Land Cover Trends Project

Middle Atlantic Coastal Plain

By Roger F. Auch 1

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map of Middle Atlantic Coastal Plain Ecoregion

Figure 1.  The Middle Atlantic Coastal Plain ecoregion.  The underlying land cover is from the 1992 National Land Cover Database (Vogelmann and others, 2001). 

 

Ecoregion Description

 

The Middle Atlantic Coastal Plain is a linear ecoregion covering approximately 89,691 km2 (34,630 mi2) that stretches from Delaware Bay and the Delmarva Peninsula in the north to nearly Jacksonville in the south (fig. 1). Portions of nine states are included (New Jersey, Pennsylvania, Delaware, Maryland, Virginia, North Carolina, South Carolina, Georgia, and Florida) (fig. 1). The ecoregion ranges in width from only a few miles (inland of Delaware Bay and extreme northeast Florida) to approximately 70 miles in areas of North and South Carolina.  The topography is primarily flat, and many soil types are poorly drained (U.S. Environmental Protection Agency, 1997).  The dominant land uses are farming and forestry, with urban development being locally significant.  The land cover is primarily a mosaic of forest, wetlands, and agriculture. Agricultural land consists mainly of cropland—growing soybeans, cotton, and some tobacco in the south and soybeans and corn further north (fig. 2). Livestock production is most pronounced as confined animal feeding operations, such as for hogs in North Carolina and poultry on the Delmarva Peninsula (fig. 3)(U.S. Department of Agriculture, 1999).   Upland forest land cover consists predominantly of pine or mixed pine and hardwood communities (fig. 4).  Wetlands are quite common across the ecoregion and include coastal marshes, bottomland hardwood forests, and shrub bogs (pocosins) (fig. 5a & 5b).  Other land covers with less extensive areas include water and mechanically disturbed land. The climate has moderate to mild winters and hot, humid summers, with 1,000 to 1,500 mm (40 to 60 in) of average annual precipitation.

 

Contemporary Land Cover Change (1973 to 2000)

 

The Middle Atlantic Coastal Plain experienced a large amount of land cover change when compared with other ecoregions in the Eastern United States, ranking third in the proportion of area changed (overall spatial change) (fig. 6).  Eighteen percent of the land area changed from one land cover to another at least once during the 1973 to 2000 study period (table 1). The amount of area changed per time interval was relatively high and appeared to increase over time, with the 1973 to1980 interval experiencing the least change and the 1992 to 2000 interval experiencing the most (table 2). Normalizing the amount of change to an annual rate to adjust for unequal time intervals still shows that 1973 to 1980 had the lowest rate of change, but indicates that 1986 to 1992 actually had the highest rate. Although the interval from 1986 to 1992 was the most dynamic, two other intervals (1980 to1986 and 1992 to 2000) also had normalized rates exceeding one percent per year, a high rate of change among those estimated for all eastern ecoregions (fig. 7).  The margin of error in our statistical estimates was relatively high, ranging from +/–1.6 percent to +/–2.6 percent at the 85-percent confidence level, indicating that land cover change had high variability across the ecoregion. 

Two of the Middle Atlantic Coastal Plain’s dominant land covers, forest and wetlands, experienced considerable net change, although there was a temporal unevenness for each of these classes across time periods (table 3).  Forest cover decreased in the first three time intervals, ranging from –0.61 to –1.58 percent, but increased +0.21 percent in the last time interval, for a net loss in area of –3.3 percent between 1973 and 2000 (fig. 8).  Some of the net loss between 1992 and 2000 was due to the conversion of forest to mechanically disturbed land associated with timber harvesting and is expected to return to forest cover at a later date.  Two time intervals (1980 to 1986 and 1992 to 2000) had noticeable decreases (–0.55 and –0.71 percent) in wetlands land cover, but the other two intervals had almost no change.  Wetlands had a net decrease of –1.29 percent during the study period, but some of the wetlands-to-mechanically disturbed land cover change between 1992 and 2000 will likely return to wetlands at a later date. The third most common land cover, agriculture, did not have a noticeable net change between 1973 and 2000, although the 1973 to 1980 interval had a small gain (+0.23 percent) that was offset by decreases during two subsequent time intervals (–0.1 percent and –0.15 percent), respectively.  The less prevalent land covers of developed and mechanically disturbed lands had substantial net gains in area but experienced somewhat different pulses of change.  The total amount of development had a nearly consistent increase across each time interval, ranging from +0.55 to +0.66 percent, to have a net change of +2.59 percent, whereas the mechanically disturbed land cover class changes showed more fluctuation of change, ranging from +0.17 for the 1992 to 2000 interval to +0.76 percent for the 1973 to 1980 period.  Overall, mechanically disturbed land had a net areal increase of +2.46 percent. 

