Documenting clearance rates

The broadscale clearance of native vegetation was identified as the biggest threat to biodiversity in the biodiversity theme report for the Commonwealth 2001 State of the Environment Report 217. Among other impacts, the clearing of native vegetation results in the destruction of habitat and loss of biological diversity; causes widespread fragmentation of ecological communities; reduces the viability of ecological communities by disrupting ecological functions; and increases the amount of habitat that is suitable for invasive species. These impacts, which represent ongoing threats to remaining native vegetation after clearing, are covered in detail in the following sections.

Preventing broadscale clearing of native vegetation is a cornerstone of sound natural resource management. Technologies such as remote sensing have allowed a more accurate estimate of the rate of clearing of woody vegetation, and help identify what vegetation types may be under threat, as well as being a useful tool for monitoring adherence to clearance regulations. The first quantitative study of land cover change undertaken at the national level covered the intensive land use zone, which is around 38 per cent of the continent 218. This study estimated that over the period 1990–95 approximately 1,218,000 ha of woody vegetation were cleared for agriculture (cropping), grazing and other activities such as urban development. Open forest and woodland ecosystems represented much of the cleared area, although the extent of clearance of closed forest such as rainforest was lower than previously estimated. These figures helped quantify the extent of clearance and the broadscale nature of the threat to native vegetation. This is particularly useful information at catchment and regional levels.

The Australian Native Vegetation Assessment 2001 219 undertaken by the National Land & Water Resources Audit (the Audit), provides indirect measures of the pressures on native vegetation by presenting national scale maps of the extent and fragmentation of native vegetation. This provides an indication of the level of clearance of native vegetation.

At State level, the Queensland Statewide Landcover and Trees Study (SLATS) project demonstrates the type of data on land cover change that can be collected and ways it can be used. As noted in the previous chapter, the project was founded in 1995 as a major vegetation monitoring initiative to investigate the overall woody vegetation cover and report on the previously unquantified extent of land clearing in Queensland. SLATS Landcover Change in Queensland 1999–2001 220 covered the period when the Vegetation Management Act 1999 was proclaimed (15 September 2000). Figure 14 shows the rates of clearing over a 10-year period, from 1991–2001 in Queensland. Average annual clearing rates were 78 per cent higher in 1999–2000 (758,000 ha/yr) than in the 1997–1999 period (425,000 ha/yr), with the 2000–2001 rates (577,000 ha/yr) being 50 per cent less than in 1999–2000. Recently introduced legislation (2004) should help reduce the rate clearance again, at least for threatened and ‘of concern’ mature native vegetation. Similar reports on rates of land clearance have been developed at catchment scale which demonstrates the type of data that may be available for regional planning 221.

Figure 14: Annual rates of clearing in Queensland 1991–2001



Source: Department of Natural Resources and Mine (2003) ‘Land Cover Change in Queensland 1999-2001.’ Department of Natural Resources and Mines, Natural Resource Sciences, Brisbane, Qld. p. 5

Technical limitations associated with the use of satellite imagery can introduce errors and inconsistencies in the estimation of vegetation clearance rates, as can the use of different definitions for vegetation communities and the difficulties in mapping non-woody vegetation. Although not perfect, estimates of vegetation clearance are indicative of the rate and extent of clearance, and of clearance “hotspots”. Relatively small scale clearing in areas that already have been largely cleared should not be overlooked, as the contribution of these patches to overall cover and connectivity in a region can be considerable (see Question 2). The issue of clearing by ‘ecological action’ is also of critical importance, where processes like the lack of recruitment can ultimately lead to the loss of vegetation, even though there is no active clearance underway. Documenting rates of clearance by processes such as these is much harder. These types of degradation of ecosystems have been conceptualised as part of an underlying slow process of desertification 222.

	Action: 3.2
	Find out what information is available on the rates of vegetation clearance in your region, and if possible, their patterns in space and time, determine what threats it might represent and how relevant policies and regulations are being applied.
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Losing habitat and the extinction debt

Native vegetation provides habitat for a myriad of plant and animal species. When it is cleared, this habitat is lost. A recent report estimating the number of native animals that are directly killed by the clearance of native vegetation, or soon after, gives some idea of the magnitude of the loss 223. The results were based on research in the Brigalow area, which previously covered 15 million hectares from central Queensland to northern NSW. The study revealed that between 1997 and 1999, when clearing rates were around 425,000 ha/yr in Queensland, about 100 million native mammals, birds and reptiles died annually as a result of the clearing of remnant vegetation (Table 9), and an estimated 190 million remnant trees were cleared each year. Many of the animals, like the trees, are killed directly by the clearing process, while the remainder die later from starvation, predators or stress. The animals do not simply move off the native vegetation and go somewhere else. While these figures are very high, they do not take into account the number and type of invertebrates or plant species that may be directly lost from the clearance of native vegetation and loss of habitat.

