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Species richness and species pool size variation across pH gradients in southern Blue Ridge forests.
Gramling, Joel*,1, Peet, Robert1, Fridley, Jason1, Wentworth, Thomas2, 1 Department of Biology, Chapel Hill, NC, USA2 Botany Department, Raleigh, NC, USA
ABSTRACT- Pärtel and Ewald have hypothesized that the relationship between local species density and soil pH is determined by regional species pool size, which in turn reflects the relative abundance of soil types during the evolutionary history of a flora. Ewald observed that calcareous sites in Central Europe have higher species density and larger species pools than acidic sites, and argues that this is the consequence of a Pleistocene bottleneck for acidiphiles. The flora of the Southern Blue Ridge Mountains, USA has always been associated with primarily acidic soils. Given the Pärtel-Ewald hypothesis, one would expect the Blue Ridge region to contain a limited pool of calciphiles. We used vegetation and soil data from 3328 100 m2 Blue Ridge forest plots to examine the generality of this hypothesis. The Blue Ridge flora with less than 20% of species confined to sites above pH 4.7 contrasts dramatically with that of Europe. However, regional species pool size increases with pH and related soil factors. Mean species density is also strongly positively correlated with soil pH. Thus, both regional species pool size and plot species density of Southern Blue Ridge forests fail to match the Pärtel-Ewald predictions. The increase in species pool with increase in pH and correlated soil factors exhibited by Southern Blue Ridge forests appears to reflect broad species distributions and tolerance for high pH conditions among species that grow predominantly under acid conditions. We conclude that high species pool size and species density on higher pH sites are consequences of generally more favorable conditions. It may be correct that the abundance of high pH specialists in Central Europe is an historical artifact, but our data contradict the assertion that evolution of a flora in a primarily low pH environment will translate into a negative correlation between pH and species density.
Key words: species, pool, regional, richness