Cumberlands and Southern Ridge and Valley Ecoregion—Ecological Land Units

The Nature Conservancy's conservation process starts by designing portfolios of conservation areas within and across ecoregions. These ecoregional portfolios represent the full distribution and diversity of native species, natural communities, and ecological systems within each ecoregion. The Conservancy develops and uses ecological land units (ELUs) as a synthetic surrogate for biological information. ELUs express the stable underlying physical features that structure a site, and each one depicts a unique combination of three factors--geology, land form, and elevation zones. Largely, the distribution of the ELUs determines the types and distribution of biodiversity features across a landscape.

For this ecoregion, a team of ecologists classified the digital elevation model (DEM) into a set of 14 landforms and four elevation zones that was deemed ecologically relevant to the distribution of plant communities across the ecoregion. Ecologists grouped original rock types from digital geology maps into 11 classes thought to be most influential in determining plant communities, and three grids were each reclassified into a particular range of digits to form a final five-digit ELU. Added together, the combination resulted in 470 unique ELU classes, which were used to characterize and select potential conservation areas that would capture the full range of biophysical habitats in an ecoregional portfolio.

The ELU data layer is also used more generally to help predict vegetation distributions, delineate ecosystems, estimate biodiversity, and design stratified sampling schemes for field inventory and remote sensing projects. The ELU concept is scalable from sites to continents with appropriate changes to the character and resolution of the input variables.