Elements of MAD (corresponding to GAP management categories I and II) were overlaid with soil productivity, elevation, and ecoregions datasets to examine the hypothesis that the Biological Reserves system in the conterminous United Stated focuses primarily on high elevation, poor soil productivity areas and does not adequately protect our biological diversity.
Scott, J. Michael, Frank W. Davis, R. Gavin McGhie, R. Gerald Wright, Craig Groves, and John Estes. 2001. Nature Reserves: Do They Capture the Full Range of America's Biological Diversity? Ecological Applications, Ecological Issues in Conservation. 11(4), pp. 999-1007.
Abstract: Less than 6% of the coterminous United States is in nature reserves. Assessment of the occurrence of nature reserves across ranges of elevation and soil productivity classes indicates that nature reserves are most frequently found at higher elevations and on less productive soils. The distribution of plants and animals suggests that the greatest number of species is found at lower elevations. A preliminary assessment of the occurrence of mapped landcover types indicates that 60% of mapped cover types have 10% of their area in nature reserves. Land ownership patterns show that areas of lower elevation and more productive soils are most often privately owned and already extensively converted to urban and agricultural uses. Thus any effort to establish a system of nature reserves that captures the full geographical and ecological range of cover types and species must fully engage the private sector.
Just for a taste, look at the similarities in this United States shaded relief map and the managed areas polygons from MAD-