Biodiversity Assessment - Avon Wheatbelt
Avon Wheatbelt
Introduction
A dissected plateau of Tertiary laterite in the Yilgarn Craton. The climate is Semi-arid (Dry) Warm Mediterranean. There are two sub-regions. The eastern part (AW1) is an ancient, gently undulating peneplain of low relief and ancient drainage that has dissected the plateau. There is no connected drainage; salt lake chains occur as remnants of the ancient drainage systems and now only function in very wet years. Residual lateritic uplands are dominated by derived yellow sandplain covered in proteaceous scrub-heaths, which have a high number of endemic plant species. Mixed eucalypt, sheoak and Jam woodlands dominate on Quaternary alluvials and elluvials. The western part (AW2) comprises gently-undulating rises to low hills with abrupt breakaways. Its drainage is re-juvenated and comprises continuous stream channels that flow in most years. Alluvial and elluvial processes are active. Residual lateritic uplands and derived sandplains are covered by areas of proteaceous scrub-heaths (which is rich in endemics); Quaternary surfaces of erosional slopes and valley floors support woodlands of Wandoo, York Gum, Jam and Casuarina.
Summary of overall condition and trend
Overall, remnant vegetation, wetlands, riparian systems, populations of species and ecosystems at risk are in poor condition, with the trend expected to decline. Extensive clearing of native vegetaion has led to extensive salinity problems (expected to affect up to 30% of the region's area). Both sub-regions have a continental landscape stress class of 1 as assessed by the Landscape Health report (1 is most stressed, 6 is least stressed).
Summary of priority management/consevation priorities
Reserve threatened ecosystems and populations of threatened species. Focus on protecting remaining populations of threatened species, both on and off reserves. Protect reserves and other ecosystem remnants low in the landscape from salinity and excessive inundation. Control weeds, fire, pathogens, feral herbivores and predators on reserves and other vegetation remnants. Halt clearing. An integrated whole-of-landscape approach to landscape management is required.
Natural values
Landuses are primarily dryland agriculture and grazing, with smaller areas of crown reserves (mainly conservation estate), mining and rural residential. The region has been subject to a very high degree of clearing for agriculture and grazing land so consequently has a high number of environmental problems, threatened ecological communities and species at risk. The region is an interface between the South-western forests and the Transitional Rainfall Zone, and its rich flora includes many endemics, particularly in Grevillea, Hakea, Verticordia, Eucalyptus, Acacia, Dryandra,Verticordia, Lhotskya, Eriostemon, Wehlia, Baeckia, Melaleuca, Chamelaucium, Micromyrtus, Thryptomene and the Asteracea families. Approximately 25% of the Declared Rare Flora in WA occurs in Eucalypt woodlands in this region. Rare features include extant populations of Critical Weight Range mammals, plant communities of granite outcrops, gypsum dunes, the Wongan Hills greenstone belt and associated laterite-capped mesas and Toolibin Lake.
Click here to link to a table of natural values within each subregion
Wetlands
There are 5 wetlands of national importance are lakes and rock pools (Yorkrakine Rock Pools, Coyrecup Lake, Dumbleyung Lake, Toolibin Lake and Yearlering Lakes System). The overall condition is fair and all are declining. Recovery will require significant management intervention. Causes are: water diversion, excessive damage (by off-road vehicles to vegetation mats, water skiers and vandalism), water pollution (fouling by stock and rabbits), exotic plants (bridal creeper Asparagus asparagoides), salination (surface inflow, rising water table) and excessive inundation, both of which are killing the remaining live trees, siltation, eutrophication (agricultural fertilisers) leading to algal blooms, and removal of surrounding vegetation.
Four wetlands are considered to be vital to the preservation of biological processes at a subregional level: Mollerin Lake System, the Buntine to Marchagee Braided Saline Drainage Line, Cowcowing Lake, and Mortlock River System). Their condition is either good or fair but all are predicted to decline due to increases in water salinity and siltation.
Nationally important wetlands
Map: IBRA map showing DIWA locations, towns, subregions, major roads and reserves and most common threatening processes.
Click here to link to a table of Australia's Important Wetlands (Directory of Important Wetlands of Australia): their type, condition, trend and threatening processes within each subregion.
Regionally important wetlands
Click here to link to a table of provisional identification of wetlands of regional significance: their type and special values within each subregion. The reliability of the overall subregional assessment is indicated.
