Tree cover and aridity projections to 2060

Future projections of tree cover and climate change are useful to natural resource managers from the local to national level as they illustrate potential changes to our natural resources and the ecosystem services they provide. By understanding these potential changes, management strategies can be set to sustain desired levels of healthy natural resources for future generations. In support of the 2010 Renewable Resources Planning Act (RPA) Assessment, this report a) details three projections of tree cover change across the conterminous United States based on predicted land-use changes from 2000 to 2060; b) evaluates nine climate projections for the same period to assess which areas of the country may become more or less arid; and c) provides an index of combined tree-cover and aridity change for nine modeled projections to illustrate which areas of the United States are projected to experience the greatest impact from tree-cover loss and increasing aridity. The index illustrates a new approach to highlight areas of ecological vulnerability or concern that may develop at the nexus of projected land use and climate change. We found that in all projections the conterminous United States loses tree cover by 2060, ranging from a 1.1 to 1.6 percent decline; and that the conterminous United States is becoming more arid by 2060, ranging from a 0.05 to 0.19 decrease in the aridity ratio. Overall, the frequency and magnitude of percent tree cover losses and aridity increases among the counties of the conterminous United States are greater than percent tree cover gains and decreases in aridity. The index illustrates that the areas at greatest risk of ecological change from tree loss and increased aridity generally are rapidly urbanizing regions of high tree cover and low aridity such as those found in the metropolitan regions of the Pacific Northwest, Southeast, and Northeast.