Palaeoecology and plant population dynamics.

The pollen record of the past 10-20 thousand years is a source of data both on long-term climatic change and on the dynamics of plant populations in response to climatic change. Time sequences of pollen accumulation rates record invasions of tree taxa over 10(1)-10(3) years. Palaeoecologists have fifted such data with simple population dynamic models that assume a constant climate. Population doubling times estimated from the pollen record are consistent with species' life-history characteristics and with estimates based on the population structure of modern forests. This palaeo-ecological approach complements palaeoclimatological studies of longeer-term (10(3)-10(5)-year) population shifts, in which population response is assumed instantaneous. Both approaches depend on population responses being fast compared to the climatic changes that cause them. Pollen data also record the more complex interactions between climate and vegetation that occur during periods of rapid climatic change, and could be used to test more realistic models of vegetation dynamics in a changing environment.