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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.
Australian Terrestrial Biodiversity Assessment 2002
Paul Sattler and Colin Creighton
National Land and Water Resources Audit, 2002
ISBN 0 642 3713
Case Study
Tiwi-Cobourg (1 & 2) Second lowest stress class
Coburg Peninsula coastline
Photo: PWCNT
Tiwi-Cobourg is a small coastal bioregion at the extreme north of the Northern Territory. It comprises one mainland section (Cobourg Peninsula), the two large Tiwi Islands (Bathurst and Melville), Croker Island, and smaller satellite islands around these. All lands in the bioregion fall under three parcels that are inalienable Aboriginal owned lands. The population is about 2750. There is little commercial land use in the bioregion, although this may change with projected major development of a forestry industry based on plantations of exotic timbers. The ecological fabric of the bioregion is influenced by the extremely seasonal climate, the highest rainfall in the Northern Territory, and frequent destructive cyclones.
The principal vegetation type is extensive open forest dominated by Eucalyptus miniata, E. tetrodonta and Corymbia nesophila. The eucalypt forests in this bioregion are the best developed in the Northern Territory. There are also large areas of "treeless plains" (shrublands and grasslands dominated by Acacia, Banksia and Lophostemon species), a vegetation type unique to this bioregion. Monsoon rainforests are also unusually well developed in this region and their highly fragmented distribution poses particular management challenges. The bioregion also contains mangroves, coastal dunelands, and small floodplains. Biodiversity information includes good documentation of traditional Aboriginal knowledge.
The region has many conservation values, including:
- at least 9 endemic plant species, 4 endemic invertebrate species, 8 endemic bird subspecies and 2 endemic mammal subspecies;
- 34 taxa listed as threatened by the Northern Territory or the Commonwealth (including 14 taxa listed under the Environment Protection and Biodiversity Conservation Act 1999);
- many major nesting colonies of seabirds, and colonial breeding sites of marine turtles; and
- one listed Ramsar wetland.
The major conservation value of the bioregion is more pervasive—the maintenance of large continuous tracts of relatively unmodified environments.
The bioregion contains only one conservation reserve, the large (2207 km²) Garig Gunak Barlu (formerly Gurig) National Park, which occupies all of Cobourg Peninsula and its satellite islands. This park is Aboriginal owned and co-managed by Aboriginal owners and the Northern Territory conservation agency.
Condition and trend
The bioregion is in good condition, and without obvious acute loss or degradation. Notwithstanding its apparent untouched naturalness, at least one bird species (the threatened Gouldian Finch) appears to have been lost over the last 150 years. There have been no recent records from Cobourg Peninsula for a further four bird species and one mammal species, and the endemic subspecies of Hooded Robin on Tiwi Islands may have disappeared in the last two decades.
The apparent paradox of biodiversity loss within a superficially intact system is a recurring theme across much of remote Australia. The paradox is resolvable by recognition of the landscape-wide degradation of habitat quality due to impacts of feral animals, spread of weeds and altered fire regimes.
Threatening processes
The underlying management problem in the Tiwi-Cobourg bioregion is lack of resources. The economic base of the bioregion is so meagre that there is little that the landowners can do to combat threats to biodiversity. Indeed, in many cases, landowners will embrace land uses or factors which are harmful to biodiversity but which may bring in resources (e.g. meat from, and trophy payments for, feral animals). Hence there is little incentive to control feral animals, and because their impacts may be subtle and remote, there is no marked trigger for a management response. The most damaging of the ferals are pigs on Bathurst Island, Croker Island and Cobourg Peninsula, buffalo on Melville Island, horses on Croker Island, and banteng on Cobourg Peninsula. Feral cats may also be a major problem on the Tiwi Islands and Croker, and their spread to Cobourg Peninsula is a potential problem. Weed impacts are relatively minor, but recently there has been a series of small infestations of several weeds with potential for major impacts. Traditional burning regimes have changed across almost all of the bioregion due to aggregation of Aboriginal people to a few settlements; less immediate dependence upon, and intimate care for, the land; and some loss of traditional management knowledge. There is now a higher incidence of extensive, hot, late dry season fires, with more marked environmental costs.
A major forestry industry on Melville Island has been approved. This will clear between 30,000 and 100,000 ha of high quality eucalypt forest and replace it with plantations of the exotic Acacia mangium.
Management responses
Although 22% of the bioregion is reserved, the reserves contain representation of only four of the 11 mapped vegetation types, and no representation of most of the endemic and threatened taxa. It is relatively easy to design additional reserve(s) on the Tiwi Islands to remedy most of this inadequacy, but this is a futile exercise unlikely to be implemented unless the Tiwi landowners can realise benefits from any new national parks. Benefits such as employment opportunities, training and income need to be clearly articulated. Given the sparsity of alternative economic options, a small investment in natural resource management and employment prospects is likely to be far more effective and accepted in this bioregion than in more developed bioregions of temperate Australia. Management costs were estimated to include:
- the establishment of a conservation reserve on the Tiwi Islands (with training and employment of some Tiwi landowners);
- support of community rangers on Croker Island;
- actions to reduce feral animals;
- removal of pioneer outbreaks of weeds and maintain surveillance for new weeds; and
- restoration of traditional burning practices.
Limiting factors
The main constraint is the lack of resources required to achieve these management objectives. National conservation management resources in Australia have often been directed at highly imperiled or degraded fragments in temperate Australia. As evidenced in this bioregion, the less obvious management needs in remote Australia can be remedied far more effectively, efficiently and cheaply.
Future scenarios
The problem with ongoing gradual degradation is that there is no trigger. Without the resource contribution described in this case study, the highly significant conservation values will continue to diminish and Aboriginal landowners will continue to look elsewhere for employment or income. Many of the proposed alternative land uses may come at considerable cost to the region's biodiversity.
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