Western Allegheny Plateau

By Kristi L. Sayler ¹

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Ecoregion Description

 

The Western Allegheny Plateau ecoregion, as defined by Omernik (1987), covers portions of eastern Ohio, southwestern Pennsylvania, northwestern West Virginia, and a small piece of northeastern Kentucky. The ecoregion covers approximately 84,500 km² (32,630 mi²) (fig. 1) and is about 72 percent forest and 23 percent agriculture.  The forest area is mostly mixed oak and mixed temperate forests that still exist today on most of the remaining rounded hills.  Dairy, livestock, and general farming, as well as residential developments, are concentrated in the valleys (fig. 2).  Pittsburgh, Pennsylvania is the largest urban area in the ecoregion and has shown some expansion despite an overall population decline in the ecoregion.  Coal mining is still active in the Pennsylvania, West Virginia, and Kentucky portions of the ecoregion and in Ohio to a lesser extent (fig. 3 and 4).  The Ohio and Allegheny River systems in the ecoregion have been adversely affected by acid mine drainage and industrial pollution, which has caused degradation of the stream habitats and loss of fish species (Cooper, 1983).  Water quality has improved somewhat, and a few species have returned. 

 

Contemporary Land Cover Change (1973 to 2000)

 

The overall spatial change from 1973 to 2000 for the Western Allegheny Plateau was 6.0 percent, which was a low amount of change compared to other ecoregions in the East (fig. 5).  An estimated 4 percent of the ecoregion changed only one time.  The other 2 percent changed multiple times and was likely the result of coal mining and timber harvesting activities (table 1), which tend to cycle through multiple land cover transitions. 

The change per time period ranged from 1.9 to 2.3 percent with margin of errors ranging from 0.4 to 0.7 percent (table 2).  The average annual rates of change show that the 1986 to 1992 period had the greatest amount of change with a rate of 0.4 percent per year (table 2 and fig. 6).  This was a period of transition for the coal mining regions of Ohio and West Virginia.  Ohio coal production was slowing down due to increasing regulations on surface mining and higher environmental emission standards (Crowell, 1995), whereas West Virginia saw an increase in the extraction of low-sulfur coal (Fox, 1999) in order to meet federal standards from the 1990 Clean Air Act.

The majority of land cover classes in the Western Allegheny Plateau experienced little change during the study period (table 3).  Forest and agriculture both showed steady declines since 1973, while developed lands increased during each time period resulting in an increase of 376 km² (147 mi²) between 1973 and 2000 (fig. 7).  Grassland/shrubland increased from 1.5 percent of the ecoregion area in 1973 to 2.6 percent in 2000. 

Mining and forest clearing activities caused the most prominent net land cover changes in the Western Allegheny Plateau ecoregion.  Net changes in the land cover classes fluctuated throughout the 1973 to 2000 period (fig. 8).  Grassland/shrubland had net increases in all four time periods, while mining and forest showed decreases in most time periods. 

With a few exceptions for timber cutting, the top three leading land cover transitions during each time period were related to coal mining activities in the ecoregion (i.e., mining to grassland/shrubland, grassland/shrubland to forest, or forest to mining).  The top seven transitions contained at least 75 percent of the total change for each time period and affected between 1,090 and 1,400 km² of land area (table 4).

 

References

 

Cooper, E.L., 1983, Fishes of Pennsylvania and the northeastern United States: University Park, Pa., Pennsylvania State University Press, 183 p.

 

Crowell, D.L., 1995, History of the coal-mining industry in Ohio: Ohio Division of Geological Survey Bulletin 72, 204 p.

 

Fox, J., 1999, Mountaintop removal in West Virginia—an environmental sacrifice zone:  Organization and Environment, v. 12, no. 2, p. 163-183.

 

Omernik, J.M., 1987, Ecoregions of the conterminous United States: Annals of the Association of American Geographers, v. 77, no. 1, p. 118-125.

