POTENTIAL EFFECTS OF GLOBAL CLIMATE CHANGE ON THE BIODIVERSITY OF PLANTS

Climatologists have observed a consistent increase in atmospheric CO2 over the past 30 years. It is predicted that CO2 levels could double the pre-industrial level of 280 ppm by the year 2100, perphaps much earlier. Climate models of doubled atmospheric CO2 predict that mean temperatures will increase between 1.5 and 4.5-degrees-C globally; these temperature changes will be greater at high latitudes. Mid-continental regions will experience lower rainfall. Predictions of species northward range shifts in response to climate change vary from 100 km to over 500 km. Historical evidence of species range movements following the Pleistocene indicate that tree species typically migrated at rates of 10 km to 40 km per century. A simulation model that predicts the migration response of trees through modem fragmented landscapes predicts migration rates much lower than Pleistocene observations. Thus migration response is likely to lag far behind rates of climatic change, potentially threatening narrowly distributed species whose predicted future ranges do not overlap with their current range. Insect pests and microbial pathogens should respond to climatic warming faster than long-lived trees. Predicted increased drought frequency may increase plant stress and thereby increase the frequency of insect outbreaks and disease. Predictions of species responses are complicated by direct effects of increased CO2, such as increased water-use. efficiency. However, response to elevated CO2 vanes among species. Thus, shifts in composition within plant communities are also likely, but are, as yet, unpredictable.