CALM Biodiversity Survey of the Agricultural Zone
June 2000, Status Report
This is a status report on the biological survey of the agricultural zone being conducted as part of the Salinity Action Plan, as at June 2000. The information presented is subject to review in the light of further information as the survey is still underway.
Background Statement
The agricultural zone of Western Australia covers all or significant parts of 6 (Geraldton Sandplains, Swan Coastal Plain, Avon-Wheatbelt, Jarrah Forest, Mallee and Esperance Sandplains) of the eight biogeographic zones recognised in temperate south-western Australia.
The area has had no previous systematic survey of the distribution and diversity of the biota of the region.
Organisation
A four year survey is being undertaken by the CALMScience Biological Survey Group with Greg Keighery as Project Leader.
For the survey, project management has been divided into four areas of responsibility:
1) Flora (terrestrial and wetlands):
2) Fauna (Terrestrial):
3) Wetland Fauna:
Approach
The area was divided into three zones for the purposes of the survey - a northern, central and southern band. Establishment and sampling of terrestrial and wetland sites has occurred in the northern, central and southern bands. Flora studies on the Dandaragan Plateau and West Midlands have been completed. Sampling of the Dandaragan and Esperance Cells is underway for invertebrates. Sampling of terrestrial fauna and flora of these cells will occur this year. Another 30 wetlands (c. 100 flora quadrats) remain to be established and scored.
GENERAL OUTCOMES
The biological survey will identify 6-10 potential natural diversity recovery catchments by 2001. The first (Lake Bryde) has been identified and action commenced in April 1999. The second in the Watheroo area has been identified and the documentation of the area’s values has been undertaken. Preliminary work has been undertaken on 2 other potential recovery catchments and a report prepared on a small scale remedial recovery catchment around Drummond Nature Reserve.
The broad scale biogeographic survey currently underway will provide an overview of the distribution and conservation needs of the terrestrial biota of the wheatbelt. There will be almost 1,000 sites established, including over 300 complete fauna/flora inventory sites that will be able to be used as monitoring sites.
Longer term studies of individual recovery catchments and more detailed surveys of communities and regions identified will be needed after 2001.
Monitoring of actions to recover catchments, and control and reverse salinity would be needed to fine tune management actions, especially in regard to potential weeds, drainage, gypsum mining and other disturbances.
General
Vegetation: The entire region has been mapped for structural vegetation at a scale of 1: 250,000 and 1:1,000,000 by J.S. Beard. These maps have been captured digitally.
Previous Studies: Numerous larger scale vegetation and flora studies, usually for individual reserves have been undertaken. These published and unpublished studies have been updated from Lyons and Gibson (1994)[ Lyons, M.N. and Gibson, N. (1994) Bibliography of location based studies in Western Australia. CALM Science Supplement One.].
Current Status of Survey
Approximately 660 terrestrial quadrats have been established, scored and databased for the three bands surveyed. Another 200 sites have been established as part of the community survey on private and local government lands. Soil samples have been collected at all sites, with approximately 400 analysed and databased.
Current Outcomes
1. The agricultural zone has an estimated vascular plant flora of ca 4,000 species, of which over 60% are endemic to the area. The region is the centre of species diversity for many of the species-rich groups (Acacia, Dryandra, Eucalyptus, Grevillea and Verticordia) that characterise the south-west of Western Australia.
2. Of these ca 4,000 species over 850 are found only in fresh or naturally saline lowlands, which are directly threatened by rising ground water and salinity. The first report on these threatened species covering the Ferns, Gymnosperms and Monocotyledons has been prepared. Several hundred other species found only in woodland sites will be under threat in the longer term. One of the outcomes of the plant survey is to identify native species of potential for revegetation. A database of species in naturally saline areas of the agricultural zone (from site and herbarium records) is being compiled, with field checking.
3. The biodiversity of the agricultural zone is much higher than previously estimated. For example:
a) Detailed surveys of the Lake Muir/Unicup reserves have documented a vascular flora of almost 1,000 species (considerably higher than Mount Lesueur).
b)The small Quairading Shire Reserve (surveyed with community volunteers) has a vascular flora of over 500 species, including two completely new species and the largest populations of two critically endangered taxa.
c) Species richness of quadrats ranges between 20 and over 90 species, equal to most northern heathlands.
d) Survey has also rediscovered one presumed extinct aquatic plant, and discovered four other previously unknown species.
4. Naturally saline areas have major biodiversity values (at least 64 threatened and priority taxa are currently restricted to these areas and several new taxa have been discovered during the survey; see flora section of wetlands report below) and these plants and the communities they occur in are at major risk from rising water tables. The survey is revealing major regional floristic differences in the salt lake chains occupying the paleodrainage systems of the Agricultural Zone.
