Loamy Terrace
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Transition T1B More details
- Transition T6A More details
- Transition T2A More details
- Transition T2B More details
- Transition T6A More details
- Transition T3A More details
- Transition T6A More details
- Transition T6A More details
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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Description
The Reference State represents what is believed to show the natural range of variability that dominated the dynamics in this ecological site prior to European settlement. This site is dominated by cool- and warm-season grasses. In pre-European times the primary disturbances included fire and grazing by large ungulates, small mammals, and insects. Favorable growing conditions occurred during the spring and the warm months of June through August. The Reference State can be found on areas with a history of proper grazing management, including adequate recovery periods between grazing events.
Submodel
Description
The Early Seral State is the result of heavy, continuous season-long grazing, frequent and severe defoliation or concentrated disturbance such as rodent activity, or heavy use area. This State can also develop as a result of invasion by highly competitive weed species. Extended periods of drought accompanied by heavy grazing can also push an ‘At Risk’ plant community phase to this State. In most cases, this phase is dominated by pioneer perennial and annual grasses, and forb species. Bare ground is also much higher in the Early Seral State than on any other plant community phase in the Loamy Terrace ecological site.
Submodel
Description
The Native/Invaded State has been invaded by Kentucky bluegrass, smooth brome, and annual bromes, but not at the level to which the plant community is dominated by these species. The plant community in this State looks very similar to the Reference Plant Community (1.1) and it functions very much like the Reference State. It is ‘At Risk’ of transitioning to the Invaded State (4.0), which is dominated by Kentucky bluegrass and smooth brome.
Submodel
Description
The Invaded State is the result of invasion of introduced cool-season grass species. This state is characterized by the dominance of Kentucky bluegrass and smooth brome, and an increasing thatch layer that effectively blocks introduction of other plants into the system. Plant litter accumulation tends to favor the more shade-tolerant introduced grass species. The nutrient cycle is also impaired, the result is typically a higher level of nitrogen, which also favors the introduced species. Increasing plant litter decreases the amount of sunlight reaching plant crowns, thereby shifting competitive advantage to shade-tolerant, introduced grass 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 to 35 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).
Submodel
Description
Any plant community can transition to the Disturbed Rangeland State. The two plant communities, Go-back and Seeded to Forage Species, are highly variable in nature. They are derived through different management scenarios, and are not related successionally. Infiltration, runoff, and soil erosion vary depending upon the vegetation present on the site.
Submodel
Mechanism
Heavy, continuous season-long grazing, frequent and severe defoliation, or heavy disturbance combined with drought, will transition this state to the Early Seral State (2.0).
Mechanism
Non-use and lack of fire for extended periods of time, long-term light grazing, and invasion of non-native cool-season grasses, will transition the Reference State to the Native/Invaded State (3.0).
Mechanism
Heavy disturbance including tillage, cropping, abandoning cropland, erosion, or seeding to improved pasture species result in a transition to the Disturbed Rangeland State (5.0).
Mechanism
If the disturbance causing severe defoliation is removed and long-term prescribed grazing is initiated and includes adequate rest periods, and normal precipitation patterns return, this plant community may transition to the Native/Invaded State (3.0). With the presence of non-native, cool-season grasses in local plant communities, it is assumed the Early Seral State will be invaded, to a certain extent, by non-native cool-season grasses. Therefore, a restoration pathway to the Reference State (1.0) is unlikely. This pathway will take an extended period of time and may not meet management objectives.
Mechanism
If the disturbance causing the severe defoliation is removed and the plant community is invaded by non-native cool-season grasses, this plant community is likely to transition to the Invaded State (4.0).
Mechanism
Heavy disturbance including tillage, cropping, abandoning cropland, erosion, or seeding to improved pasture species result in a transition to the Disturbed Rangeland State (5.0).
Mechanism
Heavy, continuous season-long grazing, or non-use and no fire, or long-term light grazing will cause a transition of the Native/Invaded State to the Invaded State (4.0). The ecological threshold can be identified by the percentage of non-native cool-season species in the Plant Community. Preliminary studies tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30 to 35 percent of the plant community and native grasses represent less than 40 percent of the plant community composition (Toledo, D. et al., 2014). Smooth brome is assumed to follow a similar ecological threshold, but this is not documented scientifically.
Mechanism
Heavy disturbance including tillage, cropping, abandoning cropland, erosion, or seeding to improved pasture species result in a transition to the Disturbed Rangeland State (5.0).
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.