Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Ann Hamblin, Bureau of Rural Sciences, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06748 5
Physical changes to natural habitats (continued)
Land cover change in the Intensive Land-use Zone from 1990 to 1995, and recent estimates to 2000 [L Indicator 2.4]
'Land cover' describes the physical state of the land surface. Most land cover change over short periods occur as the result of changes to the amount of vegetation and through human constructions.
Australia's signing of the Kyoto Protocol on greenhouse gas reductions in 1998 has stimulated research and documentation of vegetational land cover change. The protocol set 1990 as the baseline date from which changes in emissions would be measured. This posed particular problems, as earlier attempts to compile the first National Greenhouse Gas Inventory in 1994 had highlighted how little information existed about land cover change. These earlier attempts (Atlas of Australian Resources 1990, Graetz et al. 1995), demonstrated that remote sensing imagery is probably the only feasible method for obtaining accurate information over very large areas. Agricultural Land Cover Change Project update earlier estimates of rates of clearing from 1990 to 1995 (Barson et al. 2000). Figure 35 shows this project covered about 38% of Australia, including all the ILZ.
Figure 35: Area assessed for land cover change, 1990-1995.
Source: Barson et al. 2000
In 1990, 38% of the study area supported woody vegetation two metres or more high and with a crown cover of 20% or more. The most extensive woody vegetation types were open forest, woodland, low woodland and tall shrubland. By 1995 decreases in vegetation cover had occurred throughout the study area. The main causes of clearing were for agriculture and grazing (Table 15). This clearing for agricultural activities exceeded all other categories.
|State||Agriculture (including orchard management)||Grazing||Other (inc infrastructure development)||Forests||Plantation||On-farm trees||Fire|
|NSW||51 860||nd||8 070||16 130||7 580||nd||123 040|
|NT||5 870||1 070||9 550||nd||20||nd||nd|
|Qld||40 510||924 410||27 380||3 970||12 300||nd||140|
|SA||6 040||nd||460||10||8 030||700||66 320|
|Tas||230||3 800||440||27 270||8 280||1 060||1 210|
|Vic||9 240||nd||3 480||30 280||21 640||nd||25 120|
|WA||99 930||nd||20 280||12 290||5 590||nd||198 140|
|Total||213 680||929 380||69 660||90 160||67 830||1 760||414 070|
nd = no data.
Source: Barson et al. (2000).
Increases in woody vegetation also occurred in the same period (Table 16) mostly as a result of post-fire and post-harvesting regeneration. It is sobering to note that efforts at on-farm and community tree-planting schemes provided less than 1.5% of the total increase.
|Cause of change||Area (ha)||% of total|
|Native woody regeneration after fire||480 710||52.1|
|Regeneration of native forests after harvesting||189 290||20.5|
|Regeneration of woody vegetation after grazing (Qld)||113 120||12.3|
|Regeneration of woody vegetation previously cleared (WA)||112 540||12.2|
|On-farm tree planting||13 210||1.4|
|Other (e.g. orchards)||14 380||1.6|
Source: Barson et al. (2000).
In all, the net woody vegetation loss was 863 090 hectares during the study period. This might suggest that woody vegetation was lost at a rate of about 172 620 ha per year, but the periods over which the changes were measured were not always exactly five years. Barson et al. (2000) calculated the annual rate of loss to be 428 280 ha and the annual rate of increase to be 191 070 ha. These figures indicate an annual rate of loss at 237 210 ha. The major changes took place in the South Brigalow and Brigalow belts of central and southern Queensland, the Desert Uplands and the Mulga lands (Figure 36).
Figure 36: Percentage cover of remaining native woody vegetation, 1990.
Source: Barson, Randall and Bordas (2000)
Figure 37: Extent of clearing in biogeographic regions, 1990-1995.
Source: Barson, Randall and Bordas (2000)
The figures for net woody vegetation loss or gain have not been estimated with the same degree of accuracy for the post-1995 period. The Australian Greenhouse Office considers estimates of net land vegetation change highly uncertain. Nevertheless using their accounting methods there is still a net loss of carbon dioxide equivalent to a ratio of 3:1 compared with that captured by vegetation acting as a sink. The most recent National Greenhouse Gas Inventory (NGGI) estimates for clearing rates are shown in Table 17.
|State||Area cleared in 1999 (ha)||Estimated area cleared in 2000 (ha)|
|Northern Territory||3 320||12 700|
|Queensland||425 000||425 000|
|South Australia||3 396||1 600|
|New South Wales||30 000||100 000|
|Victoria||2 450||2 500|
|Western Australia||3 738||6 000|
|Total||468 844||564 800|
Sources: 1999 data from National Greenhouse Gas Inventory; 2000 estimates from ACF (2001).
Most clearing is occurring in Queensland and New South Wales. In Queensland the State-wide Land cover and Trees Study (SLATS) has been able to revise these figures from remote sensed imagery and ground-truthed data, to provide significantly more reliable estimates of recent change (DNR 2000). In Queensland clearing rates have been 47% higher in the last years of the decade than in the 1990-1995 period, when they averaged 289 000 ha/year. In the period 1995-1997 annual rates increased to 340 000 ha/yr, but 425 000 ha per year were cleared between 1997-1999. This is close to the historic high for 1988-1991 when the clearing rate was 475 000 ha/yr 25%.
Nearly 86% of recent clearance was for pasture and an estimated 33% was clearance of regrowth vegetation from previously cleared vegetation. Ten per cent of the clearance was for cropping, and 4% for the combined activities of forestry, mining, infrastructure and settlement.