5. Of the 4,000 species present in the agricultural zone over 1,500 occur low in the landscape, in riverine valleys, freshwater or primarily saline lands. Of these taxa 450 are endemic to the agricultural zone. These taxa are in danger of extinction as a consequence of rising saline groundwaters.
6. Another 400-500 taxa are centred on the agricultural zone although not confined to it. These taxa are also under immediate threat of major genetic erosion from salination and hydrological changes.
7. Areas affected by secondary salination show major declines in vascular plant biodiversity. Rich complex communities are replaced by a few succulents and weeds. Most lowland communities, including tall woodlands, Mallee and Melaleuca shrublands, freshwater and naturally saline wetlands will be lost unless remedial action is taken. The wheatbelt will lose much of its local landscape character.
8. With funding separate from the biological survey, vegetation, flora (including threatened flora), wetland vertebrate and invertebrate lists have been prepared for the Muir-Unicup natural diversity recovery catchment, and 47 monitoring sites established.
9. Approximately 200 sites have been established on private and local government lands by members of the WA Wildflower Society and results are being incorporated into the overall study. Detailed reports on the areas surveyed are placed in major libraries and a copy is held by CALMScience.
10 A major publication on the floral values of the Lake Muir Recovery Catchment is in press in CALMScience. A publication on the Floral Values of Drummond Nature Reserve (potential recovery catchment) has been submitted for publication
In summary, the wheatbelt is more biodiverse than previously realised. Patterning of this biodiversity across the landscape is being revealed via the biological survey. Salination will cause significant loss of plant communities that typify the area and a major rise in the extinction rate of native plants unless significant efforts are undertaken to reverse current threats.
Hydrological changes threaten the diverse floras of naturally saline landscapes and areas of species rich heathland and ephemeral wetlands of the northern sandplains and Swan Coastal Plain. The karst communities both subterranean and surface heaths of the northern Swan Coastal Plain are threatened by flooding and perhaps increased impact of Phythophthora species.
As noted previously 11 people are involved in the survey.
Twenty four field survey areas (organised in 4 bands) have been established from Geraldton to Esperance to achieve a regional coverage.
A total of 12 to 13 biodiversity quadrats are positioned within each field survey area:
At least one quadrat is positioned on a minimally disturbed example of each of the: 11 main geomorphic units in the landscape, as well as on a salt-affected example of two of the units.
Uncleared sites have been chosen on typical examples of each unit, preferably within a conservation reserve.
303 terrestrial biodiversity (fauna and flora) quadrats have been selected and 265 established and sampled so far.
At each biodiversity quadrat:
The assemblage of ground-dwelling arachnids and small vertebrates (spiders, scorpions, centipedes, mammals, reptiles and frogs) is sampled, and the botanists list and score the plants.
The vertebrates are sampled for 8 days in spring and another 8 in summer/autumn, using a minimum of 12 fenced pit-traps.
The arachnids are sampled using five 2-litre pit-traps which contain glycol so that they can stay open for the whole 12 months.
Bulked surface soil samples from each quadrat are collected for chemical analysis and the soil profile is described and sampled for chemical analysis. In conjunction with BIOCLIM data, these will allow modelling of species’ "environmental envelopes", including their salinity responses. The description, sampling and chemical analysis of soil profiles will allow use of Agriculture WA’s soil profile database (10,000 profiles across the wheatbelt) to interpolate the biodiversity-pattern models CALM expects to derive from the biological survey.
The survey is divided into three broad bands for field sampling:
The central band areas were sampled in 1997-98. Vertebrate and arachnid collections from this band have been identified.
The northern band areas were sampled in 1998-99. Vertebrate and arachnid sampling have been completed and the Vertebrates identified. Arachnid collections are being identified.
The southern band areas had field sampling undertaken in 1999/2000. Spring and summer arachnid collections have been collected.
Invertebrate sampling was established in the Dandarragan Plateau and Esperance Cells in 1999. Terrestrial fauna sampling of these cells will occur in 2000/2001.
During 2000/2001 financial year, the following will occur:
Birds Australia will conduct surveys of birds on a selection of the SAP Biodiversity sites (a separately funded project).
All sampling and identifications will be finalised. Compilation and analysis of the data to identify natural diversity recovery catchments.
Write-up for publication will occupy the fifth year.
The study has dramatically increased available data on the distribution, status and habitats of small wheatbelt vertebrates and arachnids species, for example:
The survey has collected over 33,000 non arachnids and 13,929 arachnids. These have been sorted into 1699 morpho-species for the Northern and Central Bands. Currently the WA Museum has recognised 329 species from the Central Band and is working on the Northern Band.
