Northern Piedmont

By Roger F. Auch ¹

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Ecoregion Description

 

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 (figs. 2a, 2b, and 2c).  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 (fig. 3a and 3b). 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). 

 

Contemporary Land Cover Change (1973 to 2000)

 

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. 4). 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 (fig. 5).  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. 6).  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 +/– 0.55 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. 7) 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) (fig. 8).

The leading land cover conversions are shown in table 4. The ecoregion gained an estimated 1,396 km² of new developed land between 1973 and 2000, a majority of it from agriculture (865 km²) and a considerable amount from forest (464 km²).  Another 59 km² of development came from mechanically disturbed land, where the actual land cover conversion (such as the bulldozing or leveling of forest or farmland for new construction) was caught still in progress.  Less significant changes included conversions back and forth between agriculture and forest land (agriculture to forest conversions were more prevalent in earlier time intervals) and forest to mechanically disturbed land (related to timber harvesting, the clearing of forest for development, or a conversion to agriculture) (fig. 9).

The main story of land cover change in the Northern Piedmont ecoregion during our study period was increased urbanization, primarily through unidirectional land cover conversion to developed land uses.  The amount of change was comparatively low but steady over time.  The great majority of this new development came at the expense of agricultural land and, to a lesser extent, forested land.

 

 

References

 

Auch, R.F., 2002, Land use/land cover change in the northern piedmont ecoregion, 1970-2000: Brookings, South Dakota, South Dakota State University, Masters thesis, 211 p.

Gottmann, J., 1961, Megalopolis— the urbanized northeastern seaboard of the United States: New York, The Twentieth Century Fund, 810 p.

Marsh, B., and Lewis, P., 1995, Landforms and human habitat, in Miller, E.W., ed., A geography of Pennsylvania: University Park, Pa., Pennsylvania State University Press, p. 17-43.

Matlack, R.G., 1997, Four centuries of forest clearance and regeneration in the hinterland of a large city: Journal of Biogeography, v. 24, p. 281-295.

Morel, H., and Gottmann, J., 1961, The woodlands, their uses and wildlife, in Gottmann, J., Megalopolis— the urbanized northeastern seaboard of the United States: New York, The Twentieth Century Fund, p. 341-383.

Sorensen, A. A., Greene, R.B., and Russ, K., 1997, Farming on the edge: DeKalb, Ill., American Farmland Trust/Center for Agriculture in the Environment.

U.S. Bureau of the Census, 1973, 1970 Census of population characteristics of the population: Washington, D.C., U.S. Government Printing Office, various state parts.

U.S. Census Bureau, 2003, American FactFinder, Basic Facts, economic characteristics- employment, income, poverty, and more; general characteristics- population and housing, accessed May 25, 2006, at http://factfinder.census.gov/servlet/BasicFactsServlet?_basicfacts= [Use “basic facts” table option, select the above subjects, select for “county”, then “state” for individual counties.]

U.S. Environmental Protection Agency, 1997, Descriptions of level III ecological regions for the CEC report on ecological regions of North America, accessed April 12, 2006, at http://www.epa.gov/wed/pages/ecoregions/na_eco.htm#Downloads

Vogelmann, J. M., Howard, S.M., Yang, L., Larson, C.R., Wylie, B.K., and Van Driel, N., 2001, Completion of the 1990s National Land Cover Data set for the conterminous United States from Landsat Thematic Mapper data and ancillary data sources: Photogrammetric Engineering & Remote Sensing, v. 67, p. 650-662.

 

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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]

 

	Overall	Number of changes
	spatial change	1	2	3	4
Percent of ecoregion	6.2	5.6	0.6	0.0	0.0

 

 

 

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

 

	Period
	1973-1980	1980-1986	1986-1992	1992-2000
Total change (% of ecoregion)	1.4%	1.5%	1.3%	2.6%
Margin of error (85% confidence level)	+/-0.5%	+/-0.3%	+/-0.3%	+/-0.5%
Average annual rate of change (%/year)	0.2%	0.3%	0.2%	0.3%

 

 

 

Table 3.  Estimated ecoregion land cover classes by percent and area (km2)

 

