Responses of plant populations and communities to environmental changes ofthe late Quaternary

The environmental and biotic history of the late Quaternary represents a cr itical junction between ecology, global change studies, and pre-Quaternary paleobiology. Late Quaternary records indicate the modes and mechanisms of environmental variation and biotic responses at timescales of 10(1)-10(4) y ears. Climatic changes of the late Quaternary have occurred continuously ac ross a wide range of temporal scales, with the magnitude of change generall y increasing with time span. Responses of terrestrial plant populations hav e ranged from tolerance in situ to moderate shifts in habitat to migration and/or extinction, depending on magnitudes and rates of environmental chang e. Species assemblages have been disaggregated and recombined, forming a ch anging array of vegetation patterns on the landscape. These patterns of cha nge are characteristic of terrestrial plants and animals but may not be rep resentative of all other life-forms or habitats. Complexity of response, pa rticularly extent of species recombination, depends in part on the nature o f the underlying environmental gradients and how they change through time. Environmental gradients in certain habitats may change in relatively simple fashion, allowing long-term persistence of species associations and spatia l patterns. Consideration of late Quaternary climatic changes indicates tha t both the rate and magnitude of climatic changes anticipated for the comin g century are unprecedented, presenting unique challenges to the biota of t he planet.