Sandy 17-20" 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
- Transition T1C More details
- Transition T1D More details
- Transition T7A More details
- Restoration pathway R2A More details
- Transition T2A More details
- Transition T2B More details
- Transition T7A More details
- Restoration pathway R3A More details
- Transition T7A More details
- Transition T4A More details
- Transition T4B More details
- Transition T7A More details
- Restoration pathway R5A More details
- Transition T5A More details
- Transition T5B More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
Description
The Reference State (1.0) represents the best estimate of the natural range of variability that dominated the dynamics in the Sandy 17-20” PZ ecological site prior to European settlement. This site, in the Reference State, is dominated by warm-season grasses and sub-dominant cool-season grass. Forbs are common and diverse. Shrub species vary depending on precipitation and slope aspect. Ponderosa pine and Rocky Mountain juniper can grow naturally on some soils adjacent to sites that have established conifer plant communities. Grazing or the lack of grazing, fire, and drought are the major drivers between plant communities.
Submodel
Description
The Shortgrass Sod State (2.0) is dominated by shortgrass species and upland sedges. This state is the result of grazing management that does not provide adequate recovery time for tall- and mid-statured warm- and cool-season grasses. The hydrologic function of this state may be altered. Runoff is high, and infiltration is low. This state is very resistant to change through grazing management alone.
Submodel
Description
The Early Successional State (3.0) is dominated by weedy annuals and biennials, sand dropseed, blue grama, and field sagewort (green sagewort). This state is the result of heavy disturbance, such as frequent and severe defoliation from rodents, or heavy livestock concentrations coupled with grazing management that does not provide adequate time for recovery in the Reference State (1.0) or the Shortgrass Sod State (2.0). State 3.0 can also be the result of a high-intensity fire and subsequent soil erosion in the Conifer State (5.0).
The hydrologic function is also likely to be dramatically altered. Runoff is high, and infiltration is low. The Early Successional State (3.0) is very resistant to change through grazing management alone.
Submodel
Description
The Native/Invaded State (4.0) has been invaded by non-native cool-season grasses but not at the levels to which the plant community is dominated by these species. The majority of species are native to this site, including cool-season mid-grasses, warm-season mid- and tall-grasses, and warm-season short-grasses. Forbs are common and diverse, and shrubs vary in amounts. The Native/Invaded State is the result of long-term non-use in combination with above-average precipitation or the result of continuous seasonal grazing or continuous season-long grazing. Because of the invasion and persistence of non-native cool-season grasses, this state is unlikely to return to the Reference State (1.0).
Submodel
Description
The Conifer State (5.0) develops if ponderosa pine, Rocky Mountain juniper, or both become established and expand on this site. As conifer canopy cover increases, the herbaceous component declines and more bare ground is exposed. As competition from herbaceous species decrease, conifers tend to establish more readily. Grazing can contribute to this transition, but the transition may also develop independently without human influence other than fire suppression and through unique climatic conditions.
Ponderosa pine regeneration in MLRA 64, specifically on the Pine Ridge escarpment, should not be directly compared to that in the Black Hills (MLRA 62) where ponderosa pine regeneration readily occurs following fire or timber harvest. MLRA 64 is much drier, and optimal conditions for ponderosa pine germination and establishment are not common. In some ways, the regeneration of ponderosa pine is more similar to the regeneration found in the drier American Southwest, where germination and establishment are strongly episodic (pulses) and at least partly controlled by climate. For example, ponderosa pine in the Southwest require a warm wet spring and an above-average water supply throughout the year for germination and seedling establishment. One study from northern Arizona showed a large cohort of ponderosa pine that established within a 2-year period between 1919 and 1920 when an optimal combination of temperature and precipitation factors occurred. This episodic event was not repeated again for 73 years (Savage et al., 1996). Successful establishment of ponderosa pine in the Great Plains is unpredictable and requires a combination of sufficient seed availability, adequate year-long soil moisture, a lack of persistent drought, and no fire that affects seedling survival (Kaye et al., 2010).
USDA and the Nebraska National Forest and Grasslands categorize ponderosa pine stand characteristics into six Vegetation Structural Stages (VSS). VSS is a method of describing forest age and tree size from seedling to old forests (M.D. Gould, personal communication, 2019).
VSS 1 (Grass/Forb): Forest openings created by disturbances, such as fire or wind throw, 0”–0.9” diameter at breast height (DBH).
VSS 2 (Shrubs/Seedlings): Developmental stage dominated by tree seedlings, saplings (1”–4.9” DBH), and shrub species.
VSS 3 (Sapling/Pole): Developmental stage dominated by young trees (5”–11.9” DBH).
VSS 4 (Mature): Trees that are larger and older than VSS 3 (12”–17.9” DBH).
VSS 5 (Late Successional): Trees 18”–23.9” DBH.
VSS 6 (Late Successional): Trees 24” DBH and greater. This stage is not likely to exist on the Pine Ridge escarpment (M.D. Gould, personal communication, 2019).
These stages can be subdivided into three canopy-closure classes: (a) less than 40 percent, (b) 40 to 70 percent, and (c) greater than 70 percent. As a general rule, the higher the percentage of cover, the higher the potential of catastrophic fire.
These vegetation structural stages are referenced in the plant community narratives and state-and-transition model.
Submodel
Description
Any plant community can transition to the Disturbed State (6.0). The two separate vegetative plant communities found in this state are highly variable. They are derived through different management scenarios and are not related by succession. Infiltration, runoff, and soil erosion vary depending upon the vegetation on the site.