Click here to link to a table of provisional identification of wetlands of regional significance: their condition, trend and threatening processes within each subregion.
Riparian Zones
The principal streams and catchments in the bioregion are the Avon, Blackwood and Moore-Hill River headwaters and the occluded salt catchment area of the Yarra Yarra River. All watercourses are reported as being in degraded as a result of virtually all native vegetation having been cleared around them. The trend is for further rapid decline. Threatening processes include vegetation fragmentation, grazing pressure, exotic weeds, pathogens, increasing salinity and altered flow regimes.
Map: Riparian threatening processes.
Click here to link to a table of riparian zones: their average condition, trend and threatening processes for each subregion. The reliability of this overall assessment is indicated.
Ecosystems at risk
Two Threatened Ecological Communities have been declared critically endangered, 2 endangered and 4 vulnerable by WA. The critically endangered communities (Morilla swamp and Toolibin Lake) are both perched freshwater wetlands with stands of living trees (Eucalyptus camaldulensis (River Red Gum), Casuarina obesa (Swamp Sheoak) and/or Melaleuca strobophylla (Paperbark )) across the lake or swamp floor. The trend listed for these two wetland areas is 'extinction' and 'rapidly declining' respectively. Key threatening processes are vegetation clearing, exotic weed invasion, increased salinity, altered flow regimes and feral animals. The others are vegetation communities on various localised hills and outcrops, their vulnerability relates mainly to their susceptability to fire and weed invasion in the context of their localised occurrence.
Map: IBRA map showing frequency of threatening processes for ecosystems.
Click here to link to a table of provisional list of threatened ecosystems in Australia: their broad vegetation type (National Vegetation Information System - Major Vegetation Subgroup), recommended status, current legislative protection as a threatened ecosystem, trend and bioregional distribution. These ecosystems are arranged in the bioregion of their principal occurrence. The reliability of the recommended status is indicated.
Click here to link to a table of provisional list of threatened ecosystems in each subregion: their threatening processes.
Click here to link to a table of provisional list of threatened ecosystems in each subregion: their recommended recovery actions
Species at risk
There are 38 plant species declared as Critically Endangered, 37 as Endangered and 34 as Vulnerable under WA state legislation. Critically Endangered fauna include 1 bird and 2 invertebrates. Endangered species include 1 mammal, 2 birds and 1 invertebrate. 2 mammals, 2 birds, 1 reptile and 1 invertebrate are declared as Vulnerable in WA. Threatening processes: Fauna: feral animals (cats and foxes), vegetation clearing, habitat fragmentation, changed fire regimes, exotic weeds, grazing pressure and changed hydrology - anything that changes ecosystem productivity and makes their populations more vulnerable to predation. Condition is 'fair'. Trend is 'declining' or 'remaining static' although the rock wallaby (Petrogale lateralis lateralis) is improving in condition under fox control. Plants: as above, except for exotic predators. Fair to poor and 'declining' or 'declining rapidly'.
Map: IBRA map showing frequency of threatening processes for species.
Click here to link to a table of species at risk in each subregion: their status, trend and subregional distribution. The reliability of the assessment of trend is indicated and whether recovery plans have been prepared.
Click here to link to a table of species at risk in each subregion: their threatening processes.
Click here to link to a table of species at risk in each subregion: their status recommended recovery actions.
Birds
Avon Wheatbelt is one of the most highly cleared bioregions in the country, yet still retains significant avian biodiversity. The Endangered Carnaby's Black-Cockatoo appears to be declining here, as elsewhere; a major proportion of the records of this species came from the bioregion. Doves make up much of the exotic species load, and some native species introduced from eastern Australia appear to have become established. An increase in reporting rates among woodland and forest birds probably occurred because birdwatchers to visited woodland fragments more often during the second Atlas period than during the first. A decline in the reporting rate of freshwater birds occurred despite the second Atlas period being wetter, possibly because of a decline in wetland quality.
Status: Moderate diversity of mainly mallee and woodland species in much altered landscape.
Rare and Threatened: Carnaby's Black-Cockatoo associated with heath and woodland with hollows.
Increasers: Australian Ringneck, Senegal Turtledove.
Indicators: Emu, Australian Shelduck, Banded Lapwing, Carnaby's Black-Cockatoo, White-browed Babbler, Yellow-plumed Honeyeater, Tawny-crowned Honeyeater, Crested Bellbird, Hooded Robin, Varied Sittella.
