Droughty Steep 19-24" PZ Cryic Beaverhead Mountains
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1B
The trigger for this transition is improper grazing management or long-term drought.
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Transition T1C
The driver for this transition is improper grazing management, intense or repeated fires, and heavy human disturbance.
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Transition T1D
Recent dry climate cycles, repeated heavy grazing or intense human activities can open the interspaces of the bunchgrass community and allow for encroachment.
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Transition T1E
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds or other viable material of these tree species.
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Restoration pathway R2A
The drivers for this restoration pathway are reclamation efforts along with proper grazing management.
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Transition T2A
Improper grazing reduces vigor of bunchgrasses and prolonged drought will provide a competitive advantage to shrubs allowing them to become co-dominant with grasses.
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Transition T2B
The trigger is the presence of seeds or other viable material of invasive species.
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Transition T2D
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds or other viable material of these tree species.
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Restoration pathway R3B
The drivers for the restoration pathway are removal of increaser species, restoration of native bunchgrass species, persistent management of invasives and shrubs, and proper grazing management
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Restoration pathway R3A
If a sufficient amount of bunchgrasses remain, chemical application or biological control in conjunction with proper grazing management, can reduce the amount of shrubs and invasive species and restore the site to the Shortgrass Community (2.2).
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Transition T3A
The driver for this transition is presence of critical population levels of invasive species. The trigger is the presence of seeds or viable material of invasive species.
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Transition T3C
Conifer tree/shrub count exceeds 2 stems per acre. The trigger of crossing a threshold is the presence of seeds and/or other viable material of these tree species.
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Restoration pathway R4C
The drivers for the restoration pathway are removal of invasive species, restoration of native bunchgrass species, persistent management of invasive species, and proper grazing management.
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Restoration pathway R4B
The driver for the reclamation pathway is weed management with possible reseeding.
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Restoration pathway R4A
The driver for the reclamation pathway is weed management with possible reseeding.
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Transition T4B
Canopy cover of conifer tree/shrub cover exceeds 2 stems per acre. The threshold change is triggered by the presence of seeds and/or other viable material of invasive species.
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Restoration pathway R5A
Brush management or prescribed fire are common restoration methods. Grazing management with deferment or rest is suggested. Proactive pest management is encouraged.
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Restoration pathway R5B
Brush management or prescribed fire are common restoration methods. Grazing management with deferment or rest is suggested. Proactive pest management is encouraged.
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Restoration pathway R5C
Brush management or prescribed fire are common restoration methods. Grazing management with deferment or rest is suggested. Proactive pest management is encouraged.
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No transition or restoration pathway between the selected states has been described
Target ecosystem state
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State 1
Reference State
Description
The Reference State of the Droughty Steep ecological site consists of three potential plant communities; 1.1 Mid-statured Bunchgrass Community, 1.2 Mixed Bunchgrass Community, and 1.3 Sagebrush/Bunchgrass Community. These are described further in their respective community details but are generally characterized by a mid-statured, cool-season bunchgrass community with moderate shrub production. Due to the increased spring and summer precipitation, these communities are often resistant to disturbance.
Community 1.1 is dominated by mid-statured, cool-season bunchgrasses such as bluebunch wheatgrass, Richardon's needlegrass, and Columbia needlegrass; with a mixed shrub component. Community 1.1 is considered the Reference Plant Community while Community 1.2 has a reduction in mid-statured bunchgrasses and an increase in short bunchgrasses and forbs. Community 1.3 is co-dominated by bluebunch wheatgrass and Idaho fescue with mountain big sagebrush as the dominant shrub.
Submodel
Description
This state is characterized by having less than 15 percent by dry weight of mid-statured bunchgrasses. It is represented by two communities that differ in the percent composition of Idaho fescue and needle and thread, and overall production. Production in this state can be similar to the Reference State (1). Some native species tend to increase under prolonged drought and heavy grazing practices. A few of these species may include Idaho fescue, Sandberg bluegrass, Cusick's bluegrass, scarlet globemallow, hairy goldenaster, and fringed sagewort. Poisonous plants such as lupine (Lupinus spp) and mountain deathcamas (Zigadenus elegans) may also increase under these conditions.
Submodel
Description
Degraded State is characterized by a near complete lack of mid-statured bunchgrasses. Idaho fescue, Sandberg bluegrass and prairie Junegrass are dominant grasses. Increaser shrubs nearly replace larger shrub species. Remaining larger shrub species are heavily hedged. This state is likely a terminal state (e.g. restoration will likely be impossible or unsuccessful without major financial and energy inputs).
