Biodiversity attribues of an isolated woodland fragment in metropolitan Perth, Western Australia

2008·3.5 MB·English

by  Stephen Reynolds

BIODIVERSITY ATTRIBUTES OF AN ISOLATED
WOODLAND FRAGMENT IN METROPOLITAN
PERTH, WESTERN AUSTRALIA
By STEPHEN REYNOLDS
School of Environmental and Life Sciences,
Charles Darwin University, Darwin NT 0909.
ABSTRACT
The macroscopic biological diversity of a small (<lha),
isolated bushland remnant at the edge of suburban Perth
comprises over 130 species. Most taxa are invertebrates or
vascular plants, whereas terrestrial vertebrates make a
minor contribution to species richness. Intensive survey of
this small fragment ensured that the flora and fauna were
satisfactorily described, however, additional species are
certain to exist and would be recorded by further scrutiny.
The conservation ‘value* of remnants is such that all areas
of bushland remaining on the Swan Coastal Plain should be
protected to preserve biodiversity values. It is suggested that
biological survey procedures as currently practiced in the
state of Western Australia do not adequately document
biological diversity.
INTRODUCTION vidual taxa occupying a specified
The south-west of Western area. Clearly, in general and on
Australia is a global biodiversity average, the larger an area, the
‘hotspot’ (Myers et ai 2000), to greater will be its diversity
which the Swan Coastal Plain (Arrhenius 1921; MacArthur and
makes a major contribution. Wilson 1963).
Although the term biological As a consequence of the species-
diversity, or its shortened form area relationship, it is especially
‘biodiversity’, is frequently used difficult to fully document the
as a descriptor for a range of biodiversity of large survey areas.
situations, it is seldom clearly Although the cumulative
defined. The simplest and number of species recorded will
therefore most widely-used be greater, many species will
measure of biodiversity is species remain undetected due to their
richness: the number of indi¬ low density (particularly rare
99
species), secretive habits, vegetation, and only moderate
inactivity (seasonal or diurnal), for areas on the urban fringe, in
or senescence. The longer and which condition gradually
more detailed a survey, the deteriorates over time as a result
greater the variety of sampling of weed infestation and anthro¬
methods, and the finer the pogenic use and incursion. There
resolution of fauna habitats or are a variety of causes (e.g.
vegetation communities recog¬ introduced predators, fire,
nised, the more representative it drought) for localised extinction.
will be in terms of characterising However, any factor that reduces
the biota of a study area, and population size will have a
therefore a region, or a biological greater potential to affect long¬
zone (see Elton (1946). for a term viability and ultimately
discussion of the validity of extirpation due to stochastic
survey data). Two principal (chance) fluctuations or acci¬
components, intensity and dental loss if the population is
duration, will ultimately small and isolated. Urban
determine the comprehensive¬ environments are a major
ness of a survey. The experience environmental concern because
of the observers and their entire landscapes are completely
familiarity with the biota of the destroyed or otherwise irretriev¬
region will also influence survey ably altered when incorporated
outcomes.
into an urban framework (see
Fragmentation and ultimately Garden et al., 2006).
