ing temperature (Figures 4-1 and 4-2). Mean annual precipitation ranges from more than 1,200 mm/yr to less than 300 mm/yr, and mean annual temperature from less than 0°C to greater than 20°C. Plant species composition varies from tallgrass prairie to shortgrass steppe, with decreasing precipitation. In addition to influencing ecosystem type, these gradients have large influences on net primary production and soil organic carbon (Sala et al., 1988; Burke et al., 1989).
There is a conventional storytelling of the development of the Great Plains.1 Originally lightly settled by native people, the region was colonized by the European-origin population of the United States in the decades following the Civil War (Powell, 1878; Webb, 1931). This settlement was encouraged by the institutional context of the United States in the nineteenth century. At that time a combination of economic, social, and political processes made land and transportation available for individuals and families who wanted to move out of more densely populated parts of the country (Opie, 1987). These settlers discovered a semiarid grassland landscape with agricultural possibilities that ranged from consistent arable cropping in the east to limited cropping and steady pasturing in the west. Some of the implications of aridity (lack of wood for building and unfamiliar prospects for agriculture, for example) delayed settlement, but demographic pressure in the more eastern United States pushed people west. With what seemed like good years of rainfall and with increasing agricultural prices in the 1910s and 1920s, an aggressive stream of would-be farmers and ranchers acquired land and attempted to farm it (Gutmann and Sample, 1995; Worster, 1992). In this conventional history, the plowing up of the grasslands for wheat, combined with the drought of the 1930s, provoked disastrous dust storms and social dislocation. While we may not agree that those were the only causes, or that the greatest areas of wheat farming suffered the worst drought and dust storms, there was a causal relationship. Plowed land is a much greater source of blowing dust than uncultivated grassland.
Despite the social and economic disruptions of the 1930s, land use changed little as a result of the Dust Bowl. Acreage planted in crops dipped during the worst of the 1930s drought, but by 1945 had recovered fully to predrought levels. The balance between cropland and pasture remained virtually stable from the 1920s through the 1990s in most plains counties (Cunfer, 2005). People responded to the problems of the 1930s by changing some of their cultivation practices (Hargreaves, 1992). Some of them migrated out of the region, although there may have been less out-