Ecological dynamics
Dominated by ponderosa pine, the Low Elevation Northern Hills Pine Forest (15+% Slope) ecological site occupies much of the territory of LRU A. There exists a historic reference state, and a managed/invaded state. Given the history of intensive use of the Black Hills and its forestry resources, much of the area today would be found in a managed /invaded state with few areas remaining in the reference state.
The ecological site is characterized by a highly variable uneven age structure canopy of ponderosa pine. Due to an increase in elevation and moisture this ecological site will maintain a hardwood component such as quaking aspen, paper birch or bur oak. Understory species such as Woods rose, Oregon grape, common juniper, bearberry (kinnikinnick), ironwood (hop-hornbeam), are common. The herbaceous layer may consist of ricegrasses, oatgrasses, yarrow, pasqueflower, a variety of asters and sedges. On this site, productivity varies due to slope percentage, where lower slopes are higher producing than steeper slopes. Sub-shrubs will increase in composition as slopes increase along with bare ground and needle cast.
Ponderosa pine is the dominant tree species in the Black Hills and tends to have dark colored bark (blackjacks) until it reaches 75 to 100 years of age, after which the bark progressively changes to a buff or orange color. Morphologically older trees are marked by the presence of thinning foliar and flat-topped crowns. Additional morphology includes larger lower branching with higher crown- based heights and furrowed or very smooth bark.
Historically spatial heterogeneity was present not only across the Black Hills but also within the smaller dense pine patches (Brown, 2006). This variation of structure consisted of a diverse landscape mosaic that varied from grasslands and stands of ponderosa pine forest with variation in forest structure due to topographically driven microclimates resulting in variation of total tree density, tree group size, proportion of trees in groups versus single random trees, and openness.
Ponderosa pine is a fire-adapted species that is, mostly driven by frequent, low-intensity surface fires that consume small seedlings, prunes lower branches from larger trees, and reduces overall surface fuel loads. With prolific spring rains and higher elevation, the historical fire regime in this ecological site is characterized as one of low-severity with a combination small patch (1-20 acre) of group torching fires and the occasional (>100 years) large patches (20- 200 Ac) group torching fires. Overall, it is estimated that only 3.3 percent of the Black Hills landscape burned as crown fire during 22 landscape fire years between 1529 and 1893 (Brown, 2008). It is estimated that only 3.3 percent of the Black Hills landscape burned as crown fire during 22 landscape fire years between 1529 and 1893 (Brown, 2008). In the central core, low- severity surface fires occurred between 16 and 20 years (Brown, 2008). Frequent surface fires maintained the ecotone between forest and grasslands by killing ponderosa pine seedlings and saplings before they could become established.
In addition to variable fire, pests, and disease- other natural disturbances played a role in the overall maintenance of diversity, structure, and density the Black Hills. The mountain pine beetle (Dendroctonus ponderosae) is an important driver of forest structure. The mountain pine beetle was first described in the Black Hills in 1901 by Andrew D. Hopkins and the first documented epidemic of bark beetles in the Black Hills occurred in 1895 (Graham et al. 2016). These beetles are native in the Black Hills and have cyclical life cycle and emergence, with a continuous endemic and less frequent epidemics in the Black Hills over the last 129 years (Graham et al. 2016). "Mountain pine beetle outbreaks in the Black Hills from 1894 through 2014 had a mean return interval of 20 years and a mean duration of 13 years (Graham et al. 2016)".
At a variable and localized scale additional disturbances include pine engraver beetles and armillaria root rot. Pine engraver beetles are non-aggressive and breed in windthrown ponderosa pine trees, trees damaged by wind, ice storms, or other non-standing trees. Armillaria (Armillaria ostoyae) has been noted across soil types and locations within the Black Hills (Boldt and Van Deusen 1974; Holah1993; Lundquist 1991; Shepperd, Wayne D.; Battaglia, Michael A. 2002).
Studies have shown the current forest contains about the same basal area (ft2/ac) on average as the historic forest. The difference, however, is that the historic forest was dominated by fewer, but much larger trees, than those present today. This suggests that there has been a simplification in structure at stand to landscape scales, with increased tree density leading to fewer gaps and more even spacing and size distributions within groups (Brown, 2008).