Submodel
Mechanism
Continuous seasonal grazing, continuous season-long grazing without change in season of use, or heavy grazing in combination with drought convert the Reference State (1.0) to the Shortgrass Sod State (2.0).
Mechanism
Frequent and severe defoliation or heavy disturbance, including usage as livestock feeding areas, prairie dog towns, and calving pastures, transition the Reference State (1.0) to the Early Successional State (3.0).
Mechanism
Invasion of non-native cool-season grasses, continuous seasonal grazing, continuous season-long grazing, long-term light grazing, or extended periods of non-use and no fire transition the Reference State (1.0) to the Native/Invaded State (4.0).
Mechanism
Long-term fire suppression, favorable climatic conditions that allow for pine regeneration and establishment, expansion of conifers, and time transition the Reference State (1.0) to the Conifer State (5.0).
Mechanism
Heavy disturbance, including soil erosion, tillage, abandonment of cropland, or seeding to improved pasture species, results in a transition to the Disturbed State (6.0).
Mechanism
Long-term prescribed grazing that includes proper stocking rates, change in season of use, and adequate time for plant recovery following grazing may convert this plant community to the Reference State (1.0). A return to normal precipitation patterns following drought helps with recovery. This transition may not be rapid or meet management objectives.
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Prescribed Grazing |
Mechanism
Frequent and severe defoliation or heavy disturbance, including usage as livestock feeding areas, prairie dog towns, and calving pastures, transitions the Shortgrass Sod State (2.0) to the Early Successional State (3.0).
Mechanism
Long-term prescribed grazing that includes proper stocking rates, change in season of use, and adequate time for plant recovery following grazing and the invasion of non-native cool-season grasses transition the Shortgrass Sod State (2.0) to the Native Invaded State (4.0). A return to normal precipitation patterns following drought will help facilitate this transition.
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Prescribed Grazing |
Mechanism
Heavy disturbance, including soil erosion, tillage, abandonment of cropland, or seeding to improved pasture species, results in a transition to the Disturbed State (6.0).
Mechanism
Removal of any management-induced disturbance coupled with long-term prescribed grazing that includes proper stocking rates, change in season of use, and adequate time for plant recovery after grazing may convert this plant community to the Shortgrass Sod State (2.0). A return to normal precipitation patterns following drought helps with recovery. This transition may not be rapid or meet management objectives.
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Prescribed Grazing |
Mechanism
Heavy disturbance, including soil erosion, tillage, abandonment of cropland, or seeding to improved pasture species, results in a transition to the Disturbed State (6.0).
Mechanism
Continuous season-long grazing moves the Native/Invaded State to the Shortgrass State 2.0. Heavy grazing in combination with expended periods of drought will also facilitate this transition. During this transition, the plant community can have the appearance of a mosaic, with sod and mixed-grass communities intermingled. As the plant community becomes dominated by shortgrasses, runoff increases and infiltration decreases.
Mechanism
Frequent and severe defoliation or heavy disturbance, including usage as livestock feeding areas, prairie dog towns, and calving pastures, results in a transition to the Early Successional State (3.0).
Mechanism
Heavy disturbance, including soil erosion, tillage, abandonment of cropland, or seeding to improved pasture species, result in a transition to the Disturbed State (6.0).
Mechanism
Prescribed burning or wildfire followed by long-term prescribed grazing move this plant community towards the herbaceous dominated Reference State (1.0). Mechanical removal of pine and juniper, through managing brush, harvesting timber, or thinning, followed by long-term prescribed grazing may also allow the understory to develop and transition to the Reference State (1.0). Trees on the steeper escarpments and in the deeper canyons may escape most fires and provide a seed source for ponderosa pine expansion in the future. This transition is most likely to occur from the Ponderosa Pine-Juniper Cover/Herbaceous Understory (VSS: 2-3) Plant Community (5.1).
Relevant conservation practices
| Practice | External resources |
|---|---|
|
Brush Management |
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Prescribed Burning |
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Prescribed Grazing |
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Forest Stand Improvement |
Mechanism
High-intensity fire and, in some cases, excessive soil erosion cause a transition from the Conifer State (5.0) to the Early Successional State (3.0). Initially, weedy species, including annual grasses and forbs, common mullein, and thistles, become established. Within a relative short time, however, upland sedges and shortgrasses dominate the plant community. Trees on the steeper escarpments and in the deeper canyons may escape most fires and provide a seed source for ponderosa pine expansion in the future. This transition can occur from any plant community within the Conifer State (3.0) but is most likely from the Ponderosa Pine-Juniper > 20% Canopy Cover/Sedge/Forb (VSS: 4-5) Plant Community (5.2).
Mechanism
The invasion of non-native cool-season grasses and either wild fire or prescribed burning move this plant community towards the herbaceous dominated Native/Invaded State (4.0). Mechanical removal of pine and juniper, through managing brush, harvesting timber, or thinning, may also allow the understory to develop and transition to the Native/Invaded State (4.0). Even though non-native cool-season grasses have invaded this plant community, long-term prescribed grazing can maintain this plant community in a productive and sustainable state. The long-term prescribed grazing should include proper stocking, change in season of use, and adequate recovery following grazing events. Trees on the steeper escarpments and in the deeper canyons may escape most fires and provide a seed source for conifer expansion in the future. This transition is most likely to occur from the Ponderosa Pine-Juniper/Shrubs/Herbaceous Understory (VSS: 2-3) Plant Community (5.1).
Model keys
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