Lost in space.

Executive summary: We scrutinized peer-reviewed literature, technical books, and key reports in order to detect any evidence for a differential ability between public and public lands to protect imperiled species in the United States. Limitations in data availability and/or in study scale limited our comparison mostly to certain contrasts of federal public versus mostly private lands. At a national scale, we found no unequivocal evidence that rates of imperilment were inherently higher or lower on federal public versus private lands. Nor could we identify conclusively that either federal public or private lands have demonstrably better rates of recovery at the national scale. Despite private lands covering 70% of the country, only 40% of ESA-listed species occur only on this land base. We found that the top 10 states with the greatest proportion of species at risk (10−63%) tend also to have the highest initial species richness. Contrary to our expectations, we found that all federal land categories contained substantially higher concentrations of imperiled species (1 to 11 species/million acres) than did private and non-federal public lands combined (<0.5 species/million acres). Across federal land management agencies, the density of species listed under the Endangered Species Act was highest on Department of Defense and lowest on Bureau of Land Management lands. We attribute our findings to certain novel ‘location effects’ for a greater representation of imperiled species on federal public lands. These include potential for federal public lands to act as the last refugia for remnant populations of scarce species, and a fortuitous placement of the combined federal land base over regions that were historically species-rich (e.g., the arc from southern Oregon to the southeastern U.S.). Department of Defense lands, which a) contain some large, relatively pristine training lands juxtaposed near large urban centers, and b) have superior national representation of bioregions, ecosystem, and community types, contribute uniquely to the locational ‘capture’ of more imperiled species compared to the other federal land management agencies.