Submodel
Description
The Invaded State is identified by being in the exponential growth phase of invader abundance where control is a priority. Dominance (or relative dominance) of noxious/invasive species reduces species diversity, forage production, wildlife habitat, and site protection. A level of 10 percent by weight invasive species composition by dry weight indicates the point that a substantial energy input such as herbicide or mechanical removal will be required to create a shift to the grassland state, in addition to a return to proper grazing management or favorable growing conditions. Prescriptive grazing that specifically focuses on grazing of the invasive plant can be used to manage invasive species. In some instances, carefully targeted grazing (sometimes in combination with other treatments) can reduce or maintain species composition of invasive species.
Submodel
Description
Douglas fir (Pseudotsuga menziesii) encroachment is common on the Droughty Steep ecological site and is generally focused in areas with east and north facing slopes; however, encroachment exists on all aspects. Under the Reference State, conifers may exist, but are limited to one to two stems per acre on north and east facing slopes and is considered a trace canopy cover.
Conifer encroachment likely occurs in the late stages of the Reference State and Altered State (see state-and-transition model) where there is an increase of bare ground and reduced vigor of mid-statured bunchgrasses due to a combination of factors. Fire suppression and improper grazing management are the two most common triggers. The exact conditions in which conifers begins to encroach vary; however, the trend points to a combination of one or more factors including moderately heavy to heavy grazing, reduced (non-existent) fire frequency, increased atmospheric carbon, and generally warmer climate (compared to that of pre-settlement). When heavy grazing occurs areas in the plant canopy open allowing for seed dispersal by bird or overland flow via rills on neighboring sites. The effects of conifer encroachment are not immediately noticed. Over time as conifer canopy increases; light and water interception increase which reduce opportunities for herbaceous plants. Literature suggests that for precipitation to penetrate the juniper canopy, events must be greater than 0.30 inches (Barrett, 2007). Increases in the conifer canopy creates perching sites for predators which reduces site suitability for greater sage grouse.
Studies (Miller et al 2000) based in a similar community to the Conifer Encroached communities of this LRU suggest following a phased approach to characterize the stand. Not unlike the Western Juniper community discussed in Miller et al., these communities of Montana exhibit three different phases based, at this time, on qualitative information.
Submodel
Mechanism
The Reference State (1) transitions to the Altered State (2) if bluebunch wheatgrass decreases to 15 percent, by dry weight, or if bare ground cover increases by 10 percent. The driver for this transition is the loss of taller bunchgrasses, which creates open areas in the plant canopy with bare soil. Soil erosion results in decreased soil fertility, driving transitions to the Altered State.
There are several other key factors signaling the approach of transition T1B: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability or evidence of erosion including water flow patterns, development of plant pedestals, and litter movement. The trigger for this transition is improper grazing management or long-term drought leading to a decrease in bluebunch wheatgrass composition to 15 percent and reduction in total plant canopy cover.
Mechanism
The Reference State (1) transitions to the Degraded State (3) when bluebunch wheatgrass is completely removed from the plant community. Idaho fescue and needle and thread are subdominant to short-statured bunchgrasses such as Sandberg and Cusick's bluegrass. The trigger for this transition is loss of most mid-statured bunchgrasses, which creates open spaces with bare soil. Soil erosion as a result of increased bare ground and shallow roots, decreasing soil fertility, driving transitions to the Degraded State. There are several other key factors signaling the approach of transition T1C: increases in soil physical crusting, decreases in cover of cryptogamic crusts, decreases in soil surface aggregate stability or evidence of erosion including rills, water flow patterns, development of plant pedestals, and litter movement. The driver for this transition is improper grazing management, intense or repeated fires, and heavy human disturbance. Rapid transition is generally realized where livestock are confined to small pastures for long periods of time such as feeding areas, horse pastures, and bull lots.
Degradation may be so extreme that traditional restoration methods may not be successful and require extensive mechanical and financial inputs.
Mechanism
Healthy plant communities are most resistant to invasion. However, regardless of grazing management, without some form of active weed management (chemical, mechanical, or biological control), the Reference State (1) can transition to the Invaded State (4) in the presence of aggressive invasive species such as spotted knapweed, leafy spurge, and cheatgrass. The Central Rocky Mountains tend to resists invasion however recent dry climate cycles, repeated heavy grazing or intense human activities can open the interspaces of the bunchgrass community and allow for encroachment. Long-term stress conditions for native species (e.g., overgrazing, drought, and fire) accelerate this transition. If populations of invasive species reach critical levels, the site transitions to the Invaded State. The trigger for this transition is the presence of aggressive invasive species with invasive species composition by dry weight approaching 10 percent.
Mechanism
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds or other viable material of these tree species.
