The synergistic, or combined, effects of habitat fragmentation and climate change represent one of the most potentially serious global change problems. People destroy or divide natural habitats for farmland, settlements, mines, or other developmental activities. Changes in climate will force individual species of plants and animals to adjust, if they can, as they have in the past. During the Ice Age many species survived by migrating to appropriate habitats. Today such migrations would be much more difficult because they would entail migration across freeways, agricultural zones, industrial parks, military bases, and cities of the 21 st century. An even further complication arises with the imposition of the direct effects of changes in CO2, which can change terrestrial and marine primary productivity as well as alter the competitive relations among photosynthesizing organisms.
The Kirtland's warbler in northern Michigan provides one example of syngergism. The species is restricted to a narrow area of jack pines that grow in sandy soil (Botkin et al. 1991). Forest gap models of growth and decline of jack pines indicate that this tree will move north with warming, but the warbler is not likely to survive the transition. This bird nests on the ground under relatively young pines, and the soil to the north is not generally sandy enough to allow sufficient drainage for successful fledging of young (Cohn 1989). Consequently, global warming could well doom the warbler to extinction in 30 to 60 years.This potential for extinction indicates how the already high rate of extinctions around the world could be exacerbated by climatic changes occurring more rapidly than species can adapt (see Pimm 1991, Peters and Lovejoy 1992, Wilson 1992).
The synergism question raises management problems of anticipating and responding to global change risk. For example, one controversial management plan would be to set up interconnected nature reserves that run north to south or from lower to higher elevation, which could reduce the likelihood of some species being driven to extinction in the event of climate changes. Alternatively, we could simply let the remnants of relatively immobile wildlife and natural plant communities remain in existing isolated reserves and parks, which could lead to some extirpations. If we do opt for more environmental safeguards by interconnecting our parks, the question then becomes how we interconnect the nature reserves. Priorities must be set and money made available for constructing natural corridors through which species can travel. For example, elevated sections of highways may be needed to allow for migration routes, similar to what was done for the caribou in the Arctic when the Alaskan pipeline was built. To examine such questions in scientific and economic detail, a multidisciplinary examination of various aspects of climatology, economics, and ecology is needed. Here we begin with a background discussion of climatic history, processes, modeling, and validation as a prelude to focusing on ecological processes, which need to be examined in order to project possible synergisms among ecology and climate change.
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