|
Ecoregion Description
|
The Southwestern Appalachians ecoregion stretches from north-central Alabama through southeastern Kentucky (fig. 1) and covers approximately 35,350 km2 (13,650 mi2). Much of the ecoregion consists of open low mountains, but some portions of the ecoregion exhibit steep slopes with local relief of up to 300 m. Approximately three-fourths of the ecoregion is covered by forest, primarily mixed oak communities and shortleaf pines. Agricultural lands are found on lower slopes and valley floors, with the greatest concentration in northeastern Alabama. Mining is a locally significant land use activity, especially in the southern part of the ecoregion where the local abundance of coal, limestone, and iron deposits led to a booming steel industry in the first half of the twentieth century. No large cities (populations > 100,000) are found completely within the ecoregion’s borders, but the greater Birmingham, Huntsville, and Chattanooga metropolitan areas are partially within the ecoregion.
|
Figure 1: The underlying land cover is from the 1992 National Land Cover Database (Vogelmann and others, 2001). The twenty-five 10 km x 10 km sample sites for the Land Cover Trends project are shown in yellow. Click on image to enlarge
|
Contemporary Land Cover Change (1973 to 2000)
|
Overall spatial change in the ecoregion (i.e., the percentage of area that changed at least one time from 1973 to 2000) was 13.9 percent (table 1), a moderately high level of change compared to most Eastern United States ecoregions (fig. 2). The total amount of change increased with each successive time period (table 2). When normalized to account for varying time period lengths, change was lower during the 1973 to 1980 period and higher and relatively steady for the last three time periods (fig. 3).
No individual land cover class changed by more than 2.6 percent of the total ecoregion area between 1973 and 2000 (table 3). However, two factors driving land cover conversion were notable in the ecoregion: (1) forestry activity and (2) mining activity. Forest cover consistently showed some of the largest net change, with fairly consistent declines in all four time periods (fig. 4). The conversion from forest to mechanically disturbed land was the most common land cover conversion for all four time periods, while mechanically disturbed to forest land (representing regeneration of cut forest lands) was the second or third most common conversion (table 4). In sum, forestry-related activities (both cutting and regeneration) was clearly one of the most significant factors affecting land cover in the ecoregion for all time periods (fig. 5).
|
Table 1: Percentage of the ecoregion touched by change. 86.1 percent of all pixels in the ecoregion were unchanged throughout the study period, while 13.9 percent were touched by change one or more times.
Table 2: Overall change estimates, margin of error at an 85 percent confidence interval, and normalized annual change for each of the four time periods.
|
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
|
Figure 3: Estimates of land cover change per time interval normalized to annual rates of change. Click on image to enlarge
|
|
Table 3: Percentages of each land cover class for the five mapped dates.
|
Figure 4: Per period net change for each mapped land cover class. Areas above the zero axis represent net gains for a land cover class, while areas below represent net losses. Click on image to enlarge
|
Mining activity was the second most important factor driving land cover change in the ecoregion (fig. 5). Much of the surface mining in the ecoregion, especially in northern Alabama, is for coal, iron, and limestone--all primary materials required for the production of steel. Birmingham, Alabama, which is partially contained within the southern portion of the ecoregion, was once known as the “Pittsburgh of the South.” The related mining and steel industries have been key components of much of the area’s economy in the twentieth century.
Figure 5: Forestry activity (forest cutting and regeneration) and mining activity (new mining and mining reclamation) account for the vast majority of change in the ecoregion. Click on image to enlarge
However, the local steel industry began to decline in the second half of the twentieth century. Imports of cheaper foreign steel into the United States increased dramatically after 1980, contributing to additional closures of steel facilities in the area (Gerard, 2001). With these declines, local demand for the raw materials of the industry also declined. As production halted at the surface mines, many were revegetated with grass/shrubland and eventually reverted back to forest lands. While 700 km2 of newly mined lands were established between 1973 to 2000, more than 1000 km2 of mined lands were reclaimed during the same time period, resulting in a net decline of more than 300 km2. The most significant decline was between 1980 and 1986 when mined land area dropped by 50 percent within the ecoregion, with very minor declines noted for the last two time periods (table 3 and fig. 4). Changes related to mined land reclamation (including mined lands reclaimed to grass/shrublands and grass/shrublands eventually reverting to forest) were significant land cover conversions for all time periods (table 4).
Other land cover conversions were generally minor in the ecoregion. Developed lands did steadily increase throughout the study period, resulting in a net gain of more than 300 km2 from 1973 to 2000. Urban centers on the fringe of the ecoregion (e.g., Birmingham) either exhibited only minor population gains or even decreased in population during the study period, but growth in the surrounding suburbs was the primary driver behind the net gain in developed land area.
Table 4: The five most common land cover conversions for each of the four time periods.
1 Terry L. Sohl - SAIC TSSC, work performed under U.S. Geological Survey contract 03CRN001 at U.S. Geological Survey, Center for Earth Resources Observation and Science, Sioux Falls, SD 57198
References
Gerard, L.W., 2001, Section 232 Investigation into the effects on national security of imports of iron ore and semi-finished steel: Comments submitted to the U.S. Department of Commerce, United Steelworkers of America.
Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., Wylie, B.K., and Van Driel, N., 2001, Completion of the 1990s National Land Cover Data for the conterminous United States from Landsat Thematic Mapper data and ancillary data sources: Photogrammetric Engineering & Remote Sensing, v. 67, p. 650-662.
|
U.S. Department of the Interior |
U.S. Geological Survey
