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.
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,
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
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
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.
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.
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
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.
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.