Vegetation

2011

 

Australia’s vegetation comprises native and exotic species, in assemblages that vary from essentially natural to completely modified. The year 1750 has been widely adopted as the reference point for comparison of pre-European vegetation with subsequent extent of Australian vegetation,44 and is used for that purpose here.

The continental extent of all forms of vegetation is summarised in Table 5.6 and mapped in Figure 5.14.

Table 5.6 Continental extent of Australian vegetation
Vegetation category Area (million hectares) Area (%)
Native shrublands and heathlands 283 37
Native grassland and minimally modified pastures 257 33
Native forests and woodlands 148 19
Annual crops and highly modified pastures 66 9
Ephemeral and permanent water features 7 1
Intensive uses (includes urban, peri-urban, mining) 3 0.4
Plantation forests 2 0.2
Perennial crops 1 0.1
Bare 1 0.1
Horticultural trees and shrubs 0.7 0.1
TOTAL 769 100

Source: Australian Bureau of Agricultural and Resource Economics and Sciences2

Native vegetation

Australia’s native vegetation can be classified into 23 major vegetation groups (MVGs), the majority of which are dominated by just two woody plant genera—Acacia and Eucalyptus.44

Extent

Three MVGs each occupy more than 10% of continental land area—hummock grasslands (18%), eucalypt woodlands (12%) and Acacia shrublands (11%). Seven MVGs together occupy less than 2% of continental land area—rainforests and vine thickets, eucalypt tall open forests, callitris forests and woodlands, low closed forests and tall closed shrublands, mangroves, heathlands and eucalypt low open forests.44

The pre-1750 and current extent of MVGs are summarised in Figure 5.15 and mapped in Figures 5.16 and 5.17.

Since European settlement, 13% of Australia’s native vegetation has been cleared and converted to other land uses, predominantly agriculture. The extent of loss varies greatly between vegetation types (Figure 5.16). The greatest areal loss of vegetation since European settlement has been in the eucalypt woodlands (MVG 5), which have been reduced by one third, to around 84 million hectares. Each of eucalypt open forests (MVG 3), mallee woodlands and shrublands (MVG 14), and other grasslands, herblands, sedgelands and rushlands (MVG 21) have suffered a similar proportional loss, from smaller original extents. The greatest proportional losses, to around 60% of their original extent, have been in casuarina forests and woodlands (MVG 8), and low closed forests and tall closed shrublands (MVG 15).

The pattern of native vegetation loss is illustrated by Figure 5.18. This shows the proportion of native vegetation remaining in each of Australia’s 18 agroclimatic regions (an agroclimatic region is defined by particular climatic parameters relevant to farming systems).45 The greatest reductions in native vegetation extent have been in eastern, south-eastern and south-western Australia, where post-1750 human settlement and agricultural land uses are greatest. More than 50% of native vegetation has been lost in six agroclimatic regions, and one-third or more in two other regions. As discussed in Section 2.1, this pattern of vegetation loss reflects that of European settlement and land use.

Condition

The condition of native vegetation depends on a suite of factors operating at a range of spatial and temporal scales. As discussed in Section 3, the most important of these are the extent of vegetation clearing and resultant patterns of fragmentation; the impacts of climate variability such as that manifested through drought, and of particular climate events such as cyclones; the effects of both historical and current management practices, such as grazing and harvesting; and the impacts of fire events and regimes.46-47

In general, vegetation condition deteriorates with diminishing remnant extent. The national rate of native vegetation clearing is now balanced by the extent of regrowth (see Section 3.2.2).48 However, the condition of much native vegetation is likely to be deteriorating, particularly fragmented remnants that are in intensive land-use areas and subjected to pressures such as grazing.

