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Vertebrates in the VRD

From John Woinarski, 2000. Vertebrate impacts: An overview. In Managing for healthy country in the VRD eds. Tropical Savannas CRC. John Woinarski is from the Parks & Wildlife Commission of the NT.

Vertebrate impacts: an overview

Studies undertaken on vertebrate biogeography in the VRD for the Tropical Savannas CRC have centred on two areas. The first has involved determining the distribution of vertebrates in the VRD in relation to other aspects of the environment such as soils and climate. The second has been measuring the response of these vertebrates to land management. A range of related activities is being undertaken and these are in varying stages of progress.

Mitchell grasslands

Work has been undertaken to look at the biodiversity impacts of various grazing intensities on Mitchell Grasslands. This has shown that the impacts are subdued across the limited range of grazing intensities currently in use. Nonetheless, some animals are more abundant at sites remote from water points. The regional abundance of these animals has probably decreased by around 50-90% of their pre-grazing levels. The management implication of this study is that water-remote sites are important for biodiversity, and that any attempt to increase the number or spread of artificial watering points will be detrimental to biodiversity.

Given the findings described above, further work is being undertaken to examine the costs and benefits of various grazing regimes from both production and biodiversity standpoints. The idea is to encourage interest in, and acceptance of, regimes that have the best results for biodiversity. This work is primarily focused on the Barkly Tablelands, but has clear relevance to the VRD.

Remote sensing and biodiversity monitoring

So far, this project has shown that there is some relationship between a land condition assessment developed from satellite data interpretation, and the type of plant and animal species found in a given area. (See completed CRC research projects Landscape health, Regional land condition and Vertebrate biogeography ) The relationship is not especially strong, however, and more definite conclusions will be available upon completion of data analysis. Should a reasonable correlation be established, ongoing rapid assessment of biodiversity status over large areas of the VRD may be possible.

Conservation planning for cracking clay environments

Cracking clay (black) soils are generally the most fertile environments in the tropical savannas. They are under increasing development pressure, most notably for horticultural development in the Katherine-Daly region and in the Ord Stage 2 area. Work is being undertaken in the VRD to provide an assessment of the conservation value of these environments and to develop conservation planning for the maintenance of those values. Initial work undertaken in a range of areas across the VRD has confirmed that the animal and plant life of cracking clay environments is distinctive and is generally represented in few conservation areas.

Conservation planning for the Sturt Plateau

Initial field surveys identified stable populations of bilbies in the far southeast of the VRD in the Cattle Creek area, the far north of their range. These populations are possibly related to the patches of ungrazed mitchell grass in the region and suggest that the area has high conservation values. The aim of the project is to identify the major conservation values of this region, encourage public appreciation of those values, and to determine the most appropriate management practices for the conservation of those values.

Vertebrates and fire

This study found that the extensive application of a single constant fire regime would lead to a regional decline in biodiversity in the VRD. The impacts of fire regimes on vertebrates on grazed loam (limestone-derived) and clay (basalt-derived) soils sites at Kidman Springs were assessed. A substantial variation in reptile and bird communities was found in association with differences in fire regimes. Marked differences were also discovered between vertebrate species in responses to fire regimes. The results of this study will be used for other work including fire management modelling and practical on-ground fire planning in Gregory National Park.

The major management problem in the sandstone ranges of the VRD is fire. A project similar to that described above has just commenced and will compare the fauna in sandstone country exposed to differing fire regimes.

Riparian strips

Strips of country associated with the rivers and creeks of the VRD typically support a richer variety of birds than that in surrounding savannas. Many bird species are either restricted totally to these riparian strips or are in are much higher abundance than in surrounding areas. Other species move between riparian and non-riparian areas on a seasonal basis, suggesting that the maintenance of both these habitats is important for their survival. Further work is being done to confirm the management implications of this study.

Biodiversity modelling

Computer modelling enables a range of management scenarios to be studied that would either be far too costly or not feasible with field experiments alone. Modelling has already been undertaken by CSIRO to examine the impacts of various fire and grazing regimes on the tree/grass character of savannas (See completed CRC research projects Modelling, monitoring and managing landscape change). Including biodiversity information in these models will provide another tool for the cost/benefit assessment of a range of possible management actions. Analysis will also be undertaken to identify which factors most critically affect biodiversity.

Bird distribution and soil/vegetation patterning

This study aims to identify the relationship between the number and type of bird species found within areas of particular soil type and vegetation. Once complete, the project should provide a broad understanding of which elements of the environment most strongly influence the richness of biological communities.

Wildlife atlas

A wide range of information has been collated on the wildlife of the VRD. An atlas is being developed based on this and possibly other vegetation information, for use as a tool for interpretation, communication and planning.

A wider range of information about the natural environment of the VRD is also being assembled in order to develop a better idea of which species and environments are currently under-represented within conservation reserves. This work clearly shows that there is a major bias towards reservation of sandstone environments, over and above that encompassing loam and particularly clay soils. Further work will be undertaken to identify specific species and sites that should be incorporated in any future development of the conservation network within the VRD.

Vertebrate diversity and landscape functionality

Landscape function analysis is a type of investigation that examines the soils and vegetation processes that shape the landscape. Measures of landscape functionality are increasingly being used to characterise landscape health. There is, however, little evidence to indicate that these measures correspond with the richness or composition of vertebrate species in particular areas. Work is therefore being undertaken to investigate this relationship and to develop a better assessment of environmental health.