Relative increases in tree density and simplification of structure have contributed to greater vertical and horizontal fuel continuity, and thus increased likelihood for incidence and extent of crown fires. More pole-sized trees (5-to-9-inch DBH) within stands also increases the likelihood of bark beetle (Dendroctonus ponderosae) outbreaks. This is a concern in the Black Hills where pine beetle outbreaks have been a major disturbance agent during the 20th and early 21st centuries.
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 (Tatina R.E., Hanberry B.B., 2022).
Due to the spread and establishment of non-native cool-season grasses and other anthropogenic disturbances in MLRA 62, the Reference Plant Community (1.1) is nearly non-existent.
State 1
Reference State
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 the bur oak is frequently in shrub form. Predominant shrubs will include juniper, Oregon grape, bearberry (kinnikinnick), ironwood (hop-hornbeam).. 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. Overall herbaceous understory decreases, while needle cast and bare ground increase.
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.
Dominant plant species
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ponderosa pine (Pinus ponderosa), tree
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quaking aspen (Populus tremuloides), shrub
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paper birch (Betula papyrifera), shrub
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bur oak (Quercus macrocarpa), shrub
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Woods' rose (Rosa woodsii), shrub
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creeping barberry (Mahonia repens), shrub
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common juniper (Juniperus communis), shrub
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kinnikinnick (Arctostaphylos uva-ursi), shrub
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Saskatoon serviceberry (Amelanchier alnifolia), shrub
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roughleaf ricegrass (Oryzopsis asperifolia), grass
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sedge (Carex), grass
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slender wheatgrass (Elymus trachycaulus), grass
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Hood's sedge (Carex hoodii), grass
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Richardson's sedge (Carex richardsonii), grass
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common yarrow (Achillea millefolium), other herbaceous
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pasqueflower (Pulsatilla), other herbaceous
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aster (Aster), other herbaceous
Community 1.1
Reference Community
Highly variable uneven age/structure, moderately dense, ponderosa pine forest with scattered hardwoods. This community evolved with periodic severe drought, episodic insect and disease outbreaks, low-intensity surface and mixed severity small patch (1-20 acres) fires with a return interval of 10 to 20 years, rare mixed severity large patch (20-200 acre) fires that occurred on a greater than 100-year interval. Severe weather events that include hailstorms, tornados, and microbursts would also contribute to forest structure. Light to moderate levels of wildlife browsing and grazing also occurred on this site prior to European-American settlement.
The expected forest canopy cover ranges from 30-60% with approximately 100 TPA around 13 inches DBH. The spatial arrangement of ponderosa pine consists of 44% groupings, 4% individual trees, and 51% openings.
In the lower elevations, a community may form consisting of a scattered bur oak understory, while in the higher elevations, quaking aspen, paper birch, or ironwood can be present throughout the site.
The dominant grasses and grass-like species include rough-leaf ricegrass, oatgrasses, slender wheatgrass, Hood’s sedge, and Richardson’s sedge. The dominant shrubs include common juniper, Oregon grape, bearberry (kinnikinnick), and chokecherry.
Herbaceous understory in this community is limited averaging between 15%-50% cover and dominated by a ground cover of needle cast, coarse woody debris, and few shrubs or sub-shrubs.
This plant community is diverse, stable, productive, and is well adapted to the Black Hills, Bear Lodge Mountains, and Dakota Hogback. Community dynamics, nutrient cycle, water cycle, and energy flow are functioning properly. Plant litter is properly distributed with very little movement offsite, and natural plant mortality is very low. This is a sustainable plant community in terms
of soil stability, watershed function, and biologic integrity.
This community self-sustained though moderate frequency low severity disturbances and mixed severity small patch disturbances (1-20 acres).
Community 1.2
No Disturbance Community
Dense highly variable uneven age/structure ponderosa pine forest.
This community evolved with a prolonged absence of 20- 100 years of insect and disease outbreaks, low-intensity surface fires and severe weather events that include hailstorms, heavy snow fall, tornados, and microbursts. Light to moderate levels of wildlife browsing and grazing also occurred on this site prior to European- American settlement.
The expected forest canopy cover is greater than 60% with approximately 148 TPA around 12 inches DBH. The spatial arrangement of ponderosa pine consists of 66% groupings, 2% individual trees, and 33% openings.
Herbaceous understory in this community is limited averaging 5-10% and dominated by a ground cover of needle cast, coarse woody debris, and few shrubs or sub-shrubs.