Historically, vegetation condition has been assessed at a range of scales and with a variety of approaches. Progress has recently been made towards developing a nationally consistent approach to assessing vegetation condition, built around state-level approaches and assessments;46 however, national-level results from this work are not yet available. In the interim, related parameters that provide insights into native vegetation condition at a continental scale are:

  • the degree of fragmentation of native vegetation (see Chapter 8: Biodiversity, Section 3.7.1)
  • annual and seasonal variation in green vegetation cover (mean annual greenness fraction—the fraction of land surface covered by photosynthesising green vegetation), which reflects variation in net primary productivity as a proxy for vegetation condition (e.g. Donohue et al.49); see Section 2.2.6 and Figure 5.10
  • the degree of vegetation modification, as assessed under the ‘Vegetation Assets, States and Transitions’ (VAST) framework developed by the Bureau of Rural Sciences.50

The VAST framework ‘classifies vegetation condition by degree of anthropogenic modification from a benchmark condition state’;51 the VAST classification framework is summarised in Table 5.7. The degree of modification of Australia’s native vegetation across Australia’s land area as assessed by VAST is illustrated in Figure 5.19. This classification is provided by continental-scale remotely sensed data, and is most useful for broad regional assessments rather than fine detail.51

Again, the continental pattern of vegetation modification reflects Australia’s history of European settlement, land clearing and agricultural land uses. The greatest extent of least-modified vegetation is in the north and centre of the continent, along the eastern and south-western ranges of mainland Australia, and in the eastern ranges and south-west Tasmania. In these zones, an average of 80% (range 70–96%) of vegetation is classified as VAST category I or II (residual or modified; for definitions, see Table 5.7). Conversely, the greatest extent of most-modified or replaced vegetation is in the intensive-use zones of the eastern and southern mainland, and in the midlands and north of Tasmania. In these zones, an average of only 40% (range 15–69%) of vegetation is classified as VAST category I or II.

Table 5.7 Vegetation Assets, States and Transitions (VAST) framework explanation of vegetation classes
Increasing modification
  Native vegetation cover
Dominant plant species indigenous to the locality and spontaneous in occurrence, i.e. a vegetation community described using definitive vegetation types relative to estimated pre-1750 types
Non-native vegetation cover
Dominant structuring plant species indigenous to the locality but cultivated, alien to the locality and cultivated, or alien to the locality and spontaneous
Vegetation cover classes Class 0: residual bare Class I: residual Class II: modified Class III: transformed Class IV:
replaced-adventive
Class V:
replaced-managed
Class VI:
removed
Criteria Areas where native vegetation does not naturally persist Native vegetation community structure, composition and regenerative capacity intact—no significant perturbation from land use or land management practice. Class I forms the benchmark for classes II to VI Native vegetation community structure, composition and regenerative capacity intact—perturbed by land use or land management practice Native vegetation community structure, composition and regenerative capacity significantly altered by land use or land management practice Native vegetation replaced with species alien to the locality and spontaneous in occurrence Native vegetation replaced with cultivated vegetation Vegetation removed

Source: Thackway & Lesslie50

Figure 5.20 illustrates the extent of modification of each of the MVGs as assessed by VAST.

Non-native vegetation

Non-native vegetation includes that comprised solely of exotic species, such as many annual and perennial crops, and native vegetation assemblages that have been significantly altered through management or invasion by exotic species. There is currently no generally agreed threshold for the level of alteration at which vegetation ceases to be classified as ‘native’,44 so there may be some imprecision in classification between, for example, VAST categories III and IV.

The dominant forms of non-native vegetation are annual crops and highly modified pastures, together comprising around 9% of Australia’s land area (Table 5.1). All other forms of non-native vegetation each comprise less than 1% of continental land area: plantation forests comprise 0.22%, perennial crops 0.14%, and horticulture 0.08% of our land area.

The major trends in non-native vegetation over the reporting period were discussed in Section 2.1. These reflected climatic, market and policy factors.

Kanowski P, McKenzie N (2011). Land: Vegetation. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/science/soe/2011-report/5-land/2-state-and-trends/2-3-vegetation, DOI 10.4226/94/58b6585f94911