Systems that become fragmented and reduced in area are expected to enter a long period of “relaxation” to lower levels of species richness. Thus there will be a substantial time lag between the loss of habitat and the loss of species. A consequence of this prolonged extinction process is that it can take decades or more for the full effects of broadscale land clearing to appear. This time lag is often referred to as an extinction debt – the future loss of species that is a consequence of past actions (Figure 15). In other words, rich habitats have been ‘borrowed’ for short-term gains and their diversity, adaptability and long-term productivity has been reduced through loss of species richness. The debt on these ‘borrowings’ is paid by future generations when it falls due in 20, 50 or more years after clearing, as local extinctions gradually become regional until entire species become extinct.

Much land clearing in Australia is estimated to be less than 30 years old, so the extinction debt from vegetation clearance is still being paid in many regions in the intensive land-use zone. A pertinent example of regional bird extinctions in the Mount Lofty ranges is given in the report Impacts of Land Clearing on Australian Wildlife 224. These impacts might be partly avoided by research and management in the short-term and large-scale habitat reconstruction in the long-term. If such actions are to be effective, they need to be targeted towards the species most at risk which may not always be those with the lowest abundance.

Table 9: The number of native animals estimated to be killed by the clearance of native vegetation in Queensland in 2002.



Source: Cogger H, Ford H, Johnson C, Holman J, Butler D (2003) ‘Impacts of Land Clearing on Australian Wildlife in Queensland.’ WWF Australia, Sydney, NSW

Figure 15: The extinction debt, where species are lost in the future due to actions in the past such as vegetation clearance. The pattern is similar whatever years are used.



Source: H, Ford H, Johnson C, Holman J, Butler D (2003) ‘Impacts of Land Clearing on Australian Wildlife in Queensland.’ WWF Australia. Sydney, NSW. p. 9

	Action: 3.3
	Find out more about the ongoing loss of native species after vegetation clearance has ceased by reading the report on the impacts of land clearing on wildlife.
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Fragmenting vegetation

The clearance and modification of native vegetation has left a legacy of patches of native vegetation of various sizes, shapes, connectivity and condition. In the intensive land-use zone (principally southern and eastern Australia), this vegetation is mostly included in the fragmented and relictual categories described in Question 2. At the patch level, fragmentation creates new edges between remnants and cleared or disturbed land, leading to ‘edge’ effects. These include physical changes to the remnant near the edge, such as different levels of exposure to the sun and wind, and changes in water cycles and the local air temperature 225. Biological changes include invasion by opportunistic species with good dispersal or colonising abilities such as weeds and feral animals, and changed recruitment and survival rates of native species due to habitat alteration.

At the landscape or regional scale, fragmentation isolates and creates barriers between patches of native bush. In most cases, recently isolated remnants can be expected to continue losing species. The loss of a population of a species (that has declined to a size that is not viable) may take considerable time if the species is relatively long-lived. Isolation and a declining density of plants may also disrupt pollinators and there may be fewer individuals from a species flowering at the same time. This can mean that pollinators are forced to visit other, related species. The result could be increased hybridisation between species, which may lead to local plant extinctions. This is one element of a major research project being undertaken on the genetic and ecological viability of plant populations in remnant vegetation 226. Preliminary results from this research indicate that small remnants near a larger source of genetic material may have a better chance of survival than the more isolated remnants.

Developing a general understanding of how fragmentation affects plant and animal populations is a critical issue that has been addressed recently in the review Impacts of Ecosystem Fragmentation on Plant Populations: Generalising the Idiosyncratic 227. This study considered the impact of processes underlying fragmentation on plant populations, concluding that studies have focused on a limited subset of plant types and concentrated heavily on reproductive output rather than actual regeneration success. No clear patterns were found that link the impacts of fragmentation on reproductive rates to the viability of plant populations. This led the authors to conclude that we must be careful about generalising the findings of fragmentation studies with different landscapes, different species and different relative importance of key processes. They felt that local conditions within fragments may also be as important as, or more important than, fragment size and isolation when considering viability of plant populations.

With increasing fragmentation and isolation, the genetic diversity of vegetation populations may be compromised 611. Small, highly fragmented populations of native vegetation have been associated with lower seed set and, in some cases, lower seed viability 610 612. This is especially problematic where high quality seed is needed for revegetation. However, the level of genetic erosion can vary significantly among species, and for many species the genetic effects of fragmentation are unknown 613.

