Highland Hills Pine Forest(0-15% Slope)

Description

The Reference State represents what is believed to show the natural range of variability that dominated the dynamics of the high elevation Black Hills forested ecosystem.

The Reference State (1.0) is dominated by a ponderosa pine overstory with possible quaking aspen, paper birch and white spruce. The hardwood and white spruce components will be present in younger stands and eventually be out competed by the pine and become less prevalent as the stand ages. The understory consists of shrubs, forbs, cool-season bunchgrasses and sedges. Predominant shrubs will include common juniper, white coralberry, shrubby cinquefoil, Oregon grape. Forbs are common and diverse. Dominant cool-season bunchgrasses will include rough-leaved ricegrass, needlegrasses, and oatgrasses. Sedges will include Hood’s sedge, dryspike sedge, and Richardson’s sedge.

Structural variation within this reference state is driven by available moisture and the length of time since disturbance. On the warmer more xeric sites pine will assume dominance over the spruce, but these processes will take longer on northern and western slopes and draw bottoms which hold moisture longer. When there is a longer time between disturbances more trees are able to grow, reducing the number of single trees and increasing the size of tree groups.

Heterogeneity at the landscape level (100-1000 acres) is largely dictated by a combination of precipitation from snowfall, spring and fall rains, and climatic variation including multiple wet years to drought years. This effects the resulting disturbance regimes namely mixed severity disturbances with either small or large patches over time that yield variation in tree densities. When there are multiple wet years there are fewer disturbances, hence increasing tree densities. When the wet periods are prolonged and followed by a drought period the disturbances have a greater likelihood of being higher severity and creating larger patch disturbances.

Primary disturbance mechanisms for this site are relatively moderate frequency (30-to-33-year interval) of mixed severity small patch (0-20 acre) disturbances, and rare (>100-year interval) mixed severity large patch (20-200 acre) disturbances. Variation of type, size, and frequency of disturbances contribute to dynamic stand maintenance or transitions. The small and large patchy nature of disturbances and longer intervals between disturbances dictate the dynamics that can occur within the natural range of variability of this site including variation in diameters at breast height (DBH) and amounts of trees per acre (TPA).

The main disturbances that drive forest structure are wildfire and mountain pine beetle infestations, both endemic and epidemic populations. Severe weather events in the Black Hills are also a significant disturbance that can result in overstory damage and treefall. Events include hailstorms, heavy snow fall, tornados, and microbursts.

Due to the pervasiveness of non-native cool-season grasses, timber management, and long-term fire suppression in the region, the true Reference State (1.0) is nearly non-existent.

Submodel

Description

The Timber managed and Invaded Herbaceous Sod State is largely the result of historic early European-American settlement of the Black Hills region. Large tracts which were logged free of regulatory restraints-prior to establishment of the Forest Reserve in 1897- were commercially clear-cut and practically stripped of all trees large enough to yield a mine timber a railroad tie. (Boldt and Van Deusen 1974). Between the mid-1870s to 1890s, the Homestake Mining Company (and their half dozen subsidiary companies) alone cut upwards of 6 million board feet of timber in the Black Hills.

In some areas, this ecological site was clear-cut for timber, then converted for use as ranch and farmsteads. In other cases, the pine overstory was lost to high intensity fire events followed by settlement. The cleared areas were often heavily grazed to supply beef and mutton for mining and logging communities. In later years these sites were often seeded to introduced grasses and clover to increase forage quality or farmed for grain crop production. In many cases the shift in land use from forest to livestock, forage, and crop production remains. Those areas that are not under intensive management resist transitioning back to a forest plant community, even though the soils still exhibit forest attributes.

The dominant understory associated with this state are introduced sod-forming grasses, introduced legumes, and weedy forbs. This state is very resistant to change through management alone.

Submodel