Sandstone Hill 25-32 PZ
Scenario model
Current ecosystem state
Select a state
Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Transition T1B More details
- Restoration pathway R2A More details
- Transition T2A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
State 1
Savannah State
Description
The Savannah State consists of two plant communities: the Midgrass Savannah Community (1.1) and the Shortgrass Community (1.2). The Midgrass Savannah Community occurred on this ecological site in a dynamically shifting mosaic over time with the Shortgrass Savannah Community. The two communities in the Savannah State shifted between one another depending on the frequency and intensity of grazing, drought, and other growing season stresses. Unlike most other Central Basin sites, the woody component is relatively constant and not driven by fire. The understory has large gaps and limited production so that it does not provide continuous fine fuels. Without continuous fine fuels, fires rarely burn hot enough to reduce the canopy cover of mature single-stemmed trees and shrubs. Fire has some influence on this site but mainly along the “seams” where the fine fuels are. Grazing management can drive the shift between the two communities in the Savannah State.
Prior to European settlement, Sandstone Hill sites had a savannah appearance with open areas dominated by midgrasses (little bluestem and sideoats grama) interspersed with scattered mottes dominated by oaks. The Midgrass Savannah (1.1) may have up to 15 percent canopy cover while the Shortgrass Savannah (1.2) will have up to 20 percent woody canopy. This transition to the Shortgrass Savannah Community (1.2) is dependent on the degradation of the herbaceous community. With proper grazing and favorable climate conditions, little bluestem and other midgrasses will remain the dominant component of the understory.
Submodel
Description
This state contains a single community, the Shrubland Community (2.1). The Shrubland State (2.0) is characterized by a shortgrass-dominated understory with scattered trees and shrubs. Bare ground and erosion will increase as the understory is degraded. Forage production will decline.
The hardwoods that made up a portion of the plant community in the Savannah State will likely be present in the Shrubland State unless they were removed by brush control. The transition to the Shrubland State will probably not cause an increase in the number or biomass production of hardwoods. However, because the production of herbaceous species will decline, the relative species composition of shrubs and trees will increase. If the hardwoods were removed, they will be slow to reestablish.
Trees and shrubs remain a part of the community, but woody species composition may vary greatly. The woody component may be similar to the woody component in the Midgrass Savannah Community (1.1). Mature oaks occur in mottes with scattered brush, though the woody component is more frequently made up of many species of widely scattered shrubs.
Submodel
Description
This state includes a single community, the Eroded Community (3.1), which is characterized by significant soil loss.
The Eroded Community is a common community on Sandstone Hill sites. Unless managers practice effective, ongoing grazing management this community will remain. Because of the availability of invasives with low palatability, this site rarely stays barren. There are examples that are degraded but not yet dominated by brush but these examples tend to be quickly reinvaded by annual forbs and grasses as well as low-palatability shrubs.
Much of this site has been disturbed to the point that significant soil loss has occurred. Once the A Horizon is eroded (partially or completely), nutrient cycling is disrupted and difficult to restore. Loss of soil is accompanied by disruption (or loss) of soil mycorrhiza. Steeper portions of this site are subject to severe erosion when the plant cover is disturbed.
The Eroded State has the potential to be a terminal state. Due to the relatively high risk of severe soil erosion of the sandy loam soils, this site can erode to the point where there is a loss of soil functionality. When this level of erosion occurs, the site loses soil structure, soil fertility, organic matter, and/or soil microflora. There are examples of the loss of the A horizon and some with the soil eroded to bedrock. Once the site loses soil horizons or soil functions, it is very difficult or impossible to return the site to one of the other States, resulting in State 3 being a terminal state. Return to another state will be the result of site restoration efforts, not typical management changes.
The likelihood of returning to the Savannah State (1.0) is improbable, and restoration would require extensive and intensive restoration efforts. Range restoration techniques can be used to restore this site on high-value lands (such as mining reclamation). This will likely require replacement of topsoil and planting of native species, though the site is often too shallow for effective reseeding. A return to reference condition should not be expected, and savannah conditions are only possible with continued inputs and management over a long period. Without periodic fire or brush management, woody species may increase and the site may resemble the woody state.
Submodel
Mechanism
The drivers for Transition T1A are improper grazing management and lack of fire or brush control. The understory will be dominated by shortgrasses, unpalatable grasses and forbs, and annual grasses and forbs. This transition is indicated by the decrease of dominant reference state midgrasses (little bluestem and sideoats grama) to less than 10 percent of species composition of the herbaceous community. Once these species are lost from the community or present only in trace amounts, grazing management usually cannot create a shift back to the reference community.
Regardless of the composition and vigor of the herbaceous component, this community will shift to the Shrubland State without effective brush control. Without adequate brush control, it will shift to the Shrubland Community in a relatively short time (5-15 years). The open areas of the savannah will have shrubs sprout every year. As these plants mature, they will fill in the open areas. Once canopy cover of woody species reaches 25 percent, the site has shifted to the Shrubland Community.
This shift can occur even with proper grazing management and if the herbaceous component remains vigorous. Brown and Archer (1999) concluded that even with a healthy and dense stand of grasses, woody species would populate the site and eventually dominate the community. As the herbaceous understory is degraded to shortgrasses, fine fuel load declines, reducing the ability to carry a brush-killing fire. This increases the risk that the site will transition to the Shrubland State (2.0)
Mechanism
Severe soil degradation can be caused by improper grazing or other soil-disturbing activities including rock harvest. In some cases, this erosion can be extreme enough to result in the loss of the entire soil layer. Long-term drought may also trigger this transition from the Savannah State (1.0) or exacerbate the effects of inappropriate grazing management on the Sandstone Hill site.
When the Sandstone Hill site is subjected to inappropriate management, the effects may be seen in a loss of vegetative cover followed by a loss of soil. In some cases, this erosion can be extreme enough to result in the loss of the A (and even B) horizons. Severe soil degradation can be caused by abusive grazing, mismanaged brush control, or other soil-disturbing activities including rock harvest or gravel mining. This loss of soil accompanies the loss of the vegetative cover associated with this site.
Mechanism
The driver for Restoration Pathway R2A is fire and/or brush control combined with the restoration of the herbaceous community. Establishment of native grasses is difficult and dependent upon natural seeding from remnant patches and seed banks. This site is often too shallow for effective reseeding. Restoration of the Shortgrass Savannah State (2.0) to the Savannah State (1.0) requires less energy input than restoring from the Shrubland Community (2.1).associated sites.
A long-term prescribed fire program may sufficiently reduce brush density to a level below the threshold of the Savannah State (1.0). Proper grazing management and stocking rates maintain the herbaceous layer in this state. With proper grazing management, midgrasses can regain dominance on the site and undesirable trends in soil organic matter, fertility, temperature, and erosion can be arrested and reversed. The extent to which the original Midgrass Savannah Community (1.1) can be re-established will depend on the extent to which soil physical and chemical properties were altered during retrogression (Heitschmidt and Stuth 1991).
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Brush Management |
|
|
Prescribed Burning |
|
|
Prescribed Grazing |
Mechanism
The driver for this transition is abusive management. The effects may be seen in a loss of vegetative cover followed by a loss of soil. In some cases, this erosion can be extreme enough to result in the loss of the A horizons. Severe soil degradation can be caused by abusive grazing or other soil-disturbing activities including rock harvest. This loss of soil results in or accompanies the loss of the vegetative cover associated with this site. Long-term drought may also trigger this transition from the Shrubland State (2.0) or exacerbate the effects of inappropriate grazing management on the Sandstone Hill site.
Model keys
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