Mechanism
The Altered State (2) has lost soil or vegetation attributes so that recovery to the Reference State (1) will require reclamation efforts such as soil rebuilding, intensive mechanical and cultural treatments, and revegetation. Examples of mechanical treatment may be brush control while cultural treatments may include prescribed grazing, targeted brush browsing, or prescribed burning. Grazing practices that promote bluebunch wheatgrass is primarily light to moderate grazing during the critical season (late June through July) or moderate grazing during the fall and dormant season. Heavy utilization may not have negative impacts (Dormaar and Willms 1998) though grazing should match the species composition of the site prior to exceeding moderate utilization.
Low intensity prescribed fires will reduce competitive increaser plants such as needle and thread and Sandberg bluegrass. A low intensity fire will also reduce big sagebrush densities. In areas with potential of annual grass infestation, fire should be carefully planned or avoided. The drivers for this restoration pathway are reclamation efforts along with proper grazing management.
Relevant conservation practices
| Practice | External resources |
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Brush Management |
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Prescribed Burning |
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Fence |
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Livestock Pipeline |
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Prescribed Grazing |
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Grazing Land Mechanical Treatment |
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Range Planting |
Mechanism
As improper grazing continues vigor of bunchgrasses will decrease, and the shorter grasses and shrubs will increase towards the Degraded State (3). Improper grazing management for this state can be defined as grazing events that exceed moderate grazing (40 to 50 percent grazing use), grazing season that exceeds half of the growing season, or grazing events that consume the plant regrowth in the same growing season. Highly managed grazing events that exceed moderate grazing levels for short timeframes are generally not included in this definition due to increased rest periods between these grazing events.
Additionally, prolonged drought will provide a competitive advantage to shrubs allowing them to become co-dominant with grasses. Shrub canopy will increase however shrubs will express low growth forms. Mat forming forbs will also increase.
Key transition factors: increase of native shrub canopy cover; reduction in bunchgrass production; decrease in total plant canopy cover and production; increases in mean bare patch size; increases in soil crusting; decreases in cover of cryptobiotic crusts; decreases in soil aggregate stability; or evidence of erosion including water flow patterns and litter movement.
Mechanism
Invasive species can occupy the Altered State (2) and drive it to the Invaded State (4). The Altered State is at risk if invasive seeds or other viable material are present. The driver for this transition is more than 10 percent dry weight of invasive species. The trigger is the presence of seeds or other viable material of invasive species.
Mechanism
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds or other viable material of these tree species.
Mechanism
The Degraded State (3) has lost soil or vegetation attributes so that recovery to the Reference State (1) will require reclamation efforts, such as soil rebuilding, intensive mechanical treatments, and/or revegetation. Studies suggest (Whitford et al 1989) a mulch with high carbon to nitrogen ratio such as wood chips or bark in low moisture scenarios can be beneficial for slow mobilization of plant available nitrogen. Biochar may also be added to the system to improve Soil Organic Carbon (SOC) which should improve Cation Exchange Capacity (CEC), microbial activity, and hydrologic conductivity (Stavi 2012). The drivers for the restoration pathway are removal of increaser species, restoration of native bunchgrass species, persistent management of invasives and shrubs, and proper grazing management. Without continued control, invasive and shrub species are likely to return (probably rapidly) due to presence of seeds or other viable material in the soil and management related increases soil disturbance.
Relevant conservation practices
| Practice | External resources |
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Brush Management |
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Prescribed Burning |
Mechanism
Since the deep-rooted bunchgrass plant community has been removed, restoration to the Altered State (2) is unlikely unless a seed source is available. If a sufficient amount of bunchgrasses remain, chemical application or biological control in conjunction with proper grazing management, can reduce the amount of shrubs and invasive species and restore the site to the Shortgrass Community (2.2). Grazing management strategies that follow light grazing and allow for long periods of rest will allow for limited recovery of remaining bunchgrasses, however grazing management alone may not directly result in restoration. Restoration methods such as reseeding may be necessary
Low intensity fire can be utilized to reduce shrub competition and allow the reestablishment of grass species. Caution must be used when considering fire as a management tool on sites with fire tolerant shrubs such as rubber rabbitbrush, as these shrubs will re-sprout after a burn. Broom snakeweed and fringed sagewort may or may not re-sprout depending on conditions (USDA Forest Service 2011).
Mechanism
Invasive species can occupy the Degraded State (3) and drive it to the Invaded State (4). The Degraded State is at risk of this transition occurring if invasive seeds or viable material are present. The driver for this transition is presence of critical population levels of invasive species. The trigger is the presence of seeds or viable material of invasive species. This state has sufficient bare ground that the transition could occur simply due to presence or introduction of invasive seeds or viable material. This is particularly true of aggressive invasive species such as spotted knapweed and cheatgrass. This transition could be assisted by overgrazing (failure to adjust stocking rate to declining forage production), long-term lack of fire, or extensive drought.
Mechanism
Conifer tree/shrub count exceeds two stems per acre. The trigger of crossing a threshold is the presence of seeds or other viable material of these tree species.