Urban development almost always has a net increase, as it tends to be a permanent change, whereas other land covers, such as forest, agriculture, wetlands, and mechanically disturbed, may experience fluctuating net changes as part of cyclic land uses.  Forest parcels may be clear-cut for wood harvesting and, subsequently, return to forest.  Land used for farming or forestry may be switched to another use to take advantage of changing economic markets. 

The leading changes in the Middle Atlantic Coastal Plain were those indicative of cyclic wood production (table 4).  Conversions from forest to mechanically disturbed land and mechanically disturbed land to forest were the leading land cover conversions for each time interval (fig. 9a & 9b).  Overall, 18,995 km2 of land fluctuated between these two land cover classes. Another way to consider forest cover in this ecoregion is to compare the percentage of land that was consistently forest between 1973 and 2000 (“stable” forest) with the percentage of land that was forest only part of the time (“dynamic” forest).  More than half (59.5 percent) of the forest area remained as forest throughout the study period, while 40.5 percent was converted to or from forest land (table 5).  The percentage of stable forest (unaltered forest that is at least 30 years of age) in the Middle Atlantic Coastal Plain was one of the lowest of all eastern ecoregions.

Other, leading land cover changes included disturbances in wetlands and increased development (fig. 10).  The transitions back and forth between wetlands and mechanically disturbed land were the third (wetlands to mechanically disturbed land) and fifth (mechanically disturbed land to wetlands) leading changes overall.  Timber harvesting of forested wetlands, such as bottomland hardwoods, appeared to account for a majority of these transitions.  The conversion of forest to developed land was either the third or fourth most common land cover change in area by time interval. The ecoregion gained an estimated 2,247 km2 of new developed land during the study period, a majority of it from forest (1,747 km2) and most of the rest from either agricultural land (253 km2) or wetlands (134 km2).

 

References

U.S. Department of Agriculture, 1999, 1997 Census of agriculture—agricultural atlas of the United States v. 2, subject series, part 1: Washington, D.C., U.S. Government Printing Office, 163 p.

 

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.

 

 

 

 

Table 1.  Percentage of the ecoregion that experienced change

 

[Most of the sample pixels remained unchanged (82.0 percent), whereas 18.0 percent changed at least once through the study period]

 

 

Overall

Number of changes

 

spatial change

1

2

3

4

Percent of ecoregion

18.0

8.1

8.7

1.0

0.1

 

 

 

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)

5.9%

6.8%

7.6%

9.1%

Margin of error (85% confidence level)

+/-1.6%

+/-2.3%

+/-2.5%

+/-2.6%

Average annual rate of change (%/year)

0.8%

1.1%

1.3%

1.1%

 

 

 

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

5980

6.7

5987

6.7

5996

6.7

6004

6.7

5996

6.7

16

0.0

Developed

5800

6.5

6299

7.0

6900

7.7

7510

8.4

8047

9.0

2247

2.5

Mechanically disturbed

2061

2.3

2757

3.1

3022

3.4

3618

4.0

3768

4.2

1707

1.9

Mining

37

0.0

49

0.1

75

0.1

109

0.1

114

0.1

77

0.1

Naturally barren

132

0.1

126

0.1

120

0.1

124

0.1

143

0.2

10

0.0

Forest

31814

35.5

30365

33.9

29807

33.2

28593

31.9

28782

32.1

-3031

-3.4

Grassland/Shrubland

243

0.3

252

0.3

426

0.5

516

0.6

424

0.5

180

0.2

Agriculture

20343

22.7

20556

22.9

20549

22.9

20458

22.8

20320

22.7

-23

0.0

Wetland

23280

26.0

23302

26.0

22796

25.4

22758

25.4

22096

24.6

-1184

-1.3

Non-mechanically disturbed

0

0

0

0

0

0.0

0

0.0

0

0.0

0

0.0

 

