Laurentian Plains and Hills

By Thomas R. Moreland, Jr. ¹

Click to see available downloads for this ecoregion

 

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 (fig. 2).  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 (fig. 3).  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 21^oC (60 to 70^oF); temperatures are usually warmer along the coast and progressively cooler to the north.  Average January temperatures vary from about –8 to –5^oC (17 to 23^oF) along the coast, becoming increasingly colder to the north.  In the northernmost portion of the ecoregion, the average January temperature is below –23^oC (–10^oF). 

 

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. 4).  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 (fig. 5).  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 0.31 percent in the 1973 to 1980 interval to 0.61 percent in the 1980 to 1986 interval, peaked at 0.89 percent in the 1986 to 1992 interval, and then declined slightly to 0.72 percent in the 1992 to 2000 interval (table 2 and fig. 6).

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 7.7 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.

Figure 7 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) (fig. 8).  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.

 

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.

 

Table 1.  Estimated overall spatial land cover change between 1973 and 2000

 

	Overall	Number of changes
	spatial change	1	2	3	4
Percent of ecoregion	9.5%	3.4	4.8	1.3	0.0

 

 

 

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]

 

 

	Period
	1973–1980	1980–1986	1986–1992	1992–2000
Total change (% of ecoregion)	2.2%	3.6%	5.3%	5.8%
Margin of error (85% confidence level)	+/–0.6%	+/–0.9%	+/–1.3%	+/–1.2%
Average annual rate of change (%/year)	0.3%	0.6%	0.9%	0.7%

 

 

 

Table 3.  Estimated area for each land cover class between 1973 and 2000

 

	1973		1980		1986		1992		2000		Net change 1973–2000
Land-use/land-cover class	km²	%	km²	%	km²	%	km²	%	km²	%	km²	%
Water	6,008	12.0	6,004	12.0	6,006	12.0	6,007	12.0	5,997	12.0	–11	0.0
Developed	903	1.8	922	1.8	945	1.9	974	1.9	1,035	2.1	131	0.3
Mechanically disturbed	440	0.9	525	1.0	938	1.9	1,215	2.4	1,083	2.2	643	1.3
Mining	47	0.1	81	0.2	91	0.2	122	0.2	112	0.2	65	0.1
Naturally barren	48	0.1	48	0.1	48	0.1	48	0.1	50	0.1	2	0.0
Forest	36,215	72.2	35,834	71.4	35,366	70.5	35,008	69.8	35,175	70.1	–1,041	–2.1
Grassland/Shrubland	108	0.2	387	0.8	448	0.9	532	1.1	476	0.9	368	0.7
Agriculture	3,897	7.8	3,892	7.8	3,858	7.7	3,819	7.6	3,782	7.5	–115	–0.2
Wetland	2,488	5.0	2,460	4.9	2,455	4.9	2,430	4.8	2,446	4.9	–42	–0.1
Non-mechanically disturbed	0	0	0	0	0	0.0	0	0.0	0	0.0	0	0.0

 

 

Table 4.  Leading land cover conversions for each of the four time periods and for the entire study period

 

			Area changed	% of all
Period	From class	To class	(km2)	changes
1973–1980	Forest	Mechanically disturbed	521	47
	Mechanically disturbed	Grassland/Shrubland	276	25
	Mechanically disturbed	Forest	160	15
	Wetland	Mining	28	3
	Forest	Developed	17	2
	Forest	Agriculture	17	2
	Grassland/Shrubland	Forest	14	1
	Agriculture	Forest	11	1
	Other classes	Other classes	53	5
			1,097	100
1980–1986	Forest	Mechanically disturbed	927	50
	Mechanically disturbed	Grassland/Shrubland	278	15
	Grassland/Shrubland	Forest	252	14
	Mechanically disturbed	Forest	234	13
	Agriculture	Grassland/Shrubland	30	2
	Agriculture	Forest	26	1
	Forest	Agriculture	22	1
	Forest	Developed	18	1
	Other classes	Other classes	58	3
			1,845	100
1986–1992	Forest	Mechanically disturbed	1,202	45
	Mechanically disturbed	Forest	557	21
	Mechanically disturbed	Grassland/Shrubland	336	13
	Grassland/Shrubland	Forest	335	12
	Agriculture	Grassland/Shrubland	56	2
	Forest	Agriculture	31	1
	Forest	Developed	25	1
	Wetland	Mining	23	1
	Other classes	Other classes	122	5
			2,687	100
1992–2000	Forest	Mechanically disturbed	1,059	36
	Mechanically disturbed	Forest	861	30
	Grassland/Shrubland	Forest	414	14
	Mechanically disturbed	Grassland/Shrubland	339	12
	Agriculture	Forest	50	2
	Forest	Developed	49	2
	Forest	Agriculture	30	1
	Mining	Wetland	15	1
	Other classes	Other classes	94	3
			2,911	100
Overall:
1973–2000	Forest	Mechanically disturbed	3,709	43
	Mechanically disturbed	Forest	1,811	21
	Mechanically disturbed	Grassland/Shrubland	1,258	15
	Grassland/Shrubland	Forest	1,015	12
	Forest	Developed	110	1
	Agriculture	Forest	107	1
	Agriculture	Grassland/Shrubland	107	1
	Forest	Agriculture	100	1
	Other classes	Other classes	356	4
			8,573	100

 

 

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.

 

 

 

Figure 2.  Wetland vista with forested hills in the distance.

 

 

 

Figure 3.  Potato field in Aroostook County, Maine.

 

 

 

Figure 4.  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.

 

 

 

Figure 5.  Logs being stacked on the edge of a forest.

 

 

 

Figure 6.  Estimates of land cover change per time interval normalized to annual rates of change.

 

 

 

 

 

Figure 7.  Net land cover changes by categories for each time interval and for the entire study period.

 

 

 

 

Figure 8.  Paper mill along the Penobscot River in Bucksport, Maine.