The Northern Piedmont ecoregion trends northeast to southwest, covering approximately 30,120 km² (11,629 mi²) in New Jersey, Pennsylvania, Delaware, Maryland, District of Columbia, and Virginia (fig. 1). The ecoregion is a transition zone between topographically flatter coastal areas to the east and more mountainous regions to the west and north. The Northern Piedmont includes the western portions of the New York, Philadelphia, Baltimore, and Washington metropolitan areas. The Northern Piedmont’s landforms include low, rounded hills, irregular plains, and open valleys (U.S. Environmental Protection Agency, 1997). Soils vary across the ecoregion, ranging from thin, stony types on prominent ridges and low mountains to fertile limestone-derived soils in some plains and valleys. The climate includes moderate winters and warm, humid summers, with more than 1,000 mm (40 in.) of precipitation falling in an average year. The ecoregion’s population grew (using aggregated county-level data) by nearly 2 million people between 1970 and 2000 to reach 11,434,000, with population density typically decreasing from east to west across the ecoregion (U.S. Bureau of the Census, 1973; U.S. Census Bureau, 2003). Land use varies, ranging from busy urban and suburban areas, to intensely farmed and thickly settled locales, to relatively quiet pastoral places. The dominant land cover classes form a mosaic of agricultural, forest, and developed lands, but the mixture varies, depending on local conditions. Agricultural land ranges from intensely cropped cornfields and horticultural nurseries to less intensely used hayfields and pastures. Forest is typically found on land that has marginal utility for contemporary agricultural use, such as steep slopes and poorer quality soils. Forested areas often are also used as various public resources (Matlack, 1997; Marsh and Lewis, 1995, p. 27; Morel and Gottmann, 1961, p. 362, p. 371-383).

Figure 1: Location map for the Northern Piedmont ecoregion. The underlying land cover is taken from the 1992 National Land Cover Database (Vogelmann and others, 2001). Outlines of the 20 km x 20 km sample sites for the Land Cover Trends project are shown in black. Click on image to enlarge

The Northern Piedmont was a fairly low changing ecoregion from 1973 to 2000, but it placed nearly in the median position when compared with other Eastern ecoregions during the same time period (fig. 2). A total of 6.2 percent of the land area changed from one land cover to another at least once during the 1973 to 2000 study period (table 1). Most of the land cover change (approximately 70 percent) was to new developed land. The amount of change by time intervals was relatively low and similar over time until the 1992 to 2000 period, which experienced a noticeable increase (table 2). Normalizing the amount of change to annual rates to avoid unequal time intervals shows the 1992 to 2000 period still to be the most dynamic (fig. 3). Although rates of change do not appear that high, they correspond to a steady increase of developed land, a near permanent type of change. The margin of error in our statistical estimates was relatively low, ranging from +/–0.3 percent to +/– 0.5 percent at an 85-percent confidence interval, indicating that land cover change tended to be more or less evenly distributed across the ecoregion (table 2).

The Northern Piedmont’s dominant land covers classified as agriculture, forest, and developed, experienced the greatest amounts of net change across the study period (table 3). Even though change was comparatively low in the ecoregion, most of the change was new development, and by the end of the study period, this land cover class gained 4.6 percent (fig. 4) and was estimated to occupy more than 27 percent of the ecoregion area (table 3). This was one of the highest percentages of development found in the Eastern ecoregions. The Northern Piedmont, along with the Atlantic Coastal Pine Barrens ecoregion to the east and the Northeastern Coastal Zone ecoregion to the northeast, make up most of Gottmann’s (1961) “Megalopolis” region, the Northeast U.S. urbanizing corridor. The Northern Piedmont’s continued urbanization can be seen in absolute population growth (+19.9 percent), increased occupied housing units (+43.8 percent), and employment gains (+39.5 percent) during the study period (Auch, 2002). The ecoregion continues its transformation from a once prominent agricultural area to an urban one. In 1997, the American Farmland Trust declared the Northern Piedmont as the second most “endangered” farming region in the United States (Sorensen et al., 1997).

Figure 3: The estimates of land cover change per time interval normalized to an annual rate of change. Click on image to enlarge

Table 1: Percentage of the ecoregion that experienced change [Most of the sample pixels remained unchanged (93.8 percent), whereas 6.2 percent changed at least once through the study period].

Table 2: Estimated amount of change by time interval, 85-percent confidence interval, and normalized annual rates of change.

Figure 2: The amount of overall spatial change estimated for the ecoregion and the proportion of the ecoregion that experienced change during one or multiple time periods. Click on image to enlarge

Figure 4: Estimated net change by land cover class for each time interval and overall study period. Click on image to enlarge