Loamy Overflow
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1b More details
- Transition T1a More details
- Transition T2a/b More details
- Transition T2c More details
- Restoration pathway R3a/b More details
- Transition T3a More details
- Transition T4a More details
- Transition T5a 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
This state description represents the natural range of variability that dominated the dynamics of this ecological site. Historically, this state ranged from a tall, warm season grass dominated site to one dominated by deciduous saplings and shrubs depending upon disturbance regime. The primary disturbance mechanisms for this site in the reference condition included periodic fire and grazing by large herding ungulates. Timing of fires and grazing coupled with weather events dictated the dynamics that occurred within the natural range of variability. Dominance during the herbaceous phases of this state shifted between warm-season and cool-season grasses. Although slight shifts in the timing of energy capture, hydrologic function and nutrient cycling between plant community phases with the Reference state may have occurred, overall the ecological process were functioning at near optimum levels. High basal density and deep root systems resulted in low runoff rates and high infiltration rates.
Small areas of trees and shrubs may have existed within this state due to irregularity of burn patterns. Small areas which escaped fire may have permitted trees/shrubs to become established. These areas may have served as a seed source for further expansion of the woody dominated plant communities as the fire frequency was altered after settlement.
Submodel
Description
This state is very similar to the reference state. The invasion of introduced cool-season sodgrasses has altered the natural range of variability for this ecological site. This state is still dominated by mid and tall native warm- and cool-season grasses, but invasive introduced cool-season sodgrasses are now present in all community phases of this state. The primary disturbance mechanisms for this state include grazing by domestic livestock and infrequent fires. Timing and intensity of grazing events coupled with weather dictate the dynamics that occur within this state. The cool-season native grasses can decline and an increase in introduced sod grasses will occur. Many times, this state appears as a mosaic of community phases caused primarily by continuous season-long grazing.
Submodel
Description
This state is the result of invasion and dominance by Kentucky bluegrass, smooth bromegrass and/or pioneer annual/perennial species depending upon the intensity and frequency of disturbance regime. Once the state is well established, even drastic events such as high intensity fires driven by high fuel loads of litter and thatch, will not result in more than a very short term reduction of these two species. These events may reduce the dominance of the sodgrasses, but due to the large amount of rhizomes in the soil there is no opportunity for the native species to establish and dominate before the non-native sodgrasses rebound and again dominate the system.
Submodel
Description
Historically, this state existed as small patches of trees and shrubs scattered across the site. Repeated intense disturbances (e.g., fire, fire coupled with grazing) would have reverted these smaller patches of trees to the herbaceous dominated Reference State (State 1) in pre-European times, while it will likely revert to the Invaded State (State 4) today. For simplification purposes, the pre-European transition returning from the wooded state to the reference state is not shown on the state and transition diagrams. Likewise the pre-European and modern day conditions of the Wooded State are combined within this state description. Community phases 4.1 and 4.2 would have occurred in pre-European times without the presence of non-native species; whereas, community phase 4.3 will only be present in modern times, and all three community phases will likely have some amounts of non-native species in the present day. Otherwise, the community pathways between 4.1 and 4.2 would generally apply in both pre-European and under modern day circumstances.
In pre-European times, periodic low intensity fires typically would have maintained these small, wooded patches in a tree dominated state. Alterations to the historic fire and grazing disturbance regimes have resulted in these scattered tree/shrub patches forming almost continuous woody dominated plant communities across the site. This state is characterized by an overstory of tall trees, an understory of shrubs and, depending upon the amount of canopy cover, an herbaceous understory of sedges and/or Kentucky bluegrass.
Submodel
Mechanism
This is the transition from the native herbaceous or herbaceous/shrub dominated reference state to the herbaceous dominated native/invaded state. This transition occurs when propagules of non-native species such as Kentucky bluegrass and/or smooth bromegrass are present and become established on the site. This occurs as natural and/or management actions (altered grazing and/or fire regime) favor a decline in the composition of the warm-season native species and an increase in cool-season sodgrasses. Chronic season-long or heavy late season grazing facilitates this transition. Complete rest from grazing and no fire events can also lead to this transition. The threshold between states is crossed when the non-natives become established on the site.
Mechanism
This is the transition from the native herbaceous or herbaceous/shrub dominated Reference State to a state that was dominated by mature trees and shrubs. Change in fire frequency allowed woody plant species to grow large enough to escape the next fire event. As trees increased in size, canopy cover increased which altered micro-climate and reduced fine fuel amounts resulting in reduced fire intensity and frequency. This would have been the primary pathway under the historic disturbance regime and would have resulted in a mosaic pattern of small wooded patches interspersed within herbaceous plant community phases.
Mechanism
T2a - This represents the transition from the more native dominated Native/Invaded State to a plant community phase dominated by non-native, cool-season rhizomatous grasses. Complete rest from grazing and elimination of fire are the two major contributors to this transition, especially when smooth bromegrass is present. Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30% of the plant community and native grasses represent less than 40% of the plant community composition.
T2b - This represents the transition from the more native dominated Native/Invaded State to a plant community phase dominated by a dense Kentucky bluegrass sod and grazing tolerant forbs. Heavy continuous season-long grazing is the major contributor to this transition. Preliminary studies would tend to indicate this threshold may exist when Kentucky bluegrass exceeds 30% of the plant community and native grasses represent less than 40% of the plant community composition.
Mechanism
This represents the transition from the Native/Invaded State (State 2) to the Wooded State (State 4) under the current disturbance regime. Lack of fire and grazing shifts the competitive advantage to the trees and shrubs. Rather than patches of trees and shrubs interspersed within herbaceous dominated plant communities as referenced in the T1a transitional pathway, this transition results in an expansion of the patches into an almost continuous woody dominated site.
Mechanism
R3a - This restoration pathway may be initiated with the combination of prescribed burning followed by high levels of prescribed grazing management. The success of this restoration pathway depends on the presence of a remnant population of native grasses in community phase 3.1. This remnant population may not be readily apparent without close inspection. The application of prescribed burning may be needed at relatively short intervals in the early phases of this restoration process. Early season burning seems to be the most effective method to achieve the desired results; however, some work has shown that fall burning may also be effective. Both prescribed grazing and prescribed burning are necessary to successfully initiate this restoration pathway.
R3b - It may be possible using selected plant materials and agronomic practices to approach something very near the functioning of the Native/Invaded State (State 2). Application of chemical herbicides and the use of mechanical seeding methods using adapted varieties of the dominant native grasses are possible and can be successful. After establishment of the native plant species, management objectives must include the maintenance of those species, the associated reference state functions, and the continued treatment of the introduced sodgrasses.
Mechanism
This pathway represents the transition from the Kentucky Bluegrass/Smooth Bromegrass/Shrub plant community phase to the Wooded State (State 4). This transition results from the complete removal of fire and grazing related disturbances. This shifts the competitive advantage to the shrubs and trees. As the woody canopy increases, only shade tolerant herbaceous species remain in the understory.
Mechanism
This transitional pathway involves a dramatic decrease in the amount and extent of the woody component of the plant community through either catastrophic fire and/or mechanical removal of the trees and shrubs. Potentially, this pathway could also be initiated or compounded with the introduction of various tree and/or shrub diseases or pests.
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.