Flat-Bottom Wooded Draw
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
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Transition T1A
Introduction of exotic cool-season grasses
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Transition T2A
Long-term heavy continuous grazing and loafing by domestic livestock.
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Transition T2B
Extended periods of no fire
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Restoration pathway R3A
Mechanical brush control perhaps followed by a successful range planting
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Restoration pathway R4A
Stand replacing fire, mechanical treatment
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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 represents the natural range of variability that dominated the dynamics of this ecological site prior to European influence. The primary disturbance mechanisms for this site in the reference condition included frequent 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. These factors likely caused the community to shift both spatially and temporally between two community phases.
Historically, multi-aged deciduous trees (such as green ash, American elm, boxelder) and shrubs (such as chokecherry, plum, western snowberry, and Saskatoon serviceberry) dominated this site. Depending upon the degree of canopy cover, a diverse herbaceous understory would include Canada wildrye, western wheatgrass, green needlegrass, Virginia wildrye, Sprengel’s sedge, northern bedstraw, and blue lettuce.
Characteristics and indicators
Because of changes in disturbances and other environmental factors (particularly the widespread occurrence of exotic species), the Reference State is considered to no longer exist.
Resilience management
If intact, the reference state should probably be managed with current disturbance regimes which has permitted the site to remain in reference condition, as well as maintaining the quality and integrity of associated ecological sites. Maintenance of the reference condition is contingent upon a monitoring protocol to guide management.
Submodel
State 2
Native/Invaded State
Description
This state is similar to State 1: Reference State but has now been colonized by the exotic cool-season grasses (commonly Kentucky bluegrass and/or smooth brome) which are now present in small amounts. Although the state is still dominated by trees and shrubs, the understory of native grasses has seen an increase in exotic cool-season grasses. These exotic cool-season grasses can be quite invasive on the site and are particularly well adapted to heavy grazing, shading, as well as long-term non-use. These exotic cool-season grasses have been particularly and consistently invasive under extended periods of no fire. To slow or limit the invasion of these exotic grasses, it is imperative that managerial techniques (e.g., prescribed grazing, prescribed burning, brush management (mechanical juniper removal)) be carefully constructed, monitored, and evaluated with respect to that objective. If management does not include measures to control or reduce these exotic cool- season grasses, the transition to State 3: Invaded State should be expected.
The invasion of Rocky Mountain juniper within State 2 occurs when a juniper seed source is present. Lack of active juniper management will lead to State 4.0 Invaded Conifer State. Active management includes prescribed fire and brush management (mechanical juniper removal). Limiting juniper seed sources is important to avoid re-invasion of juniper on the site. Active monitoring and management are needed to remove new juniper seedlings as they establish from seedbanks or dispersal.
Other exotic plants invading the site include Canada thistle, leafy spurge, hounds tongue, and common burdock. Rocky Mountain juniper, creeping juniper, and perhaps eastern red cedar may also invade the site. Annual production of this state can be quite variable, in large part due to variations in shading and the amount of exotic cool-season grasses.
Characteristics and indicators
The presence of trace amounts of exotic cool-season grasses or juniper species indicates a transition from State 1 to State 2. The presence of exotic biennial or perennial leguminous forbs (i.e., sweet clover, black medic) may not, on their own, indicate a transition from State 1 to State 2 but may facilitate that transition.
Resilience management
To slow or limit the invasion of these exotic grasses or juniper species, it is imperative that managerial techniques (e.g., prescribed grazing, prescribed burning) be carefully constructed, monitored, and evaluated with respect to that objective.
Livestock grazing needs to be timed to select for herbaceous understory with limited browsing of native shrubs or trees. Species grazing preferences change with season; weather; soil moisture; and forage palatability, availability, and variety. Grasses become less palatable, less digestible, and lose nutrient content with maturity whereas shrubs tend to retain diet quality longer. Timing of grazing is particularly important in large pastures where Flat Bottom Wooded Draw sites are present and include a high proportion of uplands forage. Upland forage is more palatable than shrubs during certain seasons (generally spring, early summer, and fall if green- up occurs). Grazing in these seasons will shift use from wooded areas especially if water is located away from these areas.
Forage selectivity is a dynamic, situation-specific phenomenon. In woody areas, cattle generally don’t browse woody plants as frequently if a sufficient supply of palatable grass is available. However, where only a few woody plants are available, animals may seek them out to obtain dietary diversity. Studies have shown the strategic placement of a supplement and strategic location of water development can result in cattle spending more time and grazing in areas with the supplement than areas without.
Prescribed burning should be applied in a manner that maintains or enhances the overstory and the competitive advantage of fire adapted native trees and shrubs to promote sprouting. Prescribed burns should be applied as needed to adequately reduce/remove excessive plant litter and maintain the competitive advantage for native species. Timing of prescribed burns (spring vs. summer vs. fall) should be adjusted to account for differences in annual growing conditions and applied during windows of opportunity to best shift the competitive advantage to the native species.
