The Nullarbor bioregion extends over most of the onshore part of the Eucla Basin - an epeirogenic basin of Cretaceous and Tertiary sediments on an irregular basement predominantly of Precambrian granite and metamorphic rocks. It has an arid, non-seasonal climate with average rainfall of 150 - 200mm. Two subregions are recognised. NUL1 is dominated by the Carlisle Plain, the northern periphery of the Bunda Plateau. Soil profiles are well developed, with a high proportion of red quartz rich sand mixed with loams and calcareous clays which is partly calcreted over calcareous sandstone. Sandplains with extensive seif dunes supporting a tree steppe of Eucalyptus gongylocarpa, Mulga and E. youngiana over hummock grassland occupy northern parts of the sub-region, but occasional breakaways and quartzite hills provide minor relief. Salt lakes supporting samphire communities and major valley floors with lake derived dunes are also present, part of an inactive palaeodrainage system which flows into the Nullarbor Karst.
Low woodlands of Acacia papyrocarpa (Western Myall) over Maireana sedifolia (bluebush) dominate its central and southern parts. NUL2 is a Tertiary limestone plain with subdued, arid karst features. It is dominated by the Nullarbor Plain, which is a vast and remarkably flat treeless plain wholly contained within the much larger Bunda Plateau and has shallow calcareous soils, thinly mantling massive limestone. It supports a Bluebush - Saltbush steppe, although low woodlands of Western Myall over bluebush are present in peripheral areas, including Myoporum platycarpum and E. oleosa in the east and west.
Summary of overall condition and trend
Condition is only fair because weeds, fire and feral predators and herbivores have substantially modified habitats over extensive areas of both sub-regions and caused numerous extinctions in indigenous mammals. Trend is declining as weeds continue to spread, displacing indigenous vegetation. The reserve system is strongly biassed, with a third of vegetation types not represented, and large areas of existing reserves severely degraded.
Continental landscape stress class 6 as assessed by the Landscape Health report (1 is most stressed, 6 is least stressed) (NUL1 = 6, NUL2 = 6) but the Nullarbor is clearly in poor condition. A high proportion of its original mammal fauna is extinct, vegetation cover has been stripped from large areas and replaced with the invasive weed Carrichtera annua, foxes and cats are ubiquitous, and until recently rabbits were so common that a rabbit skin and meat industry flourished in the region.
Summary of management/conservation priorities
Weed and feral animal control are the greatest problems, with re-establishment of healthy succulent communities, completion of the reserve system and reconstruction of original fauna the priority. Protection of cave faunas and control of fires are also important.
Dominant land uses include unallocated Crown land, grazing - leases and conservation reserves.
The Nullarbor is the worlds largest Karst system. Significant features include the shallow surface depressions (the donga, ridge and corridor terrain), collapse dolines, blowholes, drip pits, rillenkarren, rundkarren, pavements, solution pans and rockholes. Endemic reptiles, birds, plants and vegetation-types are also present, including Cinclosoma cinnamomeum and Pogona nullarbor. Nullarbor Caves provide refuge for many evolutionarily relictual troglobites and troglophiles: crustaceans, centipedes, cockroachs, carabid beetles, orthopterans, pseudoscorpions and spiders. Two vertebrate species that are also known to use the Caves are the bat, Chalinolobus morio, and the Nullarbor population of the masked owl, Tyto novaehollandiae.
Click here to link to a table of natural values within each subregion
There are no wetlands of national significance, but nine wetlands of regional significance are recognised. One, Plumridge Lakes, is a seasonally intermittent saline lake in good condition with a static trend. Another (Hampton Scarp Rockholes) comprises freshwater pools in degraded condition and static trend. Three others are seasonal/intermittent freshwater lakes and floodplains in degraded condition and declining (Lake Boonderoo, Duck Pond in Arubiddy Station and palaeodrainage channel on Gunnadorah Station). The other four are inland subterrainian karst wetlands in good condition with unknown trends (Cocklebiddy, Murra El Elevyn, Tommy Graham's and Pannikin Plains Caves). Threatening process for the surface wetlands include feral herbivores, stock and feral predators; for subterranian wetlands they are public visitation, earth works and feral predators.
Table: Australia's Important Wetlands (Directory of Important Wetlands of Australia): their type, condition, trend and threatening processes within each subregion.
There is no data available for this table within the bioregion.
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.
There is no true riparian vegetation within the sub-region.
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.
No threatened ecological communities have been declared by WA in the Nullarbor region. However, wetlands of the Nullarbor region are considered to be at risk for the reasons specified above.
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
Five cave-dwelling spiders and one cave-dwelling crustacean are listed as Vulnerable under WA State legislation. In addition 9 CWR mammals and one bird have become extinct in the region, although most persist elsewhere in WA. The invertebrates are threatened by human use of the caves, but their population trends are unknown. The vertebrates are thought to have been affected by habitat changes caused by introduced herbivores and changed fire regimes in combination with introduced predators. These threatening process threaten populations of another 3 bird and 8 plant species now considered to be at risk in the region.
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.
The treeless plains of the Nullarbor were wetter during the second Atlas period than during the first. This may account for the increase in some birds, like Emus, that have declined elsewhere. Overall, the plains contain relatively few bird species; those that are there usually being widespread. Only two limited range taxa were recorded: the Cinnamon Quail-thrush, of which the Nullarbor has an endemic subspecies, and the Princess Parrot. House Sparrows and Common Starlings were recorded along the eastern fringes, but none has yet crossed successfully. In fact, the reporting rate of both these exotic species has declined. Otherwise there was little change in reporting rate of any guilds, except freshwater birds, for which the bioregion provides little habitat anyway.
