PONDED CLAY
Scenario model
Current ecosystem state
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Management practices/drivers
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- Transition T1A More details
- Transition T2A More details
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No transition or restoration pathway between the selected states has been described
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Submodel
Description
State 2 mimics State 1 with the addition of non-native species (e.g. cheatgrass, bur buttercup,clasping pepperweed and whitetop) being present. Presence of these species reduces the site’s resistance and resiliency to disturbance and slightly alters function by altering the site’s resource availability and shifting it slightly towards the non-native species. Many non-native species are more well-adapted to extract site resources than native species by being prolific seed producers, shallow-rooted to extract water quickly when water is limiting in drought years, and through rapid uptake of available nutrients in the soils. When a disturbance does occur, the non-native species will also respond more rapidly to the disturbance further impacting the site’s resiliency and resistance.
Feedback mechanisms: Herbaceous cover provides organic matter to the soil preventing vesicular crust formation which promotes infiltration and seedling establishment. Annual ponding prevents conversion to upland vegetation.
Submodel
State 3
Silver Sagebrush dominated
Description
State 3 has three community phases depending on the amount (percent composition by weight) of silver sagebrush in relation with perennial grasses/grasslikes, native increaser forbs, and non-native species. As disturbance increases, native perennial grasses/grasslikes and forbs decrease while silver sagebrush increases. Non-natives (e.g. cheatgrass, bur buttercup, clasping pepperweed and whitetop) and native increaser forbs (e.g. povertyweed and evening primrose) are common. If disturbance is continuous and/or repeatedly impacts the plants during the critical growing season, silver sagebrush declines and non-native species increase. Ecological functional groups described in State 1 are still present in this state, however the production and resiliency of the state has been reduced by the presence of non-native species and a thick silver sagebrush overstory.
Feedback mechanisms: Reduced organic matter inputs into the soil increase the prevalence of vesicular crusts which slow infiltration, increasing water loss to evaporation, and inhibit seedling establishment. Silver sagebrush dominates the site reducing availability of light and nutrients to other species on the site.
Submodel
Description
State 4 has been hydrologically-altered through the excavation of a water hole (dug-out) in the center of the site causing it to cross an abiotic threshold. The altered hydrology of the site is controlling vegetative composition. Water holes concentrate ponded water in the center of the site, reducing the extent and duration of ponding across the site. This causes a moisture gradient change on the site which alters the vegetative composition. Hydrologic conditions on the perimeter of the site are drier than can support the species composition of the Ponded Clay ecological site. Due to concentration of water into the water hole, the perimeter of the site no longer ponds, allowing it to convert to upland vegetation. The portion of the site rmaining in the Ponded Clay ecological site will have a similar plant composition to any of the phases in the previous states. These water holes concentrate livestock and wildlife in the area which can lead to impacts including continuous heavy grazing by animals that exceeds the plant community's ability to recover, soil compaction when soils are wet, and trampling of plants. Concentrated use by livestock and wildlife favors silver sagebrush and generally causes a reduction of perennial grasses. This impact may be reduced by providing off-site water away from this water hole.
Degree of upland vegetation encroachment is influenced by climatic conditions and the size of the water hole. If available water for ponding exceeds the capacity of the water hole, the area around the water hole will pond, simulating natural conditions and facilitating growth of vegetation as described in the reference community or wet phases described in the model. Sites with smaller capacity water holes or large playas where the water hole constitutes a small fraction of the playa's total capacity are also more likely to have ponding outside of the water hole. During wet climatic cycles, available water is more likely to exceed water hole capacity.
Submodel
Mechanism
Introduction of non-native species (e.g. cheatgrass, bur buttercup, clasping pepperweed and whitetop) reduces the site's resiliency to disturbance.
Mechanism
Prolonged drought and heavy disturbance, such as continuous heavy grazing by animals that exceeds the plant community's ability to recover, favors silver sagebrush and creeping wildrye over bunchgrasses and encourages native increasers (e.g. povertyweed and evening primrose) and non-native species. Silver sagebrush dominates the site and creates a denser canopy that reduces availability of light and nutrients to other species on the site and favors the native increasers and non-natives. This reduces ecological resiliency of the site and a biotic threshold is crossed.
As perennial bunchgrass composition decreases and silver sagebrush increases, vesicular crusts also become more common on the soil surface due to reduced organic matter inputs. Vesicular crusts slow infiltration, increasing water loss to evaporation and inhibit seedling establishment of native forbs and grasses, further facilitating the dominance of the native increasers and the non-native species.
Mechanism
Excavation of a water hole (dug-out) in the center of the site alters the hydrologic function of the site causing it to cross an abiotic threshold.
Model keys
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