Low Elevation Dry Southern Hills Pine Forest

Description

The Reference State represents what is believed to show the natural range of variability that dominated the dynamics of the Low Elevation Northern Hills Forest ecological site prior to European settlement The reference state (1.0) is represented by a community dominated by ponderosa pine with bur oak and rocky mountain juniper. Rocky Mountain juniper will be further south transitioning to aspen north of highway 16 with bur oak being on the drier foothills. The shrub component is diverse, and includes rose, chokecherry, serviceberry, juniper (Juniperus spp.), buffaloberry, mountain ninebark, currants, snowberry. The herbaceous understory consists of diverse mix of grasses, many of which are warm season, including little bluestem, big bluestem, oatgrass, needlegrass and upland sedges. Forbs are common and diverse.

Structural variation within this reference state is driven by local hydrology and plant available precipitation. The primary elements of structure that are affected include: 1) variably sized perennial openings and transitional grass, forb, shrub interspaces, where natural regeneration occurs. 2) variably sized, mostly even-aged tree groups and single random trees with a balance of age classes (by trees/acre).

Heterogeneity at the landscape level (100-1000 acres) of stands or patches of the above patterns is largely dictated by a combination of local hydrology and plant available precipitation that represent productivity gradients and resulting disturbance regimes (namely frequent fire or mixed severity over time) that yield variation in stand/patch size. Site gradients from less to more productive demonstrate the following variation: 1) less productive sites typically comprised of shallow soils, ridgetops, sun exposed slopes, head slopes having lower overall tree densities, higher proportion of single random trees, and fewer trees per group. With the caveat that when surface fuels are unable to carry frequent fire. 2) more productive sites comprised of deeper soils, gullies, swales, sheltered slopes, and toe slopes having higher overall tree densities with a higher proportion of trees in groups that tend to be larger. The caveat to this latter point being that when surface vegetation is productive so too becomes fire severity to regeneration.

Variation of type, size, and frequency of disturbances result contribute to dynamic stand maintenance over time. This dynamic is result of a continuous layer of extensive and frequent low severity disturbance to infrequent and more localized mixed severity disturbances. Most notable of this layered dynamic are the mixed severity disturbances where small patch (1-20) vs large patch (20-200 acres) disturbances (fire, insects, wind, ice storms) occur. This short-term maintenance and longer-term mixed severity disturbance supports historical ponderosa pine stands that are arranged such that there were diverse groups of openings, clumps, and individual trees with variable diameters at breast height (DBH) and variable amounts of trees per acre (TPA).

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 Managed 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 clearcut 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 something 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.

In yet other areas, given the erodible soils, the forest service classified some lands as non-harvestable timber. These area's have not been harvested or managed, buck rather lack natural disturbance since the introduction of modern fire suppression.

The dominant plants 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