Western Great Plains Tallgrass Prairie

This system can be found throughout the Western Great Plains Division. It is found primarily in areas where soil characteristics allow for mesic conditions more typical of the Eastern Great Plains Division and thus are able to sustain tallgrass species. This system may be small patches interspersed within Northwestern Great Plains Mixedgrass Prairie (CES303.674) or Western Great Plains Shortgrass Prairie (CES303.672) and may also be associated with upland terraces above a floodplain system where these more mesic conditions persist. Soils are primarily loamy Mollisols that are moderately deep and rich. Those areas that contain more sandy soils should be considered part of Western Great Plains Sand Prairie (CES303.670). This system is dominated primarily by Andropogon gerardii and may also include Sorghastrum nutans, Schizachyrium scoparium, Pascopyrum smithii, Hesperostipa spartea, and Sporobolus heterolepis. Andropogon gerardii often dominates the lowland regions, although Pascopyrum smithii can be prolific if conditions are favorable. Forbs in varying density may also be present. The primary dynamics for this system include fire, climate and grazing. Fire suppression in these areas has allowed for the invasion of woody species such as Juniperus virginiana and Prunus spp. Grazing also has contributed to these changes and likewise led to a decrease of this system as overgrazing favors shortgrass and mixedgrass systems. Conversion to agriculture likewise has probably decreased the range of this system. Thus, this system likely only occurs in small patches and in scattered locations throughout the division. Large-patch occurrences are mostly isolated to slopes and swales of rolling uplands where either grazing or cultivation are more problematic.

The mesic, deep soils of this system allow for dominance by Andropogon gerardii. Other species, such as Sorghastrum nutans, Schizachyrium scoparium, Pascopyrum smithii, Hesperostipa spartea, and Sporobolus heterolepis, can also be present. In more lowland areas, Pascopyrum smithii can become more prevalent. Fire suppression can lead to the invasion of these areas by woody species such as Juniperus virginiana and Prunus spp.

This system is found primarily on loam, moderately deep, and rich Mollisols throughout the Western Great Plains Division. These soils tend to be more mesic and deep than the majority of soils within the Western Great Plains and are more typical of the Eastern Great Plains Division. This system requires more moisture than is available from precipitation in the Western Great Plains so it occurs in valleys, on lower slopes, and sometimes on floodplains (Albertson 1937, Heitschmidt et al. 1970). Occurrences are usually medium to small.

Fire, climate and grazing constitute the primary dynamic processes impacting this system. Fire may have occurred as often as every 5 years, especially in the wetter eastern portions of this system's range (Landfire 2007a). This system occurred in a landscape dominated by mixedgrass and shortgrass vegetation. These systems do not have the rapid build up of litter that occurs in tallgrass prairies further east and thus do not carry fire as readily so there were fewer fires that could affect this system.

This system developed in an area occupied by vast numbers of native ungulates, notably bison (Bos bison) but including other species, and the grazing of these species affected species composition and the patchwork of habitat. Bison preferentially favor newly burned areas and graminoids over forbs (Coppedge and Shaw 1998, Vinton et al. 1993). On unburned sites, grazing removes live and dead vegetation, allowing more light and heat to the soil surface and increasing available moisture thus favoring species, forbs or woody plants, in the case of bison grazing, that were resilient to the effects of grazing or avoided by the grazers (Damoureyeh and Hartnett 1997).

Fire suppression can allow for the invasion of woody species such as Juniperus virginiana and Prunus spp. into the prairie matrix. This is a more serious threat in the eastern portion of this system where the climate is more amenable to trees and shrubs and seed sources are more common.

This system is typically more productive than surrounding vegetation and is preferentially grazed by livestock (Branson and Weaver 1953). Many examples of this system are used for pasture or haying. Overgrazing tends to favor shortgrass and mixedgrass species and can cause the conversion of this system to the Western Great Plains shortgrass or mixedgrass systems. Prolonged haying during the early to mid summer favors cool-season species that set seed before the haying occurs. Also, invasion by introduced species such as Bromus inermis, Poa pratensis, and several weedy forbs can become more severe as grazing pressure increases.

Long-term drought will favor midgrass and shortgrass species over the tallgrass species that characterize this system. Changes to climatic patterns that increase average summer temperatures or decrease precipitation will result in a reduction of sites where this system can persist.

This system occurs throughout the Western Great Plains Division, however, grazing and conversion to agriculture have likely decreased its natural range.