	Action: 3.4
	Discover more about the impacts of fragmentation on the long-term viability of plant species and native vegetation communities and consider how this affects the management of these systems in your regions.
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Declining scattered trees

It has been estimated that there are around 20 million hectares of scattered trees on agricultural land in the temperate zone, in addition to around 6.6 million hectares occupied by clumps of trees. These numbers were estimated in a comprehensive review of Tree Decline in Agricultural Landscapes 228 which addressed the importance of scattered trees in rural landscapes, and why they are threatened. Clearing, lack of recruitment and rural dieback all contribute to the general decline in numbers of trees and their extent on farms. Death through old age and exposure to the elements also contributes to the loss of scattered trees.

While quantitative studies of rates of tree decline are limited, some estimates are starting to appear. In south-eastern South Australia, it has been predicted that 36 per cent of paddock trees will be lost by 2051 if current rates of authorised clearing and dieback continue 229. In southern NSW, research using satellite imagery points to a potential loss of all mature trees in some regions within 40 to 185 years. The loss of patches of trees <0.1 ha on the south-west slopes would result in dramatic declines in the total cover of some vegetation types, with some losing up to half of their total cover 230. Connectivity within the landscape would be considerably reduced and soil erosion and salinisation would probably increase, as well as stock losses due to exposure. These estimates highlight the need for regional strategies for the long term conservation and recruitment of scattered trees in rural landscapes. For example, the Victorian Native Vegetation Framework 231 and a number of regional vegetation plans in this State have highlighted the management of scattered trees. A useful brochure Paddock Trees: Who’ll miss them when they’re gone? 232 highlights the benefits of paddock trees and small patches of trees in rural landscapes and the main reasons why they are declining. Importantly the brochure outlines the management actions that can be taken to protect existing trees and create conditions for regeneration.

	Action: 3.5
	Read the brochure on the decline of paddock trees to find out what your landscapes might look like in the next 50–100 years and the management actions needed to start reversing this trend.
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Collecting firewood and tidying up

Firewood harvesting and the ‘tidying up’ of remnant native vegetation are now understood to be key threatening processes. In 2001 for example, the rates of extraction for firewood were estimated at around 4.5 to 5.5 million tonnes per year – which was similar to the amount of woodchips exported. These large figures are driven by the use of wood-fired heaters in cities and towns, which create a big demand for wood. ‘Tidying up’ activities involve removing standing dead wood and fallen timber, and may be done for on-farm safety, to remove obstacles to machinery, increase grazing access and productivity, reduce fire hazards and rabbit harbour and for aesthetic reasons. Local councils and other agencies also ‘tidy up’ by removing dead wood and dead trees from reserves and from along roadsides.

The removal of deadwood, either standing or fallen, can cause the broadscale change of woodlands into paddocks with isolated standing trees, little natural understorey and no woody debris on the ground.

The national report on The Impact and Use of Firewood 233 provides a comprehensive overview of the threats that the broadscale collection of firewood imposes. Inland forests and woodlands in lower rainfall zones appear to be the ecological communities most threatened by the collection of firewood. In Victoria, a total of 49 ecological communities have been listed as potentially threatened by firewood collection and in Tasmania 13 plant species have been listed as threatened. These figures emphasise the extent of the problem. At species level, several authors have implicated firewood removal in the decline of birds at local and regional level. The national report identifies the potential loss of highly specialised species of invertebrates and fungi associated with coarse woody debris as a particular concern. It is thought that the disappearance of these species from native bushland could affect ecosystem services such as nutrient cycling and plant establishment. The spread of diseases such as Phytophthora cinnamomi by firewood collectors is also considered a threat. In addition to the impacts on native vegetation, the burning of firewood in towns and cities can cause air pollution and affect human health.

In 2001, a National Approach to Firewood Collection and Use 234 was released to address some of the impacts of firewood collection, especially in the drier regions where there has already been extensive clearance of native vegetation. A number of conferences were also held that year in the southern and eastern States 235, building on the first national conference on firewood collection held in Victoria in 1999. The proceedings of these regionally-based workshops usually provide greater detail than national overviews. These conference proceedings paint a dire picture when the overall figures for firewood removal are presented. This is not to say that all firewood collection is a threat to native vegetation, especially when it is for personal use on individual properties. The level of impact will depend on the extent of the vegetation type being utilised, and the rate and amount of wood collected.

	Action: 3.6
	Read the national report on the impact and use of firewood in Australia, the national approach to its collection and use, and where relevant, the findings of regional workshops, to learn more about how the threat can be managed in your region.
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