isolation of bushland areas in The urban arc of the expanding
urban and agricultural settings is Perth megalopolis extends from
of widespread occurrence in the seaward fringe of the
southern and eastern Australia northern suburbs, north and
(Breckwoldt 1986). Loss of habitat south of the river, past
has a negative influence on Mandurah and down to
biodiversity, i.e. the number of Bunbury. With the exception of
animals and plants in an area will localised areas near Pinjarra and
decrease over time (e.g. Common¬ Yanchep, almost the entirety of
wealth of Australia 1995; Jellinek the Swan Coastal Plain has been
et al. 2004; Bennett 1990 and cleared for urban, suburban and
references therein; Grimbacher et peripheral expansion. A series of
al. 2006). The precise alterations studies have examined the
to species diversity and com¬
landscapes (e.g. Semeniuk 1988;
position will depend on the
Semeniuk and Glassford 1989;
history and nature of environ¬
Seddon 1972 and references
mental modification. The bio¬ therein), components of verte¬
diversity reduction response will brate fauna (Cooper 1995;
be acute for areas that are heavily
Davidge 1979; How and Dell 1990;
damaged, particularly where
Maryan 1984; Maryan et al. 2002;
land-forming removes all
Mawson and Massam 1995;
100
Recher and Serventy 1991; Turpin Cockburn. It is less than one
1990, 1991), vegetation (Beard hectare in size, and is sandwiched
1979) and floristics (Cresswell and between extensive cleared areas
Bridgewater 1985; Keighery and on all sides; to the south by a
Keighery 1993; Gibson et ai 1994) sandy track and railway, to the
including weeds (Keighery 1998) north by a large expanse of bare
of bushland on the Swan Coastal sand, and to the east by a wide
Plain near Perth. There is also an sandy area adjacent to a major
ever increasing quantity of road. The area lies on siliceous
unpublished material on urban white-grey Bassendean sands and
bushland remnants, and a range there is only minor soil (humic)
of information, of variable development. There is low to
quality, in consultant reports. moderate leaf-litter accumu¬
Much of this information has lation, particularly around the
been summarised in short form dominant trees that form the
in the BushPlan (Department of overstorey; Eucalyptus marginata,
Environmental Protection 1998) A llocasuarina fraseriana and
and subsequent Bush Forever Banksia attenuata. The midstorey
documents (Government of is moderately well developed and
Western Australia 2000). These the site had remained unburnt
studies show that while native for several years. Principal weeds
mammals are highly susceptible are scattered Geranium
to localised extinction in urban Pelargonium capitaturn and Veldt
remnants, components, at least, Grass Ehrharta calycina along
of various animal groups may edges.
persist. Floristic diversity may
Assessment of the flora and
also remain high, and remnants fauna was made by trapping
may support rare plant species and observation. Throughout
and communities (Kirkpatrick January and into the first half of
1986; Gibson et al. 2000). This February 2003, pit-trapping was
paper reports on the biota of an undertaken on most nights with
isolated patch of Banksia- four large buckets (30cm deep)
dominated woodland in with a 4m drift fence, and five
southern metropolitan Perth, small plastic containers (10cm
and provides an example of the deep). The number and types of
importance of remnants for animals captured were noted for
preserving biodiversity in the each trap on each day. Elliott
face of habitat loss due to traps were tried initially but
continued urban development. produced only the House Mouse
Mus musculus. 1 recorded birds by
aural and visual means; the
METHODS
species and the number of
Cocos Reserve (32°06'33"S individuals were noted on each
115°49'18"E) is situated in the occasion. Botanical survey was
suburb of Bibra Lake, City of carried out twice intensively and
101
also incidentally during and not a complete list as new species
after trapping visits. A species of invertebrates were recorded
recognition, or ‘morphospecies’ on each trapping day. Many of
approach was used to classify the the insects, spiders and acarines
majority of invertebrate taxa. were abundant at the site.
Vertebrate animals included a
single species of frog, several
RESULTS
reptiles, predominantly skinks,
A rich community of animal and and a small but apparently viable
plant species was recorded from group of sedentary and roaming
Cocos Reserve (Table 1). The birds (Table 1, Appendix 1). Seven
major contribution to faunal additional bird species were
diversity was from the inverte¬ observed passing over the site;
brate community, including at these waterbirds were not
least 70 species from 14 tax¬ included as they are exclusive to
onomic groups (Table 1). This is habitats at nearby Little Rush
Table 1. Biodiversity attributes table for Cocos Reserve.
Taxon Richness Comments
Lizards (Reptilia: Squamata) 5 species predominantly skinks
Frogs (Amphibia: Anura) 1 species moving between wetlands ?
