Population, Land Use, and Environment Research Directions (2005) / Chapter Skim
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4 Population and Environment in the U.S. Great Plains--Myron P. Gutmann, William J. Parton, Geoff Cunfer, and Ingrid C. Burke
4 Population and Environment in the U.S. Great Plains--Myron P. Gutmann, William J. Parton, Geoff Cunfer, and Ingrid C. Burke
Pages 84-105
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From page 84... ...
An additional polar air mass also shapes winter weather, creating a strong north-south gradient in air temperature and snow cover. In summer, the westerly flow weakens and polar air retreats to the north, allowing an air mass that comes from the subtropical Atlantic Ocean to bring moisture into the region.
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From page 85... ...
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)
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From page 86... ...
. Those who remained changed their farming practices between the 1930s and 1970s, by introducing techniques that reduced the risk of erosion and made better use of soil moisture, implementing improved crop varieties, enhancing nutrients through fertilization and by increasing the use of irrigation where groundwater was available (Green, 1973)
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From page 87... ...
Whether consistently provoked by environmental conditions or spurred by broader social change, the Great Plains region has experienced significant demographic changes since its colonization by people of European descent beginning in the mid-nineteenth century. The region has grown in population overall, but that growth masks two defining population patterns.
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From page 88... ...
an analysis of county-scale processes based on historical population, land use, and environmental and other data; (2) a series of historical studies of individual localities, of the experiences of farmers and their families, and of agricultural practices throughout the region; and (3)
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From page 89... ...
from 1880 through 1997.3 In addition to census-based sources, we have collected other county-level tabulations of social characteristics. We use the population and social indicators data to understand population structure and change, and the agricultural census data to understand agricultural land use.
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From page 90... ...
We have also acquired recent soil structure and elevation data, as well as data giving locations of bodies of water and streams, interpolating them to historical county boundaries. Finally, we have acquired other weather data (dust storms, for example)
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From page 91... ...
While we cannot always directly measure environmental outcomes, this analysis, based largely on land use change, is dramatic. The other two-thirds of the Great Plains, used primarily for extensive livestock grazing, has seen only limited environmental change, as cattle mimicked the ecological impacts of the native bison they replaced.
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From page 92... ...
The region experienced steady population growth as land use changed through 1930, followed by a rapid transformation from overall population growth to urban population growth. The region's rural population has been shrinking since the 1930s, in some decades quite rapidly.
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From page 93... ...
Great Plains is not limited to the direct results of local population growth and decline. Environmental changes are as much the result of largescale shifts in the market for agricultural products (driven by populations and tastes elsewhere)
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From page 94... ...
At its peak in the late 1930s, between 31 and 38 percent of the total land in the region had been converted from native grassland to cropland.4 The geographical distribution of that cropland varies from subregion to subregion because the eastern Great Plains has more rainfall than the west and is better suited for cropping. Figure 4-4 shows the growth of total area cropped in the Great Plains from 1880 through 1992, dividing the region into an eastern tier of states (North Dakota, South Dakota, Nebraska, Kansas, Oklahoma, and Texas)
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From page 95... ...
Overall Population Density 12 Square 8 per 4 0 ersonsP 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 Eastern Tier Western Tier Mile 16 c. Rural Population Density 12 Square 8 per 4 0 ersonsP 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 Eastern Tier Western Tier FIGURE 4-4 Differences between eastern tier and western tier states, 1880-1990.
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From page 96... ...
In the two-thirds of the grassland that farmers could not successfully plow for crops, environmental change has been much less dramatic. While nearly all of that land has been used for extensive grazing by cattle, and in much smaller proportions by sheep and horses, most of it remains in native vegetative cover.
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From page 97... ...
If we measure variation in land use as the choice to use the land for cropping or pasture, almost all the variation in agricultural land use in the Great Plains is explained by environmental variables, especially precipitation, temperature, soil texture, and slope (Burke et al., 1994; Burke, Lauenroth, and Parton, 1997; Gutmann et al., 2004; Lauenroth, Burke, and Paruelo, 2000; Sala et al., 1988; Cunfer, 2005)
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From page 98... ...
show that, at both the regional scale and at the level of individual counties, crop farming resulted in significant losses of soil nitrogen. Nitrogen declined most in the northeastern plains, where higher rainfall supported more vegetation and cooler temperatures slowed decomposition of plant matter.
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From page 99... ...
showing that rapid losses of soil carbon following the plowing up of grassland soils, stabilization of soil carbon levels at 50 percent of initial values after 50 years of cultivation, and substantial decreases in soil mineralization after 50 years of dryland cultivation. The high nitrogen mineralization rates following plowing up of grassland soils are consistent with the observation that nitrogen fertilizer responses are minimal for wheat fields after 30 years of
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From page 100... ...
Ramsey, North Dakota 5,000 4,000 3,000 2,000 1,000 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 FIGURE 4-6 Simulated soil carbon in four Great Plains counties.
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From page 101... ...
Model results from Pawnee and Hamilton counties show that irrigated corn-alfalfa rotations begun in the 1960s produced substantial increases in crop yields, soil carbon levels, and soil nitrogen mineralization rates. Most of the increases in soil carbon and nitrogen mineralization occurred from 1970 to 1990 because of the large increases in the amount of carbon (300 to 400 grams of carbon per square meter per year added as corn stover)
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From page 102... ...
Our next approach will be to run century ecosystem model estimates of ecosystem processes for counties that are converting to those uses, measuring the impact of uses, such as lawns, that differ from native grasses, irrigated cropland, and dryland crops. While these land uses are small in the region as a whole (see Parton, Gutmann, and Travis, 2003)
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From page 103... ...
Gutmann 2003 Blowin' down the road: Investigating bilateral causality between dust storms and population change in the Great Plains. Population Research and Policy Review 22:297-331.
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From page 104... ...
Persson 1992 Modeling soil organic matter in organic-amended and nitrogen-fertilized long-term plots. Soil Science Society of America Journal 56:476-488.
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From page 105... ...
Young, and E Knop 1994 Integrated modeling of land use and cover change: A conceptual scheme for apply ing an integration strategy to agricultural land use on the U.S.
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