|
Ecoregion Description
|
The Laurentian Plains and Hills ecoregion is located in the northeastern corner of the conterminous United States (fig. 1). This ecoregion lies entirely within the state of Maine and covers roughly the eastern half of the state. It is bounded to the north and east by Canada, to the west by the more rugged Northeastern Highlands ecoregion, to the south by the Northeastern Coastal Zone ecoregion, and to the southeast by the Atlantic Ocean. The ecoregion covers approximately 50,155 km2 (19,365 mi2). Glacial processes shaped the entire ecoregion, creating numerous lakes and wetland areas. Forests cover nearly three quarters of the Laurentian Plains and Hills. The trees are mostly spruce and fir with some maple, beech, and birch (U.S. Environmental Protection Agency, 2002). Timber harvesting is one of the most significant activities in the ecoregion. Other human alterations to the landscape include agriculture, which is concentrated on the plains in the northern portion of the ecoregion, and development. The average annual precipitation ranges from 1,041 mm (41 in) in the northern areas to about 1,168 mm (46 in) further south. July temperatures average about 15 to 21oC (60 to 70oF); temperatures are usually warmer along the coast and progressively cooler to the north. Average January temperatures vary from about –8 to –5oC (17 to 23oF) along the coast, becoming increasingly colder to the north. In the northernmost portion of the ecoregion, the average January temperature is below –23oC (–10oF).
|
Figure 1. The Laurentian Plains and Hills and surrounding ecoregions. The randomly selected sample blocks are shown along with land use/land cover data from the 1992 National Land Cover Dataset. Click on image to enlarge
|
Contemporary Land Cover Change from 1973 to 2000
|
The Laurentian Plains and Hills experienced a moderate amount of land cover change during this period in comparison to other ecoregions in the Eastern United States (fig. 2). An estimated 9.5 percent of the ecoregion’s land cover (approximately 4,765 km2 or 1,840 mi2) changed between 1973 and 2000 (table 1). Approximately 3.4 percent (1,705 km2 or 658 mi2) of the total land area changed just once, 4.8 percent (2,407 km2 or 929 mi2) changed twice, and 1.3 percent (652 km2 or 252 mi2) changed three times. Most of the change is cyclic in nature, resulting from the harvesting of timber and subsequent forest regrowth. Change per time period increased throughout the entire study period. Total change was 2.2 percent from 1973 to 1980, 3.6 percent from 1980 to 1986, 5.3 percent from 1986 to 1992, and 5.8 percent from 1992 to 2000 (table 2).
The average annual change increased from 0.3 percent in the 1973 to 1980 interval to 0.6 percent in the 1980 to 1986 interval, peaked at 0.9 percent in the 1986 to 1992 interval, and then declined slightly to 0.7 percent in the 1992 to 2000 interval (table 2 and fig. 3).
Forest was the predominant land cover, covering an estimated 72.2 percent of the ecoregion in 1973 and declining slightly to 70.1 percent by 2000 (table 3). The area covered by water was very stable, remaining at about 12 percent throughout the study period. Agriculture declined very slightly between 1973 and 2000, from 7.8 to 7.5 percent of the ecoregion. The amount of developed land increased slightly, from 1.8 percent in 1973 to 2.1 percent in 2000. The estimated percentage of the ecoregion covered by mechanically disturbed land increased steadily, from 0.9 percent in 1973 to a high of 2.4 percent in 1992, and then declined slightly to 2.2 percent in 2000. During the study period, mechanically disturbed land was almost always linked to timber harvesting rather than clearing for development or agriculture.
|
Table 1. Estimated overall spatial land cover change between 1973 and 2000
Table 2. Estimated total change for each time interval
[The average annual rate of change compensates for the unequal lengths of the different time intervals]
|
|
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. Net land cover changes by categories for each time interval 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. Estimated area for each land cover class between 1973 and 2000
|
Figure 4 portrays net land cover change in each time period. Water, wetland, mining, and natural barren land covers experienced very little change in any particular time interval and throughout the study period. Developed areas increased slightly in each time period, and the area covered by agricultural land decreased gradually in each time period. The amount of forest declined in each time interval except the last, when there was a slight increase. This change in forest was mirrored by the increase in the amount of disturbed land and grassland/shrubland in each time interval except the last, when there was a slight decrease.
Forest harvesting and regeneration was responsible for the vast majority of change in the ecoregion (table 4). The conversion of forest to mechanically disturbed land, an estimated 3,709 km2 (1,432 mi2), was the leading change throughout the study period. Much of the timber was harvested to provide pulpwood for the paper industry (Colgan, Irland, and Benson, 1986; Irland, 2004). The conversion of mechanically disturbed land to forest, an estimated 1,811 km2 (699 mi2), was the second leading change overall, and the second leading change in the last two time intervals. The third leading change overall and the second leading change in the first two time intervals was the conversion of mechanically disturbed land to grassland/shrubland, an estimated 1,258 km2 (486 mi2). The conversion of grassland/shrubland to forest, an estimated 1,015 km2 (392 mi2), was the fourth leading change over the entire study period. A minor change in comparison to those mentioned above was the conversion of an estimated 110 km2 (42 mi2) of forest to developed land. The conversion of forest to developed land increased in each interval.
From 1973 to 2000, the predominately wooded landscape of the Laurentian Plains and Hills experienced a moderate amount of land cover change. Average annual change increased from the first time interval through the third time interval, and then slightly decreased. While very little of this change resulted in an increase in development, approximately 90 percent of the change can be attributed to the cyclic harvesting of woodlands and their eventual regrowth.
Table 4. Leading land cover conversions for each of the four time periods and for the entire study period
1 Thomas R. Moreland, Jr. - U.S. Geological Survey, Eastern Geographic Science Center, Reston, VA 20192
References
Colgan, C.S., Irland, L.C., and Benson, J., 1986, The natural resource industries of Maine—An assessment and statistical portrait: Augusta: Financial Authority of Maine and Maine State Planning Office.
Irland, L.C., 2004, Maine’s forest industry—From one era to another, in Barringer, R.E., ed., Changing Maine, 1960–2010: Gardiner, Maine, Tilbury House, p. 362–387.
Irland, L.C., 1999, The Northeast’s changing forest: Petersham, Mass., Harvard Forest [distributed by Harvard University Press], 427 p.
Plantinga, A.J., Mauldin, T., and Alig, R.J., 1999, Land use in Maine—Determinants of past trends and projections of future changes, Research Paper PNW-RP-511: Portland, Oreg., U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 20 p.
U.S. Environmental Protection Agency, 2002, Primary distinguishing characteristics of Level III ecoregions of the continental United States [draft]: EPA, available online at ftp://ftp.epa.gov/wed/ecoregions/us/useco_desc.doc.
Westcott, R., and Vail, D., 1988, The transformation of farming in Maine, 1940–1985: Maine Historical Society Quarterly, v. 28, p. 66–84.
|
U.S. Department of the Interior |
U.S. Geological Survey