Status: Semi-arid avifauna, including many birds of chenopod shrublands, although some species have been lost.
Rare and threatened: No major populations.
Increasers: None indicative of landscape health.
Trend: Local increase in ground-feeding insectivores against national trend, possibly reflecting wetter conditions.
Scenario: Probably largely stable, with little evidence of further declines in birds of chenopod shrublands.
Actions: No grazing in representative areas and the adoption of reduced, conservative grazing rates in key habitat across the bioregion, along with appropriate fire regime to maintain diversity.
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.
Number of species and status
There are 40 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 .625. (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 .66. (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 .51. (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 .65. (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 unknown. (The maximum new endemism index value recorded in a bioregion is 0.93 and the minimum is 0.5).
Table: Translocated Species
There is no data available for this table within the bioregion.
The number of introduced exotic mammal species that occur within this bioregion is 9. (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 25. (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.
The conservation estate comprises parts of three large nature reserves and, in South Australia, a large National Park and part of a large Conservation Park: 'Nuytsland Nature Reserve' encompasses woodland mallee heathland, grey bush and melaleucs scrubs of the southern periphery of the region; Plumridge Nature Reserve, Great Victoria Desert Nature Reserve and South Australia's unnamed Conservation Park include sandplains, Mulga and Myall woodlands over bluebush, and samphire communities of NUL1; Nullarbor National Park comprises typical Nullarbor Plain topography with coastal cliffs, caves and a large area of treeless plain.
Twelve of the 27 vegetation-types recognised from the WA part of the region are represented in reserves so the reserve system is incomplete and biased in terms of CAR criteria. Six other vegetation-types have a high priority for reservation; all are succulent steppe communities involving saltbush, bluebush and/or grassland, although some have Salmon Gum, Gimlet, Myall or Myoporum upper strata. Overall, 16% of Nullarbor bioregion is reserved in IUCN I-IV reserves (NUL1=36%, NUL2=4.7%), so the region is IBRA Reservation Class 5; given its bias it should be classed as "3". Sub-regional bias exists with 4.7% of NUL1 reserved and 30% of NUL2 vegetation systems represented in IUCN reserves. NUL2 is considered to be of higher priority (Class 3). (i)Significant threatening processes exist (grazing, feral animals and changed fire regimes)
Constraints are primarily resource related in terms of management and research, although competition for grazing land in the western and eastern ends of the region's ends is a factor. The Aboriginal Land Agreement (Spinifex) will in all likelihood work in favor of biodiversity conservation.
Reserve management is 'fair' because biodiversity values and or management issues poorly identified, weeds are widespread, considerable degradation has occurred in vegetation and components of the fauna (especially in the Great Victoria Desert Nature Reserve), resource degradation is occurring elsewhere (though retrievable), wildfire management is non-existent, and the ongoing impact of feral herbivores is unknown.
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.
Control mechanisms for the environmental weed Carrichtera annua (Ward's Weed) need to be developed and implemented. Cave faunas on privately managed lands especially require habitat protection and further research into species' ecological requirements. Critical Weight Range mammals and regionally extinct bird populations need to be reintroduced, managed from feral predators and their habitats managed for fire and introduced herbivores. Wetland communities need to be protected by reservation and feral mammal control. Main recovery actions include habitat retention through reserves, implementation of management plan recommendations, capacity building with community, landholders, and industry concerning pastoral operations, and fire management to reduce the impact of large intense, summer wildfires on habitat and fauna populations. Further research is required to determine species status, distribution and gain increased knowledge of region's biodiversity, and cost-efficient methods for feral animal and weed control to allow re-introductions and extant populations of CWR species to recover. The main constraint is lack of resources to implement management activities. Weed, feral and fire control are region-wide priorities and significant conservation effort is required in both subregions, cave fauna management is a priority in NUL2.
Existing NRM actions include industry codes of practice particularly in relation to pastoral lease management, and integration environmental management systems with property management planning and Landcare. Declaration of reserves has the most effective NRM activity so far.
Opportunities for NRM include legislation for duty- of-care covering leasehold and other lands (threat abatement planning for vegetation, threatened species, pests and fire). Capacity building in community, landholders, industry and institutions will be required to implement these actions, and programs to increase the awareness of conservation values through education of local industries and communities are needed.
Major constraints include the need to modify the Land Administration Act, to complete negotiations related to the Spinifex Land Agreement people, and to overcome limited financial resources.
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.
Data gaps and research priorities
Prior to the Bioregional survey in 1984 no comprehensive biological study of the Eucla Basin had ever been undertaken. Other Nullarbor work had been largely opportunistic or focused on individual species or taxonomic groups. Main gaps are: No vegetation and regolith mapping at better than 1:250000 scale. Regional survey of flora and vertebrate fauna is based on very sparse sampling (95 sites across the entire region). There are few data on habitat requirements of virtually all invertebrate species, most ephemeral plants, persisting CWR mammals and uncommon vertebrate and plant species. There are no data to provide a regional context on life history (including population trend) for any species apart from rabbits, no quantitative data on the affect of exotic predators, weed colonization and fire, and only limited data on the impact of grazing on vegetation systems of pastoral leases.
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.
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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