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|5 April 1991 Version 3.d/w:i||
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This paper puts forward an ecological model for understanding the impact of greenhouse warming on the natural environment.
Its main practical conclusion is that controlling the invasion of weeds and other pest species should have a higher priority than trying to create large-scale corridors down which whole ecological communities might move. This is because the conservation of species and ecological communities in situ coupled with an active program to control competition from invading species is predicted to be the most effective strategy .
The impact of the greenhouse effect on natural terrestrial environments:
The public is increasingly aware of the significance of the greenhouse effect. There is an expectation that Governments will take preventative and remedial action urgently. However, in the ecological arena there is as yet no consensus about how this should be done.
For example, ecological theory suggests that big changes in climate will, over sufficient time, result in major changes in the species composition and relative abundance of species within ecological communities. But these changes could arise because of species adaptation and evolution in situ, or because of migration to 'track' appropriate climatic conditions. Or, of course, a mixture of the two.
In south eastern Australia there has been a great deal of movement of ecological communities as the climate has gradually changed . The very gradual drying and warming as the continent has drifted north has resulted in the replacement of most of the rainforest communities with dry-environment communities. Very few species that were once part of the rainforest seem to have evolved into new varieties or species adapted to hotter, drier conditions.
This history suggests that the correct conservation strategy for our flora and fauna is for them to be allowed or assisted to migrate as the climatic bands move. Otherwise it appears that they will perish. The Bio-Clim models showing climatic zones moving hundreds of kilometres, in some cases, reinforce the notion that species or ecological community mobility is important. People even talk of whole nature reserves or Parks being 'in the wrong place' and imply that they should somehow be 'moved'. So the strategy that comes to mind as being the most significant is the maintenance or indeed the re-establishment of corridors to provide for the necessary movement.
However this 'evidence' does not capture all of what is going on. An alternative history has played itself out in special circumstances. For example, on permanent islands, temporary islands (like the Grampians) and in quasi-islands caused by sharply differing geological zones, species have often been trapped in situ, with nowhere to go despite the climatic changes. In such cases many (most?) of the species survive despite the physiological stress, and go on to adapt in-situ. This often leads to accelerated speciation. A good example is the south west of Western Australia where the underlying geology is very broken up and diverse. The region has been subjected to far more extreme changes in climate than south eastern Australia because of the sea current switching effect caused by temperature changes and yet, unlike the south east of Australia, the species have clung on in place. The fact they have nowhere to go because they cannot migrate out is not the critical issue. What is important is that many of the plants from outside the zone, that might otherwise have been better adapted and could therefore have displaced the original species, have not been able to invade because of the barrier created by the different soil types .
So it seems that it is not so much physiological stress, but competition that decides whether most species will persist in the face of climate change. The enormous adaptability of most plants and animals is demonstrated by agriculture, domestic gardens, botanic gardens and zoos where species from extraordinarily different original environments can often survive so long as competition is kept at bay.
These special cases suggest that maintaining the stability of the species composition, that is controlling inputs of weeds and pest animals, is the critical strategy. In fact now that human land use changes have changed most natural areas into ‘islands’ it seems appropriate to use the example of natural ‘islands’ to guide us in choosing a species survival strategy.
If we adopt the basic ‘island’ model, then we have to resolve a paradox about stability and change, especially in the case of small ‘islands’. Small ‘islands’ risk the loss of species due to stochastic shocks - fires, droughts, disease, etc. It is important to have corridors or some other means of allowing species to re-colonise any ‘de-stocked’ habitat. This implies that species mobility is important. However small ‘islands’ are more prone to invasion by weeds and pests from the surrounding zone. So minimising species mobility is important. (It seems that the ideal solution would be to surround small native habitat ‘islands’ with a semi-permeable membrane! - to allow in the local natives but prevent the invasion of exotics.) Larger bush areas, being able to provide for their own restocking, do not raise this dilemma so severely.
So it seems as a universal principle we should not encourage the maximum movement of species in the face of the greenhouse effect. Instead, the conservation of native species is generally best served by maintaining as high a level of stability as the normal short run fluctuations of the environment will allow.
But if we don't encourage the movement of species how do we deal with the greenhouse effect?
This paper presents an alternative approach for discussion.
A draft strategy for protecting flora and fauna from the greenhouse effect
Any actions taken in relation to flora and fauna should comply with the objectives of the Flora and Fauna Guarantee Act. Specifically this means that action should be taken to ensure that all Victoria's native species survive.
The most important strategy for protecting the full range of our native species in the face of the greenhouse effect is to conserve them in their current locations while urgent and effective steps are taken to reverse the global warming.
For most species (think of the hundreds of species of plants and animals including micro-organisms that live in any particular patch of bush) the option of movement down corridors or deliberate translocation is not available. It seems that the onset of the greenhouse effect will be too rapid for effective corridors to be established which could allow all the species within ecological communities to move down them. Few if any corridors of the size we can afford to retain or re-create will have the correct characteristics to allow the unimpeded movement of all species. The extensive clearance of land and its private ownership, as well as the monetary cost of establishing corridors severely constrain what can be done.
But the greatest threat for most species is not the physical change in the climate but competition from species better adapted to the new conditions. So the highest priority should be placed on the control of environmental pest plants and animals (even where they are native species). This will require a massive expansion in resources and the rapid development of environmentally sensitive control techniques.
Since climate change will nevertheless put stress on many species and ecosystems every effort should be made to improve the resilience of native species, ecological communities, natural areas and habitats. To do this it will be necessary to:
Far less disruption to nature will occur if the vast majority of native species are actively assisted to survive is-situ in their existing habitats, while major efforts are made to reverse global warming. This is still the most effective strategy even if it were to take hundreds of years to bring the global climate back to something like today's conditions.
The ‘survival in-situ’ strategy will not be appropriate for some species or ecological communities. Such species and ecological communities need to be identified as soon as is technically feasible. Likely candidates are alpine and coastal species. If coastal ecological communities are to survive a rise in sea level new habitats must be allowed to develop or be created to replace those that are lost. Special arrangements will be needed on the coast to provide private land for the purpose. Alpine environments should be managed to reduce stress and encroachment. The impacts of grazing and skiing/tourism related projects need special scrutiny. Other species and ecological communities may need new habitat to be created. Some species may need to be protected out of the wild if enough suitable habitat cannot be made available.
A program of basic ecological research is needed. Species’ physiological sensitivity, vulnerability to physical changes in the environment and vulnerability to competition and predation from other species need to be investigated to determine which species are especially at risk and to identify species that could serve as useful indicators of the health of or change in ecological communities. Studies of population and ecosystem dynamics are needed. There should be investigation of early warning signs that greenhouse induced climatic changes are already affecting ecosystems. For example some of the inexplicable dieback of tree species in otherwise fairly healthy native forest may be an early warning sign.
On the basis of this research appropriate protection plans should be prepared - and implemented - urgently.
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