Ecological dynamics
Black Hills vegetation types consist of a mixture of forest and grasslands resulting from the varied topography, geology, soils, climate, and natural disturbances. Frequent fires, periodic drought, and episodic infestations of mountain pine beetles all contribute to the maintenance of large, open grasslands scattered throughout the Black Hills. Ponderosa pine is the dominant tree species in the Black Hills. It is a fire-adapted species that coexists with frequent, low-intensity fires that consume small seedlings, prune lower branches from larger trees, and reduce fuel loads on the forest floor. This site developed under Black Hills climatic conditions with short-term weather variations, light to severe grazing by bison, elk, and small mammals, sporadic natural or man-caused wildfire (often of light intensities), and other biotic and abiotic factors that typically influence soil/site development. The natural fire regime maintained this site as a grassland and the plant communities were free of non-native cool -season grasses.
Fire, or the lack of fire, and introduced non-native cool-season grasses, are major drivers, along with grazing, that shape this site as well as adjacent ecological sites. The Very Shallow site is susceptible to conifer encroachment from adjacent forest sites.
The historic native vegetation on this site consisted of mixed prairie grasses occurring on ridges and uplands. The vegetation predominately consists of warm-season grasses mixed with cool-season grasses, portraying a mixed grass prairie characteristic. Little bluestem and sideoats grama are the dominant species, along with plains muhly. Subdominant cool-season grasses include needlegrasses and wheatgrasses. Other species include blue grama, hairy grama, threeawn, bottlebrush squirreltail, and threadleaf sedge. Kentucky bluegrass and smooth brome may be present, but typically do not dominate the plant community. A diverse community of forbs make up a significant proportion in the mixture. Common forbs include stemless hymenoxys, cudweed sagewort, scurfpea, prairie coneflowers, purple coneflower, gayfeather, and asters, along with hood phlox and pussytoes in the understory. Shrubs include common juniper, creeping juniper, fringed sagewort, broom snakeweed, green sagewort, prairie rose, and a few yucca plants are scattered on the site. A few ponderosa pine and rocky mountain juniper often are scattered across this site. Rocks, and rock fragments are very noticeable and bare ground can be present, but is not common.
Changes will occur in plant communities due to short-term weather variations and impacts of native and/or exotic plant and animal species. Management actions and severe disturbances, such as periods of well-below average precipitation, severe defoliation, or no fire can also cause a shift in plant communities and/or species composition.
State 1
Reference State
This state represents what is believed to represent the natural range of variability and plant community dynamics of this ecological site prior to European settlement. This site is dominated by warm-season grasses, a diverse forb component, and various low-growing shrubs. In pre- European times, the primary disturbances included fire and grazing by large ungulates and small mammals. Favorable growing conditions occurred during the spring, and the warm months of June and July. Routine and/or occasional fires and reduced tree cover contributed to the ecological processes that maintained the reference plant community.
Community 1.1
Little bluestem-Sideoats grama /Perennial forbs/Ground Juniper
Interpretations are based primarily on the Little bluestem-Sideoats grama/Perennial forbs/Common juniper plant community phase. This also is considered to be the Reference or historic plant community. The potential vegetation is about 70 percent grass and grass-like plants, 20 percent forbs, and 10 percent shrubs. Total annual production for a normal growing year is approximately 1,200 lbs. /Ac. The community is dominated by warm-season grasses including little bluestem, sideoats grama, plains muhly, blue grama, hairy grama, and three-awn. The dominant cool-season grasses are needleandthread, prairie Junegrass, slender wheatgrass, bottlebrush squirreltail, bluebunch wheatgrass, western wheatgrass, Canada bluegrass, and threadleaf sedge. Forbs include stemless hymenoxys, hairy goldaster, cudweed sagewort, scurfpea, prairie coneflowers, purple coneflower, and dotted gayfeather. The dominant shrubs are common and creeping juniper. Other shrubs include yucca, fringed sagewort, broom snakeweed, and pricklypear cactus. It is common to have a few ponderosa pines on this site (< 2 percent cover). This plant community is productive, and resilient to disturbances such as drought and fire. It was a sustainable plant community in regards to soil/site stability, watershed function, and biological integrity.