Birds (Aves) - native taxa 13 species some resident individuals
additional birds pass over
Spiders (Arachnida: Araneae) 15+species
Mites (Arachnida: Acarina) 2 species small ground-dwelling species
Scorpions (Arachnida: Scorpiones) 1 species
Beetles (Insecta: Coleoptera) 8 species
Grasshoppers and crickets
(Insecta: Orthoptera) 8 species
Bees, ants and wasps 20+ species over half the species are ants
(Insecta: Hymenoptera)
Termites (Insecta: Isoptera) 2 species observed not trapped
Bugs (Insecta: Hemiptera) 6 species includes two cicada species
Cockroaches (Insecta: Blattodea) 2 species
Flies (Insecta: Diptera) 3 species including House Fly
Silverfish (Insecta*. Thysanura) 2 species
Earwigs (Insecta: Dermaptera) 1 species
Mantids (Insecta: Mantodea) 1 species
Centipedes (Myriapoda*. Chilopoda) 2 species both species trapped
Slaters (Crustacea: Isopoda) 1 species ? introduced species
Monocotyledons (Liliopsida) - 18 species additional sedges present
native taxa
Dicotyledons (Magnoliopsida) - 32 species mistletoe present ?
native taxa
102
Lake and other Beeliar wetlands. the biodiversity of a study area,
No nocturnal birds were survey objectives should include
observed, and the only mammals assessment of invertebrates. We
were non-native species can only begin estimating the
(Appendix 1). relative value of diversity if we
enhance the ecological in¬
To date 50 species of native
formation that is obtained.
vascular plants have been
identified at the site (Table 1, Plants and animals (particularly
Appendix 2) and others were vertebrates) are the most familiar
recorded. Strata components types of organisms and the
include six trees, 17 varieties of easiest to identify accurately,
shrubs, and the majority of the hence the level of expertise and
plant diversity in the under¬ state of knowledge is far superior
storey layer, particularly amongst to that for other groups. They are
the herbs and sedges (Appendix consequently the focus of the
2). More than 16 exotic (intro¬ majority of biological surveys;
duced) plant species occur - our principle source of data for
mainly herbs and grasses; estimating biodiversity. They are
additional species would flourish assessed in preference to micro¬
in winter. organisms, fungi, invertebrate
animals, or non-vascular plants.
The vertebrate fauna and
DISCUSSION vascular plants of the Swan
Coastal Plain and vicinity have
The persistence of a diverse
been capably described and
community of animal and plant
annotated (e.g. How 1998; Storr
species at Cocos Reserve is
and Johnstone 1988; Marchant et
exceptional given the small size
al. 1987), and in some cases,
of the reserve (< 1 ha), particularly
analysed (How and Dell 1994,
as the site is completely isolated
2000). Although there have been
from adjacent bushland. The
some surveys of terrestrial en¬
major contribution to bio¬
vironments that have examined
diversity (-80% of fauna taxa) is
specific invertebrate groups (e.g.
due to the invertebrate com¬
Andersen 1986; Rossbach and
munity. Harvey et al. (1997) also
Majer 1983; Gwynne et al 1988),
documented a rich assemblage of
comprehensive surveys of
invertebrates at urban bushland
invertebrate diversity are rare.
remnants near Perth, including
many spiders and Baeine wasps. Vertebrates are used as the main
That the majority of diversity is faunal indicators of environ¬
amongst the invertebrates is not mental health for environ¬
unexpected, because globally mental impact assessment, but it
there are vastly more inverte¬ is frequently the absence of rare
brates than vertebrates (Barnes, species, rather than the presence
1980; Wilson, 1987). This suggests of a diverse community, that tips
that in order to fully evaluate the balance in favour of
103
development. The comparative plants based on the number of
‘value’ of bushland remnants is species recorded at Cocos Reserve
therefore determined on the and using data for several other
basis of few taxonomic groups, comprehensively surveyed but
and may in some cases be relatively homogeneous sites on
strongly, and somewhat subject¬ the Swan Coastal Plain (Shenton
ively influenced by the existence Park bushland and Talbot Road
of populations of a single species. bushland), indicates an
Reduced vertebrate diversity approximate relationship of the
(particularly of prominent taxa form S = 45A0415 where S is plant
such as mammals) in remnants species richness and A is area in
due to isolation may not hectares. Sites such as the Brixton
correspond to overall faunal Street wetlands (Keighery and
diversity. Indeed, if we ex¬ Keighery 1993) with multiple
trapolate biodiversity attributes habitats and a complex array of
of the better known faunal understorey species, greatly
groups to the invertebrates, we exceed this average expectation
would anticipate that many based on area alone. This index is
species of insects and arachnids more appropriate for surveys of a
are likely to be restricted to the single vegetation type such as
Swan Coastal Plain and, by Banksia woodland or Eucalypt
extension, to specific habitats forest, but requires compre¬
within the landscape mosaic. If hensive, detailed floristic
any legitimate attempts are to be information to be a useful and
made to retain biodiversity, then potentially meaningful measure.