Trend: Probable declines in woodland species, loss of freshwater species.
Scenario: Relaxation of bird diversity in fragments, continued loss of woodland and freshwater birds.
Actions: Maximise or increase the size of and integrity of woodland fragments. Provide connectivity between seasonally variable resources. Rehabilitate catchments of major wetlands retaining values for freshwater birds. See also Action Plan for Australian Birds 2000 Coordinated Conservation Plan: Western Wheatbelt.
Click hereto download a summary report including the physical characteristics of the bioregion, a species list, and summary statistics [Excel file]. The file may open on your screen. To save it to your system 'Save as' under the File menu.
Mammals
Number of species and status
There are 53 mammal species within this bioregion. (The maximum number of species recorded in a bioregion is 86 and the minimum is 25).
Click here to link to a table of number of species in each status class for this bioregion.
Click here to link to a list of mammal species and their status for this bioregion.
Critical weight range
The critical weight range (35 - 5500 g) of mammals is the size range of Australian mammals that have been most affected by environmental changes following European settlement. In this bioregion, the proportion of mammal fauna within the critical weight range is .585. (The maximum proportion of fauna within the critical weight range recorded in a bioregion is 0.632 and the minimum is 0.222).
Faunal Attrition Index
Faunal attrition is a measure of contraction or loss of species richness with a region. A high index value means many species have declined or are extinct in the bioregion. The index can be used to compare the status of mammal fauna to regional attributes such as changes since European settlement and average annual rainfall. The Faunal Attrition Index for mammals in this bioregion is .44. (The maximum faunal attrition index value recorded in a bioregion is 0.66 and the minimum is 0).
Click here to link to a table of Faunal Attrition Index for groups of mammals shows the contributions of each group to overall patterns of faunal decline.
Faunal Contraction Index
A range contraction index is a measure of the extent to which the range inhabited by a particular species has contracted. A high index value means that many of the species comprising the region's original mammal fauna have contracted from a high proportion of the regions they originally occurred in. The faunal contraction index for the mammal fauna in this bioregion is .44. (The maximum faunal contraction index value recorded in a bioregion is 0.51 and the minimum is 0.07).
Faunal Endemism Index
Endemic species are those restricted to certain regions. Regions containing endemic species are considered to have high biodiversity conservation values because opportunities to conserve those species do not exist elsewhere. A high index value means that the species comprising the original mammal fauna typically occurred in few bioregions. The faunal endemism index value for the mammal fauna in this bioregion is .68. (The maximum faunal endemism index value recorded in a bioregion is 0.79 and the minimum is 0.52).
New Endemism Index
Extant (still surviving) species that have undergone major range contractions can be considered 'new endemics'. Bioregions that contain new endemic species are often important refugia for threatened species. The new endemism index for the mammal fauna in this bioregion is .72. (The maximum new endemism index value recorded in a bioregion is 0.93 and the minimum is 0.5).
Click here to link to a list translocated species that has/have been successfully translocated into this bioregion.
Exotic Mammals
The number of introduced exotic mammal species that occur within this bioregion is 10. (The maximum number of introduced exotic mammal species in a bioregion is 16 and the minimum is 5).
Click here to link to a list of introduced exotic mammal species for this bioregion.
Extinct mammal species
The number of extinct mammal species that previously occurred within this bioregion is 20. (The maximum number of extinct mammal species in a bioregion is 29 and the minimum is 0).
Click here to link to a list of extinct mammal species for this bioregion.
Management responses
Reserve consolidation
There are 468 Nature Reserves, and 1 Conservation Park in the bioregion. They range in size from less than one hectare to over 10,000 hectares, with an average area of 452ha in AW1 and 214ha in AW2. Most reserves are small and isolated by wheatfields. They are dominated by sandplain, pavement and breakaway surfaces high in the landscape, the uppermost reaches of valleys, and saline drainage floor surfaces.
Fifteen of 159 regional ecosystems at risk are not yet reserved but have high reservation priority. These are: sheoak, York Gum, Jam, Dodonaea scrub, Allocasuarina campestris scrub, mallee and broombush over samphire, medium woodlands and saltbush over samphire, medium valley floor woodlands, saline seeps, Morilla Swamp, Melaleuca thicket on valley floors, and canegrss on perched clay wetlands. Most are woodlands and shrubland communities on the fertile Quaternary soils of valley slopes and valley floors that have been extensively cleared to provide land for agriculture and grazing or are salt affected.
