From Tropical Topics newsletter, No. 68 June, July
2001, produced by Stella Martin, Queensland's Environmental
Protection Agency. Click on the continuing pages to read more.
Many introduced plants and animals find savanna
conditions ideal and are doing considerable damage to the
wetlands.
Buffaloes
A small number of domesticated water buffaloes were brought to
the Top End from Indonesia over 150 years ago. By the 1980s there
were an estimated 350 000 feral buffaloes. The hard hooves of these
animals cause considerable environmental degradation around
wetlands where they congregate to wallow. Their trails become
deeply eroded, sometimes allowing saltwater to invade freshwater
habitats. Reeds and other aquatic plants have been destroyed, young
trees of many species eaten away and waterholes fouled.
Buffalo numbers have dropped considerably since the Brucellosis
and Tuberculosis Eradication Campaign led to intensive removal.
Unfortunately, however, the disappearance of the buffaloes has
facilitated the spread of weeds, such as para grass, in the eroded
environment.
Pigs
Pigs cause enormous environmental damage but are much harder to
control than buffaloes. They are smaller, shelter out of sight by
day and are very mobile and very intelligent. They also reproduce
prolifically. Pigs eat almost anything, excavating the earth for
roots and soil fauna such as earthworms, and consuming the eggs of
ground-nesting birds and turtles. They trample saplings, ringbark
trees, erode wetland edges (left), contaminate water, feast on
crops and compete with native animals for food. Weeds thrive in
their wake and they can carry many diseases, including forest
dieback ( phytophora ). They also have the potential to
spread foot and mouth disease far and wide, should it ever reach
Australia.
Weeds
Two notable weeds (below) are water tolerant
grasses, introduced to increase the grazing potential of wetlands.
Unfortunately they spread rapidly, clogging irrigation and drainage
channels, infesting lagoons and creeks, displacing native
vegetation, reducing access to waterways for wildlife and
recreation and lowering oxygen levels with detrimental effects on
fish and other aquatic animals.
Para grass ( Urochloa/Brachiaria mutica ) was
introduced from tropical Africa to Queensland about 1880. It can
grow in water up to a metre deep from which it excludes all other
species, establishing itself as a dense monoculture which
completely obliterates open water. Para grass spreads rapidly, even
into rainforest next to flood plains, carrying fire into these
areas in dry times.
Olive hymenachne ( Hymenachne amplexicaulis
) was introduced to Australia in the 1970s from South America.
A ‘ponded pasture’ grass, it can grow comfortably in
water as deep as 2m. It is a severe threat to open wetlands,
replacing water lilies, reeds and all other plants, wherever it
spreads, with a dense green mass. It is important to look out for
infestations of this grass in natural areas. The illustration
(right) shows the distinctive clasping manner in which leaf base
grows around the stem of the plant.
