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Regional Trends of Biological Resources — Grasslands

Prairie Integrity and Legacies


Intercommunity Management:  Prairie Integrity

Integrity here means maintaining species and ecological processes characteristic to a particular landscape (Samson and Knopf 1993); this is an emerging goal in resource conservation (Angermeier and Karr 1994). The human-caused breakdown of barriers to dispersal that has permitted invasion of nonindigenous species has caused the extinction of more grassland species than any factor except habitat loss (D'Antinio and Vitousek 1992). Nonindigenous species include exotics, which are transported beyond their natural range, and aliens, those that colonize an altered landscape. Introducing nonindigenous species may increase the number of local species, but it reduces integrity, above- and belowground, and also the number of native species, both aquatic and terrestrial.

A more subtle threat to integrity is loss of genetic diversity. Species hybridize along forested corridors that now fragment the Great Plains (Knopf 1986). Human activity, either accidental or deliberate, moves species from one place to another at ever-increasing rates (Knopf 1992). As a result, species that evolved in isolation from one another are forced into contact. In terms of conservation of biological diversity, the loss of six bird subspecies due to the hybridization arising from these forested stepping stones and artificial corridors (Knopf 1986) rivals the loss of three species attributed to fragmentation of the eastern deciduous forest.

These recent forest patches and woody corridors that border rivers on the Great Plains also favor movement of reptiles and mammals from east to west, which contributes to the degradation of the biological diversity and integrity of the Great Plains (Knopf and Scott 1990). In 1842, in eastern Colorado, the explorer John C. Frémont observed that "antelope were tolerably abundant, wolves were seen in great numbers, and buffalo absolutely covered the plains on both sides of the (South Platte) river" but reported no deer (in Nevins 1956). In recent years, deer abundance has increased markedly, particularly that of the eastern white-tailed deer, which may replace the mule deer, known to have occurred on the western plains since before European settlement (Kufeld and Bowden 1995). Hybridization between the two deer is known to occur (Stubblefield et al. 1986).

Nonindigenous species now account for 13% to 30% of prairie species (U.S. Congress, Office of Technology Assessment 1993; C. Freeman, Kansas Natural Heritage Program, Lawrence, personal communication). Increases in distribution and abundance are inevitable without action to prevent them, as evident in the naturalization of Russian-olive trees in the western United States (Olson and Knopf 1986). Russian-olives, which were introduced from Europe in colonial times, range across the Great Plains into the West. In agricultural areas, this species interferes with farming operations; it also hinders management activities on national wildlife refuges, increases degradation of river channels, contributes to declines in river levels, and supplants native riparian tree species. Its adaptability and resistance to control measures, two life-history traits shared with other nonindigenous species, will continue to add to the management concerns associated with the ever-growing number of other nonindigenous plant and animal species.


Intracommunity Management:  Prairie Legacies

The approximate action to take after intercommunity management is to identify and retain a set of species and natural processes that sustain communities characteristic of a particular landscape (Chaplin et al. 1996). The Nature Conservancy has identified significant concentrations—legacies—of prairie species that are rare or of declining abundance (Figs. 16-23). Principally these are species that are federally listed or are species of concern that occur within certain communities and ranges of environmental features, including those from prairie wetlands to cottonwood savannahs.

Recommending the restoration of ecological processes in conservation is not new (Leopold 1933). Understanding scale, spatial and temporal, in management is new (Gibson et al. 1993).

Map 21
Fig. 16.   Priority landscapes of biological significance in the Great Plains: 1) Upper Missouri and Yellowstone rivers and watersheds in Montana and North Dakota; this area is an example of a free-flowing Great Plains river and watershed (see Fig. 17) ; 2) Glacial Lake Agassiz Interbeach Area in North Dakota and Minnesota; this area has a number of large, intact expanses of tallgrass prairie; 3) Black Hills and grasslands in South Dakota and Wyoming; these are two of the largest publicly owned examples of short-grass and mixed-grass prairies (see Fig. 18); 4) Sandhills in Nebraska and South Dakota; this is the largest dune system and one of the largest expanses of native grassland left in North America; 5) Western high plains grassland in Colorado, Nebraska, and Wyoming, which includes the Pawnee National Grassland and other adjacent short-grass prairie habitat; 6) Arikaree Sandsage Prairie in Colorado, Kansas, and Nebraska, which includes sandsage and an example of the rare cottonwood-switchgrass savanna (see Fig. 19); 7) Central Plains Wetlands in Nebraska, Kansas, and Oklahoma (areas in box plus areas indicated above box); this area is a string of significant wetlands (see Fig. 20); 8) Flint Hills in Kansas and Oklahoma, which is the largest remaining area of native tall-grass prairie; 9) Osage Cuestas Tallgrass in Kansas (in box), which has rolling to level tall-grass prairie with examples of wet savanna and bottomland forest; 10) Upper Cimarron Mesas in Colorado, Kansas, New Mexico, and Oklahoma; within this area are extensive grasslands and mesas, along with the headwaters of the Cimarron River (see Fig. 21); 11) Fort Worth Prairie in Oklahoma and Texas, which is an unbroken tall-grass prairie; 12) Texas Hill Country in Texas, which has four differing landscapes, each significant to a unique assemblage of natural and rare communities (see Fig. 22); (9 and 13) Central Platte River in Kansas; this is a shallow, braided river of immense wetland importance (see Fig. 23).
Map 20

JPEG - Figure 17
Fig. 17.  Confluence of turbid waters of the Yellowstone and clear waters of the Missouri as a result of the Ft. Peck Reservoir just upstream.
  JPEG - Figure 18
Fig. 18.  Black Hills: Cathedral Spires, South Dakota.
JPEG - Figure 19
Fig. 19.  Arikaree River, Colorado.
JPEG - Figure 20
Fig. 20.  Rainwater Basin, Nebraska.
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Fig. 22.  Texas Hill Country: San Marcos River, Texas.  The San Marcos runs through the Hill Country and is important to a large number of endemic salamanders.
JPEG - Figure 21
Fig. 21.  Upper Cimarron Mesas: Lasa, Mesa de Maya, Colorado, Cobert Mesa.
JPEG - Figure 23
Fig. 23.  Platte River with Sandhill cranes.


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