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Interdependence of plants and animals: This
figure shows NT's rainforest patches and the movement of one Torres
Strait Pigeon, TSP22, captured on October 1, 1996. The lines show
its pattern of movement between rainforest patches: over 78 days it
flew 65.5 km dropping about 10-20 seeds in each rainforest
patch.
Map courtesy of PWCNT
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A three-year study by the Parks & Wildlife Commission of the
NT, in collaboration with Northern Territory University, has
recommended a new network of land reserves to preserve the plants
and animals of the Top End's rainforest patches. Through
integrating a series of projects, scientists Owen Price, Christine
Bach, Alison Shapcott and Carol Palmer uncovered a delicate natural
balance in which the rainforest patches and their animals,
particularly those that move between patches, are reliant on one
another for survival.
Rainforest patches occupy 2700 square km of the NT—only
0.2 per cent of the land area—and are made up of 15,000 small
patches with an average size of 3.6 hectares. "Despite their
scattered and small nature, these patches include 13 per cent of
the NT's known plant species, many of them rare," said Mr Price.
"Our research has found that protecting these rainforest patches
must take into consideration the needs of the animals that use them
because without the animals the patches themselves will decline and
vice versa."
This is because each rainforest patch does not provide all the
resources some of these animals require, fruit-eating birds and
flying foxes in particular. These animals must move between
patches, while also seeking food from other surrounding habitats,
during times when few rainforest plants are fruiting. "In moving
between these patches and across the surrounding landscape, these
animals are dispersing seeds, providing new plants to maintain the
diversity of species existing in rainforests," said Mr Price.
The project's research focused on several species of
fruit-eating birds including Pied Imperial-pigeons (Torres Strait
Pigeon), Rose-crowned Fruit-doves, Figbirds, Yellow Orioles, Common
Koel and Great Bowerbirds, along with the Black Flying Fox.
"As an example of the integral part these animals play in the
survival of rainforest patches, our research found that flying
foxes deposit about 350 seeds each night into an average sized
rainforest patch at Gunn Point and birds about 190 seeds a day,"
explained Mr Price.
The research suggests that in dense areas of
rainforest—such as between Darwin and Kakadu National
Park—the loss of about half to two-thirds of rainforest
patches would likely result in the extinction of frugivore
(fruit-eating) species from remaining patches. The gradual
extinction of plant species would then be an inevitable
consequence.
In recognising this inter-dependence and studying the threshold
at which the ecological equilibrium is maintained, the study
recommends a number of guidelines for the design of reserves aimed
at protecting rainforest and the animals that use them. This
includes a suggestion that clusters of rainforest patches be
reserved. Each cluster should be made up of all of the rainforest
patches (with a minimum area of 32 square km) and a variety of
other habitats in a circle of up to 50 km radius. The report says
about seven clusters would be needed across NT to protect all flora
and fauna species associated with rainforest patches.
Mr Price said these suggestions had been made for inclusion in
PWCNT strategies, in particular a Parks Master Plan for the Darwin
region currently under development. However, he said that all
landholders could assist in protecting the delicate balance of
nature across the Top End.
"Remember, when you cut down that tree or clear that patch,
however small, the loss from the landscape could trigger a
cascading decline among plants and animals in nearby rainforest
patches that previously relied on your piece of bush remaining in
the network," he said.
