Low Elevation Northern 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 Low Elevation Northern Hills Forest ecological site prior to European settlement. The Reference State (1.0) is dominated by ponderosa pine with quaking aspen, paper birch and bur oak. Sites will generally contain either quaking aspen/ paper birch or bur oak as the dominant hardwood component. At higher elevations and in the Bearlodge Mountains bur oak is frequently in shrub form. Predominant shrubs will include western serviceberry, common juniper, bearberry (kinnikinnick), ironwood (hop-hornbeam), and russet buffaloberry. Dominant cool-season bunchgrasses will include roughleaf ricegrass, slender wheatgrass, poverty oatgrass, and Rocky Mountain fescue. Sedges will include Hood’s sedge, dryspike sedge, and Richardson’s sedge. A variety of forbs can be found as well composing 15-20% of the herbaceous understory.

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 of ponderosa pine (by trees/acre). 3) Amount and location of hardwood tree species.

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, and include a more dominant hardwood component. 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 disturbances result contribute to dynamic stand maintenance or transitions. This dynamic is a result of a continuous layer of extensive low severity disturbance with a component of localized mixed severity disturbances that either occur simultaneously or as a separate disturbance. Most notable of this layered dynamic are the mixed severity disturbances where more frequent small patch (1-20) vs less frequent 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). The quantity and distribution of hardwood species is also tied to this dynamic. Where there is a higher canopy cover of ponderosa pine both spatially and temporally there will be a decrease in hardwood species as these species are shade intolerant and require full sun to flourish.

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 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.

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. As stated earlier in the ecological dynamics, it is also important to note the change in composition in recent decades of ponderosa pine stands, whereby mainly through the mechanism of fire suppression, the dominance of white spruce has grown by an estimated 5% or more from the original 1.5% composition covered historically and may be present throughout the range of the site(Tatina R.E., Hanberry B.B., 2022). Future considerations may need to account for the possibility that portions of the site could be managed for spruce, in which case the Highland Hills Pine Forest ESD for LRU B would be best utilized as management guide.

Submodel