Effects of global climate change on biodiversity in forests of the Southern United States
Climate has not been stable in the past. Fluctuations of pine (Pinus) pollen in a 50,000-year sequence from Lake Tulane in Florida indicate that major vegetation shifts occurred during the last glacial cycle. Phases of pollen dominated by pine (indicating a wet climate) were interspersed with periods with plentiful oak (Quercus), ragweed, and marsh elder (Ambrosia type) populations (Grimm et al., 1993). During the Holocene (i.e., the last 12,000 years), climate has fluctuated with periods of cooler, warmer, wetter or drier weather than at present. The greatest changes in climate probably occurred during deglaciation, approxiamtely 12,500 to 11,000 years ago. However in parts of the United States great shifts in plant distribution and composition occurred during the past 120 years, mainly resulting from anthropogenic factors (Miller and Wigand,1994). From 1550 to 1850 a small ice age caused widespread starvation in Europe. Living things have been able to adapt to the warming since then, but widespread, rapid warming could be disastrous (Fajer and Bazzaz, 1992).