Mechanism
Restoration of the Invaded State (4) to the Reference State (1) requires substantial energy input. The drivers for the restoration pathway are removal of invasive species, restoration of native bunchgrass species, persistent management of invasive species, and proper grazing management. Without continued control, invasive species are likely to return (probably rapidly) due to the presence of seeds and/or other viable material in the soil and management related practices that increase soil disturbance. If invaded by conifer encroachment, treatment depends on the condition of the rangeland. See Plant community 4.1 for alternative measures of restoration.
Sites that have transitioned from the Degraded State (3) to the Invaded State (4) may be severely lacking soil and vegetative properties that will allow for restoration to the Reference State. Hydrologic function damage may be irreversible especially with accelerated gully erosion.
Mechanism
If invasive species are removed before remnant populations of bunchgrasses have been drastically reduced the Invaded State (4) can return to the Altered State. The driver for the reclamation pathway is weed management with possible reseeding. Continued Integrated Pest Management (IPM) will be required as many of the invasive species that can occupy the Invaded State have extended dormant seed life. The trigger is invasive species control.
Mechanism
If invasive species are removed the site could return to the Degraded State (3). Without sufficient remnant populations of preferred plants the Invaded State (4) is not likely to return to any of the other states. The driver for the reclamation pathway is weed management without reseeding. The trigger is invasive species control. The invading species cause a significant increased soil loss due to lack of ground cover (Lacey et al. 1989).
Mechanism
Canopy cover of conifer tree/shrub cover exceeds two stems per acre. The threshold change is triggered by the presence of seeds or other viable material of invasive species.
Mechanism
Depending on the level of conifer canopy cover and its impact on rangeland health, restoration efforts may simply focus on removal of coniferous trees and shrubs to restore the Conifer Encroached State (5) to the Reference State (1).
If utilizing the phases established by Miller et al., management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers with brush management or prescribed fire combined. If mechanical removal of conifers is utilized, no grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment and/or rest is suggested. Given a short time removal of a Phase I encroachment will recover to Reference. Proactive pest management is encouraged.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
Mechanism
The Conifer Encroached State (5) Phases I and II will often resemble early stages of the Mixed Sagebrush Community (2.1) of the Altered State (2) on this site. If utilizing the phases established by Miller et al., management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers by brush Management or prescribed fire combined. If mechanical removal of conifers is utilized, minimal grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment or rest is suggested. Given a short time removal of a Phase I encroachment will recover to the Altered State. Proactive pest management is encouraged.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
Mechanism
The Conifer Encroached State (5) Phases II and III will likely resemble the Degraded State (3) on this site due to reduced mid-statured bunchgrasses. If utilizing the phases established by Miller et al., management and restoration methods will vary. A large majority of the conifer encroachment in MLRA 43B will fall into the early two phases described by Miller et al. This Restoration Pathway is exceedingly rare as it is typically not cost effective for land managers to manage for a degraded state.
Phase I may exhibit None-Slight to Moderate departures from rangeland health where removal of the conifers with brush management or prescribed fire combined. If mechanical removal of conifers is utilized, minimal grazing management is needed assuming relatively conservative management had been used prior to treatment. If prescribed fire is utilized, short term grazing deferment or rest is suggested. Given a short time removal of a Phase I encroachment will recover to the Degraded State. Proactive pest management is encouraged.
Phase II Encroachment may require a more intense mechanical removal of trees/shrubs with Prescribed Fire not being a feasible method of control as this community may be at risk of catastrophic fire due to canopy density. Phase II displays a Moderate departure from Reference suggesting an overall instability of the site such as reduced herbaceous production, reduced functional/structural groups (e.g. reduced mid-statured bunchgrasses), increase rill frequency and length, and possibly increased bare ground. Increased post treatment grazing management may be necessary. Grazing management may be as simple as short term growing season deferment however long term rest may be necessary in the latter stages of Phase II encroachment. Latter stages of Phase II encroachment will likely require some short term erosion mitigation such as straw waddles as well as range planting or critical area planting to re-establish any loss of native herbaceous plants particularly mid-statured cool season bunchgrasses.
Phase III Encroachment canopy cover resembles forested sites with larger trees and shrubs. Forest management style tree removal (woody debris and logs removed from the site) will be necessary prior to any prescribed burning as to prevent the fire from burning too hot. The result of a prescribed fire on this site are typically unknown as seed sources of native herbaceous plants are usually limited to small patches. Since herbaceous plants will likely have been depleted under a Phase III encroachment, there is an opportunity for large areas of bare ground, increase rill and in some cases gully erosion. Post treatment will require range planting or critical area seeding, erosion control, pest management, and possibly soil carbon amendments (biochar). Grazing management (primarily rest) will be necessary to ensure any new seedling establishment.
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