Interior Plateau

By Mark A. Drummond ¹

Click to see available downloads for this ecoregion

 

Ecoregion Description

 

The Interior Plateau ecoregion is a series of grassland plateaus and forested uplands that are generally lower in elevation than the Appalachian Mountains to the east but higher than the plains to the south.  The ecoregion has a total area of approximately 127,810 km² (49,348 mi²) and covers large areas of western Kentucky and central Tennessee, as well as parts of Indiana, Alabama, and Ohio (fig. 1).  The Ohio River, which runs along the northern border of Kentucky, drains most of the northern part of the ecoregion. 

The relatively flat and fertile lowlands, which include the Bluegrass area of central Kentucky and the Nashville Basin in central Tennessee, attracted early settlement and farming.  Today, those areas are highly populated, including the cities of Louisville, Kentucky, and Nashville, Tennessee.  The Pennyroyal Plateau in south-central Kentucky and northern Tennessee is a dense agricultural area that also contains a distinctive “flatwood” ecosystem.  The area is characterized by oak forests and wet conditions that are caused by an underlying hard, dense fragipan soil (Chester and others, 1995). 

Rapid subsurface drainage occurs in sinkhole areas such as south-central Kentucky where extensive cave systems wind through the karst limestone landscape.  Water quality of the associated aquifers and streams is a special concern in watersheds where agriculture and coal mining are prevalent. 

Ecoregion-wide, climate conditions are humid temperate and average about 1,200 mm (47.2 in) of annual precipitation.  Oak-hickory stands are the most common forest type, although mixed stands of red cedar and hardwoods grow on many of the rockier sites and limestone glades (fig 2).  Blue-stem prairie is the most common grassland.  Historically, fire was an important natural process for maintaining open-canopied, savannah-like conditions on the plateaus (Chester and others, 1995; Hudson, 2002). 

Population has increased steadily, by approximately 40 percent between 1970 and 2000, from 4.4 million to 6.2 million people.  Automobile manufacturing has expanded into the area, and tourism and service industries are also important in several locations.  Major agricultural products include soybeans, corn, tobacco, and dairy (fig 3).  The Bluegrass area has unique land uses, including a tradition of race horse breeding and training farms and the production of high-value burley tobacco. 

 

Contemporary Land Cover Change from 1973 to 2000

 

The Interior Plateau had a relatively low rate of overall land cover change when compared to other Eastern ecoregions (fig. 4).  Between 1973 and 2000, 4.3 percent of the ecoregion underwent change, and 95.7 percent of the total area was stable.  An estimated 3.6 percent of the ecoregion changed once.  The percentage of area that underwent multiple changes was relatively low.  An estimated 0.7 percent of the area changed twice, and 0.1 percent changed three times (table 1). 

The highest total change occurred between 1980 and 1986 (1.7 percent), with an annual rate of 0.28 percent (table 2 and fig. 5).  The lowest rate of change occurred during the period between 1973 and 1980, when total change was less than 1 percent (0.8 percent) and the annual rate was 0.12 percent.

Agriculture, forest, and developed lands account for more than 96 percent of the ecoregion.  Agriculture is the major land cover and comprised 50.9 percent of the ecoregion in 1973, declining to 50 percent in 2000 (table 3).  Forest was the next highest cover type, with a high of 39 percent in 1973 and a low of 37.7 percent in 2000.  Developed land had a steady gain, from 6.9 percent in 1973 to 8.6 percent in 2000 (fig 6).  Other small gains of approximately 0.2 percent each occurred in the mechanically disturbed and the grassland/shrubland categories. 

Developed land expanded the most, with a 1.7 percent increase between 1973 and 2000 (table 3).  Net losses occurred in forest and agriculture, with net declines of 1.3 percent and 0.8 percent, respectively.  Although development generally accelerated over the 27-year study period (fig. 7), the highest rate of expansion was between 1980 and 1986 (0.6 percent), which is also the period with the highest overall rate of ecoregion change (1.7 percent).  The majority of the conversion to development, nearly 60 percent, occurred from agriculture.  Conversely, the majority of agricultural loss was to development, except in the 1973 to 1980 period when the conversion of agriculture to grassland was highest. 

Between 1973 and 2000, the most common conversion (1,373 km² or 530 mi²) was from forest cover to agriculture (table 4).  However, this conversion did not result in a net increase in agriculture because at the same time agricultural lands were being converted to developed land and to grassland/shrubland at an overall higher rate.  Conversion from agriculture to developed land was the second most common change (1,250 km² or 483 mi²).  The various gains and losses of agriculture are masked by a low net rate of change (–0.8 percent).  Cyclic changes involving mechanical disturbance of forest and subsequent reforestation were less common, although they increased through time (fig 8). 

