. Here fire is usually prevented or extinguished
due to high residential settlement and industrial development in the study
area.
Some large scale industries such as the Bayside and Hillside
Aluminium is supplied with electricity by high voltage overhead powerlines
also running through some patches of grassland, contributing to the control
of fire underneath or close to the powerlines.
Coastal grassland is one of the most threatened vegetation types in
Maputaland.
The destruction of coastal grassland, mainly through
afforestation and other agricultural activities has diminished coastal
grassland considerably in Maputaland (Lubbe, 1996). In the Western Shores
117
area of St Lucia a 56% decrease in grassland has been estimated, from 1937
to 1975 (Conlong and Van Wyk, 1991). This reduction in grasslands due to
indigenous bush encroachment is ascribed to change in management.
Weisser and Marques (1979) ascribe an 86% decrease in grassland in the
area between Richards Bay and the Mfolozi River from 1937 to 1974, as
being due to afforestation and the protection of these grasslands against fire
by conservation authorities.
Grazing has a detrimental effect on communities with little history of
grazing, but is necessary to maintain communities with a long history of
grazing (Nevch and Whittaker, 1980). This may be interpreted in two ways:
i)
grazing is a disturbance for the former system, but not for the latter:
ii)
grazing is by definition, a disturbance and the former system is
disturbance-prone while the latter is disturbance-dependent (Van
Andel et al., 1987).
Plant populations are dynamic entities, their genetic structure responding to
various types of disturbance. The rate and form of the response will, of
course, depend both on the nature of the disturbance, and on biological
attributes of the species, e.g. life history characteristics and ecological
tolerance (Snaydon, 1987).
As a result, it may be very difficult to
distinguish between change, which constitutes disturbance, and change
which is an inherent part of the system; as Van Andel and Van den Bergh
(1987) point out, the status of the change can only be determined by
studying the response of the system and comparing it with an undisturbed
control (Snaydon, 1987).
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CHAPTER 10: CONCLUSIONS
The general trend observed in this study compared to other similar projects
of the past is that the vegetation of Richards Bay is deteriorating and
becoming more disturbed.
This is mainly caused by the influence of
development in the Richards Bay Municipal area. Urban development is
increasing rapidly along with an expansion in a variety of industrial
developments. Informal settlements and surrounding township area are also
expanding and due to small scale and commercial agricultural activities
there is an increasing pressure on open spaces with natural vegetation.
The study in general showed that the vegetation in the Richards Bay
Municipal area has deteriorated considerably in comparison to results of a
study done approximately 30 years earlier by Venter (1972). This decline in
natural vegetation and plant species diversity can mainly be ascribed to the
demand that development imposes on the land for agriculture, housing and
recreational facilities.
The natural fire regime has also been altered and this has resulted in the
recruitment of invasive species, which are now displacing the indigenous
flora. The occurrence of fire in natural vegetation is dependent on several
factors: enough fuel of the right kind has to be present to support a fire, the
vegetation providing the fuel for fires is a product of both the soil and the
prevailing climate (Van Wilgen et al. 1997). Vegetation growing under
almost any climate regime can burn under certain conditions, but the
occurrence of fires is strongly dependent on the weather. For a fire to occur,
121
sufficient fine dry fuels must be present. There is much evidence that fire
has an important and usually beneficial role in maintaining the bio-diversity,
structure and function of African grassland ecosystems (Frost 1984, 1985).
Fire is also one of the key factors in maintaining the competitive balance
between trees and grasses in savannas (Van Wilgen et al., 1997). The
vegetation types of southern Africa have traditionally been mapped and
described on the basis of the species that they contain also known as a
floristic classification, rather than on the basis of their physical structure.
The floristic approach results in a large number of classes with no clear
association to their fire-related properties (Van Wilgen et al., 1997).
Plantations which also occur to a great extend in the area of the Richards
Bay Municipal area, which consist of non – indigenous trees; predominantly
species of Pinus and Eucalyptus are actively defended against fire, with
varying degrees of success. In South Africa, an average of 6430 ha (0.5% of
the planted area of 1.3 million hectares) per annum was burned over the
period 1986 – 1993 (Van Wilgen, et al., 1997). Forest and savanna mosaics
can be edaphic or anthropogenic.
Anthropogenic mosaics are usually
created in areas which were formally forested, particularly through the
process from regeneration by frequent fires or by continuous harvesting of
woody re-growth (Van Wilgen, et al., 1997).
It should be noted that according to the Conservation of Agricultural
Resources Act (Act No. 43 of 1982, as ammended in 2001) all Category 1
alien plants are prohibited and must be controlled, while Category 2 plants
(usually commercially used plants) may be grown in demarcated area
122
providing that there is a permit and that steps are taken to prevent their
spread (Henderson 2001).
