You are here: ANRA home » Natural resource topics » Vegetation and biodiversity » Assessment » Northern Territory
This web site is no longer being updated
In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Biodiversity Assessment - Central Arnhem
Central Arnhem
Introduction
This bioregion comprises gently sloping terrain and low hills on Cretaceous sandstones and siltstones and lateritised Tertiary material; yellow earthy sands and shallow stony sands. The dominant vegetation is Darwin Woollybutt Eucalyptus miniata and Darwin Stringybark E. tetrodonta open forests and woodlands with a dense grass understorey. Almost all of the bioregion is Aboriginal land. The bioregion is divided into two subregions.
Summary of overall condition and trend
Due to the very low level of development within Central Arnhem, much of this bioregion is in good condition, with both subregions scored as continental landscape stress class 5 as assessed by the Landscape Health report (1 is most stressed, 6 is least stressed). However, as with most other parts of northern Australia, this condition is being degraded by increasing density and penetration of weeds, increasing abundance and distribution of feral animals (particularly pigs and buffalo, but also horse, donkey, cats, and cane toads), and altered fire regimes. Together, these factors are causing broad-scale changes in vegetation and faunal assemblages.
Summary of conservation priorities
There are no conservation reserves in this bioregion. Some reservation is desirable, either as Indigeonous Protected Area or as cooperatively managed area. However, more important than such designation for part of the bioregion, is the imposition of improved management across the entire bioregion. This can only come about through the provision of resources and capacity building for Aboriginal owners, to encourage and allow them to combat the threatening processes affecting their lands.
Natural values
This bioregion has few localised conservation attributes. Rather, its main value for biodiversity conservation relates to its extensive areas of relatively intact ecosystems. It harbours some threatened species, including northern shrike-tit Falcunculus (frontatus) whitei, and red goshawk Erythrotriorchis radiatus. Part of the nationally significant Arafura Swamp lies in the bioregion. The small coastal area includes some sites used for breeding by threatened marine turtles.
Table: of natural values within each subregion
There is no data available for this table within the bioregion.
Wetlands
Central Arnhem includes the upstream (Goyder River) component of the nationally-listed Arafura Swamp (NT021: wetland types B4, B14, B1, B2, B9 and B10), notable for its large size, distinctive vegetation and significance for wetland biota.
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 bioregion includes parts of the catchments of many important river systems, including the Roper, Walker, Kooletong, Goyder, Blyth, Rose, Phelp and Wilton Rivers. As with other environments in this bioregions, riparian areas are generally in very good condition, although this is being destabilised over large areas by increasing abundance and distribution of some feral animals (particularly pigs and buffalo) and weeds. Unfavourable fire regimes are also degrading some riparian areas, resulting in shrinkage of the dense riparian strips.
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
All environments in this bioregion are under continuing risks through degradation by fire, feral animals and weeds. However, no environments are yet listed as threatened. Monsoon rainforests are probably the most threatened, as the isolation and small sizes of patches renders them particularly susceptible to damage, and because they particularly attract some threats (pigs, some weeds).
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
Ten threatened species have been recorded within this bioregion. For most of these species, this bioregion is not a particularly important stronghold, although the extensive relatively intact forests probably provide high quality habitat for two bird species, the northern shrike-tit and red goshawk. Six marine turtle species are known from the small coastal section of this bioregion, and this area includes some significant breeding sites for at least two of those species. The lack of representation of threatened plant species in this bioregion may reflect very limited knowledge.
There is also some evidence that there is broad scale decline affecting at least some groups of mammals and birds in this bioregion, in addition to those species currently listed as threatened.
Number of taxa in the Central Arnhem 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 | |
| Reptiles | 2 | 4 | 0 | 1 |
| Birds | 0 | 2 | 1 | 1 |
| Mammals | 0 | 1 | 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 or acacia species known from this bioregion.
Richness
The diversity of Acacia and Eucalyptus species in the two subregions of Central Arnhem is relatively low (6 and 35 species for Acacia and 17 and 32 species for Eucalyptus).
Birds
Central Arnhem is one of the least surveyed bioregions in the country. Several restricted range and threatened taxa are sure to occur there, but none were recorded on the few record sheets submitted. Not surprisingly there is also no information on trends.
Status: Moderately diverse tropical woodland bird community, probably little changed.
Rare and threatened: Probably a suite of Arnhem Land endemics in fire sensitive spinifex grassland and rainforest, but no major populations recorded in Atlas.
Increasers: No information.
Indicators: Emu, Banded Fruit-Dove, Partridge Pigeon, Varied Lorikeet, Hooded Parrot, Rainbow Pitta, Black-tailed Treecreeper, White-throated Grasswren.
Trend: Most species probably stable.
Scenario: The shift from fine-scale fire mosaic to large scale burn pattern may continue to affect sandstone taxa and granivores.
Actions: Re-establish fine scale burning mosaic.
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 50 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 .54. (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 .05. (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 .1. (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 1. (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
The lack of existing reserves in this bioregion, and the intactness of native vegetation across almost the entire region ensures that there is great flexibility in selecting candidate areas for possible inclusion in a bioregional reserve system. However, almost all lands in this bioregion is under inalienable Aboriginal ownership, so any reserve selection is entirely contingent upon the establishment of either a cooperative management agreement or through the development of Indigenous Protected Areas. Assuming that such development includes a contribution of resourcing, employment and capacity building, there is a reasonable chance of such collaboration occurring.
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
Existing recovery plans for marine turtles (and codes of practice in the commercial fishing industry to limit incidental by-catch) provide some broad-brush protective management for this group of threatened species. The Northern Territory also has a Strategy for conservation of biological diversity of wetlands, which provides some management goals and actions for wetlands across tenures.
Integrated NRM
As with many other bioregions in northern and central Australia, the most important priority for biodiversity conservation and management is not so much (additional) reservation but rather the provision of resources and capacity building to encourage and allow Aboriginal owners to more effectively manage their lands (and particularly to combat weeds and feral animals, and to reinstitute more favourable burning regimes), where possible in collaboration with government conservation agencies.
In collaboration with Aboriginal landowners and their agencies, and supported by NHT, Parks and Wildlife Commission is currently undertaking a conservation assessment and plan for a large part of this bioregion, the Arafura Swamp catchment.
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
With the exception of assessment associated with the Arafura Swamp catchment project, there is extraordinarily little documented information about the biota of this bioregion. Hence, obtaining such baseline information through wildlife survey and traditional ecological knowledge, is a major priority.
Management would also benefit from more detailed environmental mapping, in particular vegetation mapping at the scale of 1:250,000 or better.
Another priority is the monitoring of threats, their impacts and their responses to management actions.
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.
Before you download
Most publications are downloadable as PDF files. Adobe Acrobat Reader is required to view PDF files.
If you are unable to access a publication, please contact us to organise a suitable alternative format.
Key
Links to an another web site
Opens a pop-up window