- Email: [email protected]
Global warming and nature conservation
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-1Viewpoint
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Global warming and nature conservation Peter Bridgewater and S. J. Woodin
Predictions of climatic changes vary, but conservation activities must assume that some impacts wit/ occur and that species abundances and distributions will change. Effects on conservation sites wilt be important; management plans should include pfot~tjon against climatic jmpacts and monito~ng of change. Cfimatic effects cannot easily be manipulated: on some sites minimal intervention, allowing natural adjustment, will be best. As wildlife is restricted by landscape fragmentatjon, a network of greenways shoufd be estab/ish~ to facilifate movement between conservation areas. Planning in the face of uncertainty is difficult, but management goals of large populations, high bj~iversi~ and replicated conservation of ~mmunjtjes will aid adaptation to new conditions. The authors are member of Chief respectively, of the Council, Northminster PEl lUA, UK.
Chief Scientist and Scientist Directorate, Nature Conservatory House, Peterborwgh,
LAND USE POLICY April 1990
Much of the current discussion on global warming has focused on how this will affect human use of the planet. Little discussion has occurred on how this will affect the 15 million (or 30 million depending on which estimate you believe) other species with whom we share planetary living space. Yet much of our future in a warmer and wetter/drier world will depend on how these species do react. While agriculture, mariculture and forestry are looking at the species they are involved with, the bulk of species diversity is covered by nature conservation activities. In terms of scientific discussion, global warming has had a chequered history. There seems little doubt that global warming will occur over the next 100-200 years. There is still considerable scientific discussion over the extent to which that warming will occur, the consequences of that warming, including the resulting extent of sea level rise, and the possibility that the warming may itself be canceiled out by natural cooling effects through which the Earth may be about to pass. Indeed, many geologists are now showing that such warming cycles have occurred before, and with the rapidity that is in prospect. The big difference is that the present warming surge is entirely the product of human interactions. This Viewpoint cannot question or become involved with the detail of the scientific arguments. Nonetheless, it would be folly to assume that some impacts from global warming will not occur, and conservation activities
must take place against that backdrop. Frequently quoted estimates would have a warming of 1-4.5”C over a 100-year timespan. The warming will be a continuous change, and all who live on the planet will need to adjust and readjust. Those species with long generation times, such as ourselves, will be at a significant disadvantage compared with those with short (one year or less) ones. As usual the insects and other invertebrates and ephemeral plants (mostly ‘weeds’) will be in the strongest position to adapt and survive. The precise extent of warming in Britain is even less certain than the overall global predictions. Models of regional climatic responses are not yet well developed, but will be essential in determining the most effective stance for nature conservation. Conservation impact The question of most significance is what will happen to the system of Sites of Special Scientific Interest and Nature Reserves, both government owned or managed and those owned or managed by voluntary conservation agencies. The one certainty is that the direct and indirect impacts of climatic change will lead to changes in species composition, dominance and ecosystem structure, and in the distribution and abundance of species. Palaeoecological work on several continents has demonstrated that during previous warmer climates distributions and relative abundances changed; and they changed again as cooling cycles became established. In periods of clima-
165
‘Greenways would be a vital link for the movement of plant and animal species through the landscape’
166
tic change biodiversity shrank - and then swelled as climates ameliorated. This happened, however, in a world where habitats were continuous, and there were no artificial boundaries so typical of modern landscapes in all continents. This landscape fracturing by intrusive built environments and attendant transport links poses major problems to wildlife (particularly terrestrial vertebrate animals) moving between habitats. Work on ‘fossil’ CO2 in the ice caps of Antarctica has shown past increases in CO2 levels coincident with the warm periods in the last 160 000 years. However, concentrations were never as high as at present and the effects from nitrous oxide and methane were less pronounced and, in the case of the CFCs, absent. There are presently no clear scientific indications regarding rates of ecosystem change relative to climate change; they could be gradual, but equally could be abrupt and rapid. What we can say is that there 41 be a response, and that we need to prepare for it. There is a strong suggestion that too great a warming would result in the loss of particular species: rare arctrcalpine plant and animal communities are frequently mentioned. These losscs would be accompanied by a general lowering of biodiversity and general degradation of conservation value. Some of the communities for which the m~~untains of Scotland and some high peaks in England and Wales are famous may well become a thing of the past. However. it is much more likely that those communities will remain in a ‘relict’ state until some dramatic environment~~l perturb~~tion causes a severe dysfunction in the lanscape or ecosystem. It is interesting that the global warming scenarios suggest that increased climatic variability and environmental perturbations will be consequences of the greenhouse effect. Future landscapes may thus carry versions of existing communities (possibly somewhat poorer in species) until an extreme climatic event such as a hurricane-type wind, drought and associated wildfires, or excessive flooding occurs. Management plans
