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 T5 More details
- Transition T2a More details
- Transition T2b More details
- Transition T2c More details
- Transition R3a More details
- Transition R3b More details
- Transition T3 More details
- Transition T4 More details
- Transition T6 More details
- Transition T6 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 frequent 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 may occurred in timing of energy capture, hydrologic function and nutrient cycling between plant community phases within the Reference State, overall the ecological processes 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 community 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 grass 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 brome 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.
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. Repeated intense disturbances (e.g., fire, fire coupled with grazing) would have reverted these smaller patches of trees to the herbaceous dominated Reference 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 or other introduced grasses.
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 is 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
This pathway is most commonly associated with the cessation of cropping without the benefit of range or pasture seeding resulting in a “go-back” situation. This may be compounded with excessive grazing which further inhibits the establishment of perennial grasses and forbs.
Mechanism
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 brome 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.
Mechanism
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 Woody Dominated Plant Communities 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 T1a transitional pathway results in an expansion of the patches into an almost continuous woody dominated site.
Mechanism
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. Some previous efforts have shown promise with early season prescribed burning; however, fall burning may also be effective under certain circumstances. Both prescribed grazing and prescribed burning are necessary to successfully initiate this restoration pathway.
Mechanism
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 continued treatment of the introduced sodgrasses.
Mechanism
This transition is initiated by the removal of disturbance. No fire, no grazing.
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.
Mechanism
Catastrophic fire or mechanical removal of trees and shrubs would result in a shift back towards the Invaded State (State 3).
Mechanism
This transition occurs as a result of long term heavy season-long grazing or long term non-use. Heavy season-long grazing by livestock greatly lessens or eliminates tree regeneration and enhances a highly competitive herbaceous understory of Kentucky bluegrass which will further reduce tree regeneration. As the existing green ash and American elm trees mature and expire, the resulting plant community consists of a Kentucky bluegrass sod and scattered mature green ash trees.
Long term non-disturbance will also result in the same shift. Tree regeneration is limited by the accumulation of a thick layer of plant litter as well as competition from the Kentucky bluegrass understory.
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.