Due to the increase canopy cover the herbaceous understory will decrease in production and species diversity. Shrubs percentage will be decreased with the higher canopy cover.
The dominant tree species on this site is ponderosa pine with a diameter at breast height (DBH) ranging from 9 to 14 inches. Quaking aspen and paper birch will be less frequent but still scattered throughout the site.
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Community 1.3
Post Large Patch Disturbance Community-
This plant community is a successional phase of a post-fire ponderosa pine forest. It consists of open, scattered large ponderosa pine trees and seedlings with a large component of Quaking Aspen or Paper Birch. It evolved with natural disturbances including episodic insect and disease outbreaks in ponderosa pine, high-intensity stand-replacing fire, or severe weather events. This plant community is of small extent and may not develop into a mature aspen stand on all locations where this ecological site occurs. It is most likely to be found on cool moist slopes and toe slopes with northern exposures (Severson, 1976). Insects and disease in mature aspen will play a part in the decline of mature aspen stands and the lack of regeneration (Blodgett, 2017). Cool season bunchgrasses, pioneer forbs and shrubs are common.
Community 1.4
Post Large Patch Disturbance Community- Bur Oak
This community is dominated by large, scattered ponderosa pine and brush/shrub like bur oak and ironwood(hop-hornbeam). Forest canopy cover is less than 30%, with 36 TPA, and 11-inch average DBH. This community is similar to community 1.3 with the exception of the shrub like bur oak resulting from a large patch mixed severity disturbance after being in community 1.2. Also, like 1.3, this community being more open, contains higher amounts of cool season bunchgrasses, pioneer forbs, and shrubs. Once this community is present, it takes a very long time to transition to a different community compared to 1.3 which may transition very quickly.
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Pathway 1.1A
Community 1.1 to 1.2
This transition between communities is a result of the passing of time (30+ years) with no disturbance allowing for tree growth and density to increase.
Pathway 1.1B
Community 1.1 to 1.3
This transition between communities is a result of infrequent (>100 years) mixed severity large patch (20-200 acres) disturbance. This disturbance is often in the form of mixed severity fire with acres group torching or epidemic Mountain Pine Beetle outbreaks. Severe weather events hailstorms, heavy snow fall, ice storms, tornados, and microbursts can also cause large scale tree mortality leading to this transition.
Pathway 1.1C
Community 1.1 to 1.4
This transition between communities is a result of infrequent (>100 years) mixed severity large patch (20-200 acres) disturbance. This disturbance is often in the form of mixed severity fire with acres of group torching or epidemic Mountain Pine Beetle outbreaks. Severe weather events hailstorms, heavy snow fall, ice storms, tornados, and microbursts can also cause large scale tree mortality leading to this transition.
Pathway 1.2A
Community 1.2 to 1.3
This transition between communities is a result of infrequent (>100 years) mixed severity large patch (20-200 acres) disturbance. This disturbance is often in the form of mixed severity fire with acres of group torching or epidemic Mountain Pine Beetle outbreaks. Severe weather events hailstorms, heavy snow fall, ice storms, tornados, and microbursts can also cause large scale tree mortality leading to this transition.
Pathway 1.2A
Community 1.2 to 1.4
This transition between communities is a result of infrequent (>100 years) mixed severity large patch (20-200 acres) disturbance. This disturbance is often in the form of mixed severity fire with acres of group torching fire or epidemic Mountain Pine Beetle outbreaks. Severe weather events hailstorms, heavy snow fall, ice storms, tornados, and microbursts can also cause large scale tree mortality leading to this transition.
Pathway 1.3A
Community 1.3 to 1.1
This transition between communities is a result of the passing of time (30+ years) and frequent low severity disturbance such as fire and endemic Mountain Pine Beetle outbreaks.
Pathway 1.4A
Community 1.4 to 1.1
This transition between communities is a result of Frequent low severity disturbance such as fire and endemic Mountain Pine Beetle outbreaks. Severe weather events hailstorms, heavy snow fall, ice storms, tornados, and microbursts can also cause tree mortality leading to this transition.
State 2
Timber Managed and Invaded Herbaceous Sod State
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.
