An overview of recent native vegetation clearance in Australia and its implications for biodiversity
Biodiversity Series, Paper No. 6
Andreas Glanznig, Biodiversity Unit
Department of the Environment, Sport and Territories, June 1995
Since European settlement, extensive areas of the original forests and woodlands in Queensland have been cleared or severely modified. Before European settlement, forest covered an estimated 35 544 000 ha (21 per cent) of Queensland. By 1984 this had been reduced by nearly half to between 17 to 20 million ha. Woodland originally covered approximately 28 per cent of the State but has now been reduced to between 19 and 21 per cent, a loss of some 11 to 15 million ha (GOQLD 1990, p.15). Many native grassland ecosystems have also been significantly modified.
A number of forest and woodland types have been particularly affected, including the brigalow and the mulga. Over the last three decades, brigalow open forests and shrublands have been heavily impacted by clearance. During this period about six million ha of brigalow (Acacia harpophylla) dominated communities were cleared (GOQLD 1990, p.16). Most of the brigalow had disappeared by the 1970s (Gasteen 1987, p.148).
In land dominated by mulga (Acacia aneura) associations known as the Mulga Region, substantial clearance has also occurred. This Mulga Biogeographical Region occupies some 19 000 000 ha, extending from St George in the east to the South Australian border; and north from the New South Wales border to Longreach (see Figure 4). The Mulga Land Use Advisory Group noted that a survey undertaken in 1985 of a sample 3 000 000 ha in the Mulga Region revealed that mulga was overused or excessively cleared on some 2 370 000 ha or 79 per cent of the area. This finding is consistent with other studies that have shown some two-thirds of the Mulga Region exhibits evidence of active land degradation (MLUAG 1992).
Widespread native vegetation clearance is still taking place in Queensland. Recent clearing has been most extensive in the northern and north-western parts of the Brigalow Belt, and in the southern and north-eastern parts of the Desert Uplands. This has focussed primarily on gidgee (Acacia cambagei), blackwood (A. argyrodendron) and remnant brigalow communities (A. harpophylla), and on a variety of eucalypt communities. In the Brigalow Belt the eucalypt most cleared is poplar box (E. populnea) and iron bark (E. crebra and E. drepanophylla) while silver-leaved iron bark (E. melanophioia and E. whitei) and yellow jacket (E. similis) are most affected in the Desert Uplands. Acacia communities around the eastern margin of the Mitchell Grass Downs are also greatly affected (QLDDEH 1995b).
Source: Queensland Department of Environment and Heritage (1995a)
Ongoing clearing in the remainder of the Brigalow Belt, in the Mulga Lands, south-east Queensland and the lowlands of the Wet Tropics and the Central Mackay Coast is less extensive but is focussing on remnant vegetation and hence is no less significant for biodiversity protection (QLDDEH 1995b).
Recently clearing has increased in the Cloncurry area, in both the Gulf Plains and the northern part of the Mitchell Grass Downs, with gidgee communities most affected (QLDDEH 1995b). Areas where recent native vegetation clearance has occurred is shown in Figure 4.
The establishment of a State-wide satellite remote sensing program using Landsat technology to assess and monitor land clearing in Queensland was recently announced by the Queensland Government. While accurate State-wide data will be available in the foreseeable future, in the interim the general pattern of native vegetation clearance in Queensland has been determined using information sourced from the Queensland Department of Environment and Heritage, Queensland Department of Primary Industry, Queensland Department of Lands and studies undertaken at Griffith University. It must be acknowledged that it is a disjointed data set with omissions and overlaps.
The scale of recent vegetation clearance in Queensland can be gauged from a survey of clearing contractors and of areas known to have been cleared using chemical methods (for example using herbicides such as Tordon and Graslan). The survey provided the basis for a Queensland Department of Primary Industry official to estimate that about 500 000 ha and 450 000 ha were cleared in 1987-88 and 1989-90 respectively. The amount cleared includes a substantial proportion of regrowth on previously cleared land (Burrows Queensland DPI, pers comm cited in NGGIC 1994, p. 129).
The current rate of clearance remains very significant. In 1994 permits were granted to clear a total of 1 079 297 ha of leasehold land including 684 967 ha of virgin bush and 391 730 ha of regrowth and invasive woody weeds. These figures are subject to the caveat that the permits are valid for five years and allow clearing at any stage during this period, and that not all areas permitted to be cleared are actually cleared (QLDDoL 1995).
