ML18026B254
| ML18026B254 | |
| Person / Time | |
|---|---|
| Site: | Clinch River |
| Issue date: | 01/26/2018 |
| From: | US Dept of Interior, Geological Survey (USGS) |
| To: | Office of New Reactors |
| Fetter A | |
| References | |
| Download: ML18026B254 (8) | |
Text
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
USGS Home Contact USGS Search USGS Land Cover Trends Project Figure 1. Ridge and Valley ecoregion. The underlying land cover is from the 1992 National Land Cover Database (Vogelmann and others, 2001). Outlines of the thirty-two 10-km x 10-km sample sites for the Land Cover Trends project are shown in black.
Ridge and Valley By Beverly A. Friesen and Michael P. Stier 1 Click to see available downloads for this ecoregion
Ecoregion Description
The Ridge and Valley is a long, narrow ecoregion that stretches approximately 1,600 km (995 mi) from the southeastern corner of New York to northeastern Alabama, including portions of seven additional states in between:
New Jersey, Pennsylvania, Maryland, West Virginia, Virginia, Tennessee, and Georgia (fig.
1). Major cities within this ecoregion are Birmingham, Alabama, and Chattanooga and Knoxville, Tennessee. This northeast to southwest trending area occupies 44,589 km² (17,216 mi2) and is nestled between generally higher, more rugged mountainous terrain with greater forest cover. The roughly parallel ridges and lowland valleys that comprise this area are the result of extreme folding and faulting events (Omernik, 1987) (fig. 2).
Elevations range from 152 to 1,311 m (500 to 4,300 feet). Three land cover types dominate the ecoregion: forests at about 56 percent, agricultural lands at about 30 percent, and developed areas at about 9 percent. Managed lands comprise more than 13 percent of the area, ranging from State parks to wild and scenic rivers (Conservation Biology Institute, 2001). The Blue Ridge Parkway, a designated parkway administered by the National Park
- Service, dips into part of the eastern edge of the ecoregion in Virginia, as do small portions of Shenandoah National Park.
Change from 1973 to 2000
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Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
The Ridge and Valley ecoregion experienced relatively low change as compared to most Eastern U.S. ecoregions, with 5.5 percent of its land changing during the study period (fig. 3). Of the land that did change, 4.1 percent changed once and 1.4 percent changed two or more times (table 1).
In this ecoregion, multiple changes often indicate cyclic disturbances; most of the multiple changes in this ecoregion are accounted for by areas of clear-cuts and forest regrowth (fig. 4).
The overall change per time interval for the Ridge and Valley ecoregion ranges from a low of 1.3 percent from 1980 to 1986 to a high of 2.6 percent from 1992 to 2000. All estimates have an associated margin of error of less than plus or minus one percent, although the margin of error increased with the higher amount of change in the 1992 to 2000 interval (table 2). When normalized to account for varying time period lengths, land cover change showed a gradual increase over the study period, from 0.2 percent to 0.3 percent annual change per time interval (table 2 and fig. 5). The 1992 to 2000 interval was the most active period.
Forest, agriculture, and developed areas account for almost 96 percent of the land cover in this ecoregion. Table 3 shows the percentage of each land cover class for the five respective mapped dates. Forest declined from 57.3 percent in 1973 to 55.8 percent in 2000 (table 3). Mechanically disturbed lands (clear-cut) showed an increase starting in the 1986 to 1992 period. A small decline in agriculture, from 31.2 percent to 30.5 percent, was recorded from 1973 to 2000. This decline was due both to abandoning agricultural fields and to converting agricultural land for developed uses.
Decreases in both forested and agricultural cover were countered by a 1.4 percent net increase in developed areas, from 7.9 percent in 1973 to 9.3 percent in 2000. Figure 6 summarizes these net changes by land cover type for each time period.
The four most common land cover transitions by time interval are reported in table 4.
The greatest change over the duration of the study was consistently the conversion of forest to mechanically disturbed lands, followed by mechanically disturbed lands back to forest (forest regrowth). The amount of land that changed from forest to mechanically disturbed lands nearly doubled between the 1986 to 1992 period (535 km²) and the 1992 to 2000 period (1,030 km²). These changes were due to the clearing of trees. In contrast, only 491 km² of mechanically disturbed land grew back to forest cover in the same time period.
Other leading conversions were cyclic changes from forest to agriculture and agriculture to forest, along with unidirectional changes from agriculture and forest to development.
The amount of land converting from both forest and agriculture to development doubled in the 1992 to 2000 period as compared to any previous period. This was the same time period when the amount of clear-cutting doubled. Although many clear-cut areas have regrown to forest, mechanically disturbed lands represent a temporary state of transition that can also lead to permanent development. The quantity of clear-cuts, coupled with the increased amount of forested and agricultural lands converting to development, highlights the net loss of forest in this ecoregion over time. These changes also suggest a possible accelerating trend in clearing both forested and agricultural lands for development.
Increases in development and mechanically disturbed lands and decreases in forested and agricultural lands in the Ridge and Valley ecoregion are corroborated by the Southern Forest Resource Assessment from the National Resource Inventory data of the U.S.
