Biodiversity publications archive

Native vegetation clearance, habitat loss and biodiversity decline

An overview of recent native vegetation clearance in Australia and its implications for biodiversity
Biodiversity Series, Paper No. 6

Andreas Glanznig, Biodiversity Unit
Department of the Environment, Sport and Territories, June 1995

Executive summary

It is a common wisdom that most of the native vegetation cleared in Australia occurred last century and early this century. This is not the case. In the last 50 years as much land was cleared as in the 150 years before 1945. Extensive clearing for agriculture occurred in the 1960s and 1970s and significant clearing is still taking place. Evidence of continued excessive clearing of native vegetation in Australia has concerned the National Landcare Advisory Committee.

This concern is reinforced by the National Greenhouse Gas Inventory which provides estimates that indicate in 1988 and 1990 some 700,000 ha and 650,000 ha of native vegetation (including regrowth) were cleared respectively. The magnitude of native vegetation lost during 1990 equates to over one million rugby football fields, or over two rugby football fields being cleared every minute.

The current rate of clearance remains very significant. In Queensland alone permits to clear a total of 1,079,297 ha of leasehold land including 684,967 ha of virgin bush and 391,730 ha of regrowth and invasive woody weeds were granted in 1994. These figures are subject to the caveat that the permits are valid for five years and allow clearing at any stage during this period, and not all areas permitted to be cleared are actually cleared.

This paper shows that recently most clearance occurred in:

A proportion of the overall amount cleared is remnant vegetation which plays an important role in biodiversity conservation. The clearance rate in certain areas is particularly high. For example, a recent study has shown that 70 per cent of all remaining native woody vegetation has been cleared in just eight years (1977 to 1984-85) in an area of northern New South Wales in the vicinity of the Queensland border town of Goondiwindi. If this trend continues it can be expected that native vegetation will be virtually cleared from the area by the year 2000.

Internationally, Australia has a relatively high rate of native vegetation clearance. A comparison between the estimated annual rates of clearance in 1990 indicates that the amount of native vegetation cleared in Australia was more than half that cleared in the Brazilian Amazonia.

The data set out in this paper demonstrates that at a national level it is currently not possible to measure with any definable accuracy the present or recent rate of native vegetation clearance. The most economically feasible way to map and measure these changes is by comparative analysis of remotely sensed data acquired at appropriate time intervals. This method has been used to produce the most accurate State-wide data reported in this paper (eg. Victoria and Tasmania).

To meet this challenge, the Commonwealth Government recently committed $3.4 million to support a joint Commonwealth/State project to develop a better database on land clearing in Australia through collection and analysis of satellite monitoring data. Another recent initiative is the announcement by the Queensland Government of a package of measures, including the use of satellite remote sensing technology, to accurately assess tree clearing rates.

The rate and scale of recent clearance has significant implications for Australia's biodiversity. Native vegetation clearance, acting as a multiplier with other threats such as feral animals and weeds, is responsible for the disruption of ecosystems and the loss, fragmentation and degradation of habitat. The result is that many species are now in decline.

The view of two independent working groups, expressed in a paper to the Prime Minister's Science Council in 1992, was that the factors causing biodiversity loss centred primarily on habitat destruction or modification and that 'first and foremost, by far the major factor has been clearing of natural vegetation'.

The future impact of the current extent of native vegetation clearance is of concern. It may take decades, even centuries for the impact to be fully manifest. For example, the effect of habitat fragmentation on the population viability of a species can take centuries to become evident.

Another example is the disruption of ecological processes, such as water cycles, which can take decades to become apparent. Recent research indicates that over a span of some four decades, annual rainfalls in south-western Australia declined in areas which had been extensively cleared. Other research for the same region shows that water tables are rising beneath cleared land at rates of between 0.1 and 1.0 m/year and inferred that most of the surviving remnant vegetation will become severely degraded due to salinity within a generation. The effects of changed water cycles on land productivity are well known and many areas are now threatened by salinity and other forms of land degradation. For example, in the Murray Darling Basin, a study of dryland salinity concluded that 'changed land use, particularly broadscale clearing of native vegetation and its replacement with systems which use less water, is the principal cause of secondary dryland salinity'.

The gradual degradation of habitat by the removal of the understorey of forest and woodland remnants, through grazing for example, is also significant since it can lead to the loss of species and genetic variability.

Furthermore, the current pattern of native vegetation clearance has led to the release of large amounts of greenhouse gases. The National Greenhouse Gas Inventory Committee estimates that in 1990 forest clearing for agriculture contributed some 27.3 per cent of the total net emissions in carbon dioxide equivalent. These calculations are subject to the caveat that there is much uncertainty associated with the estimation of greenhouse emissions from native vegetation clearance.

While uncertainties associated with the data need to be reduced, enough evidence exists to highlight the serious nature of environmental damage caused by excessive native vegetation clearance. To guide actions by Commonwealth, State and Local Governments, the National Strategy for Ecologically Sustainable Development includes the precautionary principle which states that 'where there are threats of serious or irreversible environmental damage, lack of full scientific certainty should not be used as a reason for postponing measures to prevent environmental degradation'.

Despite the lack of complete information, the need for strengthened action to retain native vegetation has been recognised by governments in the National Strategy for Ecologically Sustainable Development, the National Greenhouse Response Strategy, the draft National Strategy for the Conservation of Australia's Biological Diversity and the National Landcare Program. This need was recently affirmed by the Australian and New Zealand Environment and Conservation Council which agreed that accelerated action to encourage the retention of native vegetation is a high priority in Australia. The draft National Biodiversity Conservation Strategy provides a timetable which also acknowledges the pressing need for action, that is 'by the year 2000 Australia will have arrested and reversed the decline of remnant native vegetation' and 'avoided or limited any further broad-scale clearance of native vegetation, consistent with ecologically sustainable management and bioregional planning, to those instances in which regional biological diversity objectives are not compromised'.

Recent initiatives which will contribute to this end include the Commonwealth Government's commitment of a further $7.5 million to the One Billion Trees Program.