we have an obligation to Flora surveys often focus on
examine other components of vegetation communities rather
the biota in greater detail, refine than floristic composition per se
methods of investigation and (although composition may be
analysis to establish criteria and used to delineate communities),
guidelines for preservation of and assessment of representation
biodiversity values, determine is usually made on this basis, as is
the full range of taxa that exist, the case for the Perth region
and investigate ecological (Government of Western
relationships more thoroughly. Australia 2000). The analysis
Considering the small size of the presented here, although highly
Cocos Reserve remnant, it simplistic in its current form,
supports a diverse array of plant suggests an alternative or
taxa. Over 50 native species have complementary method for
been recorded and more are evaluating sites that is specific¬
likely to occur, particularly ally relevant to interpretations
additional sedges, low shrubs, based on biodiversity.
herbs (including orchids),
Limitations of the current
mistletoes and weeds. Species-
survey are primarily in relation
area curve extrapolations for
to duration, in that the data for
104
fauna were collected over a five although they would have to
week period (longer than most traverse areas of bare soil with no
fauna assessment surveys), and in shelter. Invertebrates appeared to
timing, because although be relatively active at the time of
summer is an appropriate time to trapping, but 1 am not aware of
survey reptiles (How 1998) and any studies that give a clear
many insects, it may be less indication of the most appro¬
suitable for other fauna. Most priate time (or times) to collect
floristic work was carried out in invertebrates in the south-west
summer, so while the list is of Western Australia.
comprehensive for that season, it Bushland remnants often
is possible that plants without support a range of fauna species
remnant dry season structures (How and Dell 1994; Kitchener
could have been missed. and How 1982; this study) and
Additional fauna species would vegetation communities (e.g.
be recorded during trapping in Keighery and Keighery 1993), and
other seasons, and certain species have value as habitat (Hodgson et
are not amenable to capture by al. 2006) even when of small size
trapping, hence further (Jellinek et al. 2004). However, in
opportunistic searches would urban areas these sites are so
contribute to a more compre¬ sparsely distributed that
hensive evaluation. The com¬ effective and comprehensive
paratively small size of the study retention of all biological attri¬
area facilitated complete bird butes is no longer a feasible
surveys on each occasion based objective. The emphasis must
on observation and call identi¬ instead be placed on the
fication, but migrant or nomadic retention and persistence of as
species may use the area in other great a variety of ecosystem
seasons. The reptile list is likely components as possible. Given
to be adequate but incomplete the rapid rate of attrition of
because species accumulation bushland in the Perth region, the
through trapping may take only reasonable conclusion
many years (How 1998). Familial seems to be, that in order to
composition is however similar maintain biodiversity (including
to other herpetofaunal surveys all its components), any remain¬
(e.g. Davidge 1979; How and Dell ing areas of bushland in urban
1994; Maryan et al. 2002) in that and suburban areas must be
the majority of species were retained, and areas on the
skinks. The presence of the expanding fringe should be
Moaning Frog Heleioporus cyrei in protected from degradation and
summer was unusual as there loss. Proposals to delete portions
was no rain at the time. Other of the landscape and their
frog species may move through biological components need to
the area from local wetlands be examined very closely,
during the winter months, particularly, strategically and
105
specifically in areas of urban obtained to inform relevant and
expansion where so few reasonable management de¬
examples of diverse bushland cisions, including selection and
remain, and in a region where allocation of areas with the sole
there are numerous endemic objective of nature conservation.
taxa (Hopper 1979; Keighery 1996;
Beard et al. 2000). The choices
that are made now will ACKNOWLEDGEMENTS
determine the future of
K. McCreery assisted with plant
biodiversity in the region.
collection and identification. V.