 

References

 

Chester, E.W., Noel, S.M., Baskin, J.M., Baskin, C.C., and McReynolds, M.L., 1995, A phytosociological analysis of an old-growth upland wet woods on the Pennyroyal Plain, southcentral Kentucky, USA: Natural Areas Journal, v. 15, p. 297–307.

 

Hudson, J.C., 2002, Across this land—A regional geography of the United States and Canada: Baltimore, The Johns Hopkins University Press, 474 p.

 

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	4.3	3.6	0.7	0.1	0.0

 

 

 

Table 2.  Total and annual rates of land cover change for each time interval

 

	Period
	1973–1980	1980–1986	1986–1992	1992–2000
Total change (% of ecoregion)	0.8%	1.7%	1.4%	1.6%
Margin of error (85% confidence level)	+/–0.2%	+/–0.5%	+/–0.4%	+/–0.4%
Average annual rate of change (%/year)	0.1%	0.3%	0.2%	0.2%

 

 

 

Table 3.  Land cover area, including net change 

 

	1973		1980		1986		1992		2000		Net change 1973–2000
Land-use/land-cover class	km²	%	km²	%	km²	%	km²	%	km²	%	km²	%
Water	1,976	1.5	1,986	1.6	1,993	1.6	2,009	1.6	2,026	1.6	50	0.0
Developed	8,859	6.9	9,087	7.1	9,829	7.7	10,291	8.1	11,011	8.6	2,152	1.7
Mechanically disturbed	37	0.0	18	0.0	127	0.1	150	0.1	322	0.3	285	0.2
Mining	111	0.1	230	0.2	138	0.1	176	0.1	161	0.1	51	0.0
Naturally barren	1	0.0	1	0.0	1	0.0	1	0.0	1	0.0	0	0.0
Forest	49,864	39.0	49,532	38.8	48,981	38.3	48,710	38.1	48,149	37.7	–1,715	–1.3
Grassland/Shrubland	1,021	0.8	1,161	0.9	1,278	1.0	1,265	1.0	1,263	1.0	243	0.2
Agriculture	65,005	50.9	64,831	50.7	64,524	50.5	64,269	50.3	63,938	50.0	–1,067	–0.8
Wetland	935	0.7	943	0.7	938	0.7	939	0.7	938	0.7	3	0.0
Non-mechanically disturbed	0	0	21	0	0	0.0	0	0.0	0	0.0	0	0.0

 

 

 

Table 4.  Leading land cover conversions for the four time periods of the study

 

			Area changed	% of all
Period	From class	To class	(km2)	changes
1973–1980	Forest	Agriculture	218	20
	Agriculture	Grassland/Shrubland	210	19
	Grassland/Shrubland	Forest	124	11
	Forest	Developed	105	10
	Agriculture	Developed	103	10
	Other classes	Other classes	320	30
			1,080	100
1980–1986	Agriculture	Developed	464	22
	Forest	Agriculture	460	22
	Forest	Developed	235	11
	Agriculture	Grassland/Shrubland	207	10
	Grassland/Shrubland	Forest	195	9
	Other classes	Other classes	574	27
			2,135	100
1986–1992	Forest	Agriculture	365	21
	Agriculture	Developed	281	16
	Grassland/Shrubland	Forest	218	13
	Agriculture	Grassland/Shrubland	193	11
	Forest	Developed	125	7
	Other classes	Other classes	544	32
			1,726	100
1992–2000	Agriculture	Developed	403	20
	Forest	Agriculture	330	17
	Forest	Mechanically disturbed	288	15
	Forest	Developed	240	12
	Agriculture	Forest	165	8
	Other classes	Other classes	556	28
			1,982	100
Overall:
1973–2000	Forest	Agriculture	1,373	20
	Agriculture	Developed	1,250	18
	Forest	Developed	704	10
	Agriculture	Grassland/Shrubland	694	10
	Grassland/Shrubland	Forest	663	10
	Other classes	Other classes	2,239	32
			6,923	100

 

 

 

 

Figure 1.  Interior 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.  A roadside vista of pastureland, forest and farms in the central part of the ecoregion, south-central Kentucky.

 

 

 

Figure 3.  A tobacco field in central Tennessee.

 

 

Figure 4.  Overall spatial change from 1973 to 2000 for all Eastern U.S. ecoregions.  The entire bar shows the overall spatial change, while the gradients indicate the percent of ecoregion area that changed during one or multiple periods. 

 

 

 

Figure 5.  Estimates of land cover change per time interval normalized to annual rates of change.

 

 

 

Figure 6.  Interstate 24 and suburban development outside of Nashville, Tennessee.

 

 

 

Figure 7.  Land cover changes are shown for the four time intervals of the study.

 

 

 

Figure 8.  Forest clearance near the eastern edge of the ecoregion.