	1973		1980		1986		1992		2000		Net change 1973-2000
Land-use/land-cover class	km²	%	km²	%	km²	%	km²	%	km²	%	km²	%
Water	457	1.5	460	1.5	460	1.5	465	1.5	465	1.5	8	0.0
Developed	6826	22.7	7100	23.6	7384	24.5	7606	25.3	8222	27.3	1396	4.6
Mechanically disturbed	38	0.1	47	0.2	69	0.2	69	0.2	75	0.2	37	0.1
Mining	83	0.3	89	0.3	102	0.3	112	0.4	119	0.4	36	0.1
Naturally barren	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
Forest	11102	36.9	11059	36.7	10985	36.5	10929	36.3	10656	35.4	-446	-1.5
Grassland/Shrubland	21	0.1	19	0.1	15	0.0	13	0.0	9	0.0	-12	0.0
Agriculture	11365	37.7	11120	36.9	10880	36.1	10702	35.5	10350	34.4	-1015	-3.4
Wetland	228	0.8	226	0.7	225	0.7	225	0.7	224	0.7	-4	0.0
Non-mechanically disturbed	0	0	0	0	0	0.0	0	0.0	0	0.0	0	0.0

 

 

 

Table 4.  The leading land cover changes by time interval

 

			Area changed	% of all
Period	From class	To class	(km2)	changes
1973-1980	Agriculture	Developed	192	46
	Forest	Developed	79	19
	Agriculture	Forest	43	10
	Mechanically disturbed	Forest	27	6
	Forest	Mechanically disturbed	20	5
	Other classes	Other classes	59	14
			420	100
1980-1986	Agriculture	Developed	129	28
	Forest	Developed	76	17
	Mechanically disturbed	Forest	37	8
	Forest	Mechanically disturbed	35	8
	Agriculture	Forest	29	6
	Other classes	Other classes	154	33
			460	100
1986-1992	Agriculture	Developed	186	49
	Forest	Developed	89	23
	Agriculture	Forest	54	14
	Forest	Mechanically disturbed	39	10
	Mechanically disturbed	Forest	22	6
	Other classes	Other classes	-10	-3
			380	100
1992-2000	Agriculture	Developed	359	46
	Forest	Developed	220	28
	Forest	Mechanically disturbed	61	8
	Mechanically disturbed	Developed	34	4
	Forest	Agriculture	34	4
	Other classes	Other classes	81	10
			789	100
Overall:
1973-2000	Agriculture	Developed	865	42
	Forest	Developed	464	23
	Forest	Mechanically disturbed	156	8
	Agriculture	Forest	148	7
	Mechanically disturbed	Forest	108	5
	Other classes	Other classes	308	15
			2,049	100

 

 

 

 

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 yellow.

 

 

 

 

Figure 2a  (top).  Typical Northern Piedmont farm near Frederick, Md. Photo Thomas Moreland, Jr.  Figure 2b (center) A drive through a forested area of Ecoregion 64 in northern Virginia. Photo Thomas Loveland.  Figure 2c (bottom).  Traffic passing through a commercial area in King of Prussia, Pa., approximately 16 miles northwest of downtown Philadelphia. Photo Roger Auch.

 

 

 

 

 

 

 

Figure 3a  (above).  Corn field on the outskirts of New Holland, Pa. in intensely-cropped Lancaster County. Photo Roger Auch.  Figure 3b (below).  Pasture with a horse fence nestled among the forested hills near Charlottesville, Virginia.  Breeding thoroughbred horses is a long-standing tradition in the Northern Piedmont. Photo Thomas Loveland.

 

 

 

Figure 4.  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.

 

 

 

Figure 5.  New development along US-322 in southeast Chester County, Pa.  Most of the housing in the background appeared to have been built during the study period. Photo Roger Auch

 

 

Figure 6.  The estimates of land cover change per time interval normalized to an annual rate of change.

 

 

Figure 7.  Estimated net change by land cover class for each time interval and overall study period.

 

 

 

Figure 8.  An increasingly common scene in Ecoregion 64: the interface between developed and agricultural land uses, in this example in Frederick County, Md. Photo Thomas Moreland, Jr.

 

 

 

Figure 9.  A young stand of planted pines in Fauquier County, Va. Photo Roger Auch.