Community 1.2
Sedge/Grama grass/Forbs/Ground Juniper/Ponderosa Pine (2-5% Cover)
Figure 9. Very Shallow PCP-1.2
This plant community is a result of continuous season-long grazing or heavy, continuous grazing with no change in season of use between grazing years. Drought or extended periods of below normal precipitation also can be a driver. The potential plant community is made up of approximately 65 percent grasses and grass-like species, 15 percent forbs, and 20 percent shrubs and trees. Dominant grasses include blue grama, hairy grama, threadleaf sedge, and plains muhly. Little bluestem, sideoats grama, needleandthread, and some wheatgrass will be present, but in small amounts. Some introduced cool-season species such as Kentucky bluegrass and smooth brome may also be present. Forbs contribute substantially to the biomass production in this plant community, as do the low-growing shrubs. Ponderosa pine can be scattered throughout the site, but will not exceed 5 percent canopy cover. The herbaceous species within this plant community are well-adapted to grazing.
Pathway 1.1A
Community 1.1 to 1.2
Continuous season-long grazing or heavy, continuous grazing with stocking rates above the carrying capacity for the entire growing season will cause a decrease in little bluestem, sideoats grama, and the mid-stature cool-season grasses. Blue and hairy grama and threadleaf sedge will increase in the plant community, along with low-growing shrubs and possibly ponderosa pine. Drought or long periods of below normal precipitation can accelerate this shift in the plant community.
Pathway 1.2A
Community 1.2 to 1.1
Long-term prescribed grazing, which provides grazing deferment during the growing season, along with stocking rates not exceeding carrying capacities and periodic fire, prescribed burning, or brush management can restore this plant community phase to PCP 1.1. Normal or above-normal precipitation can help shift this plant community back to 1.1.
State 2
Pine-Juniper State
This state is dominated by ponderosa pine and ground juniper. This transition is a result of heavy, continuous grazing and lack of frequent fire or no use and no fire, resulting in encroachment of ponderosa pine. Areas of intermediate and dense ponderosa pine canopy were found to reduce precipitation reaching the forest floor by an average of 20 percent (Wrage, 1994). If pine encroachment is moderate to severe, the soil surface may be covered with up to 1 inch of pine needles and duff. Native warm-season grasses such as bluestems, sideoats grama and blue grama, and cool-season grasses such as wheatgrass and needlegrass decline as overstory canopy cover increases. Shade-tolerant grasses, such as slender wheatgrass, poverty oatgrass, bluegrasses, and rough-leaved ricegrass will increase, as well as common and creeping juniper. In the absence of fire, this plant community phase will be resistant to change. Ponderosa pine canopy can continue to increase over time, reducing herbaceous production and increasing bare ground. This state will have lower water infiltration rates, increased runoff, and a higher potential for soil erosion.
Community 2.1
Ponderosa pine (15% cover)-Ground Juniper
This plant community is characterized by the dominance of Ponderosa pine, common juniper and creeping juniper and is the result of heavy, continuous, season-long grazing and no fire, or no use and no fire. Ponderosa pine make up approximately 15 percent of the plant community and shrubs approximately 20 percent. Grasses and forbs make up approximately 65 percent of the plant community. Dominant grass and grass-like plants include bluegrass, slender wheatgrass, rough-leaved rice grass, poverty oatgrass, and upland sedge. Dominant forbs include cudweed sagewort, coneflower, and pussytoes. Prevalent shrubs include fringed sagewort, poison ivy, and broom snakeweed. Most of these shrubs rarely exceed one foot in height. Rocky Mountain juniper may be present, but does not dominate.
Transition 1A
State 1 to 2
Continuous season-long grazing with stocking rates above the carrying capacity for the entire growing season, combined with the absence of fire to control conifer seedling establishment, or no use, no fire and pine encroachment will lead toward a pine-juniper-dominated state, State 2. More shade-tolerant grasses will become dominant in this state.
Restoration pathway 2A
State 2 to 1
Prescribed burning or mechanical brush management plus long-term prescribed grazing may move the Pine-Juniper State back to the Reference State depending upon the plant community and climatic conditions. This could be a long-term process, and the results may not achieved or meet management goals.
