ECOLOGY/EVOLUTION

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Science  21 May 2004:
Vol. 304, Issue 5674, pp. 1079
DOI: 10.1126/science.304.5674.1079a

The distributions of plant species and vegetation zones in the Northern Hemisphere have shifted and fluctuated dramatically in response to changes in climate. Reconstructing these spatial and temporal migrations from fossil pollen assemblages has become routine for paleoecologists and has revealed the dynamism and impermanence of plant communities and their species compositions.

In a synthesis of vegetation dynamics of North America using data from 759 fossil pollen sites deposited in the North American Pollen Database, Williams et al. track the changes that have taken place since the last glacial maximum, 21,000 years ago. Their data visualization (www.ngdc.noaa.gov/paleo/pubs/williams2004/williams2004.html) shows in detail how plant species respond individualistically—such that many species associations tend to be ephemeral—and it shows how these shifts scale upwards to biomes: large-scale entities defined as associations of plant functional types (e.g. steppe, tundra, deciduous forest). Biomes exhibit considerable dynamism, too, emerging and vanishing with the passage of time. — AMS

Ecol. Monogr. 74, 309 (2004).

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