The central band survey (less than a third of the study area) has collected 33 Scorpions (Previously 13 recorded for the entire Wheatbelt), 24 Centipedes (Previously 23 recorded) and 329 Spiders (Previously 128 recorded).
The sampling recorded 20-50 (average = 34) arachnid species per quadrat.
In the northern and central bands 113 species of small ground-dwelling vertebrates (reptiles, mammals and frogs) were recorded, compared with Museum records of 130 species for the whole agricultural region. The sampling recorded an average of 9 species of vertebrate per quadrat.
Although all vertebrates encountered belonged to described species, 60-70% of the arachnids were undescribed. At least 40% (210 of 500+ species) of the region's arachnids, and 25% (31 of 125 species) of its small ground-dwelling vertebrates, have distributions centred on the agricultural region or are endemic to it. Strong biogeographic patterns are apparent across the region in these faunas, and different communities of species occur on the different soil-types within survey areas (sands, clays, loams, saline floors etc).
A significant decline in the biodiversity of terrestrial animals is apparent at secondarily saline quadrats (even partially affected), which have an average of 30% fewer species than their non-salinised counterparts.
Wetlands were chosen to cover the full range of wetland types within the study area (Water quality, geographic spread, primary and secondary saline sites and wetland morphology).
Floristics
The 225 wetlands sampled for aquatic invertebrates had approximately 650 quadrats established on them to document the floristics of these wetlands. Another 30 wetlands and ca. 100 quadrats will be sampled this year.
Preliminary results have uncovered numerous new records and major range extensions of rare and priority flora. Several new taxa of Samphires (Halosarcia spp) have been discovered. The study is confirming the high floral values of naturally saline areas and regional floristic differences in the salt lake chains. The central/western wheatbelt naturally saline areas are a conservation priority because of the threat of hydrological changes.
Fauna
Of the 61 more common waterbird species in the south-west, only 16 prefer strongly saline (more than 20,000 mg/L) or hypersaline (more than 50,000 mg/L) conditions. Data from a 1981-85 survey of the south-west showed that an average of 5 waterbird species used hypersaline wetlands, compared with 20 in saline wetlands and 40 in fresh wetlands containing live trees and shrubs. Death of shrubs and trees in many wheatbelt wetlands due to salinity has caused a 50% decrease in the number of waterbird species using them. If the trend of increasing salinity continues, only 16 species, plus 3 or 4 species that use freshwater dams, will persist in the wheatbelt out of an original waterbird fauna of more than 60 species.
Survey work to date in wheatbelt wetlands has collected about 700 invertebrate species, distributed in 139 families and 270 genera. About 50% appear to be described species and approximately 15% (c.105 species) are only known from the Wheatbelt.
Provisional data suggests numerous species are restricted to naturally saline wetlands, mostly Parartemia (Fairy Shrimps), Coxiella (snails), Ostracods and Copepods (Crustaceans). These may form a significant endemic component in south-west Western Australia.
South-west Western Australia has a highly rich and endemic aquatic fauna of microinvertebrates, especially Crustacea
Of these, 253 species (45%) are restricted to fresh water with salinity less than 3,000 mg/L. However, 35 of the species occur on granite rock outcrops where salinity is unlikely to occur, leaving 218 species (39% of the fauna) that are vulnerable to increasing salinity. If all wetlands in the wheatbelt became saline (more than 10,000 mg/L), most of these 218 species will disappear from the wheatbelt.
Species richness declines with salinity and the average number of invertebrate species present in fresh wetlands is about 50, in wetlands with salinity 20,000 mg/L about 25, in wetlands with salinity 50,000 mg/L about 12 and in wetlands with salinity greater than 100,000 mg/L about 4 (see attached graph). As a rule of thumb, doubling salinity halves the number of aquatic invertebrate species.
Caveats that must be attached to the above statements at this stage of the work are that probably not all wetlands will become saline, some species will persist in dams, and plenty of species have ranges that extend outside the wheatbelt.
Project Objective
Vegetation transects (2-5 per wetland, 80 in total) have been established at all 25 wetlands. Reference photos have been taken on each transect, Airphotos showing position of transects and biophysical boundaries have been captured on GIS. Over 6,000 trees tagged on transects and vegetation profiles constructed for each transect. Three major reports on these transects have been prepared and are lodged in Woodvale library. Monitoring bores have been established adjacent to these transects at 20 of these wetlands. Waterbirds and invertebrates (macro and microinvertebrates) have been sampled at 23 wetlands to prepare baseline data, 5 wetlands have been resampled.
Monitoring of wetlands has shown that: