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Regional Trends of Biological Resources — Grasslands

Prairie Past and Present

In the past, grassland dominated central North America (Fig. 2) and, during the warm, dry interglacial times, reached—as the prairie peninsula—into parts of Wisconsin, Illinois, Indiana, and eastern Ohio (Bazzaz and Parrish 1982). The main bodies of native grassland, now vastly altered, are the tall-grass prairie extending from Canada (Manitoba) and Minnesota south to Texas; the mixed-grass prairie from Canada, Montana, and North Dakota south to Texas; and the short-grass prairie extending from eastern Wyoming south to western Texas and eastern New Mexico. In the north, the natural grasslands are bordered on the west by coniferous forests of the Rocky Mountains and on the east by oak savannah (Anderson 1983) and aspen parkland in Manitoba and northwest Minnesota, with the transition from prairie to forest often abrupt (Great Plains Flora Association 1986). Across the Great Plains, coniferous and deciduous forest types meet only in the valley of the Niobrara River in north-central Nebraska, and isolated stands of both forest types occur in the Black Hills of South Dakota.

Figure 2: Map of Short-, Mixed-, and Tall-grass distributions in the central plains states. Inset map of U.S. showing study area.
Fig. 2.   Extent of historical (pre-European) tall-grass, mixed-grass, and short-grass prairies on the North American Great Plains.

Table 1.   Summary of the estimated past area, current area, and percent decline of tall-grass, mixed-grass, and short-grass prairies.
Prairie type
Past area (hectares)a Current area (hectares)a Decline (percent)
Manitoba 600,000 300 99.9
Illinois 8,500,000 930 99.9
Indiana 2,800,000 404 99.9
Iowa 12,000,000 12,140 99.9
Kansas 6,900,000 1,200,000 82.6
Minnesota 7,300,000 30,000-60,000 99.2-99.6
Missouri 6,000,000 32,000 99.5
Nebraska 6,100,000 123,000 98.0
North Dakota 130,000 120 99.9
Oklahoma 5,200,000 N/Ab N/Ab
South Dakota 2,600,000 20,000 99.2
Texas 7,200,000 720,000 90.0
Wisconsin 2,400,000 1,000 99.9
Alberta 8,700,000 3,400,000 60.9
Manitoba 600,000 300 99.9
Saskatchewan 13,400,000 2,500,000 81.3
Nebraska 7,700,000 1,900,000 75.3
North Dakota 14,200,000 4,500,000 68.3
Oklahoma 2,500,000 N/Ab N/Ab
South Dakota 1,600,000 480,000 70.0
Texas 14,100,000 9,800,000 30.5
Saskatchewan 5,900,000 840,000 85.8
Oklahoma 1,300,000 N/Ab N/Ab
New Mexico N/Ab 1,255,200 N/Ab
South Dakota 179,000 116,350 35.0
Texas 7,800,000 1,600,000 79.5
Wyoming 3,000,000 2,400,000 20.0
a Estimates of past and current area based on information from The Nature Conservancy's Natural Heritage Data Center Network; Provinces of Alberta, Manitoba, and Saskatchewan; universities; and state conservation organizations.
b N/A means information is not available.

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