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, grazing and potential conifer encroachment shaped this site and adjacent ecological sites. Between 1388 and 1900, fire intervals in the Black Hills ranged from 16 to 20 years (Brown and Hull-Sieg, 1996). In the absence of fire, ponderosa pine and/or Black Hills spruce can encroach on this site, but it appears to be uncommon in this LRU. The reason is not fully understood, but competition with cool-season grasses which dominate the site could be hindering the establishment of pine seedlings.
Changes will occur in the plant communities due to short-term weather variations, impacts of native and/or exotic plant and animal species, and management actions. Severe disturbances, such as periods of well-below average precipitation, severe defoliation, or no fire and no use can also cause significant shifts in plant communities and species composition. The historic native vegetation on this site consisted of mixed prairie grasses occurring on ridges and uplands. The vegetation predominately is cool-season grasses mixed with warm-season grasses, sedges, shrubs and a diverse forb community. Bearded wheatgrass, western wheatgrass, Columbia needlegrass, needleandthread, porcupinegrass, and prairie Junegrass are the dominant cool-season grasses. Plains muhly and prairie dropseed are the dominant warm-season grasses. Subdominant cool-season species include Richardson needlegrass and threadleaf sedge. Kentucky bluegrass and timothy can be present, but typically do not dominate the plant community. Forbs make up a significant proportion of the mixture. Common forbs include stemless hymenoxys, Indian paintbrush, dotted gayfeather, cudweed sagewort, stiff goldenrod, prairie coneflower, hairy goldaster, hood phlox, and pussytoes. Shrubs include shrubby cinquefoil, common juniper, fringed sagewort, and skunkbush sumac. Ponderosa pine or Black Hills spruce can be present, but are sparsely scattered across the site. Rocks and rock fragments are very noticeable, and bare ground can be present but is not common.
The following diagram illustrates the common plant community phases that can occur on the site and the transition pathways between communities. These are the most common plant community phases based on current knowledge and experience, and changes will be made as more data is collected. Narratives following the diagram contain more detail pertaining to the ecological processes.
State 1
Reference State
This state represents the natural range of variability that dominates the dynamics in this ecological site. This site is dominated by cool-season grasses with warm-season grasses being subdominant. A diverse group of forbs make up a significant portion of the plant community and shrubs are common. In pre-European times the primary disturbances included fire and grazing by large ungulates and small mammals.
Favorable growing conditions during the spring as well as the warm months of June and July along with routine or occasional fires, inhibits conifer encroachment and contributes to the ecological processes that maintain the reference plant community. Today a similar state can be found in areas where proper livestock use has occurred.
Community 1.1
Wheatgrass-Needlegrass-Prairie dropseed/Sedge/Forbs/Conifer (< 1%) Plant Community
Figure 9. SwLy - B - PCP 1.1
Interpretations are based primarily on the Wheatgrass-Needlegrass-Prairie dropseed/Sedge/Forbs/Conifer (< 1%) plant community phase. This is also considered to be the reference or historic community. The potential vegetation is about 75 percent grass, 15 percent forbs, and 10 percent shrubs and trees. Average annual production for this plant community phase on a median year is 1,400 lbs/Ac. The community is dominated by mid-stature cool season grasses with warm season grasses being subdominant. The dominant grasses include bearded wheatgrass, western wheatgrass, Columbia needlegrass prairie junegrass and needleandthread/porcupinegrass. Plains muhly and prairie dropseed are the dominant warm season grasses. Subdominant cool season species include Richardson needlegrass, and threadleaf sedge. Forbs are common and diverse including; stemless hymenoxys, Indian paintbrush, dotted gayfeather, cudweed sagewort, stiff goldenrod, prairie coneflowers, hairy goldasters, hood phlox and pussytoes. Shrubs include, shrubby cinquefoil, common juniper, fringed sagewort, and green sagewort. Ponderosa pine or Black Hills spruce can be present but sparsely scattered across the site and typically will not exceed 1 percent canopy cover.
