Clay Loam
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
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Transition T1B
Excessive soil disturbance following by introduction of forage species
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Restoration pathway R2A
Reintroduction of fire and regular disturbance return intervals
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Transition T2A
Excessive soil disturbance following by introduction of forage species
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Transition T3A
Absence of disturbance and natural regeneration over time
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
Select a state
Mechanism
Shrubs make up a portion in the Savannah State (1), hence woody propagules are present. Therefore, the Savannah State (1) is always at risk for shrub and tree dominance and the transition to the Woodland State (2) in the absence of fire and brush management. The driver for Transition T1A is lack of fire and/or brush control. The mean fire return interval in the Savannah State (1) is 2 to 5 years. Most fires will burn only the understory. Even with proper grazing and favorable climate conditions, lack of fire for 8 to 15 years will allow trees and shrubs to increase in canopy to reach the 40 percent threshold level to produce enough fuel for a burn. The introduction of aggressive woody invader species increases the risk and accelerates the rate at which this transition is likely to occur. This transition can occur from any community within the Savannah State (1). It is not dependent on degradation of the herbaceous community, but on the lack of some form of brush control. The trigger for this transition is that shrubs are reaching 3 feet of height; the height most shrubs start reproducing. Improper grazing, prolonged drought, and a warming climate will provide a competitive advantage to shrubs, which will accelerate this process.
Mechanism
The transition to the Converted State from the Savannah State occurs when the savannah is plowed for planting to cropland or hayland. The size and density of brush will require heavy equipment and energy-intensive practices (i.e. rootplowing, raking, rollerchopping, or heavy disking) to prepare a seedbed. The threshold for this transition is the plowing of the savannah soil and removal of the woody plant community. The Converted State (3) includes cropland, tame pasture, and go-back land. The site is considered “go-back land” during the period between cessation of active cropping, fertilization, and weed control and the return to the “native” states. Agronomic practices are used to convert rangeland to the Converted State and to make changes between the communities in the Converted State (3). The driver for these transitions is management’s decision to farm.
Mechanism
Restoration of the Woodland State (2) to the Savannah State (1) requires substantial energy input. The driver for this restoration pathway is removal of woody species, restoration of native herbaceous species, and ongoing management of woody species. Without maintenance, woody species are likely to increase again.
Mechanism
The transition to the Converted State from the Woodland State occurs when the savannah is plowed for planting to cropland or hayland. The size and density of brush will require heavy equipment and energy-intensive practices (i.e. rootplowing, raking, rollerchopping, or heavy disking) to prepare a seedbed. The threshold for this transition is the plowing of the savannah soil and removal of the woody plant community. The Converted State (3) includes cropland, tame pasture, and go-back land. The site is considered “go-back land” during the period between cessation of active cropping, fertilization, and weed control and the return to the “native” states. Agronomic practices are used to convert rangeland to the Converted State and to make changes between the communities in the Converted State (3). The driver for these transitions is management’s decision to farm.
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.