Substantial clearance has occurred in a number of regional areas. Information on recent clearance is not publicly available for most regions. Exceptions are parts of the Desert Uplands Biogeographic Region where quantitative data based on tree clearing permits is available for the Jericho and Belyando Shires (see Figure 5 below).
Source: Queensland Department of Environment and Heritage (1995a)
In Jericho Shire tree clearing permits issued since 1990 have allowed a total of 458 209 ha to be cleared (217 533 ha of 'virgin' bush and 240 676 ha of regrowth) while in Belyando Shire tree clearing permits issued since 1990 have allowed 214 499 ha to be cleared (174 974 ha of 'virgin' bush and 39 525 ha of regrowth) (QLDDEH 1995a).
In south-central Queensland and south-east Queensland, studies based on aerial and satellite imagery data have been undertaken to accurately assess the rate and scale of native vegetation clearance. The locations of the study areas is shown in Figure 6 below.
The south-central Queensland study area (see Figure 6 below) comprises some 7.5 million hectares which is approximately four per cent of the State. Interpretation of Landsat imagery found that between 1972-73 and 1990, an estimated 1 018 000 ha was cleared to some extent. For this period, the average clearing rate of 43 000 ha was more than double the rate for the previous 100 years (Smith 1994; Smith et al 1994).
Source: Smith (1994 p.4), Catterall and Kingston (1993, p.8)
It was also found that, historically, clearance was selective throughout the study area and some vegetation communities whose land resources had a greater potential for increased production were favoured for clearing. Since clearing commenced around the 1850s, 86 per cent of the original brigalow and belah scrub and 80 per cent of the mulga communities have been affected to some extent by clearing while almost two-thirds of the grassy open woodlands and grasslands (65 per cent) and softwood scrub (63 per cent) have been wholly or partially cleared (Smith 1994; Smith et al 1994).
Significant losses of native vegetation have also occurred in the growth areas along the Queensland coastal zone, particularly south-east Queensland and the Cairns-Townsville and Rockhampton areas (Hamilton and Cox 1994; Crome, Foran and Moore 1994).
A study has assessed the extent of loss for the coastal region of south-east Queensland (a 30 km strip) from approximately Gympie to the Queensland, New South Wales border. It is based on hardcopy satellite imagery combined with aerial photography which allows quantitative summaries of the current state of bushland cover to be derived using Geographical Information Systems (GIS) analysis. The study area covers approximately 19 000 km2 and includes all the most rapidly expanding population centres in south-east Queensland. An assessment of recent bushland loss for the period 1974-89 was undertaken on a part of the total area (Area B) as shown in Figure 7.
Source: Catterall and Kingston (1993, p.8)
Within Area B, the mainland strip covers 1413 square kilometres and estimated losses for different vegetation types are summarised in Table 5.
|Plant community||Percentage lost of 1974 area|
|Eucalypt moist forests||16|
|Eucalypt dry forests||36|
|All bushland lost||33|
1. Includes grassland/sedgeland areas associated with wetter heathland.
Source: Catterall and Kingston (1993, p.39)
In general all lowland vegetation communities in mainland areas of coastal south-east Queensland have been acutely affected and many bushland losses have been associated with rapid urban expansion, including development of low density 'rural residential' style areas. The study concludes that in this 15-year period a total of 33 per cent of the 1974 bushland cover on the coastal south-east Queensland mainland was cleared and that if these patterns of clearance continue all current bushland will be cleared by 2019 (Catterall and Kingston 1993, pp. vii,42).
These findings are consistent with another study undertaken in the Brisbane City local area. The analysis found that in eight years, between 1982 and 1990, 45 km² (17 per cent) of the total 264 km² bushland area was cleared for urban development (Catterall 1990; BCC 1990). The Brisbane City Council equates this rate to 'three football fields per day' (BCC 1993).
To strengthen its land management capacity, the Queensland Government recently announced a package a measures and released a draft Statewide policy for land clearing for public consultation. The key features of the package are the use of satellite remote sensing technology to assess tree clearing rates, tree clearing guidelines and standards for specific areas based on vegetation and soil types, and increased penalties for illegal tree clearing.