Southwestern Appalachians

By Terry L. Sohl ¹

Click to see available downloads for this ecoregion

 

Ecoregion Description

 

The Southwestern Appalachians ecoregion stretches from north-central Alabama through southeastern Kentucky (fig. 1) and covers approximately 35,350 km² (13,650 mi²).  Much of the ecoregion consists of open low mountains, but some portions of the ecoregion exhibit steep slopes with local relief of up to 300 m.  Approximately three-fourths of the ecoregion is covered by forest, primarily mixed oak communities and shortleaf pines (fig. 2). Agricultural lands are found on lower slopes and valley floors, with the greatest concentration in northeastern Alabama.  Mining is a locally significant land use activity, especially in the southern part of the ecoregion where the local abundance of coal, limestone, and iron deposits led to a booming steel industry in the first half of the twentieth century.  No large cities (populations > 100,000) are found completely within the ecoregion’s borders, but the greater Birmingham, Huntsville, and Chattanooga metropolitan areas are partially within the ecoregion.

 

Contemporary Land Cover Change (1973 to 2000)

 

Overall spatial change in the ecoregion (i.e., the percentage of area that changed at least one time from 1973 to 2000) was 13.9 percent (table 1), a moderately high level of change compared to most Eastern United States ecoregions (fig. 3).  The total amount of change increased with each successive time period (table 2).  When normalized to account for varying time period lengths, change was lower during the 1973 to 1980 period and higher and relatively steady for the last three time periods (fig. 4).

No individual land cover class changed by more than 2.6 percent of the total ecoregion area between 1973 and 2000 (table 3).  However, two factors driving land cover conversion were notable in the ecoregion: (1) forestry activity and (2) mining activity.  Forest cover consistently showed some of the largest net change, with fairly consistent declines in all four time periods (fig. 5).  The conversion from forest to mechanically disturbed land was the most common land cover conversion for all four time periods, while mechanically disturbed to forest land (representing regeneration of cut forest lands) was the second or third most common conversion (table 4).  In sum, forestry-related activities (both cutting and regeneration) was clearly one of the most significant factors affecting land cover in the ecoregion for all time periods (fig. 6 and 7).

Mining activity was the second most important factor driving land cover change in the ecoregion (fig. 6).  Much of the surface mining in the ecoregion, especially in northern Alabama, is for coal, iron, and limestone--all primary materials required for the production of steel.  Birmingham, Alabama, which is partially contained within the southern portion of the ecoregion, was once known as the “Pittsburgh of the South.”  The related mining and steel industries have been key components of much of the area’s economy in the twentieth century. 

However, the local steel industry began to decline in the second half of the twentieth century.  Imports of cheaper foreign steel into the United States increased dramatically after 1980, contributing to additional closures of steel facilities in the area (Gerard, 2001).  With these declines, local demand for the raw materials of the industry also declined.  As production halted at the surface mines, many were revegetated with grass/shrubland and eventually reverted back to forest lands.  While 700 km² of newly mined lands were established between 1973 to 2000, more than 1000 km² of mined lands were reclaimed during the same time period, resulting in a net decline of more than 300 km² (fig. 8).    The most significant decline was between 1980 and 1986 when mined land area dropped by 50 percent within the ecoregion, with very minor declines noted for the last two time periods (table 3 and fig. 5).   Changes related to mined land reclamation (including mined lands reclaimed to grass/shrublands and grass/shrublands eventually reverting to forest) were significant land cover conversions for all time periods (table 4). 

Other land cover conversions were generally minor in the ecoregion.  Developed lands did steadily increase throughout the study period, resulting in a net gain of more than 300 km² from 1973 to 2000.  Urban centers on the fringe of the ecoregion (e.g., Birmingham) either exhibited only minor population gains or even decreased in population during the study period, but growth in the surrounding suburbs was the primary driver behind the net gain in developed land area.

 

References:

Gerard, L.W., 2001,  Section 232 Investigation into the effects on national security of imports of iron ore and semi-finished steel: Comments submitted to the U.S. Department of Commerce, United Steelworkers of America.

