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 and haying, that shape this site as well as adjacent ecological sites. The Valley Loamy site does not appear to be as susceptible to conifer encroachment as other “upland” Loamy sites in MLRA 62, but it can occur. Aspen commonly occur along the margins of this site, adjacent to forested sites. Kentucky bluegrass, timothy, and smooth brome are common cool-season grass species throughout MLRA 62. Because the Black Hills have higher precipitation amounts and have cooler spring and fall periods, non-native cool-season grasses can easily become established and become the dominant species on this site.
The Reference State illustrates what is thought to have existed prior to European settlement. It is very difficult to locate a Reference plant community due to the introduction and spread of non-native cool-season grasses. Plant community phase 2.1 is most similar to the Reference State, but because of the persistence of non-native cool-season grasses, a restoration pathway to the Reference State is not believed to be achievable.
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 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 nearly equal portions of cool- and warm-season grasses, a diverse forb component, and various shrubs. In pre-European settlement 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 removed pine encroachment, and contributed to the ecological processes that maintained the Reference plant community.
Community 1.1
Big bluestem- Rhizomatous wheatgrass-Needlegrass/Mixed Shrubs
Interpretations are primarily based upon the Big bluestem-Rhizomatous wheatgrass-Needlegrass/Mixed Shrubs plant community phase. This also is considered to be the Reference or historic plant community. The potential vegetation is about 75 percent grass and grass-like plants, 15 percent forbs, and 10 percent shrubs. Total annual production for a normal growing year is approximately 3,000 lbs./Ac. The community has nearly equal percentages of cool-season and warm-season grasses. The dominant warm-season grasses are big bluestem, prairie dropseed, and switchgrass. The principal cool-season grasses include western wheatgrass, bearded wheatgrass, slender wheatgrass, green needlegrass, Columbia needlegrass, and needleandthread. Other grasses and grass-like include Indiangrass, prairie Junegrass, porcupine grass, threadleaf sedge, and Richardson’s sedge. Forbs include stiff sunflower, stiff goldenrod, lupine, American vetch, yarrow, prairie smoke, and prairie coneflower. The dominant shrubs are western snowberry, hawthorn, leadplant, and prairie rose. Aspen clones are common along the margin of the Valley Loam site adjacent to forested sites. This plant community was productive and resilient to disturbances such as drought and fire. It was a sustainable plant community in regard to soil/site stability, watershed function, and biological integrity.
Community 1.2
Rhizomatous wheatgrass-Needlegrass/Mixed Shrubs
This plant community phase is the result of continuous season-long grazing without adequate recovery or continuous seasonal grazing during the early summer growing season every year. These grazing patterns will reduce the percentage of warm-season grasses and increase the percentage of cool-season grasses. Wet spring and fall precipitation patterns and dry summer months, in combination with grazing, can also cause a shift in the plant community toward a cool-season -dominated community. The removal of other natural disturbances, such as periodic fire and no-use, can cause a shift in the plant species to create a cool-season grass-dominated plant community. The potential vegetation consists of approximately 70 percent grasses and grass-likes, 15 percent forbs, and 15 percent shrubs and trees. The community is dominated by cool-season grasses, including western wheatgrass, bearded wheatgrass, slender wheatgrass, green needlegrass, needleandthread, and Columbia needlegrass. Warm-season grasses include big bluestem, prairie dropseed, and blue grama. Other grasses and grass-like plants in this phase include porcupine grass, prairie Junegrass, threadleaf sedge, and Richardson’s sedge. Forbs include goldenrod species, lupine, yarrow, prairie smoke, and prairie coneflower. Dominant shrubs include western snowberry, prairie rose, and hawthorn. Aspen clones are common along the margin of the Valley Loam site adjacent to forested sites. This plant community was productive and resilient to disturbances such as drought and fire. It’s a sustainable plant community in regard to soil/site stability, watershed function, and biological integrity.
Pathway 1.1A
Community 1.1 to 1.2
Long-term moderate to heavy grazing pressure without adequate recovery time, extended periods of below normal precipitation, and/or fire followed with intensive grazing by livestock or wildlife can move this PCP 1.1 to PCP 1.2.
Pathway 1.2A
Community 1.2 to 1.1
Grazing that provides adequate recovery, normal to above normal precipitation, and a normal fire regime without intensive grazing by livestock or wildlife can move PCP 1.2 back to PCP 1.1.
State 2
Native/Invaded State
This state represents what is most typically found on this site. The natural range of variability is influenced by the presence of non-native cool-season grasses, especially smooth brome, Kentucky bluegrass, and timothy that can dominate the dynamics of this ecological site. Proper grazing management and periodic burning will maintain the productivity of this state. Heavy grazing without adequate recovery, excessive haying, and extended periods of non-use and no fire can put this state at risk of crossing a threshold to the Introduced/Invaded State.
Community 2.1
Rhizomatous wheatgrass-Big bluestem-Needlegrass-Bluegrass/Mixed Shrub
Figure 9. Valley Loam Plant Community Phase 2.1
This plant community phase 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 75 percent grass and grass-like plants, 15 percent forbs, and 10 percent shrubs and trees. Total annual production for a normal growing year is approximately 2,800 lbs./Ac. The community is dominated by cool-season grasses and tall and mid-height warm-season grasses. The dominant cool-season grasses include western and bearded wheatgrass, green needlegrass, needleandthread, and porcupine grass. Kentucky bluegrass and/or other non-native cool-season grasses can make up 2 to 5 percent of the plant community. Dominant warm-season grasses are big bluestem, prairie dropseed, and switchgrass. Other grasses include slender wheatgrass, Richardson’s needlegrass, thread-leaf sedge, and Richardson’s sedge. The dominant shrubs are western snowberry, leadplant, hawthorn, and rose. This plant community is productive and resilient to disturbances such as drought and fire. It is a sustainable plant community in regard to soil/site stability, watershed function, and biological integrity. Management strategies must include techniques that will not cause Kentucky bluegrass 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.
