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 mountain pine beetle infestations 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.
Fire, or the lack of fire, and introduced non-native cool season grasses, are major drivers, along with grazing and haying, that shape this site as well as adjacent ecological sites. This Loamy site does not appear to be as susceptible to conifer encroachment as other Loamy sites in MLRA 62, however it can occur on the margins. Aspen may also occur on the margins between forest sites and the Loamy site in LRU-B. Kentucky bluegrass, timothy and smooth brome are common cool season grass species throughout MLRA 62. Because the Black Hills have higher precipitation amounts and cooler spring and fall periods than the surrounding MLRA 61, these non-native cool season grasses can easily invade and become established on this site. Improper grazing management, and non-use and/or no fire can cause these species to become the dominant species in the plant communities.
Changes will occur in plant communities due to short-term weather variations, impacts of native and/or exotic plant and animal species. Management actions, severe disturbances, such as periods of well-below average precipitation, severe defoliation, excessive haying or no fire and no use can also cause significant shifts in plant communities and/or species composition.
This site developed under Black Hills climatic conditions with short-term weather variations, light to severe grazing by bison, elk insects 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.
The Reference State illustrate what is thought to have existed prior to European settlement. It is very difficult to locate a Reference plant community with the introduction and spread of non-native cools season grasses. Plant community phase 2.1 is most similar to the Reference State but because of the persistence of non-native cools season grasses a restoration pathway to the Reference State is not believed to be achievable.
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. The Reference State is unlikely to occur with the introduction of non-native cool-season grasses which are common throughout the MLRA. This site was dominated by cool-season grasses, a diverse forb component and various shrubs. In pre-European times the primary disturbances included fire, insects and grazing by large ungulates and small mammals. Favorable growing conditions occurred during the spring, and warm months of June and July. Routine and/or occasional fires, reduced tree cover and contributed to the ecological processes that maintained the reference plant community.
Community 1.1
Needlegrass-Rhizomatous wheatgrass/Forbs/Shrubby cinquefoil
Figure 8. Loamy LRU-B Central High Country - Near PCP 1.1
Interpretations are based primarily on the Needlegrass-Rhizomatous wheatgrass/Forb/Shrubby cinquefoil plant community phase. This is also considered to be the Reference or historic plant community. The potential vegetation consists of 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 2,700 lbs. /Ac. The community is dominated by cool-season grasses including Richardson’s needlegrass, green needlegrass, porcupine grass, bearded wheatgrass, slender wheatgrass, Columbia needlegrass, western wheatgrass and Pumpelli bromegrass. The dominant warm-season grass is prairie dropseed. Other grasses and grass-like include; prairie Junegrass and Richardson’s sedge. Forbs include goldenrod, lupine, American vetch, yarrow, prairie smoke, and blue-eyed grass. The dominant shrub is shrubby cinquefoil. This plant community was 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.
State 2
Native Invaded State
This state represents what is most typically found on this site. The natural range of variability is influences by the presence of non-native cool-season grasses, especially Kentucky bluegrass, smooth brome and timothy that can dominate the dynamics of this ecological site.
Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30 percent of the plant community and native grasses represent less than 40 percent of the plant community composition. Plant communities dominated by Kentucky bluegrass have significantly less cover and diversity of native grasses and forb species. (Toledo, D. et al., 2014). Proper grazing management and periodic burning will maintain the productivity of this state. Heavy grazing without adequate recovery, excessive haying, extended periods of non-use and no fire can put this state at risk of crossing a threshold.
Community 2.1
Needlegrass-Rhizomatous wheatgrass-Bluegrass-Smooth brome/Red clover-Forbs/Cinquefoil
Figure 9. Loamy LRU-B (Central High Country) PCP 2.1
This plant community phase most closely resembles the PCP 1.1; however, non-native cool-season grasses have invaded the site and will persist in the plant community under the current Black Hills climatic conditions.
The potential vegetation consists of about 70 percent grass and grass-like plants, 20 percent forbs, and 10 percent shrubs. Total annual production for a normal growing year is variable due to the amount of non-native cool-season grasses, but could average approximately 2,400 lbs./ac. The community is dominated by cool-season grasses. The dominant cool-season grasses include Richardson’s needlegrass, green needlegrass, bearded wheatgrass, and porcupine grass. Kentucky bluegrass, smooth brome, and other non-native cool-season grasses can make up 5 to 10 percent of the plant community. Other grasses include prairie dropseed, slender wheatgrass, and Richardson’s sedge. Forbs are diverse and include red clover, yarrow, biscuit root, cinquefoil, prairie smoke, goldenrod, lupine, and cudweed sagewort. The dominant shrub is Shrubby cinquefoil. This plant community is productive and resilient to disturbances such as drought and fire. It is a sustainable plant community in regards to soil/site stability, watershed function, and biological integrity. Management strategies must include techniques that will not cause Kentucky bluegrass, smooth brome, and other non-native cool-season grasses to increase significantly as this could put the plant community at risk of transition to the Introduced/Invaded State.