 

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., Wylie, B.K., and Van Driel, N., 2001, Completion of the 1990s National Land Cover Data 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 touched by change

 

[86.1 percent of all pixels in the ecoregion were unchanged throughout the study period, while 13.9 percent were touched by change one or more times]

 

	Overall	Number of changes
	spatial change	1	2	3	4
Percent of ecoregion	13.9	6.3	6.4	1.1	0.1

 

 

 

Table 2.  Overall change estimates and normalized annual change for each of the four time periods

 

[Margin of error at an 85 percent confidence interval]

 

	Period
	1973-1980	1980-1986	1986-1992	1992-2000
Total change (% of ecoregion)	3.7%	5.5%	6.2%	7.3%
Margin of error (85% confidence level)	+/-1.2%	+/-1.5%	+/-1.8%	+/-2.3%
Average annual rate of change (%/year)	0.5%	0.9%	1.0%	0.9%

 

 

 

Table 3.  Percentages of each land cover class for 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	165	0.5	175	0.5	201	0.6	209	0.6	221	0.6	56	0.2
Developed	634	1.8	652	1.8	736	2.1	824	2.3	955	2.7	321	0.9
Mechanically disturbed	384	1.1	314	0.9	543	1.5	819	2.3	1020	2.9	636	1.8
Mining	551	1.6	600	1.7	295	0.8	281	0.8	233	0.7	-318	-0.9
Naturally barren	1	0.0	1	0.0	1	0.0	1	0.0	1	0.0	0	0.0
Forest	27583	78.0	27425	77.6	27186	76.9	26875	76.0	26635	75.4	-948	-2.7
Grassland/Shrubland	139	0.4	305	0.9	549	1.6	528	1.5	467	1.3	327	0.9
Agriculture	5823	16.5	5803	16.4	5772	16.3	5745	16.3	5750	16.3	-74	-0.2
Wetland	60	0.2	60	0.2	60	0.2	60	0.2	59	0.2	-1	0.0
Non-mechanically disturbed	0	0	7	0	0	0.0	0	0.0	0	0.0	0	0.0

 

 

Table 4.  The five most common land cover conversions for each of the four time periods

 

			Area changed	% of all
Period	From class	To class	(km2)	changes
1973-1980	Forest	Mechanically disturbed	302	23
	Mechanically disturbed	Forest	295	22
	Forest	Mining	239	18
	Mining	Forest	115	9
	Mining	Grassland/Shrubland	101	8
	Other classes	Other classes	261	20
			1,313	100
1980-1986	Forest	Mechanically disturbed	531	27
	Mining	Grassland/Shrubland	298	15
	Mechanically disturbed	Forest	256	13
	Grassland/Shrubland	Forest	187	10
	Mining	Forest	154	8
	Other classes	Other classes	505	26
			1,931	100
1986-1992	Forest	Mechanically disturbed	789	36
	Mechanically disturbed	Forest	421	19
	Grassland/Shrubland	Forest	283	13
	Mining	Grassland/Shrubland	136	6
	Forest	Mining	134	6
	Other classes	Other classes	436	20
			2,199	100
1992-2000	Forest	Mechanically disturbed	1,003	39
	Mechanically disturbed	Forest	726	28
	Grassland/Shrubland	Forest	244	9
	Mining	Grassland/Shrubland	136	5
	Forest	Mining	94	4
	Other classes	Other classes	384	15
			2,587	100
Overall:
1973-2000	Forest	Mechanically disturbed	2,626	33
	Mechanically disturbed	Forest	1,698	21
	Grassland/Shrubland	Forest	750	9
	Mining	Grassland/Shrubland	671	8
	Forest	Mining	610	8
	Other classes	Other classes	1,675	21
			8,030	100

 

 

 

 

Figure 1.  The underlying land cover is from the 1992 National Land Cover Database (Vogelmann and others, 2001).  The 10 km x 10 km sample sites for the Land Cover Trends project are shown in yellow.

 

 

 

Figure 2.  Forest covers approximately three-fourths of the ecoregion, and is the prevalent land cover on most hilly and mountainous slopes.

 

 

 

Figure 3.  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 4.  Estimates of land cover change per time interval normalized to annual rates of change.

 

 

 

Figure 5.  Per period net change for each mapped land cover class.  Cylinder areas above the zero axis represent net gains for a land cover class, while areas below represent net losses. 

 

 

 

 

Figure 6.  Forestry activity (forest cutting and regeneration) and mining activity (new mining and mining reclamation) account for the vast majority of change in the ecoregion.

 

 

 

 

Figure 7.  Over 2,600 km² of forest was cut between 1973 and 2000 as part of timber harvesting operations in the ecoregion.  The majority of cut lands related to the timber industry were replanted or allowed to naturally regenerate to forest.

 

 

 

Figure 8.  Mining activity has been an important component of the economy in much of the ecoregion.  However, actively mined lands have declined between 1973 and 2000, and many older mines have either been reclaimed or allowed to naturally revegetate.