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When History Matters: Scale, Time, Climate and Tree Diversity

Matt S. McGlone
Global Ecology and Biogeography Letters
Vol. 5, No. 6 (Nov., 1996), pp. 309-314
Published by: Wiley
DOI: 10.2307/2997586
Stable URL: http://www.jstor.org/stable/2997586
Page Count: 6
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When History Matters: Scale, Time, Climate and Tree Diversity
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Abstract

Palaeoecological insights have had only a limited impact on modern ecological thinking, and tend to be used in an unsophisticated manner. Recent successes in correlating tree diversity with contemporary climate and, in particular, energy, have led to claims that explanations for tree diversity based on historical processes or events are superfluous. However, diversity-energy correlations are strong only at regional scales, and fail to predict diversity at small plots within latitudinal bands, or between continents. Moreover, tree diversity cannot have responded to global glacial-interglacial energy fluctuations because plant species cannot evolve that rapidly nor, in most areas of the world, can migration plausibly adjust regional floral diversity. Thus contemporary climate or energy, while yielding excellent correlations with plant diversity, has no explanatory power. Palaeoecological studies show that cycles of forest migration, fragmentation, reduction, and re-expansion are forced by glacial-interglacial climate cycles at high to mid latitudes. These in turn reduce opportunities for habitat specialization, rapidly eliminate species that remain rare throughout a glacial-interglacial cycle, and promote genetic continuity between populations. The result is increasingly impoverished regional floras with increasing latitude, and hence the latitudinal tree species gradient. Contemporary climate regimes act as a surrogate for the sum total of past climatic states and their effects on diversity, and hence the strong regional climate correlations with tree diversity.

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