Cottonwood-Willow-Riparian
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
Invasion of reed canarygrass
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Transition T2A
Improperly managed grazing during times of year when willow is most vulnerable to decline or most susceptible to overuse.
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Transition T2B
Alteration of hydrologic function
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Restoration pathway R3A
Restoration of hydrologic and biotic process and function
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Transition T3A
Alteration of hydrologic function
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Restoration pathway R4A
Restoration of hydrologic and biotic process and function
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Transition T4A
Time elapsed in the presence of sufficient sediment loads
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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This represents the historical reference state in pristine conditions. This state may be uncommon due to widespread invasion of reed canarygrass into this site. Erosion and deposition processes are within a historical range of variation, variability in depth to water table, and seasonal fluctuations support native vegetation and vegetated communities include all historical functional and structural groups. The historical disturbance regime is intact and driven primarily by climate which influences drought and flood cycles. The resilience and resistance of the site is bolstered by negative feedback between vegetation establishment and hydrologic processes that maintains a dynamic equilibrium with geomorphological processes.
Submodel
Description
This state is similar to the reference state yet includes a component of invasive species such as reed canarygrass and meadow foxtail. Ecological process and function have not been altered fundamentally by this low level invasion, yet resistance and resilience is decreased. Erosion and deposition processes are still within a historical range of variation, yet are at risk of transitioning to a less stable state. Variability in depth to water table and seasonal fluctuations support native vegetation. Vegetated communities include all historical functional and structural groups, yet composition and richness may be reduced. The historical disturbance regime is intact and driven primarily by climatic influences such as drought and flood cycles. The resilience and resistance of the site is bolstered by negative feedback between vegetation establishment and hydrologic processes that maintains a dynamic equilibrium with geomorphological processes. This state is common due to widespread invasion of reed canarygrass in the Western United States.
Description
Relative to the current potential state, basin wildrye has decreased while bluegrasses increase or invade. With further deterioration, willow and other palatable shrubs decrease, unpalatable shrubs increase, annuals invade and bareground increases. Erosion and bank instability will increase and is at risk of transitioning to State 4. Decreased bank stability make the site vulnerable to channel widening and incision during large runoff events and transitioning to state 4. Reed canarygrass may provide bank stability of overhanging banks, yet it declines where connectivity to the water table is not available. This state also includes stable analogue channels that have reformed following channel incision, widening, and the creation new floodplains.
Description
Streambanks have become unstable from loss of vegetation and the channel degrades becoming deeper and wider in the process. Subsurface flows are affected. The water table drops and storage of water for the late season flows is reduced. Plants well adapted to a drier climatic regime increase or invade and production drops. Reed canarygrass has become strongly dominant where woody riparian vegetation has been reduced. Channel widening and incision are common in this state as unstable banks and vegetation loss create a positive feedback loop that decreases resilience to runoff events. Abandoned floodplains transition into terraces and are dominated by drought adapted species that do not require a connection to the water table.
Mechanism
Improperly managed grazing during times of year when willow is most vulnerable to decline or most susceptible to overuse.
Mechanism
This transition may be the result of several disturbances that lower water tables beyond depths that support riparian woody vegetation, alter sediment supply and transport leading to scouring and channel incision, or directly increase flow velocities or flashiness. These may include: alteration of streamflow by irrigation or impoundment leading to a lowering of the water table during times of year when riparian woody vegetation is dependent; removal of beaver; direct manipulation of channel morphology (namely straightening for agricultural or development purposes); removal of large woody debris or large woody debris sources, from channels or adjacent forests and significant alterations of upland watershed vegetation altering peak discharge or sediment loads.
Mechanism
Restoration of hydrologic and biotic process and function through rehabilitation of channel and vegetation structure may be possible but will require considerable inputs, time and cost. This may require the placement of large woody debris, creation or removal of impoundments, alteration of water withdrawals, management changes to adjacent agricultural or grazing practices, or mechanical manipulation of stream channel courses among other intensive interventions. Restoration options will be highly site specific and may not be possible in many circumstances.
Mechanism
This transition may be the result of several disturbances that lower water tables beyond depths that support riparian woody vegetation, alter sediment supply and transport leading to scouring and channel incision, destabilize banks, or directly increase flow velocities or flashiness. These may include: alteration of streamflow by irrigation or impoundment leading to a lowering of the water table during times of year when riparian woody vegetation is dependent; removal of beaver; direct manipulation of channel morphology (namely straightening for agricultural or development purposes); removal of large woody debris or large woody debris sources, from channels or adjacent forests; sustained improperly managed grazing for many seasons; and significant alterations of upland watershed vegetation altering peak discharge or sediment loads. This state will be more vulnerable to these changes compared to state 2 given less stable banks and lower cover of riparian woody vegetation.
Mechanism
Restoration of hydrologic and biotic process and function through rehabilitation of channel and vegetation structure may be possible but will require considerable inputs, time and cost. This may require the placement of large woody debris, creation or removal of impoundments, alteration of water withdrawals, management changes to adjacent agricultural or grazing practices, or mechanical manipulation of stream channel courses among other intensive interventions. Restoration options will be highly site specific and may not be possible in many circumstances.
Mechanism
Given time, if natural channel evolution processes are allowed to take place, and sediment loads are sufficient, the stream will form an entrenched floodplain at a lower depth then the original. The original floodplain will become a terrace, disconnected from the water table and supporting drought adapted plant species. The resulting riparian area will be more confined and of significantly less extent than originally and the capacity of the basin to store water will be reduced considerably.
Model keys
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