Historical U.S. cropland areas and the potential for bioenergy production on abandoned croplands.

Agriculture is historically a dominant form of global environmental degradation, and the potential for increased future degradation may be driven by growing demand for food and biofuels. While these impacts have been explored using global gridded maps of croplands, such maps are based on relatively coarse spatial data. Here, we apply high-resolution cropland inventories for the conterminous U.S. with a land-use model to develop historical gridded cropland areas for the years 1850-2000 and year 2000 abandoned cropland maps. While the historical cropland maps are consistent with generally accepted land-use trends, our U.S. abandoned cropland estimates of 68 Mha are as much as 70% larger than previous gridded estimates due to a reduction in aggregation effects. Renewed cultivation on the subset of abandoned croplands that have not become forests or urban lands represents one approach to mitigating the future expansion of agriculture. Potential bioenergy production from these abandoned lands using a wide range of biomass yields and conversion efficiencies has an upper-limit of 5-30% of the current U.S. primary energy demand or 4-30% of the current U.S. liquid fuel demand.