Central Arnhem

Bioregional Description

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.

Special 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.

• 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 stress class 5. 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 priority management/conservation priorities
   
  There are no conservation reserves in this bioregion. Some reservation is desirable, either as IPA 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.
• Wetlands
  • Nationally important 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.
     
  • Other wetlands of subregional significance
     
• Riparian zones
  
  The bioregion includes parts of the catchments of many important river systems, including the Roper, Walker, Koolatong, Goyder, Blyth, Rose, Phelp, Mainoru and Wilton Rivers. As with other environments in this bioregion, 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.
• 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).
• Species at risk
  
  Ten threatened species have been recorded from 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 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.

  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	National		Northern Territory
	endangered	vulnerable	endangered	vulnerable
reptiles	2	4	0	1
birds	0	2	1	1
mammals	0	1	0	1

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.

• Other flora values for eucalypts and acacias
  1. Endemism
     
     There are no endemic eucalypt or acacia species known from this bioregion.
      
  2. 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
  
  This bioregion was inadequately sampled to assess trends for the period between the two bird Atlases.
• Mammals
  
  The mammal fauna of this bioregion has been relatively resilient. Of 52 species recorded, 1 has become extinct, 1 has suffered severe decline, 2 have suffered decline and 48 have been stable.

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 IPAs. Assuming that such development includes a contribution of resourcing, employment and capacity building, there is a reasonable chance of such collaboration occurring.
• 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 & Wildlife Commission is currently undertaking a conservation assessment and plan for a large part of this bioregion, the Arafura Swamp catchment.

Further Information and Gaps

• Major data gaps and research priorities for bioregion
  
  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.
• Other information

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