Refugia for biological diversity in arid and semi-arid Australia
Biodiversity Series, Paper No. 4
S.R. Morton, J. Short and R.D. Barker, with an Appendix by G.F. Griffin and G. Pearce
Biodiversity Unit
Department of the Environment, Sport and Territories, 1995
16. Management issues
The terms of reference for our investigation ask for consideration of the types and extent of threats to biological diversity in refugia, of the potential to reverse degradation within them, of the possibilities of eliminating threats, and of current land uses and land management. Our approach is first to ask whether the threats to biological diversity within the refugia we have recognised differ in any important ways from those discussed in the wider literature concerning arid Australia. It becomes quickly apparent that such is not the case. The threatening processes that have been identified and discussed repeatedly over the last 20 years or more are precisely the same ones mentioned in numerous other places (e.g. Foran et al. 1990; Morton and Price 1994; James et al. 1995). They are as follows:
- Land degradation and potential loss of biological diversity resulting from over-grazing by domestic stock. This vital issue has been the subject of substantial debate, research, and extension and management effort. Although there is dispute as to the exact extent and significance of degradation, all scientists who are active in the arid zone agree that it continues to occur (e.g. Morton and Price 1994).
- Land degradation resulting from over-grazing by feral animals (horses, donkeys, goats, pigs, and camels) and rabbits. Again, the losses to animal production in the rangelands and the potential loss of biological diversity are widely recognised by land-managers and scientists alike (e.g. Morton and Price 1994).
- Alterations in hydrology due to human activities, primarily but not exclusively drawdown in the Great Artesian Basin due to numerous uncapped bores (e.g. Harris 1992).
- Removal of the environments on which animals depend through clearing. This effect is occurring only at the margins of the arid zone, where land is still being cleared for agriculture (e.g. Noble et al. 1990).
- Depredations of exotic predators, the fox and the cat, but in some insular situations also introduced rats and mice. Many authors have identified these animals as a serious threat to the persistence of the vertebrate component of our fauna (e.g. Kinnear et al. 1988; Burbidge 1989; Newsome 1993).
- Invasions by weeds constitute an acute and formidable problem for biological diversity. Although arid Australia seems to be experiencing relatively fewer problems in this regard than other parts of the continent, invasions tend to be focussed on certain key habitats (Humphries et al. 1991).
- Uncontrolled fire is significant in some places (e.g. Pearson 1991).
Each of these threatening processes has been discussed at length elsewhere. Each has the potential to compromise the integrity of the refugia we have nominated. Indeed, some of the refugia exist primarily because some or all of those threatening processes do not exist in a particular location; this is the case especially with the Islands, which escape the effects of most of these problems (and, for that reason, managers fully understand the importance of continuing to ensure the exclusion of such effects from these islands). Although we have not exhaustively surveyed the management plans that might apply to all the refugia described here, it is clear that there is widespread recognition among managers of these problems. There are formidable technical barriers to be overcome, as well as social and political effects, before such threatening processes can be brought under control. What is the prognosis for such advances?
- The causes of land degradation by grazing stock are well understood, and the scientific solutions are also moderately clear, i.e. at critical times, reduce the numbers of herbivores that are eating too much plant biomass on land of inherently low productivity (Pickard 1993). However, these problems will not be solved until the key social and political issues are the subject of public debate.
- Land degradation springing from feral herbivores is technically more difficult to solve than that caused by domestic stock because the animals causing the damage are uncontrolled and usually economically less valuable than stock. Intensive efforts continue into improvement of traditional methods of control as well as investigations of novel techniques.
- Drawdown of artesian waters has long been recognised as a substantial problem, and efforts have begun to cap bores and thereby limit the problem. The primary limitation here is money to complete the process.
- Clearing of land seems to be continuing apace. Solutions to this problem must involve careful cost/benefit analysis, land-use planning and public debate.
- Control of exotic predators relies upon the same suite of issues as discussed above under control of feral herbivores.
- Control of weeds is dependent upon better management of grazing animals, both domestic and feral; on more stringent control of plant introductions (Lonsdale 1994); and on protection from invasion of areas with high conservation value, such as refugia. In instances of existing weed invasions, some direct control measures may be urgently required.
- The principles of fire management are, in general terms, understood well enough for action to begin: protect fire-sensitive environments by burning away from them at strategic times; elsewhere, create a diversity of fire regimes by judicious intervention. The major limitation is financial, although debate may sometimes be necessary to convince the public that management burning is necessary for persistence of biological diversity in certain places.
Is there any evidence that refugia might be important for maintenance of natural populations which help regulate pest outbreaks, or assist in reducing land degradation? The only example which emerged from our literature review concerns the straw-necked ibis Threskiornis spinicollis, which depends for breeding on some of the wetland refugia which have figured so prominently in our review. Straw-necked ibis are major predators of Orthoptera (grasshoppers and crickets) in farmlands (Carrick 1962), and thus the protection of their breeding refugia may enhance pest control. The Macquarie Marshes constitute an example of such an effect (Brooker 1992).
In brief, then, refugia in arid Australia suffer from the same threatening processes that affect the remainder of the landscape. Thus, management of refugia requires that the same suite of issues be addressed as have been widely discussed with respect to arid Australia in recent times. Despite the universal nature of these management issues, though, it must be recognised that the refugia identified in this report require the utmost care if their relictual, endemic and significant species are to persist. These refugia are some of the places where our community stands to lose the most unusual organisms unless our management improves. They might act as a stimulus to action, such that mitigation of the threatening processes described above benefits refugia first of all but spreads outward into the rest of the arid landscape.