At the margins: Agriculture, subsidies and the shifting fate of North America's Native Grassland.

We examined patterns of shifting cropland cultivation in the US Great Plains from the dust bowl to the beginning of the 21st century, by comparing land-cover data from 400 sample sites across the region from the 1930s, 1950s, 1970s and, 1990s and 2000s. We argue that understanding the use of marginal land for cultivation in the Great Plains since the Great Depression requires understanding the interacting dynamics of demography, technology, and policy. The small area land-cover data are nested within 50 target counties across the region. We draw on these dynamics, and their interactions with a range of policy programs aimed at reducing environmental impacts of agriculture, to tell the story of how and when marginal lands have been brought into use. In a multi-level panel design, macro- and micro-level covariates were used to predict levels of encroachment on marginal soils. We conclude that land retirement programs (like the Conservation Reserve Program) have had a generally stabilizing effect on the micro-level patterns of land use in recent decades, but that increased levels of encroachment on marginal soils and native grassland remain a problem in areas with higher or increasing population densities.