Community 2.2
Rhizomatous wheatgrass-Bluegrass-Smooth brome/Weedy forbs/Mixed Shrubs
This plant community evolved under continuous season-long grazing, or seasonal grazing with no change in season of use, or no use and no fire, or heavy continuous grazing that exceeds carrying capacity, or excessive haying. This plant community phase is made up of approximately 85 percent grass and grass-like plants, 10 percent forbs, and 5 percent shrubs and trees. The community is dominated by cool-season grasses, with most of the warm-season grass component replaced by smooth brome and Kentucky bluegrass, along with other non-native cool-season grasses. The dominant cool-season grasses include western and bearded wheatgrass, Richardson’s needlegrass. Kentucky bluegrass or other non-native cool-season grasses can make up 10 to 20 percent of the plant community. Forbs may tend to be weedy and invasive. Common shrubs include western snowberry and green sagewort. This plant community is at risk of crossing a threshold to the Introduced/Invaded State.
Pathway 2.1A
Community 2.1 to 2.2
Non-use and no fire and/or continuous season-long grazing or seasonal grazing occurring at the same time every year, or heavy continuous grazing or excessive haying will cause an increase in non-native cool-season grass species moving this plant community to PCP 2.2.
Pathway 2.2A
Community 2.2 to 2.1
Prescribed grazing and forage harvest management that provided adequate recovery and change in season of use, along with normal precipitation regime and fire may reduce the percent of non-native cool-season grasses in PCP 2.2 and restore the tall warm-season component typical of PCP 2.1.
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 smooth brome, Kentucky bluegrass, and timothy in the plant communities. These species will out-compete the native bluestems, needlegrasses, and wheatgrasses and replace them in the plant community. The nutrient cycle is impaired, which results in a higher level of nitrogen that 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. Preliminary studies 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).
Community 3.1
Smooth brome-Kentucky bluegrass /Weedy forbs/Mixed Shrubs
Figure 10. Valley Loam Plant Community Phase 3.1
This plant community is dominated by smooth brome, Kentucky bluegrass, and/or other non-native cool-season grasses making up 30 percent or more of the plant community. This plant community evolved under no use and no fire, or with heavy continuous season-long grazing, or seasonal grazing with no change in season of use, or excessive haying.
This plant community is made up of approximately 85 percent grasses and grass-like species, 10 percent forbs, and 5 percent shrubs. Dominant grasses include Kentucky bluegrass, smooth brome, and possibly timothy. Rhizomatous wheatgrasses and some needlegrasses may still be found in the plant community. Forbs commonly found in this plant community include cudweed sagewort, goldenrod, and western ragweed. Production will be significantly reduced when compared to the interpretive plant community. The period when palatability is high is relatively short, as smooth brome and Kentucky bluegrass matures rapidly. Energy capture also is reduced. Runoff is high and biological activity in the soil likely is reduced significantly in this phase.
State 4
Early Seral State
This state is the result of very heavy disturbance such as cropping, concentrated livestock feeding areas, or rodent activity. 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 also can 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 made up of 60-80 percent grasses and grass-like species, 15 to 35 percent forbs, and 2 to 5 percent shrubs. The percentage of bare ground can be very high in this plant community. The dominant grass often is smooth brome and Kentucky bluegrass. Other grasses may include annual bromegrass (field brome and cheatgrass), sedge, sand dropseed, and western wheatgrass. The dominant forbs include fetid marigold, sweetclover, western ragweed, cudweed sagewort, and other invasive species. The dominant shrubs include fringed sagewort and broom snakeweed. A wide variety of other early seral plant species can occupy this site in varying amounts. This plant community is susceptible to invasion of Canada thistle and other non-native species because of the relatively high percentage of bare ground.
Transition 1A
State 1 to 2
Invasion and/or encroachment of non-native grasses such as Kentucky bluegrass, smooth brome, and timothy, and disruption of natural disturbance regimes, typically as a result of fire suppression following settlement, led this state over a threshold to the Native/Introduced State 2.0.
Transition 2A
State 2 to 3
Introduction or increase of non-native cool season grass species in the plant community. Non-use and no fire. Excessive haying of native grass species and or heavy continuous grazing. This transition is most likely going to occur from PCP 2.2
Transition 2B
State 2 to 4
Severe and frequent defoliation, which can be exacerbated by drought and/or additional livestock or wildlife use. Heavy disturbance areas, including livestock feeding areas and cropping, also can cause this transition to the Early Seral State.
Restoration pathway 3A
State 3 to 2
Early season prescribed burning followed by long term prescribed grazing to promote establishment of native species. Chemical and/or mechanical treatment followed by seeding of native species may accelerate the reestablishment of structural functional groups similar to PCP
2.1 , but the resulting plant community may not achieve management goals. This restoration pathway can take many years and may not be successful in the end.
Transition 3A
State 3 to 4
Severe and frequent defoliation, livestock feeding, heavy disturbance, excessive haying and cropping will push this plant community to the Early Seral State.
Restoration pathway 4A
State 4 to 2
Removal of severe grazing disturbance (frequency and intensity), normal precipitation and fire regime, and time. Chemical and/or mechanical treatment followed by seeding of native species may accelerate the reestablishment 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 may not be successful in the end.
Transition 4A
State 4 to 3
Removal of severe grazing disturbance (frequency and intensity) and normal precipitation regime. Chemical and/or mechanical treatment followed by seeding of native and/or introduced species can transition this plant community back to the Introduced/Invaded State.
