Biodiversity, although recognized as encompassing several levels of biological organization, is often thought of as species diversity. Three diversity estimates were calculated for the conterminous United States using satellite data acquired from the Advanced Very High Resolution Radiometer (AVHRR): land cover richness, vegetation richness, and vegetation clustering. Vegetation richness and vegetation clustering showed a scale-dependent relationship to elevation across the range of quadrat sizes from 500 to 50,000 mi 2. All diversity measures increased east to west, with a rather abrupt transition at the Colorado Front Range. The longitudinal diversity gradients found in this study are in contrast to the reported latitudinal and longitudinal gradients for species diversity.
Wickham, J.D.; Wade, T.G.; Jones, K.B.; Riitters, Kurt H.; O''Neill, R.V. 1995. Diversity of ecological communities of the United States. Vegetatio, Vol. 119: 91-100