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Contemporary Land Cover Change in the Western Allegheny Plateau Ecoregion
By Kristi L. Sayler 1
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Ecoregion Description
The Western Allegheny Plateau ecoregion, as defined by Omernik (1987), covers portions of eastern Ohio, southwestern Pennsylvania, northwestern West Virginia, and a small piece of northeastern Kentucky. The ecoregion covers approximately 84,500 km2 (32,630 mi2) (fig. 1) and is about 72 percent forest and 23 percent agriculture. The forest area is mostly mixed oak and mixed temperate forests that still exist today on most of the remaining rounded hills. Dairy, livestock, and general farming, as well as residential developments, are concentrated in the valleys. Pittsburgh, Pennsylvania is the largest urban area in the ecoregion and has shown some expansion despite an overall population decline in the ecoregion. Coal mining is still active in the Pennsylvania, West Virginia, and Kentucky portions of the ecoregion and in Ohio to a lesser extent. The Ohio and Allegheny River systems in the ecoregion have been adversely affected by acid mine drainage and industrial pollution, which has caused degradation of the stream habitats and loss of fish species (Cooper, 1983). Water quality has improved somewhat, and a few species have returned.
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Figure 1. Western Allegheny Plateau and surrounding ecoregions. The 40 randomly selected 100-km˛ sample blocks are shown along with land use/land cover from the 1992 National Land Cover Dataset. Click to enlarge image
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Contemporary Land Cover Change (1973 to 2000)
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The overall spatial change from 1973 to 2000 for the Western Allegheny Plateau was 6.0 percent, which was a low amount of change compared to other ecoregions in the East (fig. 2). An estimated 4 percent of the ecoregion changed only one time. The other 2 percent changed multiple times and was likely the result of coal mining and timber harvesting activities (table 1), which tend to cycle through multiple land cover transitions.
The change per time period ranged from 1.9 to 2.3 percent with margin of errors ranging from 0.4 to 0.7 percent (table 2). The average annual rates of change show that the 1986 to 1992 period had the greatest amount of change with a rate of 0.4 percent per year (table 2 and fig. 3). This was a period of transition for the coal mining regions of Ohio and West Virginia. Ohio coal production was slowing down due to increasing regulations on surface mining and higher environmental emission standards (Crowell, 1995), whereas West Virginia saw an increase in the extraction of low-sulfur coal (Fox, 1999) in order to meet federal standards from the 1990 Clean Air Act.
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Table 1: Amount of overall spatial change detected in the ecoregion and proportion of the ecoregion that experienced change during one or multiple time periods
Table 2: Raw estimates of percent change in the ecoregion computed for each of the four time periods and associated margin of error at a 85 percent level of confidence
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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 to enlarge image
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Figure 3: The estimates of land cover change per time interval normalized to an annual rate of change. The Western Allegheny Plateau is highlighted in black. Click to enlarge image
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The majority of land cover classes in the Western Allegheny Plateau experienced little change during the study period (table 3). Forest and agriculture both showed steady declines since 1973, while developed lands increased during each time period resulting in an increase of 376 km2 (147 mi2) between 1973 and 2000. Grassland/shrubland increased from 1.5 percent of the ecoregion area in 1973 to 2.6 percent in 2000.
Table 3: Proportion of the ecoregion covered by each land cover class during each of the five mapped dates
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Mining and forest clearing activities caused the most prominent net land cover changes in the Western Allegheny Plateau ecoregion. Net changes in the land cover classes fluctuated throughout the 1973 to 2000 period (fig. 4). Grassland/shrubland had net increases in all four time periods, while mining and forest showed decreases in most time periods.
Figure 4: Per period net change for each land cover class. Areas above zero represent net gains for a land cover class, while areas below represent a net loss. Click to enlarge image
With a few exceptions for timber cutting, the top three leading land cover transitions during each time period were related to coal mining activities in the ecoregion (i.e., mining to grassland/shrubland, grassland/shrubland to forest, or forest to mining). The top seven transitions contained at least 75 percent of the total change for each time period and affected between 1,090 and 1,400 km2 of land area (table 4).
Table 4: Leading land cover conversions during each of the four time periods
1 Kristi L. Sayler – U.S. Geological Survey, Center for Earth Resources Observation and Science, Sioux Falls, SD 57198
References
Cooper, E.L., 1983, Fishes of Pennsylvania and the northeastern United States: University Park, Pa., Pennsylvania State University Press, 183 p.
Crowell, D.L., 1995, History of the coal-mining industry in Ohio: Ohio Division of Geological Survey Bulletin 72, 204 p.
Fox, J., 1999, Mountaintop removal in West Virginia—an environmental sacrifice zone: Organization and Environment, v. 12, no. 2, p. 163-183.
Omernik, J.M., 1987, Ecoregions of the conterminous United States: Annals of the Association of American Geographers, v. 77, no. 1, p. 118-125.
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U.S. Department of the Interior |
U.S. Geological Survey
