State of the Environment 2011 (SoE 2011)
State of the Environment 2011 Committee. Australia state of the environment 2011.
Independent report to
the Australian Government Minister for Sustainability, Environment, Water, Population and Communities.
Canberra: DSEWPaC, 2011.
5 Land
2.3 Vegetation
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.
| 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
Source: Australian Bureau of Agricultural and Resource Economics and Sciences2
Figure 5.14 Extent of all forms of vegetation across Australia, 2009
2.3.1 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).
Source: Australian Government Department of the Environment and Water Resources44
Figure 5.15 Current and pre-1750 extent of Australian major vegetation groups
Source: Australian Government Department of the Environment and Water Resources44
Figure 5.16 Estimated pre-1750 distribution of major vegetation groups in Australia
Source: Australian Government Department of the Environment and Water Resources44
Figure 5.17 Current distribution of major vegetation groups in Australia
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.
Figure 5.18 Percentage of Australian native vegetation remaining, by agroclimatic region
Letters indicate agroclimatic categories; numbers indicate subcategories for each region.45
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.
| → 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 |
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| 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.
Source: Environmental Resources Information Network, Australian Government Department of Sustainability, Environment, Water, Population and Communities, 2011
Figure 5.20 Extent of modification of major vegetation groups, as assessed by VAST
2.3.2 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.
| Component | Summary | Assessment grade | Confidence | ||||
|---|---|---|---|---|---|---|---|
| Very poor | Poor | Good | Very good | in grade | in trend | ||
| Native vegetation extent—outside intensive land-use zones | More than 90% of the original native vegetation remains in central and northern mainland Australia, and in Tasmania’s central highlands and south-west |  |
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| Native vegetation extent—within intensive land-use zones | Less than 50% of the original native vegetation remains in most of Australia’s major primary production regions, and in many settled coastal regions | |
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| Native vegetation condition—outside intensive land-use zones | Although there are exceptions associated with invasive species or management regimes, the degree of modification of most vegetation outside the intensive land-use zones is relatively small. The proportion of each major vegetation group classified in VAST categories I or II (residual or modified) averages 80% |  |
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| Native vegetation condition —within intensive land use zones | The proportion of each major vegetation group classified in VAST categories I or II (residual or modified) averages 40% | |
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| Recent trends | Improving | Stable | Confidence | Adequate high-quality evidence and high level of consensus |
| Deteriorating | Unclear | Limited evidence or limited consensus | ||
| Evidence and consensus too low to make an assessment | ||||
| Grades | Very good: The environmental values of native vegetation are, or approximate, those that would be found in undisturbed vegetation; community structure, composition and regenerative capacity are intact | |||
| Good: The environmental values of native vegetation are suboptimal, but community structure, composition and regenerative capacity remain largely intact | ||||
| Poor: The environmental values of native vegetation are significantly compromised and are unlikely to recover without intervention) | ||||
| Very poor: The environmental values of native vegetation have largely been lost | ||||
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