Global Change and Our Common Future Papers from a Forum (1989) / Chapter Skim
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14. Threats to Biological Diversity as the Earth Warms
14. Threats to Biological Diversity as the Earth Warms
Pages 139-158
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From page 139... ...
Conservation now focuses primarily on conserving entire interdependent webs of species -- an ecosystem approach. We now know that not only are all the biological pieces of the planetary jigsaw puzzle interdependent, but also that human society itself, even in an age of gene splicing, engineered food crops, and modern medicine, is vastly more dependent than most people realize upon the natural diversity of living organisms .
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From page 140... ...
Although our knowledge of most species is overshadowed by our ignorance -- indeed, most of the possibly 30 million species of organisms have not even been named -- by extrapolation from species that have been investigated we can safely say that a large number are valuable. For example, of some 1500 previously uninvestigated plant species assayed for pharmacological activity, at least 15 percent promised medicinal importance (Caufield, 1985~.
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From page 141... ...
The result of such habitat destruction is to erase some species entirely and to leave others as remnant populations surviving in habitat fragments surrounded by cleared and hostile land. Understanding the effects of this fragmentation is key to understanding how climate change will impact wild ecosystems in the disturbed landscape of the twentieth and twenty-first centuries.
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From page 142... ...
Even widespread species are likely to have drastically curtailed ranges, at least in the short term. Moreover, human encroachment and habitat destruction will make wild populations of many species small and vulnerable to local climate changes.
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From page 143... ...
A final point, important in understanding species response to climate change, is that weather is variable, and extreme events, like droughts, floods, blizzards, and hot or cold spells, may have greater effects on species distributions than does average climate per se (e.g., Knopf and Sedgwick, 1987~. For example, in northwestern forests global warming is expected to increase the frequency of fires, leading to rapid alteration of forest character (Franklin, 1990~.
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From page 144... ...
middens in the southwestern United States show that during the wetter, moderate climate of 22,000 to 12,000 years ago, there was not a concerted shift of plant communities. Instead, species responded individually to climatic change, forming stable but, by present-day standards, unusual assemblages of plants and animals (Van Devender and Spaulding, 1979~.
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From page 145... ...
MAGNITUDE OF PROJECTED LATITUDINAL SHIFTS If the proposed CO2-induced warming occurs, species shifts similar to those in the Pleistocene will occur, and vegetation belts will move hundreds of kilometers toward the poles (Davis and Zabinski, 1990; Frye, 1983; Peters and Darling, 1985~. A 300-km shift in the temperate zone is a reasonable minimum estimate for a 3°C warming, based on the
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From page 146... ...
is largely unsuccessful at germinating seeds below 15°C and is bounded to the north by the 15°C July mean isotherm (Marshall, 1978~. Moisture extremes exceeding physiological tolerances also determine species' distributions.
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From page 147... ...
Local extinctions may occur as climate change causes increased frequencies of droughts and fires, favoring invading species. One species that might spread, given such conditions, is Melaleuca quinquenervia, a bamboo-like Australian eucalypt.
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From page 148... ...
If the climatic optima of temperate zone species do shift hundreds of kilometers toward the poles within the next 100 years, then these species will have to colonize new areas rapidly. To survive, a localized species whose present range becomes unsuitable might have to shift poleward at several hundred kilometers or faster per century.
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From page 149... ...
For many species, all of these conditions will be met by humancaused habitat destruction, which increasingly confines the natural biota to small patches of original habitat, patches isolated by vast areas of human-dominated urban or agricultural lands. Habitat destruction in conjunction with climate change sets the stage for an even larger wave of extinction than that previously imagined, based on consideration of human encroachment alone.
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From page 150... ...
informed guesses can be made at least about the general direction of change, specifically that most areas will tend to be hotter and that continental interiors in particular are likely to experience decreased soil moisture. How might the threats posed by climatic change to natural communities be mitigated?
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From page 151... ...
Nonetheless, even were the production of all greenhouse gases stopped today, it is very likely that there are now high enough concentrations in the air to cause ecologically significant warming after a brief lag period (Rind, 1989~. Therefore, those concerned with the conservation of biological diversity must begin to plan mitigation activities.
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From page 152... ...
o Flexible zoning around reserves may allow us to actually move reserves in the future to track climatic optima, as, for example, by trading present rangeland for reserve land. The success of this strategy, however, would depend on a highly developed restoration technology capable of guaranteeing, in effect, the portability of species and whole communities.
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From page 153... ...
1-8) and Preparing for Climate Change: Proceedings of the First North American Conference on Preparing for Climate Change: A Cooperative Approach (J.C.
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From page 154... ...
Lovejoy, eds. Proceedings of World Wildlife Fund's Conference on Consequences of Global Warming for Biological Diversity.
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From page 155... ...
Lovejoy, eds. Proceedings of World Wildlife Fund~s Conference on Consequences of the Greenhouse Effect for Biological Diversity.
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From page 156... ...
1989. The dynamic greenhouse: feedback processes that may influence future concentrations of atmospheric trace gases and climatic change.
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From page 157... ...
Lovejoy, eds. Proceedings of World Wildlife Fund's Conference on the Consequences of the Greenhouse Effect for Biological Diversity.
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From page 158... ...
Proceedings of World Wildlife Fund's Conference on Consequences of the Greenhouse Effect for Biological Diversity. Yale University Press, New Haven, Conn., forthcoming.
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