In order to fully appreciate the
Mawson, M. Naunton and K.
biodiversity attributes of a
Christian provided comments on
bushland area, we need to take a
a previous version of the manu¬
fine-scale local viewpoint, but a
script. Trapping and floristic
regional perspective. These two
work was carried out under
aspects are not always com¬
licences from the WA Depart¬
patible, and it is not until the
ment of CALM.
level of knowledge becomes
adequate that rational decisions
can be made about biodiversity
REFERENCES
conservation within the context
of representative reservation. ANDERSEN, A.N. 1986. Diversity,
The Swan Coastal Plain is a seasonality and community
special case in that it is the focus organization of ants at adjacent
of urban expansion, but it has heath and woodland sites in
also been the focus of detailed south-eastern Australia. Australian
biological study. However, even Journal of Zoology 34: 53-64.
in this instance where there is an
ARRHENIUS, O. 1921. Species and
acceptable level of under¬
area. The Journal of Ecology 9: 95-
standing of biodiversity com¬
99.
ponents, there is an inadequate
BARNES, R.D. 1980. Invertebrate
basis for approaching bushland
Zoology. Saunders College,
conservation that is specifically
Philadelphia.
relevant to biotic significance. In
order for a rational system to be BEARD, J.S. 1979. Vegetation Survey
designed that has sufficient of Western Australia. The Vegetation
cohesion to ensure that it is of the Perth Area, Western Australia.
culturally and politically persua¬ Map and explanatory memoir, I ;
sive, there is a requirement for a 250 000 series. Vegmap Publi¬
strategic and systematic ap¬ cations, Perth.
proach that has explicit goals. BEARD, J.S., CHAPMAN, A.R. and
This system must have the GIOIA, P. 2000. Species richness
capability to incorporate the and endemism in the Western
findings of biological surveys Australian flora. Journal of Bio-
and utilise the information geography Hi 1257-1268.
106
BENNETT, A.F. 1990. Habitat processes. Austral Ecology 31: 126-
Corridors: Their Role in Wildlife Ha
Management and Conservation. GIBSON, N., KEIGHERY, B.J.,
Department of Conservation and KEIGHERY, G.J., BURB1DGE, A.H.
Environment, Melbourne.
and LYONS, M. 1994. A Floristic
BRECKWOLDT, R. 1986. The Last Survey of the Southern Swan Coastal
Stand. Managing Australia's Plain. Unpublished report for the
Remnant Forests and Woodlands. Australian Heritage Commission
Australian Government Publish¬ prepared by the Department of
ing Service, Canberra. Conservation and Land Manage¬
ment and the Conservation
COMMONWEALTH OF AUS¬
Council of Western Australia,
TRALIA, 1995. Native Vegetation
Perth.
Clearance, Habitat Loss and
Biodiversity Decline. Biodiversity GIBSON, N., KE1GHERY, G., and
Unit Paper No. 6. Canberra. KE1GHERY, B. 2000. Threatened
plant communities of Western
COOPER, N.K. 1995. Vertebrate
Australia. 1. The ironstone
fauna of an isolated bushland
communities of the Swan and
reserve (No. 18325) in inner Perth.
Scott Coastal Plains. Journal of the
The Western Australian Naturalist
Royal Society of Western Australia
20: 21-28.
83:1-11.
CRESSWELL, l.D. and
GOVERNMENT of WESTERN
BRIDGEWATER, P.B. 1985. Dune
AUSTRALIA. 2000. Bush Forever
vegetation of the Swan Coastal
Volume 2 - Directory of Bush Forever
Plain, Western Australia. Journal of
Sites. Government of Western
the Royal Society of Western
Australia, Perth.