 

 


Table 4.  Leading land cover changes by time interval

 

 

 

 

Area changed

% of all

Period

From class

To class

(km2)

changes

1973-1980

Forest

Mechanically disturbed

2,408

46

 

Mechanically disturbed

Forest

1,646

31

 

Forest

Developed

444

8

 

Forest

Agriculture

277

5

 

Mechanically disturbed

Wetland

191

4

 

Other classes

Other classes

295

6

 

 

 

5,261

100

 

 

 

 

 

1980-1986

Forest

Mechanically disturbed

2,128

35

 

Mechanically disturbed

Forest

2,116

35

 

Wetland

Mechanically disturbed

592

10

 

Forest

Developed

498

8

 

Mechanically disturbed

Grassland/Shrubland

179

3

 

Other classes

Other classes

595

10

 

 

 

6,108

100

 

 

 

 

 

1986-1992

Forest

Mechanically disturbed

2,805

41

 

Mechanically disturbed

Forest

1,928

28

 

Forest

Developed

503

7

 

Mechanically disturbed

Wetland

426

6

 

Wetland

Mechanically disturbed

392

6

 

Other classes

Other classes

771

11

 

 

 

6,825

100

 

 

 

 

 

1992-2000

Mechanically disturbed

Forest

3,097

38

 

Forest

Mechanically disturbed

2,866

35

 

Wetland

Mechanically disturbed

791

10

 

Forest

Developed

302

4

 

Mechanically disturbed

Agriculture

191

2

 

Other classes

Other classes

931

11

 

 

 

8,178

100

Overall:

 

 

 

 

1973-2000

Forest

Mechanically disturbed

10,207

39

 

Mechanically disturbed

Forest

8,788

33

 

Wetland

Mechanically disturbed

1,903

7

 

Forest

Developed

1,747

7

 

Grassland/Shrubland

Grassland/Shrubland

1,113

4

 

Other classes

Other classes

2,613

10

 

 

 

26,371

100

 

 

 

Table 5.  Sample block forest pixels-stability vs. change

 

 

Number

Percentage of

Land cover from 1973 to 2000

of pixels

Forest pixels

Forest at any time

464,020

100.0%

Stable Forest (unchanged)

276,005

59.5%

Dynamic Forest (affected by

188,015

40.5%

or resulting from change)

 

 

 

 

Refer to caption

 

Figure 1.  The Middle Atlantic Coastal Plain ecoregion.  The underlying land cover is from the 1992 National Land Cover Database (Vogelmann and others, 2001).  The Land Cover Trends

20 km x 20 km sample blocks are shown as hollow yellow squares.

 

 

Refer to caption

 

Figure 2.  Farm growing corn and soybeans near Salisbury, Md. Photo Thomas Loveland

 

Refer to caption

 

Figure 3.  Cotton field and confined animal feeding units, raising either hogs or poultry, on a farm in North Carolina.  Photo Thomas Loveland

 

Refer to caption

 

Figure 4.  Even age (a forestry management term) loblolly pine forest parcels near Marion, S.C. Photo Thomas Loveland

 


 

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Figure 5a (top).  Forested wetland (bottomland hardwoods) in the South Carolina part of Ecoregion 63.  Figure  5b (bottom).  Coastal wetland located in extreme southeast Georgia.  Photos Thomas Loveland

 

 

Refer to caption

 

Figure 6.  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.

 

 

Refer to caption

 

Figure 7.  The estimates of land cover change per time interval normalized to an annual rate of change.

 

Refer to caption

 

Figure 8.  Estimated net percentage change by land cover class by time interval and overall study period.

 


 

Refer to caption

 

Refer to caption

 

Figure 9a (top).  Tree debris, or slash, left over from a forest clear-cut on the eastern shore of Maryland. This is classified as mechanically disturbed land. Figure 9b (bottom).  Field of young pine trees west of Charleston, S.C. Photos Thomas Loveland

 

 

Refer to caption

 

Figure 10.  Newer subdivision located just off Interstate 95 west of St. Mary’s, Ga.

Photo Thomas Loveland

 

 



[1] SAIC TSSC, work performed under U.S. Geological Survey contract 03CRN001 at USGS Center for EROS

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