Clayey Overflow

Description

This State represents the natural range of variability that dominated the dynamics of this ecological site. This State was dominated by cool- season grasses. In pre-European times, the primary disturbance mechanisms for this site in the Reference condition included somewhat frequent fire and grazing by large herding ungulates. Timing of fires and grazing coupled with weather events dictated the dynamics that occurred within the natural range of variability. A combination of disturbances such as fire followed by grazing during below average precipitation periods, or a severe single disturbance such as extended periods of below average precipitation would have caused a decline in tall warm-season grasses and green needlegrass. This would have resulted in a simplification of the plant community with dominance by western wheatgrass.
The Reference State may be difficult to locate in this MLRA with the introduction of non-native cool-season grasses. Plant Community Phase 2.1 is most similar to the Reference Plant Community but because of the persistence of non-native cool-season grasses, a restoration pathway to the Reference State is not believed to be achievable.

Submodel

Description

This State is similar to the Reference State in terms of dominant plant composition and production. However, the invasion of introduced non-native cool-season sodgrasses alters the natural range of variability for this ecological site. This state is still dominated by mid- and tall native warm- and cool-season grasses, but invasive introduced cool-season sodgrasses are now present in all community phases of this state. The primary disturbance mechanisms for the Native/Invaded State include grazing by domestic livestock and infrequent fires. Timing and intensity of grazing events coupled with weather dictate the dynamics that occur within this state. The cool-season native grass can decline and an increase in introduced sodgrasses will occur. Many times, this state appears as a mosaic of community phases caused primarily by continuous season-long grazing.

This state represents the more common range of variability that exists with higher levels of grazing management but in the absence of periodic fire followed by short-term intensive grazing. This state is dominated by cool-season grasses, with warm-season grasses being subdominant. It can be found on areas that are properly managed with grazing and/or prescribed burning, and sometimes on areas receiving occasional short periods of rest.

Submodel

Description

This State is the result of invasion and dominance of introduced species. This state is characterized by the dominance of Kentucky bluegrass and smooth brome, and an increasing thatch layer that effectively blocks introduction of other plants into the system. Plant litter accumulation tends to favor the more shade tolerant, introduced grass species. The nutrient cycle is also impaired, and the result is typically a higher level of nitrogen which also favors the introduced species. Increasing plant litter decreases the amount of sunlight reaching plant crowns thereby shifting competitive advantage to shade tolerant, introduced grass species. Studies indicate that soil biological activity is altered, and this shift apparently exploits the soil microclimate and encourages growth of the introduced grass species. Once the threshold is crossed, a change in grazing management alone cannot cause a reduction in the invasive grass dominance. Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30 percent of the plant community and native grasses represent less than 40 percent of the plant community composition. Plant communities dominated by Kentucky bluegrass have significantly less cover and diversity of native grasses and forb species (Toledo, D. et al., 2014).

Submodel

Description

This State can be transitioned from any Plant Community. The two separate vegetative Plant Communities are highly variable in nature. They are derived through different management scenarios, and are not related successionally. Infiltration, runoff, and soil erosion varies depending on the vegetation present on the site.

Submodel