Thin Claypan
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1 More details
- Transition T2b More details
- Transition T2a 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 mid statured, rhizomatous cool season grass dominated with lesser amounts of short statured, warm season grasses site to one dominated by a short statured, warm season grasses with lesser amounts of the mid statured cool season rhizomatous grass, 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 within this state shifted between warm-season and cool-season grasses. This change would have shifted the timing of energy capture and slightly altered the hydrologic function between plant community phases within the Reference State. Plant community phases within the Reference state were very resilient and able to recover ecological function following disturbances. Overall, the ecological processes were functioning at near optimum levels within this State.
However, prolonged drought and heavy grazing pressure, like that associated with perennial water sources, may have resulted in a complete elimination of the mid statured cool season grass component from this state. Although not illustrated on the diagram, this would have resulted in the crossing of a threshold to a warm season short grass dominated steady state.
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 native cool and warm season grasses, but 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 of grazing coupled with weather events dictate the dynamics that occur within this state. The 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 of introduced species with remnant amounts of native, short statured grasses and forbs. This state is characterized by the dominance of Kentucky bluegrass and possibly smooth bromegrass, and an increasing thatch layer that effectively blocks introduction of other plants into the system. Due to soil chemistry and structure issues, remnant populations of inland saltgrass and blue grama may be present on those areas where the claypan occurs in close proximity to the soil surface. In appearance, this plant community phase may resemble a site with “spot grazing” issues even when no grazing has occurred.
Plant litter accumulation tends to favor the more shade tolerant introduced grass species. The nutrient cycle is also impaired, and 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. 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 Kentucky bluegrass. These events may reduce the dominance of Kentucky bluegrass, but due to the large amount of rhizomes in the soil there is no opportunity for the native species to establish and dominate before Kentucky bluegrass rebounds and again dominates the system.
Submodel
Mechanism
This is the transition from the native cool season grass dominated reference state to a state that has been invaded by introduced cool season grass species. When propagules of Kentucky bluegrass are present, this transition occurs as natural and/or management actions favor a decline in the composition of cool and warm season native grasses and an increase in cool season introduced sodgrasses. Chronic season long or heavy late season grazing facilitate this transition. Complete rest from grazing and no fire events can also lead to this transition. The threshold between states is crossed when Kentucky bluegrass or other non-native grasses become established on the site.
Mechanism
Complete rest from grazing and elimination of fire are the two major contributors 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. The opportunity for high intensity spring burns is severely reduced by early green up and increased moisture and humidity at the soil surface and grazing pressure cannot cause a reduction in sodgrass dominance. Production is limited to the sod forming species. Infiltration continues to decrease and runoff increases, energy capture into the system is restricted to early season low producing species. Nutrient cycling is limited by root depth of the dominant species. This transition typically leads to the 3.2 Kentucky Bluegrass/Forb Plant Community Phase.
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. This transition typically leads to the 3.1 Inland Saltgrass/Kentucky Bluegrass/Blue Grama Plant Community Phase.
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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.