for potentially threatened systems therefore need to be drawn up with a specific focus on the need to monitor and protect - minor environmental change and. where possible, protect from dramatic impacts. Conservati~~n decisions to perpetuate such communities need to be carefully thought through. There may well be a greater need for effort to be directed at other conservation activities. Certainly some species in southern England. presently rare, are likely to become more common. New combinations of species may also arise. The vast range of nature reserves, however, contain representations of ecosystems and landscapes whose distributions are broadly consistent with the most currently quoted range of expected climatic variation. From the ecological viewpoint the extent of overall change to our total species/ ecosystems may not be large. save for that resulting from severe environmental perturbation or for communities at extreme ranges. Because of this uncertainty conservation, particularly management of resources to promote the greatest span of biological diversity> will be of immense inlport~~il~e in maintaining the necessary landscape heterogeneity. Conservation activities have naturally focused in the past on the rare and beautiful but perhaps too little on the matrix of the less rare but more important. The propensity for environmental change or extreme environmental events to cause problems in particular reserves. areas or sites means that iand uses should encompass the est~lblishlnent. maintenance and improvement of a network of ‘greenways’ (landscape corridors) bctween areas of high biological divcrsity. Greenways would be a vital link for the movement of plant and animal species through the landscape. Agenties on which this would impact include the Nature Conservancy Council (NCC), the County Conservation Trusts, the Royal Society for the Protection of Birds, the Countryside Commission for England and Wales, the C[)untryside Commission for Scotland and the Ministry of Agriculture, Fisheries and Food (MAFF).
LAND USE POLICY Aoril 1990
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‘There is a temptation to say that nothing can be done’
LAND USE POLICY April 1990
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These greenways could be part of the general landscape matrix, formed from environmentally sensitive areas, national parks, conservation headlands in fields, small woodland plots and so on. Such land will be of great help in ensuring the stability and maintenance of the nation’s biodiversity. Many actual and potential greenways already exist in the form of railway and road corridors. The importance of these transport links for humans may we11 be echoed by the needs of flora and fauna. One concern in such a proposal is that such corridors are also very effective in the dissemination of introduced flora and fauna, which may well find the prevailing climatic conditions very suitable for estabtishment. Biodiversity in general, and particularly individual plant and animal species, may give ‘early warning’ of changes in much the same way as lichens and bryophytes provided sensitive air pollution indicators in past years. Monitoring sites for such species change, particularly those sites which are known biogeographic/ ecosystem boundaries, is a benefit that conservation can contribute to other land users. For it is across sites that changes will first be detected. Other ‘markers’ of change will include thermophifous (warm-loving) insects (some ~e~~~o~~e~u, dragonflies, etc); species which are currently at their ecological limits and thus suffer from stress caused by climatic change; plant communities known to be at their European limits; coastal communities and ecosystems. In the last case, current research by the NCC on changes to coastal saltmarshes in eastern England is making a most useful contribution to the consideration of future action on coasial protection. Rising sea levels (again, with rather elastic limits on the expected changes) will have a severe impact on the highconservation-value ‘soft coasts’ seaward of the sea defences in eastern England. Considerable care will be needed in developing a strategy for coastal management in these areas. In other sites there will be gains and losses, but the generally dynamic nature of coastal systems will pose little
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I Viewpoint
overall threat to conservation value; indeed it may well increase in some areas. Undoubtedly a change of climate will favour some terrestrial and marine species not presently components of Great Britain’s flora and fauna. The whole question of coping with increased plant and animal immigration, and the vexed question of sponsoring translocations as a response to climate change. will be the most pressing concerns for conservation agencies such as the NCC. Such new organisms as may arrive will undoubtedly include a number which pose a threat to native plant and animal species, further emphasizing the potential for ecosystem instability. Other species may ultimateiy enhance our total diversity - but inevitably after a period of instabiIity. ~anagem~nr and dynamics