In New South Wales recent figures have been produced by the Department of Land and Water Conservation based on remotely sensed data and field checking (DLWC 2001). These indicate that between 1995 and 1997 the total amount of clearing was 58 490 ha at an annual rate of 32 800 ha. Between 1997 and 2000 the total amount of clearing was 32 546 ha or an annual rate of 14 028 ha.
Figure 38: Losses and gains of carbon from clearing versus other agricultural and forestry activities.
For updated information see http://www.greenhouse.gov.au/inventory/index.html
Source: AGO (2001a)
The ACF figures are described as 'conservative estimates based on the best available data' (ACF, 2001) including clearing permits and individual observations. The figures for the NGGI have been obtained from various sources. The Queensland figure is based on the SLATS survey quoted above. The figures for Western Australia and South Australia are based on clearing permits. The figures for Victoria, ACT, Tasmania and the Northern Territory are based on average clearing rates from 1991-1995. The figure for New South Wales is based on a 1998 report which has been superseded (DLWC 2001).
The figures above indicate the difficulty of obtaining consistent and up-to-date figures for land clearing. The Australian Greenhouse Office is currently processing Landsat TM imagery for the whole of Australia to obtain a mosaic of the entire continent for the year 2000. This information, and a similar mosaic developed from historical records for 1990, are still in preparation, and not available for this report.
The subsection 'Legislative and social responses' outlines the legislative and regulatory changes that have occurred since the last State of the Environment report (1996) was produced. In all states and territories except the Northern Territory, vegetation management regimes have resulted in reduced net losses of woody vegetation.
A much more comprehensive picture of all vegetation accessions and losses, together with assessments on vegetation condition will be available by 2002 through the National Vegetation Information System (NVIS). The NVIS initiative will bring together existing vegetational mapping and databases held in different agencies for the first time in Australia, together with current information being gathered using a systematic and uniform framework.
The impacts of changes to the woody vegetation component across Australian landscapes are many. Here they are considered under some headings that reflect ecosystem processes.
The Murray-Darling Basin Ministerial Council's Basin Salinity Management Strategy seeks to hold instream salinity in the main channel of the Murray at Morgan, South Australia, to an average of 800 EC units over the next 30 years (Murray Darling-Basin Ministerial Council 2000).
This strategy will require changes to current practices throughout the basin. These are identified as:
- cessation of clearing of woody vegetation,
- change in farming practices,
- improvements of water use efficiency, and
- large increases in planting of perennial vegetation for commercial products.
The continuation of clearing of woody vegetation in Queensland is therefore viewed with great concern by other members of the Council. They contend that areas are being cleared in Queensland at a rate and to an extent similar to that which occurred in Western Australia and Victoria in the past. Such a level of change has given rise to significant salinity problems in these states. The right to further agricultural development is therefore being challenged by the right to drinking and irrigation water quality further downstream.
Carbon is released into the atmosphere by clearing operations through burning of felled timber, disturbance of the soil, and oxidation of organic matter. The amounts so released have been computed for all components of the system: whole trees, surface litter and grasses, roots, and soil carbon (AGO 2001a; for updated information see http://www.greenhouse.gov.au/inventory/index.html ). Nationally accepted methods are used to produce regular National Greenhouse Gas Inventories, which are reported to the Secretariat of the United Nations Framework Convention on Climate Change. Because the areas and types of vegetation cleared are subject to various uncertainties, the Australian Greenhouse Office cautions that their published figures are estimates with significant uncertainties attached. The net value of carbon emissions minus carbon sinks is the number that is significant in relation to compliance with the Kyoto Protocol: this figure is the sum of all losses minus all gains. At present, Australia's agriculture and forestry are not in balance, as losses from agriculture outweigh gains from vegetation production (principally forestry) by 2 to 1.
Clearing of native habitat is seen as the single most threatening process for biodiversity loss and species extinction in Australia. The Environmental Protection and Biodiversity Conservation Act 1999 (Cwlth) specifically identifies this process as resulting from deliberate clearing of native vegetation, and from passive loss of remnant vegetation through landscape deterioration. This issue is treated in detail in the Biodiversity Theme Report.
An open, park-like landscape with scattered trees and a grassy understorey is one that is strongly appreciated by Australians, urban or rural (Seddon 1997, Carey 1999). This landscape has overtones of the Arcadian ideal of the 18th century, but may also draw upon folk memory of defensible spaces in forest glades, and attractiveness for hunting game (Sharma 1995). Treeless landscapes are out of fashion, and seem stark and unappealing; emotional concern for trees and tree preservation may stem more from this aesthetic appeal to today's taste than from any rational appreciation of the role that woody and perennial vegetation plays in ecosystem processes (Ridley and Joffr 1999).
Current land cover changes in Australia are perpetuating the trend that has been established over the past two centuries-the continuing reduction in the net woody vegetational cover, replacing it in most instances with crops and pastures. The predominant shift is from open woodlands to pastures, although there has been some increase in cropping area in Queensland.
Given the relatively poor performance of grazing industries compared with cropping, particularly with more intensive cropping activities in the past two decades in most parts of Australia, it is of concern that so much clearing is predominantly for pasture activities. Some clearing for control of woody regrowth may seem justified in terms of more effective grazing management, but clearing in areas of low farming or pastoral profitability seems to be symptomatic of a failure of effective policies for these regions as a whole (ANZECC and ARMCANZ 1999, Kerin and Hyder Consulting 2000).