This plant community is productive and resilient to disturbances such as drought and fire. This is a sustainable plant community in regards to soil/site stability, watershed function, and biological integrity.
Community 1.2
Wheatgrass-Plains muhly/Sedge/Forb/Shrub/Conifer (<1%) Plant Community
Figure 10. SwLy-B PCP 1.2
This plant community is a result of continuous season-long grazing, heavy continuous grazing, or seasonal grazing without a change in season of use. The potential plant community is made up of approximately 70 percent grasses, 15 percent forbs, and 15 percent shrubs and trees. Dominant grasses include western wheatgrass, bearded wheatgrass, plains muhly, and sedges. Forbs contribute substantially to the biomass production in this plant community, and are common and diverse. Needlegrasses have decreased dramatically and may be nearly absent from the site. Shrubs species including shrubby cinquefoil and common juniper have increased. Ponderosa pine or Black Hills spruce can be scattered throughout the site but, will not exceed 1 percent canopy cover. The herbaceous species within this plant community are well-adapted to grazing.
Pathway 1.1A
Community 1.1 to 1.2
Wheatgrass-Needlegrass-Prairie dropseed/Sedge/Forbs/Conifer (< 1%) Plant Community
Wheatgrass-Plains muhly/Sedge/Forb/Shrub/Conifer (<1%) Plant Community
Continuous season-long grazing or heavy continuous grazing with stocking rates above the carrying capacity for the entire growing season or seasonal grazing during the early portion of the growing season every year will cause a decrease in wheatgrasses and needlegrasses, and an increase of plains muhly and sedges.
Pathway 1.2A
Community 1.2 to 1.1
Wheatgrass-Plains muhly/Sedge/Forb/Shrub/Conifer (<1%) Plant Community
Wheatgrass-Needlegrass-Prairie dropseed/Sedge/Forbs/Conifer (< 1%) Plant Community
Long-term prescribed grazing that provides adequate recovery and change in season of use, along with normal precipitation regime and periodic fire can restore the wheatgrass and needlegrass components of this plant community.
State 2
Shortgrass State
This state is dominated by short-grass species and sedges, and is the result of continuous season-long grazing or heavy continuous grazing. Desirable species have been over-utilized and removed or greatly reduced in the plant community. The site has increased runoff and, depending upon the percentage of bare ground, the site can be susceptible to erosion. This state can be very resistant to change.
Community 2.1
Wheatgrass-Plains muhly/Sedge/Forb/Shrub/Conifer (<1%) Plant Community
Figure 11. SwLy-B PCP 2.1
This plant community is a result of continuous season-long grazing, heavy continuous grazing, or seasonal grazing without a change in season of use. The potential plant community is made up of approximately 70 percent grasses, 15 percent forbs, and 15 percent shrubs and trees. Dominant grasses include western wheatgrass, bearded wheatgrass, plains muhly, and sedges. Forbs contribute substantially to the biomass production in this plant community. Needlegrasses have decreased dramatically and may be nearly absent from the site. Forbs are common and diverse. Shrubs species including shrubby cinquefoil and common juniper have increased. Ponderosa pine or Black Hills spruce can be scattered throughout the site, but will not exceed 1 percent canopy cover. The herbaceous species within this plant community are well-adapted to grazing.
Transition 1A
State 1 to 2
Continuous season-long grazing or heavy continuous grazing will cause a transition from the Reference State to a plant community dominated by shortgrass species in the Shortgrass State. Ponderosa pine may increase on this site, but typically will not develop into canopy cover greater than 8 percent.
Restoration pathway 2A
State 2 to 1
Long-term prescribed grazing which provides growing season grazing deferment, along with stocking rates not exceeding carrying capacities and periodic fire or prescribed burning, can restore this plant community to the Reference State. The Shortgrass State can be resistant to change and grazing deferments, but favorable growing conditions will in time help to reestablish the plant community; however, management goals may not be achieved.