In most nature reserves there has been little opportunity to understand the ecosystem dynamics. Moreover, there is often an implied assumption that the conditions existing when reserves were established are static. Thus there has been no consideration of the possible destabilizing or perturbing effect that climatic change will have. Now that rapid change is likely, there is a temptation to say that nothing can be done because little is known about the effects of current climatic fluctuations. It is obvious that climatic change will affect abundances of plants and animals and lead to changed species dominance, altered species composition and ultimately altered ecosystem structure. These effects cannot be manipulated easily, if at all. We need to identify the cases where natural adjustment or adaptation is possible in a management process. Such cases will be where: the necessary variability and diversity are present in the ecosystem; a response can take place even though some elements cannot migrate because of habitat fragmentation; ranges can change readily and the adaptive response is unlikely to be negated due to the biota com-
167
ing into conflict with human activities. Where the above occur, minimal interventional management is possible. Nevertheless most reserves will require active management for the maintenance of patch dynamics or the mitigation of the perturbations caused by climatic change, introduced predators or competitors. management action taken must then be chosen to give the biota conserved within reserves the best chance of responding dynamically as did ancestral popuiations to what are assumed to be analogous past climatic changes. Our biggest problem is to assess the risks of species loss and the costs of species retention. This is difficult as we need to predict the likely outcome of climatic change, but cannot wait for that prediction to be proven. We must choose between courses of management actions, each of which will have a financial cost as well as a cost and potentiat benefit to the conserved biota. Site managers need to choose a course of action in the face of uncertainty. Nevertheless, the uncertainty is not
166
absolute: there is knowledge of the response of the biota to past variations in climate. There is knowledge of how ecosystems responded to exotic predators and competitors and to disturbances at a range of time intervals. It is possible to express preferences for management goals, for example that high population numbers (larger gene pool, better chance of surviving chance extinction) are preferred to small numbers or to extinction; that high species richness is preferred to a depauperate biota (because of higher capacity of the ecosystem to respond to change); that similar biotic assemblages be retained in several reserves. Futhermore, it is possible to make statements based on personal judgements about the likely outcome of any management action as it will affect our preferred management goals. Thus it should be possible to make choices between courses of action so that retention of conservation values is maximized and possible loss minimized . In all the uncertainty we know that continued good conservation practice can only assist all Iand uses to adjust to the new conditions.
LAND USE POLICY April 1990
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-1Viewpoint
>sv*._.. . . ..
. ..-*..
Global warming and nature conservation Peter Bridgewater and S. J. Woodin
Predictions of climatic changes vary, but conservation activities must assume that some impacts wit/ occur and that species abundances and distributions will change. Effects on conservation sites wilt be important; management plans should include pfot~tjon against climatic jmpacts and monito~ng of change. Cfimatic effects cannot easily be manipulated: on some sites minimal intervention, allowing natural adjustment, will be best. As wildlife is restricted by landscape fragmentatjon, a network of greenways shoufd be estab/ish~ to facilifate movement between conservation areas. Planning in the face of uncertainty is difficult, but management goals of large populations, high bj~iversi~ and replicated conservation of ~mmunjtjes will aid adaptation to new conditions. The authors are member of Chief respectively, of the Council, Northminster PEl lUA, UK.
Chief Scientist and Scientist Directorate, Nature Conservatory House, Peterborwgh,
LAND USE POLICY April 1990
Much of the current discussion on global warming has focused on how this will affect human use of the planet. Little discussion has occurred on how this will affect the 15 million (or 30 million depending on which estimate you believe) other species with whom we share planetary living space. Yet much of our future in a warmer and wetter/drier world will depend on how these species do react. While agriculture, mariculture and forestry are looking at the species they are involved with, the bulk of species diversity is covered by nature conservation activities. In terms of scientific discussion, global warming has had a chequered history. There seems little doubt that global warming will occur over the next 100-200 years. There is still considerable scientific discussion over the extent to which that warming will occur, the consequences of that warming, including the resulting extent of sea level rise, and the possibility that the warming may itself be canceiled out by natural cooling effects through which the Earth may be about to pass. Indeed, many geologists are now showing that such warming cycles have occurred before, and with the rapidity that is in prospect. The big difference is that the present warming surge is entirely the product of human interactions. This Viewpoint cannot question or become involved with the detail of the scientific arguments. Nonetheless, it would be folly to assume that some impacts from global warming will not occur, and conservation activities