State 3
Introduced/Invaded State
This state is the result of invasion and dominance of introduced species. This state is characterized by the dominance of timothy and smooth brome into the system. These species in combination will out-compete the native needlegrasses and wheatgrasses and replace them in the plant community. The nutrient cycle is impaired, resulting in a higher level of nitrogen which favors the introduced species. Studies indicate that soil biological activity is altered, and this shift apparently exploits the soil microclimate and encourages growth of the introduced grass species. Once the threshold is crossed, a change in grazing management alone cannot cause a reduction in the invasive grass dominance.
Community 3.1
Timothy-Smooth brome/Red clover-Stiff goldenrod
Figure 10. Loamy LRU-B (Central High Country) PCP 3.1
This plant community is dominated by timothy and smooth brome. It developed under heavy and continuous season-long grazing, no use and no fire or excessive haying.
The plant community is made up of approximately 85 percent grasses and grass-like species, 10 percent forbs, and 0-2 percent shrubs. Total annual production is variable but may be similar to the interpretive plant community. This will depend on species composition and management. Biological diversity is greatly diminished, and the energy flow and nutrient cycle is greatly altered. This plant community is very resilient and resistant to change.
State 4
Early Seral State
This state is the result of very heavy disturbance such as cropping or concentrated livestock feeding areas. This state can develop as a result of invasion by highly competitive weed species such as Canada thistle, hound’s tongue, leafy spurge, or knapweeds. Heavy grazing can also push an at-risk plant community phase to this state. In most cases, this phase is dominated by annual and/or pioneer perennial species. The percentage of bare ground typically is much higher than on any other plant community phase.
Community 4.1
Pioneer Perennial/Introduced Species, Bare Ground
This plant community developed under continuous heavy grazing or heavy disturbances such as heavy use areas, abandoned cropland, and livestock feeding areas. The potential plant community is very variable. The percentage of bare ground can be very high in this phase of the plant community. This plant community is susceptible to invasion of Canada thistle and other non-native species because of the relatively high percentage of bare ground.
State 5
Conifer State
This state is greatly influenced by conifers: primarily ponderosa pine, but spruce and birch can also be present. The ponderosa pine canopy was found to significantly reduce precipitation reaching the forest floor by an average of 30 percent due to interception in areas of intermediate and dense canopy (Wrage, 1994). This state will develop when conifers encroach onto the site from adjacent forest sites or ecological sites that have been invaded. Encroachment and the establishment of conifers on this site is primarily the result of no fire and grazing management that reduced the competitive nature of the native herbaceous plant community. Once conifers become established on this site, non-native cool-season grasses will increase, especially in the shaded areas.
Community 5.1
Native-Introduced Grasses/15 to 30% Ponderosa Pine
This plant community phase is the result of no use and no fire, or on sites that have had heavy continuous grazing resulting in increased bare ground where pine seedlings can become established. The potential vegetation is approximately 60 percent grasses and grass-like plants, 5 percent forbs, 2 -5 percent shrubs and up to 30 percent conifers. The majority of grasses will be cool-season species with Kentucky bluegrass increasing because of its tolerance to shade.
Transition 1A
State 1 to 2
Invasion and/or encroachment of non-native cool-season grasses such as Kentucky bluegrass, smooth brome, and timothy; no use and no fire; continuous season-long grazing or heavy continuous grazing; and/or excessive haying led this state over a threshold to the Native/Introduced State 2.0.
Transition 6A
State 1 to 4
This transition can occur from States 1, 2, 3 to the Early Seral State with heavy disturbance including frequent and severe defoliation, heavy continuous grazing, excessive haying, livestock feeding areas, or cropping.
Transition 2A
State 2 to 3
Continuous season-long grazing, heavy continuous grazing and/or excessive haying, or no use or no fire can cause a transition to a plant community phase that is dominated by non-native cool-season grasses.
Transition 6A
State 2 to 4
This transition can occur from States 1, 2, 3 to the Early Seral State with heavy disturbance including frequent and severe defoliation, heavy continuous grazing, excessive haying, livestock feeding areas, or cropping.
Transition 2B
State 2 to 5
Encroachment of conifers due to no use and or no fire can transition this plant community to a conifer-dominated state.
Restoration pathway 3A
State 3 to 2
Mechanical and/or chemical treatment followed by seeding of native cool-season grasses may restore the structural functional groups found in the Native/Introduced State. Subsequent management including long-term prescribed grazing and possibly prescribed burning may in time help to re-establish the plant community phase 2.1, however, management goals may not be achieved. This restoration pathway can take many years and in the end may not be successful.
Transition 6A
State 3 to 4
This transition can occur from States 1, 2, 3 to the Early Seral State with heavy disturbance including frequent and severe defoliation, heavy continuous grazing, excessive haying, livestock feeding areas, or cropping.
Restoration pathway 4A
State 4 to 2
Removal of severe grazing disturbance (frequency and intensity), normal precipitation, long-term prescribed grazing, and time. Chemical and/or mechanical treatment followed by seeding of native species may accelerate the re-establishment of structural/functional groups similar to PCP 2.1; however, the resulting plant community may not achieve management goals. This restoration pathway can take many years and in the end may not be successful.
Restoration pathway 5A
State 5 to 2
Reintroduction of fire or prescribed burning and/or mechanical brush management to remove encroachment, followed by long term prescribed grazing to promote re-establishment of native species may accelerate the re-establishment of structural/functional groups similar to PCP 2.1; however, the resulting plant community may not achieve management goals.