AS more land is earmarked for agricultural
development in the Top End, researchers are asking if there is a
way biodiversity can be maintained within broadscale clearing. And
if there is a way to do this, what type of bushland, and how much
of it, is needed to sustain animal species? By Leonie
Norrington
Some early findings of a recent survey in the Northern
Territory’s Litchfield Shire suggest that if large enough
patches of bushland are left intact within agricultural
developments, they may benefit biodiversity and therefore the
overall environment.
The survey was part of a project at the Parks and Wildlife
Commission of the NT—a partner agency with the Tropical
Savannas CRC—investigating the effects of clearing on native
animals and the place patches of bushland might have in minimising
local animal extinction.
Through his research, project leader Dr Owen Price hopes to find
out how clearing impacts on local wildlife and if biodiversity can
be maintained within agricultural areas, what type of bushland is
needed to sustain animal species. The research will provide
guidelines for sustainable landscape planning.
The survey collected information on plants and animals at six
different sites in the Shire; patches of bushland, mango orchards,
cleared land and uncleared bushland. The patches of bushland varied
in their isolation; corridors connected some, while others were
completely isolated and surrounded by cleared land. The smallest
patch was a one-quarter hectare ‘bush block’, the
largest a 50-hectare patch of crown land that has never been
cleared. Researchers then sampled plant and animal numbers within a
4 km radius of the centre of each site.
The study found that most species will not use cleared sites or
mango orchards. The abundance of 28 animal species in the 4 km
radius zones decreased if bushland patches in those zones were too
small or if the animals were isolated from bushland. Many mammals
and small bird species were in this group. For example, quolls were
found only in fragments where at least 65 per cent of the
surrounding area (within 4 km) was also woodland.
However, a few species, such as the bandicoot and crow,
responded positively to fragmentation. This suggests that they
prefer the new habitat mosaic created by changed land uses.
According to Owen, bandicoots might use a bushland patch as a base
from which they can feed in the surrounding agricultural land at
night. The quality of bushland in these patches may also be
important, as well as the amount and quality of the bushland in
surrounding areas.
Broad-scale clearing, and the subsequent destruction of habitat,
is the major cause of animal extinction. Until recently there was
little broadscale clearing in the Top End, but more areas are now
being proposed for development. Already 100 km2 of Litchfield
Shire, on the outskirts of Darwin, has been cleared for
horticultural and rural living. There is now a proposal to develop
2700 km2 of land for agriculture in the Daly Basin, south of
Darwin.
“Wherever habitat is changed, some species will be
lost,” says Owen. “But other species may maintain a
stable population if we retain the right mix of bushland within the
agricultural matrix. We have to find a balance.” PhD student
Brooke Rankmoore’s work will also add to the picture when she
studies, in more detail, the movements of some the species
identified.