Encroachment of Helichrysum kraussii and other woody species such as A.
karroo, P. guavaja and L. camara into grassland and wetlands were
observed. The general conclusion is drawn that fire per se favours the
development and maintenance of a predominantly grassland vegetation by
destroying the juvenile trees and shrubs and preventing the development of
more mature plants to a taller, fire-resistant stage (Huntley and Walker,
1982).
In order to prevent further degradation of the remaining intact natural
vegetation future developments should be carefully planned and located if
possible in the least sensitive areas. Important vegetation types should be
conserved and incorporated into the MOSS of the Richards Bay Municipal
area and therefore this study could play a role in meeting the conservation
objectives.
The species composition in Forest vegetation has changed in some of the
Forest communities occurring in the study area of Richards Bay.
The
Acacia karroo Woodland community that was observed in a study by the
CSIR (1993) is now incorporated in the Isoglossa woodii – Macaranga
capensis Tall Closed Forest and the Chromolaena odorata – Melia
azedarach Short Forest. The large extend of alien invasive species occurring
in the latter community, gives an indication of extensive clearance of Dune
Forest and Swamp Forest vegetation.
Alien invasive species and other
123
woody schrubs started to encroach such gaps in forest canopies and out
compete original vegetation species.
The Barringtonia racemosa – Ficus tricopoda Tall Swamp Forest
community is becoming smaller in the study area in comparison to studies
done by Venter (1972) and Weisser et. al. (1995). The Swamp Forest
community of Richards Bay study area is now represented by small stands
of B. racemoca occurring along the shores of the four freshwater lakes of
Mzingazi, Nzesi, Chubu and the Estuary. This plant community also occurs
along rivers and drainage channels surrounding these waterbodies. Because
of the ecological function these communities have on these waterbodies their
conservation as a buffer zone is important. A total clearance of these plant
communities for rural and urban development purposes will have severe
impact on the turbidity of these waterbodies leading to the siltation and
eutrophication of these fresh water sources. Brugueria racemosa and Ficus
tricopoda are also listed as endangered and protected tree species by South
African legislation. All stands of these forests should be protected.
Swamp Forest was once common along drainage channels and rivers in the
eSikhawini township area, but has now been severely invaded by Psidium
guajava (Guava trees), Lantana camara (Lantana shrub) and Melia
azedarach (Syringa tree).
The township of Vulindlela shows a serious
Schinus terebinthifolius (Brazilian pepper tree) as well as a severe Psidium
guajava invasion. All these alien species should be eradicated.
The Mangrove Short Closed Forest community is also still represented by
large homogenic stands of Avicenia marina. Mangrove communities not
124
only support a highly nutrient rich environment in the Estuary but also play a
key role in providing a suitable habitat for a high diversity in fauna in and
around the estuary. These large stands also play an important role in flood
attentuation. All stands of these forests should be protected.
Wetland communities occupy a relatively small area and are vulnerable to
disturbance and have become significantly degraded within the study area.
It is recommended that Grassland and Wetland communities should be
excluded from all development options.
It is recommended that the Richards Bay Town Council plan the
Metropolitan Open Space System (MOSS) bringing the ecological areas of
importance into consideration.
These vegetation types and its plant
communities usually support a larger system. This would be areas where
Sand Dune or Strand vegetation, the Mangrove Forest vegetation and the
Mosaics of Swamp Forest vegetation and its associated fringing Papyrus and
Reedswamps, occur.
It is strongly recommended that all new developments in the Richards Bay
area be subjected to a proper ecological investigation as part of the
Environmental Impact Assessment process, as prescribed and outlined in
terms of sections 24 and 24D of the National Environmental Management
Act, 1998 (Act No. 107 of 1998), listed activities in the Schedule under the
Environmental Impact Assessment Regulations, 2006, made under section
24(5) of the Act and published in Government Notice No. R. 385 of 2006.
125
In particular, we need to distinguish between variation in space and time, but
also such aspects as the pattern of change in space or time, and the rapidity
with which change occurs in it.
In an ecological context, the term “disturbance” indicates change in the
condition of an organism, population or community caused by an external
agency, often man. Such changes usually imply a shift towards sub-optimal
conditions, since we can usually assume that the organisms were previously
adapted to the existing environmental conditions (Van Andel and van den
Bergh, 1987).
After the sudden change in management (disturbance as an event) the
grassland communities diverged.
However, after a certain stage, the
management treatment can no longer be considered “disturbance” since the
community adapts to the new regimes (Van Andel, et al., 1987).