Australia 67:137-148
GR1MBACHER, P.S., CATTERALL,
DAVIDGE, C. 1979. A census of a
C.P. and KITCH1NG, R.L. 2006.
community of small terrestrial
Beetle species’ responses suggest
vertebrates. Australian Journal of
that microclimate mediates
Ecology 4:165-70.
fragmentation effects in tropical
DEPARTMENT OF ENVIRON¬ Australian rainforest. Austral
MENTAL PROTECTION. 1998. Ecology 31: 458-470.
Perth's Btishplan. Department of
GWYNNE, D.T., YEOH, P. and
Environmental Protection, Perth.
SCHATRAL, A. 1988. The singing
ELTON, C. 1946. Competition and insects of King’s Park and Perth
the structure of ecological gardens. The Western Australian
communities. Journal of Animal Naturalist 17: 25-71.
Ecology 15: 54-68.
HARVEY, M.S., WALDOCK, J.M.,
GARDEN, ]., MCALPINE, C, HOW, R.A., DELL, J. and KOSTAS,
PETERSON, A., IONES, D. and E. 1997* Biodiversity and
POSS1NGHAM, H. 2006. Review of biogeographic relationships of
the ecology of Australian urban selected invertebrates from urban
fauna: a focus on spatially explicit bushland remnants, Perth,
107
Western Australia. Memoirs of the remnant urban bushland. Austral
Museum of Victoria 56: 275-280. Ecology 29: 294-304.
HODGSON, P., FRENCH, K. and KE1GHERY, G.J. 1996. Phyto¬
MAJOR, R.E. 2006. Comparison of geography, biology and con¬
foraging behavior of small, urban- servation of Western Australian
sensitive insectivores in con¬ Epacridaceae. Annals of Botany 77:
tinuous woodland and woodland 347-355.
remnants in a suburban land¬
KEIGHERY, G. 1998. The weeds of
scape. Wildlife Research 33: 591- Garden Island - an annotated list.
603.
The Western Australian Naturalist
HOPPER, S.D. 1979. Biogeo- 22:61-76.
graphical aspects of speciation in
KEIGHERY, G.J. and KEIGHERY,
the southwest Australian flora. B.J. 1993. Floristics of Reserves and
Annual Review of Ecology and
Bushland Areas of the Perth Region
Systematics 10: 399-422. (System 6). Parts V-IX. Wildflower
HOW, R.A. 1998. Long-term Society of Western Australia (Inc.),
sampling of a herpetofaunal Perth.
assemblage on an isolated urban KIRKPATRICK, J.B. 1986. The
bushland remnant, Bold Park, viability of bush in cities - ten
Perth. Journal of the Royal Society of years of change in an urban grassy
Western Australia 81:143-148. woodland. Australian Journal of
HOW, R.A. and DELL, J. 1990. Botany 34: 691-708.
Vertebrate fauna of Bold Park, KITCHENER, D.J and HOW, R.A.
Perth. The Western Australian 1982. Lizard species in small
Naturalist 18:122-131. mainland habitat isolates and
HOW, R.A. and DELL, J. 1994. The islands off south-western Western
zoogeographic significance of Australia. Australian Wildlife
urban bushland remnants to Research 9: 357-363.
reptiles in the Perth region, MACARTHUR, R.H. and WILSON,
Western Australia. Pacific Con¬ E.O. 1963. An equilibrium theory
servation Biology 1: 132-140. of insular zoogeography. Evolution
HOW, R. and DELL, J. 2000. 17: 373-387.
Ground vertebrate fauna of MARCHANT, N.G., WHEELER,
Perth’s vegetation remnants: I.R., RYE, B.L., BENNETT, E.M.,
impact of 170 years of urbani¬ LANDER, N.S. and
zation. Pacific Conservation Biology MACFARLANE, T.D. 1987. Flora of
6:198-217. the Perth Region. Western Aus¬
JELLINEK, S., DRISCOLL, D.A. and tralian Herbarium, Perth.
KIRKPA1 RICK, J.B. 2004. Environ¬ MARYAN, B. 1984. Herpeto-
mental and vegetation variables fauna of an urban area near
have a greater influence than Perth, Western Australia. The
habitat fragmentation in Western Australian Naturalist 19:
structuring lizard communities in 174-183.
108