Vegetation

2016

 

Forests and woodlands together represent about 16 per cent of the area of the Australian continent (124.7 million hectares); of this, 41 per cent is in Queensland, 18 per cent in New South Wales, 15 per cent in Western Australia and 12 per cent in the Northern Territory (ABARES 2014). The National inventory report 2012 reported a net gain in forest cover in Australia between 2005 and 2012 of 1.6 million hectares (DoE 2014c). The continental extent of all forms of vegetation is summarised in Table LAN5 and mapped in Figure LAN26 (ABARES 2014).

Eucalyptus forests make up 74 per cent of Australia’s national forest estate, Acacia forests 8 per cent, Melaleuca forests 5 per cent, and rainforest types just 3 per cent of the total (Figure LAN27). Industrial plantations of exotic species contribute 2 per cent of the total forest extent (ABARES 2014), but produced 82.7 per cent of the wood supplied by Australian forests in 2012–13.

Table LAN5 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 (including 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 Sciences, Integrated Vegetation Cover dataset 2009, used under CC BY 2.5

Native vegetation

Numerous reports have analysed Australia’s native vegetation condition and extent since 2011. The precise figures—for example, relating to clearing, conversion and regrowth—differ depending on the data and methodology used; however, the overarching picture remains consistent. Rates of clearing have generally decreased in Australia since a peak in 2006, and have stabilised in most states since 2011. However, in Queensland, clearing increased during the period 2011–14.

The rate of reclearing (i.e. clearing of forest cover that has regrown on previously cleared land) has also remained relatively stable since 2011 (DoE 2015).

Extent

Many vegetation communities in Australia have been heavily cleared since European settlement. For example, approximately 30 per cent of Australia’s land area was covered in forest before European colonisation; today, only about 16 per cent of the land area is forest (MPIG & NFISC 2013). Deforestation rates have decreased in each successive decade since the 1980s, and have also decreased as a proportion of the amount of primary (old-growth) native forest left (Evans 2016). However, about 1 million hectares of forested land were cleared in 2000–14, although much of this area was regrowth (Figure LAN5). For most years, the level of tree clearing in Queensland is greater than the combined total for all other states and territories. The main cause of clearing is for pasture (Figure LAN28a). About 75 per cent of clearing takes place on freehold land (Figure LAN28b), even though this only accounts for 31 per cent of the landscape (Evans 2016).

The scale and rate of clearing vary among vegetation communities. A recent report by Tulloch et al. (2015) showed that, of 75 vegetation communities assessed (according to the Australian Government’s National Vegetation Information System—NVIS 4.1, and excluding nonvegetation and cleared vegetation types), 32 per cent had lost at least 20 per cent of their original extent, and 7 communities had lost more than 40 per cent of their original extent. The 3 most heavily cleared communities (mallee with a tussock grass understorey, brigalow, and temperate tussock grasslands) together previously covered more than 170,000 square kilometres of Australia, and each has less than 20 per cent of its original extent remaining. In comparison, 19 vegetation communities have lost a very small proportion (less than 2 per cent) of their original extent.

Condition

Vegetation condition is effectively a subjective assessment of the health of an ecosystem, and so takes into account a suite of factors operating at different spatial and temporal scales. The most important factors are the extent of a community relative to its former extent, the extent of invasion by invasive species, and the degree of fragmentation within that remnant extent. Climatic impacts, such as the effects of drought, flood and wind storms, have been affecting vegetation for millennia, but these effects can be magnified if communities are limited in extent or highly fragmented. Much of Australia’s remaining forest, shrubland, grassland and open woodland ecosystems are now degraded or fragmented (Tulloch et al. 2015, Evans 2016). A result of fragmentation is that smaller patches of habitat are now a common feature in many landscapes and represent an increasingly large component of remaining habitat for many ecosystems (Tulloch et al. 2015). Approximately 22 per cent of major vegetation communities in Australia have more than 50 per cent of their remaining extent in patches less than 1000 hectares. The contribution of patches less than 5000 hectares has increased in almost all areas of Australia, and significantly so along the east coast and in the south-west (Figure LAN6b). Other anthropogenic impacts, such as weeds, feral animal grazing and altered fire regimes, decrease vegetation condition.

Historically, vegetation condition has been assessed at a range of scales and using a variety of approaches. Progress has recently been made towards developing a nationally consistent approach to assessing vegetation condition; 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 (Figure LAN6)
  • 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 and indicates risk of erosion; see Figure LAN22)
  • the degree of vegetation modification, as assessed under the ‘vegetation assets, states and transitions’ (VAST) framework developed by the Bureau of Rural Sciences.

The degree of modification of Australia’s native vegetation across Australia’s land area as assessed by VAST is illustrated in Figure LAN29. This classification is provided by continental-scale remotely sensed data, and is most useful for broad regional assessments rather than fine detail.

Again, the continental pattern of vegetation modification reflects Australia’s history of European settlement, land clearing and agricultural land uses, and—perhaps less obviously—the legacy of 50,000 years of Indigenous land management practices. 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 of Tasmania. In these zones, an average of 80 per cent (range 70–96 per cent) of vegetation is classified as VAST category I or II (residual or modified; for definitions, see Table LAN6). 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 per cent (range 15–69 per cent) of vegetation is classified as VAST category I or II.

Figure LAN30 illustrates the extent of modification of each of the major vegetation groups, as assessed by VAST.

Table LAN6 Vegetation assets, states and transitions (VAST) classification framework

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 class

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 & Leslie (2008)

Non-native vegetation

Non-native vegetation includes vegetation comprising solely 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’, 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, which together comprise around 9 per cent of Australia’s land area (Table LAN2). All other forms of non-native vegetation each comprise less than 1 per cent of the continental land area: plantation forests comprise 0.26 per cent, perennial crops 0.14 per cent, and horticulture 0.08 per cent of our land area. Although there is currently interest in increasing the extent of irrigated agriculture, particularly across northern Australia, assessments of soil suitability and availability of predictable water supplies suggest that this is only likely to affect 1 per cent of the continental land area (Grice et al. 2013)

Metcalfe D, Bui E (2016). Land: Vegetation. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/land/topic/2016/vegetation-0, DOI 10.4226/94/58b6585f94911