Constraints on reserve acquisition:
- Some ecosystems have already been cleared below below CAR thresholds (generally below 10%).
- Most remaining areas of lowland ecosystems will be lost to salinity.
- Insufficient resources to acquire and manage an increased conservation estate. More than 1000 reserves, mostly as tiny fragments.
- There is competition with other government agencies and local government for remaining fragments.
Both subregions are IBRA Reservation Priority Class 1 as clearing has been extensive, and rising saline groundwater threatens up to 30% of the landscape. The reserve management standard is poor: salinization is not managed (except at Toolabin). Fox baiting occurs on 9.7% of the conservation reserve estate. Fires are infrequent. Weed control is minimal.
Click here to link to a table of comprehensiveness, adequacy and representativeness (CAR) of the National Reserve System in terms of ecosystems and area sampled and a ranking of reserve management. The bioregional priority for consolidating the National Reserve System is based on this CAR analysis and threat.
Table: Bioregional and subregional priorities and ecosystem priorities to consolidate the National Reserve System and associated ecosystem constraints.
There is no data available for this table within the bioregion.
Off-park conservation for species and ecosystem recovery
Priority species and ecosystems include: CWR mammals and threatened birds; biota of granite outcrops, and flora with Interim Recovery Plans, of roadsides and of lowland communities. Recovery actions for all species and ecosystems include habitat retention through reserves, private lands and other state lands, as well as weed control, feral animal control, fencing, fire management, survey and mapping work, incentives for landholders to conserve communities, control of mining activites, pumping to control water table (especially lowland areas), translocation, revegetation, germplasm storage and capacity building with local government authorities and landholders. However, constraints on some of these actions include: many species are locally extinct (particularly mammals), habitat patches of large enough area no longer exists in the bioregion, predators need to be controlled, there is no viable technology to control salinity, lack of survey data and knowledge on habitat requirements, and lack of staff resources.
Both AW1 and AW2 have priority rank of 1 for off-reserve conservation.
Integrated NRM
NRM initiatives that are currently available include incentives for re-vegetation, fencing remnant vegetation and abating threats such as dieback, feral animals, fire, salinity and weeds. To this end, industry codes of practice and integrated regional management plans exist, and environmental management systems are being prepared. State agencies and NGO's are interacting to build capacity among land-holders and to implement strategic plans, including new industries based on native biota, particularly deep rooted perennial plants. Main constraints on success include: the lack of resources (human and infrastructure) for implementation, lack of rigour in the NRM area, and the generally very poor understanding of the relevant socio-political processes, lack of technical solutions that are economically viable, need for more controls on land clearing and drainage. While various Acts protect wildlife and soils, but there is no "duty of care" legislation.
Both AW1 and AW2 have a NRM rank of 1, which indicates major constraints to implement effective NRM actions to achieve biodiversity outcomes
Map: IBRA map showing frequency of recovery actions (species).
Map: IBRA map showing frequency of recovery actions (ecosystems).
Map: IBRA map showing existing projects part of NRM.
Click here to link to a table of contribution of integrated Natural Resource Management to the protection of biodiversity in each subregion: existing measures and effectiveness.
Click here to link to a table of contribution of integrated Natural Resource Management to the protection of biodiversity in each subregion: feasible opportunities and comments.
Further Information & Gaps
Data gaps and research priorities
Field survey of biodiversity in relation to physical landscape attributes is required in vegetation remnants. Robust biodiversity surrogates need to be identified, as does population viability in the context of the region's fragmented landscape and fire. A standardised database and GIS application is also essential for data querying and management.
References
Environment Australia 2000. Revision of the Interim Biogeographic Regionalisation of Australia (IBRA) and the Development of Version 5.1. - Summary Report. Department of Environment and Heritage, Canberra.
A complete list of references is available by clicking here.
Further information
View the Landscape Health in Australia report.
View the Terrestrial Biodiversity Assessment 2002 report.
Download the Terrestrial Biodiversity Assessment 2002 Database - Biodiversity Audit Data Entry System (BADES), and specifications
Click here to link to a table of some major data gaps in each subregion in terms of protecting biodiversity.
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