Regional Interpretation - Great Plains
Great Plains | Intermountain West | Southwest | Texas and Oklahoma | Other
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The Great Plains region include the most productive rangeland in the United States due in large part to generally reliable summer precipitation, a long growing season, and deep, fertile soils. Rangeland in this region are typically dominated by grasslands. Some of the best rangeland and farmland in the world is found in the Great Plains of the United States. These areas supported large herds of bison and other grazing animals prior to European settlement. Today, much of this land has been converted to rain-fed and irrigated crop production. Where rangeland remains, they typically occur on areas that are marginally suitable for crop production.
When the area was first being settled in the late 1800s, periods of adequate rainfall attracted large numbers of settlers. However, periodic droughts occurred, causing economic recessions and turning fields into dry wastelands. This happened several times in the 1800s and early 1900s, with the worst dust bowls occurring in the Depression years of the 1930s. Major droughts occur approximately every 20 years (1890s, 1910s, 1930s, 1950s, and 1970s). The 1990s witnessed yet another period of serious drought conditions, especially in the southern Great Plains with some of the hottest and driest conditions that this region has ever experienced.
Soil and Site Stability
Soil and site stability shows little departure from reference condition throughout most of the Great Plains (Figure 1). The combination of high precipitation and relatively deep, fertile soils when compared to many rangelands in the United States contribute to a high level of resilience. These factors support a highly productive plant community that allows the land to resist degradation and recover quickly when degradation does occur. High levels of plant productivity are usually associated with low amounts of bare ground and negligible intercanopy gaps (Figures 2 and 3), even when the land is degraded. Well developed soils high in organic matter, plant and litter decomposition, root biomass, and associated fungi contribute to high aggregate stability.
In the Great Plains, soil aggregate stability is typically lower in the Sandhills of western Nebraska and Badlands of southwestern South Dakota (Figure 4) compared to other areas of this region. Somewhat lower stability occurs 'naturally' in these areas due to their lower potential to form stable soil aggregates; the Sandhills are formed on relatively coarse sandy soils, and the soils of the Badlands have high levels of salt, which makes soil aggregates disperse more easily. However, less than 10 percent of the non-Federal rangeland acres in these areas had at least moderate departure for soil and site stability (Figure 1).
Some of the southwestern parts of this region showed more significant departures from reference conditions for soil and site stability. There are at least two possible explanations for this difference. One is that these areas are more fragile, receive less precipitation and are the driest areas of the Great Plains. They are associated with lower plant production and therefore, less residual cover and litter. As a result, these lands are more prone to wind erosion. The second explanation is that many parts of Kansas, Oklahoma, and eastern Colorado were cultivated prior to and during the Dust Bowl years (1930s) and drought periods (1950s, 1970s, and 1990s) before reverting to rangeland. Less resilient ecological sites may still exhibit the effects of these events.
The same factors that explain why most of the land in the Great Plains shows little departure from reference condition for soil and site stability also explain why hydrologic function is at or near potential throughout most of this region. Relatively high precipitation and deep soils support productive plant communities, maintaining a high degree of soil cover even when they are degraded (Figure 5). In some areas, significant increases of invasive exotic and native plants (e.g. eastern redcedar, Juniperus virginiana L., Figure 6) have resulted in increased rates of runoff and erosion.
Of all of the attributes, biotic integrity showed the greatest departure in this region (Figure 7), largely due to the high density and cover of invasive plants, including exotic herbaceous (Figures 8-12) and native woody species (Figures 13-15). Many of the non-native species were accidentally introduced and are tenacious. Although many exotic species are considered to negatively affect ecosystem services, others have more benign effects. Several introduced species, such as annual brome grasses, Kentucky bluegrass (Poa pratensis L.), and Canada thistle (Cirsium arvense (L.) Scop.) are now so widespread that complete eradication would be expensive, if not impossible. Invasive species data included in this report provide an objective starting point for focusing efforts on management and control.
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