must take place against that backdrop. Frequently quoted estimates would have a warming of 1-4.5”C over a 100-year timespan. The warming will be a continuous change, and all who live on the planet will need to adjust and readjust. Those species with long generation times, such as ourselves, will be at a significant disadvantage compared with those with short (one year or less) ones. As usual the insects and other invertebrates and ephemeral plants (mostly ‘weeds’) will be in the strongest position to adapt and survive. The precise extent of warming in Britain is even less certain than the overall global predictions. Models of regional climatic responses are not yet well developed, but will be essential in determining the most effective stance for nature conservation. Conservation impact The question of most significance is what will happen to the system of Sites of Special Scientific Interest and Nature Reserves, both government owned or managed and those owned or managed by voluntary conservation agencies. The one certainty is that the direct and indirect impacts of climatic change will lead to changes in species composition, dominance and ecosystem structure, and in the distribution and abundance of species. Palaeoecological work on several continents has demonstrated that during previous warmer climates distributions and relative abundances changed; and they changed again as cooling cycles became established. In periods of clima-
165
‘Greenways would be a vital link for the movement of plant and animal species through the landscape’
166
tic change biodiversity shrank - and then swelled as climates ameliorated. This happened, however, in a world where habitats were continuous, and there were no artificial boundaries so typical of modern landscapes in all continents. This landscape fracturing by intrusive built environments and attendant transport links poses major problems to wildlife (particularly terrestrial vertebrate animals) moving between habitats. Work on ‘fossil’ CO2 in the ice caps of Antarctica has shown past increases in CO2 levels coincident with the warm periods in the last 160 000 years. However, concentrations were never as high as at present and the effects from nitrous oxide and methane were less pronounced and, in the case of the CFCs, absent. There are presently no clear scientific indications regarding rates of ecosystem change relative to climate change; they could be gradual, but equally could be abrupt and rapid. What we can say is that there 41 be a response, and that we need to prepare for it. There is a strong suggestion that too great a warming would result in the loss of particular species: rare arctrcalpine plant and animal communities are frequently mentioned. These losscs would be accompanied by a general lowering of biodiversity and general degradation of conservation value. Some of the communities for which the m~~untains of Scotland and some high peaks in England and Wales are famous may well become a thing of the past. However. it is much more likely that those communities will remain in a ‘relict’ state until some dramatic environment~~l perturb~~tion causes a severe dysfunction in the lanscape or ecosystem. It is interesting that the global warming scenarios suggest that increased climatic variability and environmental perturbations will be consequences of the greenhouse effect. Future landscapes may thus carry versions of existing communities (possibly somewhat poorer in species) until an extreme climatic event such as a hurricane-type wind, drought and associated wildfires, or excessive flooding occurs. Management plans
for potentially threatened systems therefore need to be drawn up with a specific focus on the need to monitor and protect - minor environmental change and. where possible, protect from dramatic impacts. Conservati~~n decisions to perpetuate such communities need to be carefully thought through. There may well be a greater need for effort to be directed at other conservation activities. Certainly some species in southern England. presently rare, are likely to become more common. New combinations of species may also arise. The vast range of nature reserves, however, contain representations of ecosystems and landscapes whose distributions are broadly consistent with the most currently quoted range of expected climatic variation. From the ecological viewpoint the extent of overall change to our total species/ ecosystems may not be large. save for that resulting from severe environmental perturbation or for communities at extreme ranges. Because of this uncertainty conservation, particularly management of resources to promote the greatest span of biological diversity> will be of immense inlport~~il~e in maintaining the necessary landscape heterogeneity. Conservation activities have naturally focused in the past on the rare and beautiful but perhaps too little on the matrix of the less rare but more important. The propensity for environmental change or extreme environmental events to cause problems in particular reserves. areas or sites means that iand uses should encompass the est~lblishlnent. maintenance and improvement of a network of ‘greenways’ (landscape corridors) bctween areas of high biological divcrsity. Greenways would be a vital link for the movement of plant and animal species through the landscape. Agenties on which this would impact include the Nature Conservancy Council (NCC), the County Conservation Trusts, the Royal Society for the Protection of Birds, the Countryside Commission for England and Wales, the C[)untryside Commission for Scotland and the Ministry of Agriculture, Fisheries and Food (MAFF).
