Overall, national rates of broadscale land clearing have fallen dramatically. However, substantial clearing continues in many areas. In addition, the legacies of past land clearing will continue to operate for some decades as old trees and small remnants of native ecosystems isolated in mostly cleared landscapes die, and recruitment of new plant seedlings, fungi and animals is hindered by changed fire regimes, altered soil properties, exposure to predators and reduced ability to find mates. Addressing these legacy effects will be complex, long term and potentially expensive.
The Assessment of Australia’s terrestrial biodiversity 200815 concluded that:
… broad-scale land clearing has been largely brought under control in the jurisdictions that accounted for most of the clearing in 2002: New regulatory frameworks in Queensland and New South Wales have dramatically reduced the level of approved clearing of remnant vegetation nationally in the past five years. (p. 150)
While this statement remains generally true, the additional analyses reported in Chapter 5: Land reveal a slightly more complex situation:
The annual rate of forest loss in the mapped intensive-use zone over the decade to 2010 averages 1.1 million hectares (range 0.7 million – 1.5 million hectares). This loss has been offset by forest expansion averaging 1 million hectares annually (range 0.6 million – 1.3 million hectares). As a consequence, there was a small net gain of forest in Australia in 2007–10, for the first time since the early 1990s. The overall average net rate of forest change in the area mapped over the decade to 2010 was a loss of around 160 000 hectares annually. As the 2006 SoE report103 noted, ‘regrowth’ vegetation and its environmental values are generally different in many respects from the vegetation that has been cleared.
Consistent with the conclusion by the Assessment of Australia’s terrestrial biodiversity 2008, Chapter 5: Land concludes that:
Rates of land clearing averaged around one million hectares annually over the period 2000–10, and were balanced by the extent of regrowth—although the character and values of the original and regrowth vegetation are often different.
Although average figures suggest that the pressure on biodiversity from land clearing is reducing or stable in many parts of Australia, more detailed data are needed to assess the significance of these changes for biodiversity. For example, relatively high levels of clearing have continued in parts of north-eastern Queensland and in the headwaters of the Murray–Darling Basin, which could have far-reaching impacts.104 Research in the Northern Territory suggests that rates of land clearing there, in conjunction with changed fire regimes and invasive species, have been sufficient to cause major, and somewhat unexpected, changes in biodiversity.105 Although there have been major advances in re-establishing vegetation cover (see Chapter 5: Land), replacing mature native vegetation with regrowth seldom provides the same environmental values as the original vegetation.
Decreases in broadscale clearing have been beneficial for many bird species; however, clearing of northern woodlands and of forests is an emerging threat. Continued clearing of old growth native forest in Tasmania and the legacy of past clearing across large parts of Australia are two major factors degrading the remaining habitat for birds.85
The Queensland Herbarium has collected and published some of the most detailed data on land clearing of any state. These data demonstrate the level of detail necessary to identify where pressures are highest and where interventions might be needed. Past clearing has been uneven across the state—it is concentrated in the south-east, as is most of Queensland’s population. Clearing since 1997 has also been greatest in the south–eastern and southern parts of the state and there is a wide range in extent of clearing, from virtually zero to more than 3.5% annually.104 Clearing of some of the subregions at the top of the Murray–Darling Basin has been much more extensive than the Queensland average (Figure 8.14). Understanding clearing at this scale is important for understanding and managing ecological processes that operate at a range of scales. For example, the clearing in the top of the Murray–Darling Basin is likely to have implications not only for biodiversity in those subregions, but also for freshwater-dependent biodiversity living lower in the Basin.
Fragmentation of habitat is one of the two most frequently cited pressures for EPBC-listed species (the other being invasive species).15Figure 8.15 shows the highly fragmented nature of vegetation systems to the west of the Great Dividing Range in eastern Australia, across much of southern Australia and in the south-west. These areas, not surprisingly, coincide with the areas in which numbers and proportions of threatened species occur (Figures 8.5, 8.6, 8.8 and 8.9).