The Southeastern Plains is the largest ecoregion in the East, covering approximately 336,000 km² (130,000 mi²) and extending from near the Gulf of Mexico in the south to Maryland in the north (fig. 1). The irregular, relatively flat plains of the ecoregion are covered by a mosaic of cropland, pasture, forest, and wetland. The ecoregion is characterized by long growing seasons and abundant rainfall, but the relatively poor sandy soils found in much of the ecoregion limit agricultural competitiveness with many other regions. Natural forests of pine, hickory, and oak once covered most of the ecoregion, but much of the natural forest cover has been replaced by heavily managed timberlands. Only one significant urban center (population >100,000) is found within the interior of the ecoregion (Montgomery), with several others scattered on or near the ecoregion boundaries (Baltimore, Washington, D.C., Alexandria, Richmond, Columbus, Columbia, Macon, and Tallahassee).

Figure 1: The underlying land cover is from the 1992 National Land Cover Database (Vogelmann and others, 2001). The eleven, 20 km x 20 km sample sites for the Land Cover Trends project are shown in yellow. Click on image to enlarge

The footprint of change in the ecoregion (i.e., the percentage of area that changed at least one time from 1973 to 2000) was 20.4 percent (table 1), very high compared with most Eastern U.S. ecoregions (fig. 2). Rates of change per period increased steadily through time (table 2). When normalized to account for varying time period lengths, annual rates of change increased through the first three time periods, peaking during the 1986 to 1992 time period, and declining slightly during the last time period (table 2 and fig. 3).

Despite high overall rates of change, trends for individual land cover classes from 1973 to 2000 (table 3) partially mask the dynamic nature of the ecoregion. Forest cover showed just a modest decline from 1973 to 2000, with a net decline of 1.3 percent, or 4,121 km², yet the Southeastern Plains is home to an extremely dynamic timber industry. Planted pine was rarely found in the region in 1950, but now comprises nearly 50 percent of pine forests in the southeastern United States (fig. 4). The primary land cover transition for every time period is forest to mechanically disturbed, a transition that primarily represents clear-cutting of forest lands (table 4). More than 41,000 km² experienced this transition during the study period. The second most common transition for every time period is mechanically disturbed to forest, a transition that represents the regrowth of forest on previously cut lands. Nearly 33,000 km² experienced this transition during the study period, and mechanically disturbed land showed net increases for all time periods (fig. 5). Managed pine plantations in the ecoregion have planting and cutting cycles as short as twenty years. In addition, newly cut forest patches quickly revegetate to forest cover, whether through natural regeneration or through direct replanting. This leads to a relatively rapid cyclic pattern of forest management, as evidenced by the high percentage of changed areas experiencing two or more transitions during the 1973 to 2000 study period (table 1). This cyclic nature of forest cutting in the ecoregion results in the low net change in total forest cover, but high overall rates of change for each time period.

Table 2: Overall change estimates, margin of error at an 85% confidence interval, and normalized annual change for each of the four time periods.

Figure 3: Estimates of land cover change per time interval normalized to annual rates of change. Click on image to enlarge

Table 1: Percentage of the ecoregion touched by change. 79.6 percent of all pixels in the ecoregion were unchanged throughout the study period, while 20.4 percent were touched by changed one or more times.

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 4: Planted pine and large commercial pine plantations were nearly absent in the South in 1950, but by 2000 covered nearly as large an area as natural pine forest (Conner and Hartsell, 2002) Click on image to enlarge

Table 5: Forest use in the Southeastern Plains, as defined by both forest and mechanical disturbed cover.

Table 3: Percentages of each land cover class for the five mapped dates.

Figure 5: Per period net change for each mapped land cover class. Area above the zero axis represent net gains for a land cover class, while areas below represent net loss. Click on image to enlarge