Stony Overflow - High Central

Description

The Reference State represents what is believed to show the natural range of variability that dominated the dynamics of the Stony Overflow ecological site prior to European settlement. This site in the Reference State (1.0) is dominated by cool-season bunchgrasses, sedges, and a very diverse forb component. Shrubby cinquefoil and snowberry are the dominant shrubs. Trees include quaking aspen, scattered ponderosa pine, and white spruce. Aspen will primary occur along the margin of the Stony Overflow site adjacent to forested slopes. In pre-European times, the primary disturbance mechanisms for this site in the reference condition included grazing and browsing by large ungulates, periods of below and above average precipitation, and periodic fire. Timing of fires and herbivory coupled with weather events dictated the dynamics that occurred within the natural range of variability. Today the primary disturbance is from the lack of fire, concentrated livestock grazing, and wildlife browse. Grasses that are desirable for livestock and wildlife can decline and a corresponding increase in less desirable or more grazing-resistant grasses will occur. Favorable growing conditions occurred during the spring and the warm months of June through August. Today a similar state will be difficult to find due to the predominance and invasiveness of non-native cool-season perennial gasses.

Submodel

Description

The Native/Invaded State represents the more common range of variability that exists with higher levels of grazing management but in the absence of periodic fire due to fire suppression. This state is dominated by cool-season bunchgrasses, sedges, and shrubby cinquefoil. It can be found on areas that are properly managed with grazing and on some areas receiving periodic rest. Native cool-season grasses and sedges will decline as non-native cool-season grasses increase. Non-Native cool-season grasses will make up less than 15 percent of total annual production in this state. Preliminary studies indicate that when Kentucky bluegrass exceeds 30 percent of the plant community and native grasses represent less than 40 percent of the plant community composition, a threshold has been crossed to an Invaded State (3.0). These invaded plant communities that are dominated by Kentucky bluegrass will have significantly less cover and diversity of native grasses and forb species (Toledo, D. et al., 2014).

Submodel

Description

The Invaded State is the result of invasion and dominance of non-native cool-season grass species on the site. Dominate grasses include Kentucky bluegrass, timothy, and redtop. Continuous season-long grazing or heavy continuous grazing will result in an increase of non-native grasses and forbs. Non-use and no fire will result in an increasing thatch layer that tends to favor the more shade tolerant non-native grass species. The nutrient cycle is impaired, resulting in a higher level of nitrogen which also favors non-native species. Studies indicate that soil biological activity is altered, and this shift apparently exploits the soil microclimate and encourages growth of the non-native grass species. Once the threshold is crossed, a change in grazing management alone cannot cause a reduction in the invasive grass dominance. Preliminary studies 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