Climate change and the survival of forest species

The fossil record provides many examples of changes in geographical distributions of plants in response to changing clilmate. These examples provide a basis for predicting response to future climate. The accumulation of greenhouse gases in the atmosphere will soon cause climatic warming. With CO2 doubling, global temperatures are expected to rise 3 degrees +/- 1.5 C degrees. If emission of greenhouse gases continues to increase at the present rates, globabl warming will average 0.3 degrees C per decade for the next century. Can the flora adjust easily? Or will climatic change cause extinction? The survival of many taxa through a series of glacial-interglacial cycles during the Pleistocene suggests that most plant species in the temperate zone have been able to disperse to keep pace with climatic changes in the past. Temperate zone trees survived the last glacial maximum as small populations in refugia in southeastern United States. As the ice sheets melted and the climate warmed at teh end of the glacial interval, these plants were able to disperse northward hundreds of kilometers to occupy their present-day range. Future greenhouse warming, however, differs from climatic changes in the past: the rate of change will be at least one order of magnitude more rapid. Examples from the most recent time of relatively rapid change exist - the warming just at the end of the last glacial interval in northwestern Europe fossils from warmth-requiring species of water plants and beetles are found earlier than the oldest fossils from trees. This suggests that the climate became warm enough for trees several centuries before trees began to grow on the local landscape. Dispersal of tree seeds was insufficient to track the change in temperature, or development of soils was not rapid enough to provide appropriate habitats for trees.