Booth-Yellow 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 and meadow foxtail into the site.
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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. Removal of willow by mechanical means.
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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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Restoration pathway R4B
Time elapsed with adequate sediment loads and hydrologic function to support natural channel evolution processes
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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 reference state in pristine conditions. 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 feedbacks 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 canary grass and meadow foxtail. Ecological process and function have not been altered fundamentally by this low level of 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 and 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 climate which influences drought and flood cycles. The resilience and resistance of the site is bolstered by negative feedbacks between vegetation establishment and hydrologic processes that maintains a dynamic equilibrium with geomorphological processes. This state is common due to widespread invasion of reed canary grass in the Western US.
Description
Relative to the Current Potential State, much of the willow cover and original understory has been lost, the primary channel is becoming unstable, and the floodplain is becoming disconnected yet the water table is still present. Chanel types are E, sinuosity is greater than 1.5, gradient is less than 0.2/100 ft and width to depth ratio is less than 12. With further deterioration, erosion and bank instability will increase and risk a transition 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
This state is characterized by straightened reaches with higher gradients, reduced sinuosity, unstable banks and disconnected floodplains. Chanel types are C, sinuosity is less than 1.5, gradient is greater than 0.2/100 ft and width to depth ratio is greater than 12. Reed canarygrass and meadow foxtail have become strongly dominant where willows and other woody riparian vegetation have been reduced. This leads to bank erosion and reduced stream shading (less than one percent in mid-summer). 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. Point bars may still support narrowleaf willow and are characterized by gravels, as sand and silt has been lost. Abandoned floodplains transition into terraces and are dominated by drought adapted species that do not require a connection to the water table to persist. Plant communities within this state will vary depending on water table levels, past disturbance history, fire, drought and current management. Currently, insufficient data exists to model the dynamics between these communities but possible phases include:
Quackgrass-Kentucky bluegrass (higher water table or irrigated);
Basin big sagebrush/Kentucky bluegrass-Annuals (primary channel deeply incised, loss of floodplain connectivity and overland flows);
Basin big sagebrush(western juniper)/Annuals (water table lowered, primary channel deeply incised, floodplain disconnected);
Annuals-Deep rooted biennial and perennial forbs (water table lowered, primary channel deeply incised, floodplain disconnected);
Mechanism
Invasion of reed canarygrass and meadow foxtail into the site.
Mechanism
Improperly managed grazing during times of year when willow is most vulnerable to decline or most susceptible to overuse. Removal of willow by mechanical means.
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 adequate, 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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