Land: Vegetation

Independent report to the Australian Government Minister for the Environment and Heritage
Beeton RJS (Bob), Buckley Kristal I, Jones Gary J, Morgan Denise, Reichelt Russell E, Trewin Dennis
(2006 Australian State of the Environment Committee), 2006

8.1 Vegetation

The most visible indicator of land condition is the extent and quality of vegetation cover. Nationally the picture is deceptive—about 87 per cent of Australia’s original native vegetation  cover remains, but its condition is variable and masks an underlying issue of the decline of many ecological communities. Some ecological communities occupy less than 1 per cent of their original extent as a result of clearing for agriculture, and many others are highly fragmented . In addition, the components of many ecosystems, especially the understorey in forests and woodlands, have been severely disrupted.

Some regions, such as agricultural areas in south-eastern Australia and the south-west Western Australian wheat belt, have particularly suffered from over-clearing. The result in those areas is a landscape with ageing mature trees that have a radically changed, or non-existent, native grass and shrub understorey. Many trees are affected by dieback, and continued grazing of the understorey means they are not being replaced. The legacy of these effects further reduces the capacity of the environment to recover from a range of pressures associated with its use (see ‘Biodiversity’).

Australia’s rangelands occupy more than 75 per cent of the continent and include a diverse group of variably disturbed ecosystems such as tropical savannas, woodlands, shrublands and grasslands. They are home to a significant number of rare, threatened and endangered fauna and flora species, and include a number of World Heritage sites. The rangelands are extensively grazed, but there is evidence that some pastoral rangelands have improved over the last decade (Watson 2006).

Clearing of native vegetation  is an ongoing threat to Australia’s environment. Between 2000 and 2004, 1.5 million hectares of forest (which includes native and non-native vegetation) was cleared across the continent. After forest regrowth, the net change was a loss of 287 000 hectares (Figure 32). The rates of deforestation and forest regrowth vary across the states and territories (Figure 33), but there has been a recent increase in some states in advance of stronger clearing legislation. It is expected that most states will be clearing less native vegetation in the future as clearing regulations are progressively applied.

The concern about vegetation change extends beyond the number of hectares cleared or replanted each year. It is often the case that the replacement vegetation, whether natural regeneration or planted trees, is not like the communities that were previously cleared. For example, dense woody shrubs may form a monoculture in place of a naturally occurring, complex ecosystem. It is not possible to derive ecosystem complexity data from the data provided, however desirable this information may be, because the data are collected to monitor national-scale trends through time.

The picture is also confused by definitional issues. The area of forest discussed in this report corresponds to the international definition of forest and is the native and non-native vegetation that has at least 20 per cent canopy cover and could grow to at least two metres tall with a minimum of 0.2 hectares. Other systems of vegetation measurement, such as that used to assess key threatening processes, include all native vegetation across the entire continent, including sparse woody vegetation and non-woody vegetation such as grasslands. The states and territories also have variable definitions in the legislation they use to manage and protect vegetation. Despite its deficiencies from an ecological viewpoint, the forest (international definition) dataset is the only nationally consistent, long-term dataset available.

 J Lyons-Reid Left: sparse woody vegetation (less than 20 per cent canopy cover).
Right: forest (more than 20 per cent canopy cover).
Photos: J Lyons-Reid

Historically, almost all clearing in Australia has been for agricultural production. It was initially driven by a condition in many early leases to clear a specified number of hectares each year. Later came financial support from government agencies and new land clearing technologies developed by CSIRO. While community and government attitudes have changed, most clearing is still for agricultural production.

Clearing for commercial plantation forestry has also been significant. The plantation estate  is still expanding—from 1.66 million hectares in 2003 to 1.72 million hectares in 2004 (Figure 34). Although this is only 2 per cent of the Australian continent, the issue with this activity is that it occurs in sites of high forest production value, which often have high biodiversity values as well. From this perspective, the trend towards establishing plantations on former agricultural land rather than on native forest land, especially over the last 11 years, can be seen as positive (Figure 35). In some areas, however, social dislocation and loss of previous agricultural heritage landscapes can accompany such developments when entire farming communities are replaced with a private plantation that is managed by one person.

Figure 35: Previous land use of commercial forestry plantations

 Previous land use of commercial forestry plantations

Note: Data include industrial plantations only; (1) includes approximately 1 per cent of native grassland
Source: Wood et al (2001) and National Forest Inventory (2005)

Urban clearing for housing and infrastructure continues in biologically rich habitats along the Australian coast; it is a consequence of the continued urbanisation of the Australian coastline . Clearing in these areas is of concern because it often occurs in already fragmented habitats, some of which are quite small in extent, and many of which were ice age species refugia and hence have high conservation value. In aggregate, urban areas occupy about 24 per cent of the coastal fringe between Hervey Bay (Queensland) and Queenscliffe (Victoria).

Land clearing is not the only cause of vegetation and habitat loss. Major habitat changes have occurred in both northern and southern Australia due to a range of pressures, including grazing and changed fire regimes (see ‘Biodiversity’). A 2005 analysis of grazing pressure  relative to biomass showed that 62 per cent of the continent consists of areas where biomass is low and is therefore at risk from any level of grazing intensity—the rangelands and areas of minimal use.

Although grazing animals have different impacts, the combined impact of all domestic and non-domestic herbivores is significant. Total grazing pressure is one of the leading causes of vegetation changes (especially to grasses) and soil erosion. Australia has an estimated 28.5 million cattle and 103.1 million sheep in 2005-06 (ABARE 2006). The number of cattle has increased by an estimated 0.6 million from 2001-02 to 2005-06, and sheep numbers have decreased by 3.1 million over the same period. There were major reductions in the national flock during the previous decade. Kangaroo numbers have decreased because of the drought. The situation with other grazing species is unknown.