#PHOTOTIME BARBARA HALL DRIVERS#
#PHOTOTIME BARBARA HALL SERIES#

Based on a random stratified sample of 400 study sites across the Great Plains, the data offer repeat observations of fixed geographic areas, nested within larger contexts.

#PHOTOTIME BARBARA HALL SERIES#

In this paper we take a closer look at cumulative levels of disturbance in native grasslands, using a new high resolution time series of land-cover data, developed specifically to examine the dynamics of land use. Indeed, there is an increasing awareness that more native grassland is at risk of conversion and that biophysical limits and policy do not constrain short-term expansion to the degree they once did. At various times in the last 60 years, changing technology and economic conditions permitted farmers to expand production to less productive land, and the amounts of land shifting in and out of crop production has grown. However, recent research offers less assurance about the limits of disturbance( Fargione et al. Cunfer (2005) has argued that the stabilization of crop expansion in the Great Plains region as a whole is mainly a function of natural limitations, illustrating that cropland reported in the agricultural census reached stable levels well before public policy set out to explicitly limit production. While the land area devoted to crops has declined six percent nationally since 1945, cropland use in the Corn Belt, Northern Plains, Pacific Northwest, Mountain and Pacific regions has expanded slightly. These aggregate trends mask regional variation and movement in the location and intensity of crop production. Land used for crops has fallen back to levels first recorded nearly a century earlier in 1910, down from a peak of 383 million acres in the 1982 census to 340 million in the 2002 census ( Lubowski et al. Roughly 34 million acres were enrolled in the Conservation Reserve Program(CRP) between 19, augmenting land retirement efforts first set in motion in 1956, with the Soil Bank program ( Sullivan 2004). In the aggregate, the conservation successes have been extensive. Through a combination of price supports and land retirement, farm policy has reduced some of the environmental impacts of agriculture. 2005), the loss of natural habitat to agriculture has slowed considerably since the mid-20 th century in the United States( Brown et al. 2011, Pimentel & Pimentel 2006), and terrestrial carbon ( Baer et al. has disturbed natural ecosystems enormously over the last 200 years, resulting in significant declines in biodiversity ( Fargione et al. While agriculture activity in the Great Plains of the U.S. We conclude that land retirement programs and production subsidies have worked at cross purposes, destabilizing micro-level patterns of land use in recent decades, increasing levels of switching between cropland and grassland and reducing the size of remaining areas of native grassland in the U.S. We modeled the sequences and magnitudes of changes in the interpreted air photo data in a multi-level panel model that included soil quality and slope of sample areas and agricultural activities and employment reported in the U.S. Sample areas were chosen using a stratified random design based on the Public Land Survey grid with in the target counties, in several clusters across the region.

The spatially explicit land-cover data were interpreted from aerial photographs taken at three time points (1950s, 1970s and 2000s).

The research compares land-cover data from 400 sample areas, selected from and nested within 50 counties, to aggregate data from the agricultural and population censuses. Its central aim is to evaluate the dynamics of grassland preservation and conversion, across the region, and to identify areas of grassland that were never plowed during the period. Great Plains in the last half of the twentieth century.

#PHOTOTIME BARBARA HALL DRIVERS#

This paper examines drivers of land-cover change in the U.S.

Phototime barbara hall