 

 

Table 1.  Amount of overall spatial change detected in the ecoregion and proportion of the ecoregion that experienced change during one or multiple time periods

 

	Overall	Number of changes
	spatial change	1	2	3	4
Percent of ecoregion	6.0	4.0	1.8	0.2	0.0

 

 

 

Table 2.  Raw estimates of percent change in the ecoregion computed for each of the four time periods and associated margin of error at a 85 percent level of confidence

 

	Period
	1973-1980	1980-1986	1986-1992	1992-2000
Total change (% of ecoregion)	2.1%	2.0%	2.3%	1.9%
Margin of error (85% confidence level)	+/-0.6%	+/-0.8%	+/-0.6%	+/-0.5%
Average annual rate of change (%/year)	0.3%	0.3%	0.4%	0.2%

 

 

 

Table 3.  Proportion of the ecoregion covered by each land cover class during each of the five mapped dates

 

	1973		1980		1986		1992		2000		Net change 1973-2000
Land-use/land-cover class	km²	%	km²	%	km²	%	km²	%	km²	%	km²	%
Water	1079	1.3	1116	1.3	1118	1.3	1120	1.3	1126	1.3	47	0.1
Developed	5909	7.0	5976	7.1	6034	7.1	6192	7.3	6358	7.5	449	0.5
Mechanically disturbed	75	0.1	84	0.1	74	0.1	245	0.3	239	0.3	165	0.2
Mining	892	1.1	1024	1.2	863	1.0	574	0.7	511	0.6	-381	-0.4
Barren	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
Forest	54674	64.5	54298	64.1	54387	64.2	54159	63.9	53942	63.7	-732	-0.9
Grassland/Shrubland	1300	1.5	1581	1.9	1683	2.0	1965	2.3	2201	2.6	901	1.1
Agriculture	20682	24.4	20524	24.2	20445	24.1	20349	24.0	20216	23.9	-465	-0.5
Wetland	128	0.2	134	0.2	134	0.2	134	0.2	145	0.2	17	0.0
Non-mechanically disturbed	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0

 

 

 

Table 4.  Leading land cover conversions during each of the four time periods

 

			Area changed	% of all
Period	From class	To class	(km2)	changes
1973-1980	Forest	Mining	331	19
	Mining	Grassland/Shrubland	258	15
	Grassland/Shrubland	Forest	201	11
	Forest	Grassland/Shrubland	174	10
	Forest	Agriculture	119	7
	Agriculture	Grassland/Shrubland	105	6
	Agriculture	Mining	96	5
	Other classes	Other classes	475	27
			1,759	100
1980-1986	Grassland/Shrubland	Forest	414	24
	Mining	Grassland/Shrubland	402	23
	Forest	Mining	202	12
	Forest	Agriculture	113	7
	Agriculture	Mining	82	5
	Agriculture	Grassland/Shrubland	74	4
	Forest	Grassland/Shrubland	69	4
	Other classes	Other classes	361	21
			1,717	100
1986-1992	Mining	Grassland/Shrubland	372	20
	Grassland/Shrubland	Forest	238	12
	Forest	Mechanically disturbed	223	12
	Forest	Mining	174	9
	Forest	Grassland/Shrubland	159	8
	Mining	Forest	124	7
	Agriculture	Forest	110	6
	Other classes	Other classes	507	27
			1,907	100
1992-2000	Forest	Mechanically disturbed	214	13
	Mining	Grassland/Shrubland	202	13
	Grassland/Shrubland	Forest	141	9
	Forest	Grassland/Shrubland	138	9
	Mechanically disturbed	Forest	135	8
	Agriculture	Forest	133	8
	Forest	Mining	127	8
	Other classes	Other classes	524	32
			1,614	100
Overall:
1973-2000	Mining	Grassland/Shrubland	1,234	18
	Grassland/Shrubland	Forest	993	14
	Forest	Mining	835	12
	Forest	Mechanically disturbed	580	8
	Forest	Grassland/Shrubland	540	8
	Forest	Agriculture	391	6
	Agriculture	Forest	381	5
	Other classes	Other classes	2,043	29
			6,997	100

 

 

 

 

Figure 1.  Western Allegheny Plateau and surrounding ecoregions. The 40 randomly selected 100-km² sample blocks are shown along with land use/land cover from the 1992 National Land Cover Dataset.

 

 

 

Figure 2.  Forested hills with corn and oats in the valley.

 

 

 

Figure 3.  Coal mining southwest of Brookville, Pennsylvania.

 

 

Figure 4.  Coal mining south of East Palestine, Ohio.

 

 

 

Figure 5.  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 6.  The estimates of land cover change per time interval normalized to an annual rate of change. The Western Allegheny Plateau is highlighted in black.

 

 

 

Figure 7.  Suburban development southeast of Pittsburgh, Pennsylvania.

 

 

 

Figure 8.  Per period net change for each land cover class. Areas above zero represent net gains for a land cover class, while areas below represent a net loss.