The geography of private forests that support at-risk species in the conterminous United States

Previous efforts to identify important conservation areas in the United States suggest that private lands play a vital role in protecting biodiversity.  However, such views will remain speculative until conservation practitioners indicate where and how much biodiversity is associated on private lands.  In this study, we present a coarse-scale, first approximation of where privately owned forests support at-risk species in the coterminous United States.  Species at risk are defined to be globally critically imperiled (< 5 viable populations), globally imperiled (6-20 viable populations), or vulnerable species (21-80 populations) or those species listed under the U.S. Endangered Species Act and include vertebrate animals (588), vascular plants (1,899), selected invertebrate animals (1,133) and non-vascular plants (84).  We develop a spatially explicit database of species location to rank fourth-level watersheds by several indices that relate to the occurrence of at-risk species associated with private forests.  These indices include a count of at-risk species associated with private forests, a density index that attempts to account for the species-area relationship and the variation in forest area within watersheds, and a third index that estimates the proportion of forest-associated species found on private lands.  The results of our study indicate that two-thirds of the watersheds in the coterminous U.S. contain species at risk associated with private forests, with counts ranging from 1 to 101 species.  In almost all of these watersheds, there is at least one species that is found only on private forests.  Those watersheds with the greatest amounts are found in the Southeast, Mid-Atlantic and Pacific Northwest regions as well as California.  Sustaining these private forests will be a key challenge for the conservation community as many of them are threatened by resource extraction and land use conversion.