Department of Agriculture Natural Resources Conservation Service (Wear, 2002). This study shows that for the southern states from 1982 to 1997 strong economic growth led to population growth and increased urbanization at the expense of both agricultural and forested lands. This trend was more noticeable in the southern part of the ecoregion, which also coincides with the largest urban centers in the area, namely Birmingham, Chattanooga, and Knoxville (fig. 7). Forecasts for the northern, central, and southern Ridge and Valley areas show continued and increased forest loss between 1992 and 2020, with higher losses predicted for the southern region. Development pressures are likely to continue driving land use conversions in the Ridge and Valley ecoregion into the foreseeable future (fig. 8).
References
Conservation Biology Institute, 2001, Protected Areas Database (PAD) (2nd ed.): Corvallis, Oreg.,
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
CBI, available on DVD.
Omernik, J.M.,
1987, Ecoregions of the conterminous United States: Annals of the Association of American Geographers, v. 77, no. 1, p. 118-125.
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 Set for the coterminous United States from Landsat Thematic Mapper data and ancillary data sources: Photogrammetric Engineering &
Remote Sensing, v. 61, p. 650-662.
Wear, D.N., 2002, Land Use, in Wear, D.N., and Greis, J.G., eds., Southern Forest Resource Assessment, General Technical Report SRS-53: Asheville, N.C., U.S. Department of Agriculture, Forest Service, Southern Research Station, p. 153-173.
Table 1. Amount of overall 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 5.5 4.1 1.4 0.0 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 an 85-percent confidence level
[Estimates of change per period normalized to an annual rate of change for each of the four time periods]
Period
1973-1980 1980-1986 1986-1992 1992-2000 Total change (% of ecoregion) 1.5%
1.3%
1.6%
2.6%
Margin of error (85% confidence level)
+/-0.5%
+/-0.4%
+/-0.4%
+/-0.6%
Average annual rate of change
(%/year) 0.2%
0.2%
0.3%
0.3%
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 2433 2.2 2594 2.3 2704 2.4 2710 2.4 2717 2.4 283 0.3 Developed 8797 7.9 9032 8.1 9292 8.4 9615 8.7 10295 9.3 1498 1.3 Mechanically disturbed 471 0.4 481 0.4 459 0.4 586 0.5 1067 1.0 595 0.5 Mining 222 0.2 223 0.2 253 0.2 264 0.2 278 0.3 56 0.1 Barren 8
0.0 20 0.0 11 0.0 11 0.0 11 0.0 3
0.0 Forest 63618 57.3 63318 57.0 63018 56.8 62848 56.6 61990 55.8
-1628
-1.5 Grassland/Shrubland 93 0.1 94 0.1 125 0.1 113 0.1 113 0.1 21 0.0 Agriculture 34641 31.2 34526 31.1 34424 31.0 34139 30.7 33821 30.5
-820
-0.7 Wetland 760 0.7 756 0.7 756 0.7 756 0.7 750 0.7
-10 0.0
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
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 during each of the four time periods
Area changed
% of all Period From class To class (km2) changes 1973-1980 Forest Mechanically disturbed 416 25
Mechanically disturbed Forest 366 22
Forest Agriculture 173 10
Agriculture Forest 165 10
Other classes Other classes 566 34
1,686 100
1980-1986 Forest Mechanically disturbed 375 25
Mechanically disturbed Forest 339 23
Forest Agriculture 174 12
Agriculture Developed 145 10
Other classes Other classes 462 31
1,495 100
1986-1992 Forest Mechanically disturbed 535 30
Mechanically disturbed Forest 419 24
Agriculture Forest 248 14
Agriculture Developed 155 9
Other classes Other classes 423 24
1,780 100
1992-2000 Forest Mechanically disturbed 1,030 36
Mechanically disturbed Forest 491 17
Agriculture Developed 331 12
Forest Developed 316 11
Other classes Other classes 668 24
2,836 100 Overall:
1973-2000 Forest Mechanically disturbed 2,355 30
Mechanically disturbed Forest 1,616 21
Agriculture Forest 792 10
Forest Agriculture 756 10
Other classes Other classes 2,278 29
7,796 100
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
Figure 2. The Ridge and Valley topography is typified by forests dominating the hills, and development and agriculture occupying the valleys.
Figure 3. Change in percent of total area of all Eastern U.S. ecoregions. Each bar shows the proportion of the ecoregion that experienced change on 1, 2, 3, or 4 dates.
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
Figure 4. Regrowth of a clear-cut area in central Alabama.
Figure 5. Estimates of change per period normalized to an annual rate of change for each of the four time periods.
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
Figure 6. Net change by period for each mapped land cover class. Positive numbers represent a net gain for that land cover, while negative numbers represent a net loss for the land cover.
Land Cover Change https://landcovertrends.usgs.gov/east/eco67Report.html[10/9/2017 2:51:33 PM]
Figure 7. Industry is fairly common, especially along the interstates and interstate exits in the northern part of the ecoregion in Pennsylvania and Virginia, and in the southern part of the ecoregion around the cities of Birmingham, Chattanooga, and Knoxville.
Figure 8. A new overpass under construction in 2001 near State College, Pennsylvania.
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