Biodiversity Assessment - Victoria Bonaparte
Victoria Bonaparte
Introduction
Phanerozoic strata of the Bonaparte Basin in the north-western part are mantled by Quaternary marine sediments supporting samphire - Sporobolus grasslands and mangal, and by red earth plains and black soil plains with an open savanna of high grasses. Outcrops of Devonian limestone karst in the west support tree steppe and vine thicket. Plateaux and abrupt ranges of Proterozoic sandstone, known as the Victoria Plateau, occur in the south and east, and are partially mantled by skeletal sandy soils with low tree savannas and hummock grasslands. In the south east are limited areas of gently undulating terrain on a variety of sedimentary rocks supporting low Snappy Gum over hummock grasslands and also of gently sloping floodplains supporting Melaleuca minutifolia low woodland over annual sorghums. Dry hot tropical, semi-arid summer rainfall. The bioregion is divided into 3 subregions, reflecting major geomorphological differences.
Summary of overall condition and trend
Most of this bioregion is in good condition, largely spared from intensive land use. However, some pastoral areas have suffered some degradation, and feral animals (pig, donkey, horse, water buffalo and cattle) are widespread and abundant. Fire regimes have changed substantially over the last century, generally to now comprise a higher frequency of extensive hot late dry season fires. Weeds are becoming more abundant and widespread, particularly in riparian areas and wetlands, and some exotic pasture grasses are still being deliberately spread. One of the bioregion's major rivers, the Ord, has been substantially modified by impoundment and water use. Large-scale expansion of the Ord horticulture area has been proposed recently, and this would substantially affect the Keep River and its floodplain area. Reflecting the disparity in land-use intensity across this bioregion, the three subregions have been allocated three different continental stress classes: 3, 4 and 5 as assessed by the Landscape Health report (1 is most stressed, 6 is least stressed).
Summary of conservation priorities
The existing reserve system is limited and biased towards more rugged areas. Further expansion would be required to achieve a CAR regional reserve network. There are two other main NRM priorities - the extensive integrated management of feral animals, fire and weeds across the less developed bulk of the bioregion, and the establishment of sustainable land-use practices in those sections of the bioregion (to be) used for intensive horticulture.
Natural values
Much of this bioregion is very sparsely populated, and comprises rugged ranges and gorges supporting a rich biota which is largely a subset of that of the even more dissected north Kimberley. In marked contrast, the bioregion also includes substantial areas of lowland valleys, floodplains and significant wetlands. Threatened species present include the gouldian finch, two species of freshwater sharks and the Angalarri grunter, an endemic fish.
Click here to link to a table of natural values within each subregion
Wetlands
The bioregion includes all or part of five nationally significant wetlands: Legune wetlands (NT030: wetland types B6, B10, B13 and C2), the Ord estuary system (WA099: wetland types A6, A7, A8 and A9), Parry floodplain (WA100: wetland types B4, B1, B2, B6, B10, B14 and B17), and the artificial wetlands of Lake Argyle (WA097: wetland type C1) and Lake Kununurra (WA098: wetland type C1, B1 and B9). These are generally in good condition, although livestock and feral animals affect at least parts of the Legune, Parry and Ord estuary sites, weeds are expanding on most of these wetlands, and the Ord and Parry wetlands are affected by water use and horticultural practices.
There are many other wetlands of significance in the bioregion, although there has been no detailed assessment of their values. The bioregion includes some spectacular wilderness rivers, most notably the Fitzmaurice River. The lower reaches of the Victoria and Keep Rivers support significant waterfowl breeding colonies and feeding/roosting sites for migratory shorebirds. There are unusually extensive areas of rice-grass Xerochloa floodplain grasslands in patches of the Victoria, Ord and Keep systems.
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
Major river systems in the bioregion include the Fitzmaurice, Victoria (including its tributary Baines, Angalarri and Ikymbon Rivers), Keep, Ord, Pentecost and Chamberlain. The condition of the riparian zones is variable, depending upon land use. Those rivers flowing mainly through non-pastoral lands (such as the Fitzmaurice) are mostly in near pristine condition, albeit affected somewhat by weeds and feral animals. Riparian areas of some other systems have been degraded by exposure to unrestricted access by livestock, although this situation is improving as riparian areas are exclosure-fenced and there is a greater reliance on artificial water sources. Riparian areas in the lower Ord system have been substantially modified by impoundment and water use: in some areas the reduced seasonal variability of water flow has benefitted some components of riparian vegetation, leading to more extensive patches of rainforest-type vegetation. Heavy infestations of weeds (such as noogoora burr, parkinsonia, and castor-oil plant) are a feature of most riparian systems.
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
There has been no formal assessment of the threatened status of ecosystems across most of the bioregion. In the Western Australian portion of the bioregion the following communities may be at risk: wild rice Oryza australiensis grasslands on alluvial flats of the Ord (threatened by clearing and changed fire regimes); an invertebrate community at Zebedee Springs, El Questro station (through impacts of tourism); vine thickets of limestone Ningbing ranges (by changed fire regimes), and rainforests and paperbark forests associated with lowland and mound springs (by grazing pressure, changed fire regimes and weeds). Across the bioregion there is also concern for the savanna communities generally (with broad-scale decrease of fire-sensitive plants such as Callitris intratropica), rainforests, wetlands, heathlands on sandstone and sandplains, and riparian areas, due to the pervasive impacts of changed fire regimes, weeds, livestock and feral animals.
