This paper examines drivers of land-cover change in the U.S. Great Plains in the last half of the twentieth century. 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. 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. The spatially explicit land-cover data were interpreted from aerial photographs taken at three time points (1950s, 1970s and 2000s). 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. 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. Censuses of Agriculture and Population. 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. Great Plains.

中文翻译：

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美国平原的土地转变：草地转变驱动因素的多层次建模（1956-2006）

本文研究了 20 世纪后半叶美国大平原土地覆盖变化的驱动因素。其中心目标是评估整个地区草原保护和转化的动态，并确定在此期间从未耕种过的草原区域。该研究比较了来自 50 个县的 400 个样本区域的土地覆盖数据，以汇总来自农业和人口普查的数据。从三个时间点（1950 年代、1970 年代和 2000 年代）拍摄的航空照片解释了空间明确的土地覆盖数据。样本区域是使用基于公共土地调查网格的分层随机设计选择的，在目标县中，在该地区的几个集群中。我们在多级面板模型中对解释的航空照片数据的变化序列和幅度进行建模，该模型包括美国农业和人口普查中报告的土壤质量和样本区域的坡度以及农业活动和就业。我们得出的结论是，土地退休计划和生产补贴是相互矛盾的，破坏了近几十年来土地利用微观模式的稳定，增加了农田和草地之间的转换水平，并减少了美国大平原原生草地的剩余面积。 .