Loamy Overflow - South

Description

The Reference State represents what is believed to show the natural range of variability that dominated the dynamics of the Loamy Overflow - South ecological site prior to European settlement. This site in the Reference State (1.0) is typically dominated by shrubs, cool- and warm-season grasses and sedges in the understory, an overstory of deciduous trees, and scattered ponderosa pine. In pre-European times, the primary disturbance mechanisms for this site in the reference condition included periods of below and above average precipitation, periodic fire, beaver activity, and browsing and herbivory by large ungulates. 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 and Canada thistle.

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 shrubs, cool- and warm-season grasses and sedges, and an overstory of deciduous trees. It can be found on areas that are properly managed with grazing and on some areas receiving periodic rest. Native cool- and warm-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. 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

In pre-European time the Dense Shrub State was common along most streams and floodplains throughout the majority of the Black Hills. Today this community is of minor extent. Prior to European settlement, ponderosa pine density was lower in the uplands, resulting in lower evapo-transpiration rates and higher water yields into stream hydrologic systems. The dense shrub plant communities consisted of a mixture of several willow species including Bebb willow, yellow willow, and sandbar willow. Other shrubs included river birch, redosier dogwood, wild rose, raspberry, and currant.

Beaver dam complexes were also common on most Black Hills drainages which regulated water flow and maintained high water table levels, creating conditions suitable for dense stands of willow and dogwood. By the latter part of the 1800s, beaver numbers were low, and populations were restricted to remote areas of the Black Hills. Riparian ecosystems likely degraded rapidly following beaver removal, generating substantial long-lasting effects.

Placer mining activities during the Black Hills gold rush of the 1870s and 1880s had severe effects in some riparian areas as did the transportation routes along streams, and the expansion of agriculture including farming and livestock production that supplied beef and mutton for mining communities (Froiland, 1990).

Dramatic changes in the functional and structural groups that make up diverse riparian plant communities are a result of physical disturbances from past and present use and management. Non-native plant species, both introduced as forage species and invasive species, substantially reduced shrub communities and transitional deciduous trees (Parrash,1996).

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, redtop, and smooth brome. 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 introduced grass species. The nutrient cycle is impaired, resulting in a higher level of nitrogen which also favors introduced 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 this 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

Description

This Conifer State consists of areas where tree canopy increases to a level that impedes the reproductive capability of the major native perennial grass species. The increase in conifer canopy is a result of encroachment from forest sites, or the expansion of ponderosa pine due to long-term fire suppression. This state is reached when mature ponderosa pine canopy cover reaches approximately 25 percent or more. With continued long-term fire suppression and no timber management, the conifer canopy can eventually become closed with much of the herbaceous understory lost.

Submodel