Australia Yearbook - 2009-10

The cost in monetary terms of introduced
species on Australia’s landscape is significant.
The cost of weeds to Australian agriculture
alone is estimated to exceed $4 billion a year.
This does not take into account costs
associated with enviromental, health or social
impacts, which are often difficult to value. In
Kakadu National Park, $500,000 a year is
spent trying to eradicate just one woody weed
species (Mimosa pigra). In 1999, more than $2
million was spent over just one month to
eradicate the black striped mussel from the
waters around Darwin.
Unsustainable use of natural
resources
Use of resources is unsustainable if the rate of
use of a resource exceeds natural replacement,
or the conditions for replacement, e.g. soil
health, are not maintained. Unsustainable use
of natural resources, for example through
over-fishing and over-intensive agricultural
activity, is a significant contributor to
biodiversity decline.
Invasion of the Yellow Crazy Ant
on Christmas Island
The endemic red land crabs (Geocarcoidea
natalis) of Christmas Island are an
important species in influencing the unique
structural characteristics and species
composition of the island’s vegetation. The
invasion of yellow crazy ants (Anoplolepis
gracilipes) on the island has led to the
reduction in numbers of the red crabs, and
this has resulted in changes to the rates of
seedling recruitment of rainforest trees and
litter breakdown. This in turn has changed
patterns of nutrient availability and has led
to a rapid shift in forest structure and
composition in the rainforest ecosystem.
This has flow-on effects on other species
that rely on the rainforest ecosystems of the
island. For example, the Christmas Island
Pipistrelle bat (Pipistrellus murraryi) has
declined severely since the late 1980s and is
now presumed extinct. 14
7. PERCENTAGE OF ESTIMATED PRE–1750 NATIVE VEGETATION REMAINING BY IBRA BIOREGION
Vegetation Remaining
0 - 10%
11 - 30%
31 - 50%
51 - 70%
> 70%
Source: Australian Government Department of the Environment, Water, Heritage and the Arts.
14 Year Book Australia 2009–10