The Shortgrass Steppe
The Shortgrass Steppe
The Region and Research Sites
The central grassland region of North America (Fig. 1.1) is the largest contiguous grassland environment on earth. Prior to European settlement, it was a vast, treeless area characterized by dense head-high grasses in the wet eastern portion, and very short sparse grasses in the dry west. As settlers swept across the area, they replaced native grasslands with croplands, most intensively in the east, and less so in the west (Fig. 1.2). The most drought-prone and least productive areas have survived as native grasslands, and the shortgrass steppe occupies the warmest, driest, least productive locations. James Michener (1974) provided an apt description of the harshness of the shortgrass region in his book Centennial:… It is not a hospitable land, like that farther east in Kansas or back near the Appalachians. It is mean and gravelly and hard to work. It lacks an adequate topsoil for plowing. It is devoid of trees or easy shelter. A family could wander for weeks and never 4 nd enough wood to build a house. (p. 64)… The objective of this chapter is to introduce the shortgrass steppe (Fig. 1.3) and its record of ecological research. First we present an ecological history of the shortgrass steppe since the Tertiary, and provide the geographic and climatic context for the region. Second we describe the major research sites, and the history of the three major entities or programs that have shaped much of the science done in the shortgrass steppe: the U.S. Department of Agriculture (USDA)–Agricultural Research Service (ARS), the International Biological Programme (IBP), and the Long-Term Ecological Research (LTER) Program. Grasses have been an important component of the shortgrass steppe of North America since the Miocene (5–24 million years ago) (Axelrod, 1985; Stebbins, 1981). Before that, during the Paleocene and Eocene (34–65 million years ago), the vegetation was a mixture of temperate and tropical mesophytic forests. Two causes have been proposed as explanations for this ancient change from forest to grassland. First, global temperatures decreased rapidly during the Oligocene (24–34 million years ago), creating conditions for a drier climate. These drier conditions, combined with a renewal of the uplift of the Rocky Mountains that had begun during the Paleocene, left the Great Plains in a rain shadow.
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