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Ecoregion Description
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The Piedmont ecoregion is transitionally located between flat coastal plains to the southeast and the Appalachian Mountains to the northwest (fig. 1). The typical landscape is rolling with steep-sided hills and some plains, and the ecoregion is underlain by metamorphic and igneous rock (EPA 1999). The pre-European vegetation was mostly forests of oak-hickory and mixed oak-pines (Johnson and Sharpe 1976). The Piedmont became an important farming region during the 19th century, but farmland reverted to forest during each economic downturn beginning with the Civil War. Piedmont farmers faced competition from other regions while coping with problems of soil erosion, declining soil fertility, and increased expenses associated with boll weevil management (Hart 1980; Kovacik and Winberry 1987; Manners 1979). Additionally the small fields and steep slopes of the ecoregion hindered the use of farm machinery (Hart 1978). As Piedmont farmers lost their comparative advantages, forestry and land development became more competitive uses of land, and the region gradually reverted to pine and hardwoods intermixed with farms and developed areas (Brender 1974; EPA 1999).
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Figure 1: The Piedmont Ecoregion is a hilly, transitional ecoregion between the flatter areas near the Atlantic coast and the mountainous Appalachian ecoregions. Click on image to enlarge
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Contemporary Land Cover Change (1973 to 2000)
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Nearly 15 percent (14.5) of Piedmont lands were converted to a different cover type during the study period (table 1). This rate was relatively fast compared with other eastern ecoregions (fig. 2). Three-fifths of the converted land changed cover types only one time, while two-fifths was converted two, three, or in a handful of cases, four times. Most Piedmont land was stable (85.5 percent) and was not converted to a different cover type. At late 20th twentieth century land conversion rates, it would take 187 years for the entire ecoregion to be converted to new land cover types.
Land conversion rates varied temporally with the conversion rate during the fastest period being more than twice that of the slowest period (table 2). Conversion rates ranged from a low of 0.5 percent annually during the 1973 to 1980 period to a high of 1.1 percent annually during the 1986 to 1992 period (fig. 3).
Statistical confidence in the estimates of the rates of land cover change in the Piedmont varied over time (table 2). The margin of error at 85 percent confidence was smallest during the 1973 to 1980 period when land cover change was estimated to be slowest, and largest during the rapidly changing 1986 to 1992 period.
Figure 2: The overall spatial change in all Eastern U.S. ecoregions. Each bar chart shows the proportion of the ecoregion that experienced change on 1, 2, 3, or 4 dates. Click on image to enlarge
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Table 1: Percent of ecoregion with land covers that were converted.
Table 2: Land Conversion Rates: 1973 to 2000
Figure 3: Change by Time Interval Normalized to Annual Rates. Click on image to enlarge
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Figure 4 provides an overview of the net land cover change by time period. Developed covers increased steadily and more rapidly throughout the 28-year study period, except during the 1980 to 1986 period. The 1980 to 1986 decline in the rate of land cover change may have been the result of national efforts to curb inflation, with one result being greatly reduced new housing construction through the early 1980s (National Association of Home Builders, 2006). The mechanically disturbed land cover class increased in area during the first three periods and then lost area during the 1992 to 2000 period, perhaps because of the decline of commercial forest harvesting associated with the ecoregion’s population growth (Van Lear and others, 2004). Forest and agriculture steadily declined as more land shifted to developed cover to accomodate the Piedmont’s population growth.
Eight common land conversions accounted for 96 percent (by area) of the change in the Piedmont (table 3). The top two changes were from forest to mechanically disturbed and from mechanically disturbed to forest, which represented the cyclical process of forest harvesting and regrowth. Three of the common conversions resulted in one-way conversions to developed land, and the forest to water conversion provided potable water for the Piedmont’s growing population.
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Figure 4: Net land changes in the Piedmont. Click on image to enlarge
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Table 3: Eight of the most common Piedmont Ecoregion land conversions: 1973 to 2000.
The major land cover types in the Piedmont are forest, agriculture, developed land, and water bodies (table 4). The four cover types accounted for more than 97 percent of the ecoregion in both 1973 and 2000, but their relative proportions did change. Developed land cover types increased 38 percent from 11.9 to 16.4 percent of the ecoregion. The Piedmont is located in the Sun Belt, which grew rapidly during the latter part of the 20th century. After 1960, the Piedmont’s population increased faster than the rest of the nation through the remainder of the 20th century. The population increased from 7.6 million to 13.8 million (U.S. Census Bureau) accounting for an 82 percent increase compared with 38 percent for the conterminous United States. The new residents placed demands on the ecoregion’s land cover that resulted in additional land being developed. Meanwhile, water bodies increased areally nearly 9.8 percent, most likely to meet the need for public drinking water in the ecoregion, which has scant groundwater supplies (Hodler and Schretter 1986). Forested area declined from 59.8 to 55.1 percent of the ecoregion, for an 8 percent decline, but forested land still accounted for more than half of the ecoregion in 2000. Most converted forest became developed. Forest provided a disproportionate 70 percent of the land that was converted to developed uses (fig. 5). Agriculture accounted for approximately one-quarter of the newly developed land, which was equivalent to its proportion of the ecoregion.
During the past 200 years, most of the Piedmont’s original forests were converted to farmland, but when the farms were unable to remain nationally competitive, much of the ecoregion became reforested. The Land Cover Trends Project captured the most recent chapter of Piedmont land change. During the last third of the 20th century, the Piedmont became one of the fastest growing regions in the nation. This new growth placed significant demands upon the ecoregion’s land covers and resulted in the conversion of forest and farmland to developed and water uses.
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Table 4: Area and Percent of Area in Each Land Cover in km2: 1973 to 2000
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Figure 5: Sources of developed land. Click on image to enlarge
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1 Darrell E. Napton – U.S. Geological Survey Visiting Scientist, Center for Earth Resources Observation and Science, Sioux Falls, SD 57198; Geography Professor, South Dakota State University, Brookings, SD 57007
References
Brender, E. V. 1974. Impact of past land use on the lower piedmont forest. Journal of Forestry 72:34-6.
Environmental Protection Agency. 1999. Primary Distinguishing Characteristics of Level III Ecoregions of the Continental United States. EPA Site: http://www.epa.gov/wed/pages/ecoregions/level_iii.htm. Accessed May 10, 1999.
Hart, John Fraser. 1980. Land Use Change in a Piedmont County. Annals of the Association of American Geographers 70(4): 492-527.
Hart, John Fraser. 1978. Cropland Concentrations in the South. Annals of the Association of American Geographers 68(4): 505-517.
Hodler, Thomas W., and Howard A. Schretter. 1986.The Atlas of Georgia. Athens: The Institute of Community and Area Development, and the University of Georgia.
Johnson, Carter W., and David M. Sharpe. 1976. An Analysis of Forest Dynamics in the Northern Georgia Piedmont. Forest Science, 22(3): 307-322.
Manners, Ian R. 1979. The Persistent Problem of the Boll Weevil: Pest Control in Principle and Practice. Geographical Review. Vol. 59 No. 1 pp. 25-42.
National Association of Home Builders. 2006. Housing Starts. http://www.nahb.org/generic.aspx?genericContentID=554, accessed February 24, 2006.
U.S. Census Bureau. Various years. http://www.census.gov/prod/www/abs/decennial/index.htm
Van Lear, D.H., R.A. Harper, P.R. Kapeluck, and W.D. Carroll. 2004.
History of Piedmont Forests: Implications for Current Pine Management. USDA Forest Service General Technical Report SRS-71, 127-131.
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U.S. Department of the Interior |
U.S. Geological Survey