LAND USE POLICY Aoril 1990
..-
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‘There is a temptation to say that nothing can be done’
LAND USE POLICY April 1990
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These greenways could be part of the general landscape matrix, formed from environmentally sensitive areas, national parks, conservation headlands in fields, small woodland plots and so on. Such land will be of great help in ensuring the stability and maintenance of the nation’s biodiversity. Many actual and potential greenways already exist in the form of railway and road corridors. The importance of these transport links for humans may we11 be echoed by the needs of flora and fauna. One concern in such a proposal is that such corridors are also very effective in the dissemination of introduced flora and fauna, which may well find the prevailing climatic conditions very suitable for estabtishment. Biodiversity in general, and particularly individual plant and animal species, may give ‘early warning’ of changes in much the same way as lichens and bryophytes provided sensitive air pollution indicators in past years. Monitoring sites for such species change, particularly those sites which are known biogeographic/ ecosystem boundaries, is a benefit that conservation can contribute to other land users. For it is across sites that changes will first be detected. Other ‘markers’ of change will include thermophifous (warm-loving) insects (some ~e~~~o~~e~u, dragonflies, etc); species which are currently at their ecological limits and thus suffer from stress caused by climatic change; plant communities known to be at their European limits; coastal communities and ecosystems. In the last case, current research by the NCC on changes to coastal saltmarshes in eastern England is making a most useful contribution to the consideration of future action on coasial protection. Rising sea levels (again, with rather elastic limits on the expected changes) will have a severe impact on the highconservation-value ‘soft coasts’ seaward of the sea defences in eastern England. Considerable care will be needed in developing a strategy for coastal management in these areas. In other sites there will be gains and losses, but the generally dynamic nature of coastal systems will pose little
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I Viewpoint
overall threat to conservation value; indeed it may well increase in some areas. Undoubtedly a change of climate will favour some terrestrial and marine species not presently components of Great Britain’s flora and fauna. The whole question of coping with increased plant and animal immigration, and the vexed question of sponsoring translocations as a response to climate change. will be the most pressing concerns for conservation agencies such as the NCC. Such new organisms as may arrive will undoubtedly include a number which pose a threat to native plant and animal species, further emphasizing the potential for ecosystem instability. Other species may ultimateiy enhance our total diversity - but inevitably after a period of instabiIity. ~anagem~nr and dynamics
In most nature reserves there has been little opportunity to understand the ecosystem dynamics. Moreover, there is often an implied assumption that the conditions existing when reserves were established are static. Thus there has been no consideration of the possible destabilizing or perturbing effect that climatic change will have. Now that rapid change is likely, there is a temptation to say that nothing can be done because little is known about the effects of current climatic fluctuations. It is obvious that climatic change will affect abundances of plants and animals and lead to changed species dominance, altered species composition and ultimately altered ecosystem structure. These effects cannot be manipulated easily, if at all. We need to identify the cases where natural adjustment or adaptation is possible in a management process. Such cases will be where: the necessary variability and diversity are present in the ecosystem; a response can take place even though some elements cannot migrate because of habitat fragmentation; ranges can change readily and the adaptive response is unlikely to be negated due to the biota com-
167
ing into conflict with human activities. Where the above occur, minimal interventional management is possible. Nevertheless most reserves will require active management for the maintenance of patch dynamics or the mitigation of the perturbations caused by climatic change, introduced predators or competitors. management action taken must then be chosen to give the biota conserved within reserves the best chance of responding dynamically as did ancestral popuiations to what are assumed to be analogous past climatic changes. Our biggest problem is to assess the risks of species loss and the costs of species retention. This is difficult as we need to predict the likely outcome of climatic change, but cannot wait for that prediction to be proven. We must choose between courses of management actions, each of which will have a financial cost as well as a cost and potentiat benefit to the conserved biota. Site managers need to choose a course of action in the face of uncertainty. Nevertheless, the uncertainty is not
166
absolute: there is knowledge of the response of the biota to past variations in climate. There is knowledge of how ecosystems responded to exotic predators and competitors and to disturbances at a range of time intervals. It is possible to express preferences for management goals, for example that high population numbers (larger gene pool, better chance of surviving chance extinction) are preferred to small numbers or to extinction; that high species richness is preferred to a depauperate biota (because of higher capacity of the ecosystem to respond to change); that similar biotic assemblages be retained in several reserves. Futhermore, it is possible to make statements based on personal judgements about the likely outcome of any management action as it will affect our preferred management goals. Thus it should be possible to make choices between courses of action so that retention of conservation values is maximized and possible loss minimized . In all the uncertainty we know that continued good conservation practice can only assist all Iand uses to adjust to the new conditions.
LAND USE POLICY April 1990