Plant species turnover along productivity gradients in eastern North Carolina

Species turnover, or β-diversity, is a landscape-level metric describing the distribution of biological diversity, and has been investigated far less than traditional, site-level diversity measures.  We investigated the turnover in plant species composition along a gradient of net primary productivity in two ecoregions in North Carolina.  We addressed the following questions: 1. how does plant species composition change along productivity gradients within each of two ecorgions; and 2. how does species turnover within an ecoregion compare to turnover along a productivity gradient spanning both ecoregions?  For pairs of randomly-selected sites within the two ecoregions, we calculated similarity of plant species composition, using species range maps.  For each of the plot pairs, we also calculated the difference in productivity, using MODIS satellite data.  We then used general linear models to calculate the decay of similarity along productivity gradients within each of the two ecoregions, as well as across both ecoregions.  Our results indicate that species turnover rates along productivity gradients differ between the Coastal Plain and Southeastern Plain ecoregions.  Furthermore, species turnover was most rapid when assessed along a gradient that spans the two ecoregions.  These results have implications for conservation and the placement of reserves across landscapes in the region.  They also add to our knowledge of the ways in which diversity relates to ecosystem functioning in plant communities at the landscape level.