The
succssional pathway of a community also determines the chance of
reversibility.
The successional rain’ (Klötzli, 1981) is particularly
important. Dispersal of diaspores, either in space or in time (seed bank), of
species that disappeared is a prerequisite for recovery (Van Andel, et al.,
1987).
The importance of Grasslands (Discussion document, 1998):
- Grasses provide an effective and tenacious vegetation cover over the soil,
thereby protecting it from erosion.
- If mown, grassland can be maintained as low-cost sport fields and
playgrounds.
119
Problems associated with Grasslands (Discussion document, 1998):
- Most abundant grass species are of very limited value for maintaining
domestic grazing animals.
- Low level of richness in indigenous species makes these grasslands of
very low priority for nature conservation.
- Taller-growing grasses, especially Hyparrhenia spp. offer screening
which encourage dumping of rubble and litter.
General
Vegetation plays various important roles in the Richards Bay MOSS and the
surroundings (Discussion document, 1998).
-
Vegetation can contribute to maintenance of a healthy environment
through the removal of harmful substances from air and water at a
fraction of the cost that would be incurred by using man-made
alternatives.
-
If properly managed plant communities will function indefinitely barring
the occurrence of some natural disaster;
-
Vegetation can contribute to suppressing noise
-
Vegetation can screen unsightly features.
120
Photo 8.3: Overgrazed hygrophilous grassland with secondary sand dune
forest at the back (June 2002).
4. Imperata cylindrica – Sporobolus fimbriatus Temporary Hygrophilous
Grassland
This grassland community is mostly found in moist places along rivers or
wetland situations. The community is characterised by species group D,
containing several diagnostic species. These species include the woody
Bridelia micrantha, but most diagnostic woody species are aliens e.g.
Lantana camara, Chromolaena odorata and Schinus terebinthifolius.
Diagnostic grass species are Sporobolus fimbriatus, Aristida junciformis
and Panicum repens, while diagnostic forbs species include Centella
asiatica,
Schistostephium
rotundifolium,
Crotalaria
natalitia
and
Abildgaardia ovata.
100
Sporobolus fimbriatus usually grows in moist places next to rivers, drainage
channels and along roadsides as well as in the shadow under trees (Van
Oudtshoorn, 1999). The species also grows in well drained soils. The
species is also widely distributed throughout southern and east Africa (Van
Oudtshoorn, 1999).
Aristida junciformis already occurred as the predominant species in the
Coastal Bushveld – grassland as observed in the early seventies (Venter,
1972).
Aristida junciformis commonly grows in open grassveld.
This
species is also associated with high rainfall areas as well as wetter areas like
wetlands (Van Oudtshoorn, 1999).
Although Aristida junciformis may
generally occur within most soil types it is more characteristically to poor
and stony soil types and clay soils in wetland areas (Van Oudtshoorn, 1999).
This species is an unpalatable grass for grazing and provides very little
nutritional value for grazing purposes. In areas where selective overgrazing
occurs, Aristida junciformis will tend to increase, where-after it will form
dense dominant stands in grassveld (Van Oudtshoorn, 1999).
Aristida junciformis occurred mainly in sampling plots where overgrazing
was observed. If grazing activity is not better managed and regulated it is
possible that Aristida junciformis may become dominant, replacing most
other species in this kind of community.
Panicum repens grows in or close to temporary or permanent water sources
and is also associated with sandy and saline soils.
Panicum repens is
regarded as a good grazing grass (Van Oudtshoorn, 1999). Where Panicum
101
repens occurs it may indicate a healthy and good grazing grassveld, which
occurred in some areas of the Richards Bay municipal area in the past.
5.
Paspalum
distichum
–
Eragrostis
chloromelas
Temporary
Hygrophilous Grassland
This grassland occurs in disturbed moist areas within the study area. It is
characterised by species group E, with the grasses Eragrostis chloromelas
and Chloris gayana and the forbs Dissotis canescns and Pycnostachys
reticualtus as the diagnostic species.
Other prominent species are Paspalum distichum, which is the dominant
grass, and Cyperus rotundus.
Paspalum distichum grows in or close to water.
The species may be
regarded as a weed in crop fields occurring in areas with high rainfall. The
species grows in a variety of soil types from sand to clay (Van Oudtshoorn,
1999). Paspalum distichum is regarded as a palatable grazing grass that can
withstand heavy grazing. Although when this species becomes established
in an area, it is very difficult to eradicate (Van Oudtshoorn, 1999). The
species is originally from tropical Africa and America, but is distributed
today throughout the tropics, worldwide (Van Oudtshoorn, 1999).
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