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
Twenty-three species occurring in this bioregion are listed as threatened at Commonwealth or State/Territory level. Note that there is a major disparity in the status assigned to many plant species, due to a revision of the status of all NT plant species. As all of the plant species listed are NT endemics, this revised assessment is likely to be applied also at the Commonwealth scale.
Number of taxa in the Victoria-Bonaparte bioregion listed as threatened at national and/or NT level (nb this table includes only species definitely recorded from the bioregion (rather than putative occurrences based on modelling) and presumed to be still extant in the bioregion).
| Taxa | Commonwealth | Northern Territory | ||
|---|---|---|---|---|
| Endangered | Vulnerable | Endangered | Vulnerable | |
| plants | 0 | 0 | 1 | 5 |
| fish | 0 | 2 | 0 | 1 |
| reptiles | 2 | 4 | 0 | 1 |
| birds | 1 | 5 | 1 | 3 |
| mammals | 0 | 2 | 0 | 1 |
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.
Eucalypts and Acacias
Endemism
There are no endemic eucalypt species and one endemic acacia species in this bioregion: Acacia richardsii.
Richness
Species richness is high for the largest and best-known subregion 1, with 83 species of Acacia and 60 species of Eucalyptus, but low for the two other subregions (5-18 species for Acacia and 8-21 species for Eucalyptus).
Birds
This diverse bioregion had extraordinarily high reporting rates of finches, especially during the second Atlas period, during which time seed-eating birds were a special focus for research in the area. The bioregion is particularly important for the Endangered Gouldian Finch. Two reasons for the abundance of native granivores is the agricultural development around the Ord River irrigation scheme and the almost complete absence of exotic granivores. While reporting rates of grassland birds and obligate ground-feeding granivores increased, birds that feed on both grass and insects were reported less frequently. This bioregion was much wetter than during second than the first Atlas period, which is reflected in the higher reporting rate of freshwater birds, contrary to the national trend.
Status: Moderately diverse mix of tropical woodland and grassland birds; also contains exceptionally large perennial wetlands.
Rare and threatened: Gouldian Finch in woodlands.
Increasers: Cattle Egret.
Indicators: Emu, Australian Bustard, Varied Lorikeet, Black-tailed Treecreeper, Purple-crowned Fairy-wren, Jacky Winter.
Trend: Increases in reporting rates of all finches associated with agriculture, and freshwater birds.
Scenario: Possible long-term loss of fire sensitive species.
Actions: Reimpose mosaic burning, at least in representative habitats. No grazing in representative areas and the adoption of reduced, conservative grazing rates in key habitat across the bioregion. As clearing continues for agriculture, secure representative areas within a functional landscape.
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 56 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 .482. (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 .09. (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 .11. (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 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.
Exotic Mammals
The number of introduced exotic mammal species that occur within this bioregion is 8. (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 4. (The maximum number of extinct mammal species in a bioregion is 29 and the minimum is 0).
Table: Extinct Species
There is no data available for this table within the bioregion.
Management responses
Reserve consolidation
Partly associated with proposals for increased horticultural developments, some large areas have been added to, or foreshadowed for, the reserve system. These would contribute substantially to improving the comprehensiveness of the existing network, although the representation of lowland fertile areas is still limited.
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.
Click here to link to a table of bioregional and subregional priorities and ecosystem priorities to consolidate the National Reserve System and associated ecosystem constraints.
Off-park conservation for species and ecosystem recovery
There is one formal off-reserve conservation agreement established in the bioregion, which excludes livestock from an important breeding colony of the endangered gouldian finch. At another breeding site for this species (Mt Thymanen on the military training area of Bradshaw Station), the Department of Defence is developing a management plan to institute appropriate burning regimes and to limit other disturbances.
Integrated NRM
There is a priority for enhanced integrated (across tenures and jurisdictions) broad-scale management of weeds, feral animals and fire across the entire bioregion. In those parts of the bioregion affected by intensive horticulture, the management of water resources is a major issue, and a water allocation plan is critical. In pastoral areas, exclosure fencing of riparian areas would reduce impacts.
NRM issues in this bioregion are being considered systematically through the recently established Ord-Bonaparte Project.
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
An assessment of the amount of biodiversity data available in this bioregion has been completed recently, indicating large areas with little information. There has been no systematic biodiversity sampling across the bioregion as a whole. The available information is also limited by some cross-jurisdictional problems in data access and integration.
Management would benefit from more detailed environmental mapping, in particular vegetation mapping at the scale of 1:100,000, or better (1:50,000) for those areas subject to development pressure.
Currently in this bioregion, there is no substantial monitoring program which includes as a major goal the assessment of trends in biodiversity conservation (although there are well-established pastoral monitoring programs in both the NT and WA portions of the bioregion). Such a program should be a management priority.
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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