Rocky Hill 25-28" PZ
Scenario model
Current ecosystem state
Select a state
Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
Absence of disturbance and natural regeneration over time, may be coupled with excessive grazing pressure
More details -
Restoration pathway R2A
Adequate rest from defoliation, followed by reintroduction of historic disturbance regimes
More details -
Transition T2A
Absence of disturbance and natural regeneration over time, may be coupled with excessive grazing pressure
More details -
Restoration pathway R3A
Adequate rest from defoliation and removal of woody canopy
More details -
No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
State 1
Tall/Midgrass Savanna State
Description
The reference plant community for the Rocky Hill ecological site is a Tallgrass/Midgrass Savanna Community with a diverse forb component and a significant population of shrubs and trees. This site is dominated by tallgrasses including Indiangrass, big bluestem, and little bluestem. Sideoats grama is the predominant midgrass species. The most common forbs are bushsunflower, Mexican sagewort, Engelmann daisy, gayfeather, basketflower, western ragweed, and gray goldaster. Trees and shrubs are an important of the historic plant community as well. The most common trees include live oak, elm, and hackberry. Shrubs such as flameleaf sumac, skunkbush sumac, bumelia, elbowbush, lotebush, catclaw acacia, and pricklypear are found on the site as well.
The Little Bluestem Savanna Community occurs when little bluestem increases on the site, and becomes the dominant species as Indiangrass and big bluestem decrease. A viable population of the original tallgrasses is present. This is still a very productive plant community, but it has less diversity than the tallgrass savanna community. Midgrasses such as sideoats grama, Texas wintergrass, dropseeds, and silver bluestem occupy a significant part of the plant community. Species composition of forbs, shrubs, and trees remains stable in this phase.
In the Midgrass Community, tallgrasses decline. They are being replaced by midgrasses such as sideoats grama, Texas cupgrass, dropseeds, and Texas wintergrass. Lower successional forbs begin to replace some of the original perennial forbs. Large rocks and boulders are obvious, but bare ground is minimal. Remaining tallgrasses are usually found adjacent to larger rocks or in protected areas, but some still occur in the open areas. Density and canopy of shrubby species such as lotebush, bumelia, sumacs, pricklypear and yucca begins to increase.
Submodel
Description
The Midgrass/Shrub Community marks the drastic transition from a productive tallgrass and midgrass plant community to a site that is dominated by lower successional perennial grasses, shortgrasses, forbs, and annual species. Bare ground becomes more evident and begins to appear in the interspaces between the individual grass plants. This makes the site more susceptible to the invasion of undesirable brush and weed species from adjacent sites. Erosion becomes a concern, especially on the steeper slopes. Pricklypear, yucca, catclaw acacia, lotebush, and sumacs increase significantly and the site is invaded by mesquite. Due to the amount of rock on the soil surface, a few tallgrasses still exist between the rocks and in other inaccessible areas.
Submodel
Description
As the site continues to deteriorate to the Woodland State because of mismanagement and/or extreme climatic conditions, tallgrasses, midgrasses, and perennial forbs continue to decline and are replaced by opportunistic species that are more tolerant of grazing and drought. Herbaceous species are primarily limited to early successional perennial grasses and forbs, annual grasses and forbs, and sedges. The density and canopy of trees and shrubs is the dominant vegetation feature of the site. Sparse herbaceous vegetation is scattered among the rocks on the soil surface.
Submodel
Mechanism
Abusive grazing, resulting from overstocking and continuous grazing, leads to a drastic change in the herbaceous plant community. Higher successional midgrasses such as sideoats grama and Texas cupgrass are replaced by silver bluestem, dropseeds, buffalograss, and lower successional grasses including threeawns, Texas grama, red lovegrass, and annual grasses. Increased bare ground enables opportunistic forbs such as western ragweed, broomweed, and annuals to replace higher successional forbs. Elimination of fire from the ecosystem is a major cause of the significant increase in the frequency, density, and canopy of invasive shrubs such as mesquite, lotebush, pricklyash, catclaw acacia, pricklypear, and yucca.
Mechanism
Once the site has deteriorated to this state, it is no longer capable of recovering to the reference plant community through the implementation of management practices alone. Brush Management practices are needed to eliminate non-native species, control undesired native species, and reduce overhead canopy to allow understory species to establish and produce. At this stage, there is not a viable population or seed source of the original plant community, so Range Planting is needed to re-establish native grasses and forbs that were components of the original plant community. However, Brush Management and Range Planting are difficult and very expensive on this site because of the rough, rocky, and steep terrain. Labor-intensive hand treatment methods or aerial application may be the only options available for brush management and range planting on this site in some instances. If the original plant community can be restored, Prescribed Grazing and Prescribed Burning are essential to the recovery and maintenance of the desired plant community.
Relevant conservation practices
| Practice | External resources |
|---|---|
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Brush Management |
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Prescribed Burning |
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Range Planting |
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Prescribed Grazing |
Mechanism
The combination of long-term overstocking, continuous abusive grazing, and elimination of fire can eventually result in this site being dominated by trees and shrubs. In many cases, overstory and midstory canopies may exceed 40%. The understory plant community is characterized by sparse herbaceous vegetation consisting primarily of low successional grasses and forbs, shade tolerant species, and annuals. Soil erosion hazard is increased by the amount of bare ground, especially on steeper slopes.
Mechanism
Once the site has reached this stage, it is highly unlikely that the reference plant community can ever be restored in a reasonable time frame with the existing technology and management options. However, selected areas can be treated and managed to open up the canopy, establish beneficial vegetation, and manipulate the plant community to benefit wildlife habitat.
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Brush Management |
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Prescribed Burning |
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Range Planting |
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Prescribed Grazing |
Model keys
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The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.