Dominant plant species
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ponderosa pine (Pinus ponderosa), tree
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smooth brome (Bromus inermis), grass
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Kentucky bluegrass (Poa pratensis), grass
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timothy (Phleum pratense), grass
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redtop (Agrostis gigantea), grass
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red clover (Trifolium pratense), other herbaceous
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white clover (Trifolium repens), other herbaceous
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oxeye daisy (Leucanthemum vulgare), other herbaceous
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common yarrow (Achillea millefolium), other herbaceous
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cinquefoil (Potentilla), other herbaceous
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Canada thistle (Cirsium arvense), other herbaceous
Community 2.1
Managed Forest
This plant community is a result of forest activities focused on timber management. Virtually all of the Black Hills unreserved and operable forest acres have been cut over at least once; many acres have received multiple partial cuts. (Boldt and Van Deusen 1974). Current structure is based on the management or silvicultural system that was implemented by forestry professionals. There are a variety of forest harvest systems that have been utilized. These dictate the resulting and future forests structure of the site.
One of the primary forest structures resulting from forest management is a single story of evenly spaced trees. The resulting tree size might very from saplings to larger diameter trees. Although the spacing within the site will be fairly uniform different sites will have different spacings ranging from 10ft to 150ft between trees. Generally, the larger the tree the greater the spacing will be between trees.
Another common resulting structure of forest management is a site with two separate canopy layers of trees. One layer is commonly made up of lager diameter trees that have a spacing often wider then 30ft. The other layer is seedling and sapling sized trees, these trees may be at an even spacing between 10 and 16 feet apart or they may not be evenly spaced.
There are other management objectives and silvicultural systems that result in different forest structures other than then ones previously listed. These structures usually include leaving trees of all sizes from seedling to large dimeter trees in varying amounts. The resulting spatial distribution is generally also uneven with areas of different forest densities.
Natural regeneration is the most common following timber management changing the forest structure and need for future management throughout time. Planting of trees maybe done in large fire burn areas,
Community 2.2
Invaded Herbaceous Sod State
This plant community is a result of the loss of the overstory ponderosa pine, either from high-intensity fire or timber harvest, followed by heavy continuous grazing, invasion of non-native cool- season grasses, and in some cases seeding to forage or crop species. It is characterized by a dominance of non-native cool- season grasses including timothy, smooth brome, Kentucky bluegrass, and redtop. Forbs will include red and white clover, ox- eye daisy, western yarrow, cinquefoil, and Canada thistle. Native plants, including ponderosa pine, have great difficulty becoming established in this plant community. This site can be renovated through tillage and seeding of introduced forage species. The renovated plant community can remain productive through prescribed grazing with proper stocking rates, change in season of use, and adequate time for plant recovery following grazing event.
Pathway 2.1A
Community 2.1 to 2.2
During early European-American settlement of the Black Hills this ecological site, in some areas, was clear-cut for timber and then used for 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 either invaded by or seeded to introduced grasses and clover to increase forage quality or farmed for grain crops.
Pathway 2.2A
Community 2.2 to 2.1
Tree Planting
Transition T1A
State 1 to 2
The transition to this community from the reference community is a result of timber harvest designed to achieve forest management objectives. These treatments will follow one of the silvicultural treatments below. Which will dictate the resulting structure and composition of the site.
• Thinning: a treatment made to reduce stand density of trees primarily to improve growth, enhance forest health.
o Thinning from above: removal of trees from dominant or codominant crown classes or canopy layers in order to favor those in lower crown classes or layers.
o Thinning from below: removal of trees from lower crown classes or canopy layers in order to favor those in upper crown classes or layers.
o Thin throughout the dimeters: the removal of trees to control stand spacing and favor desired trees, using a combination of thinning criteria without regard to crown position.
o Variable density: the removal of trees that deliberately creates non-uniform conditions through a stand.
• Even Age: regenerate and maintain a stand with a single age class.
o Overstory Removal: The cutting of trees comprising an upper canopy layer in order to release advance regeneration in an understory.
o Patch Cutting: removing all of the live trees from areas that are 2 acres in size or smaller.
o Seed Tree: cutting of all trees except for a small number of widely dispersed trees retained for seed production and to produce a new age class.
o Shelterwood: The cutting of most trees, leaving those needed to produce sufficient shade to establish a new age class.
• Uneven Age: methods regenerate and maintain a multiage structure by removing some trees in all size classes either singly, or in small groups.
o Group Selection: a group of trees are removed, and new age classes are established in openings created.
o Single Tree Selection: Individual trees of all size classes are removed more or less uniformly throughout the stand, to promote growth of remaining trees and to provide space for regeneration
