Connecting fine- and broad-scale species-area relationships of Southeastern US Flora

Although the rate that species accumulate with area has long been regarded as an important component of fine-scale community structure and several studies have examined this rate in meta-analyses, few if any studies have systematically examined fine-scale species-area relationships using a consistent survey protocol over a large region. We examined fine-scale species-area relationships using the extensive database of the Carolina Vegetation Survey (North Carolina, South Carolina, Georgia, and Tennessee, USA), including 1472 plots wherein vascular plant richness was recorded for each of six subplot sizes regularly spaced on a log(10) scale, from 0.01 to 1000 m(2). Contrary to prevailing theory, our data closely and consistently fit an Arrhenius (power law) species-area model, echoing broader-scale patterns. Species accumulation rate (Z) values fell within a narrow range (95% between 0.2 and 0.5) despite a 30-fold range in 1000-m(2) richness. When we added regional- and global-scale richness estimates to our results, a Preston-type triphasic curve emerged. We suggest that (1) fine-scale species-area relationships are remarkably consistent and (2) full-scale species-area curves reveal scale dependencies in diversity data that are not accounted for by current species-area theory.