Submodel
Description
This state is the result of invasion and dominance by the exotic cool-season grasses (commonly Kentucky bluegrass, smooth brome, and/or crested wheatgrass). It may be characterized by mature and decadent green ash scattered across the site and a lack of green ash regeneration in the sapling, shrub, and herbaceous layers. Kentucky bluegrass, smooth brome, and/or crested wheatgrass along with forbs dominate the herbaceous layer. Other exotic plants (e.g., hound’s tongue, common burdock, leafy spurge, Canada thistle) may also invade the site. Remnant chokecherry clumps may be scattered throughout the site. The exotic cool-season grasses have the greatest effect on the ecological processes, such as green ash seedling recruitment and restoration potential, due to their ability to form a dense sod and thatch layer inhibiting seed/soil contact.
These exotic cool-season grasses can be quite invasive on the site and are particularly well adapted to heavy grazing. They also often form monotypic stands. As these exotic cool-season grasses increase, both forage quantity and quality become increasingly restricted to late spring and early summer due to the monotypic nature of the stand, even though annual production may increase. Native forbs generally decrease in production, abundance, diversity, and richness compared to that of State 1: Reference State. Once the state is well established, prescribed burning and grazing techniques have been largely ineffective in suppressing or eliminating these exotic cool-season grasses, even though some short-term reductions may appear successful.
Characteristics and indicators
This site is characterized mature green ash and an herbaceous understory constituting greater than 30 percent of the annual production and native grasses constituting less than 40 percent of the annual production.
Resilience management
Light or moderately stocked continuous, season-long grazing or a prescribed grazing system which incorporates adequate deferment periods between grazing events and proper stocking rate levels will maintain this State. Application of herbaceous weed treatment, occasional prescribed burning and/or brush management may be needed to manage noxious weeds and increasing shrub (e.g., western snowberry) populations. A green ash/chokecherry plant community, as found in State 2, will not return without restoration. Research indicates that restoration would be difficult, requiring either a coincidence of increasingly unlikely biological and environmental conditions or large expenditures of time and money.
Submodel
Description
This state is characterized by a dominance of Rocky Mountain juniper in all layers with scattered mature/decadent green ash trees. Common juniper, creeping juniper, and eastern red cedar may also be present. Depending upon juniper density, the herbaceous layer may be minimal to non-existent and dominated by needlecast. The hydrologic function of this state has changed compared to that of State 1: Reference State and State 2: Native/Invaded State. The shallow rooting structure of the juniper and lack of native perennial grass species has reduced infiltration and increased the potential of erosion.
Characteristics and indicators
The dominance of woody species (by cover and production) distinguishes this state from other herbaceously dominated states.
Resilience management
This state is resistant to change in the long-term absence of fire. Restoration efforts would require the use of prescribed fire, mechanical treatment, and prescribed grazing. Considerable time and effort will be required to restore to other States.
Submodel
Mechanism
This is the transition from the State 1: Reference State to the State 2: Native/Invaded State due to the introduction and establishment of exotic cool-season grasses, typically Kentucky bluegrass and/or smooth brome. This transition is inevitable and corresponded to a decline in native woody canopy and a decline in native grasses and forbs; it may be due to wood-cutting, overgrazing by livestock and wildlife, invasion of cool- season exotic grasses, and multiyear drought. The threshold between states is crossed when Kentucky bluegrass, smooth brome, crested wheatgrass, or other exotic species became established on the site.
This transition was most likely to happen when the site was in Community Phase 1.2 and was prompted when an agent of change enhanced opportunities for non-native perennial grasses (primarily Kentucky bluegrass and smooth brome) to invade and eventually dominate the herbaceous vegetation layer. Agents of change could have included partial mortality of green ash (disease and fire) that reduced shading, plus improper grazing that reduced the competitive ability of native herbaceous species. Other potential agents of change may include surface disturbances, such as flash flows of runoff rainwater. Green ash draws, especially those near transportation corridors, were vulnerable to invasion by exotic cool-season grasses.
Constraints to recovery
Current knowledge and technology will not facilitate a successful restoration to Reference State.
Mechanism
This transition from the State 2: Native/Invaded State to State 3: Invaded State generally occurs with long-term heavy continuous grazing and loafing by domestic livestock. Exotic cool-season grasses, commonly Kentucky bluegrass and/or smooth brome, become the dominant graminoids. Recruitment of green ash ceases.
Studies indicate that a threshold may exist in this transition when both Kentucky bluegrass exceeds 30% of the plant community and native grasses represent less than 40% of the plant community composition. Similar thresholds may exist for other exotic cool-season grasses.
Constraints to recovery
Variations in growing conditions (e.g., cool, wet spring) will influence effects of various management activities on exotic cool-season grass populations.
Mechanism
This transition from the State 2: Native/Invaded to State 4: Invaded Conifer State generally occurs during extended periods of no fire, allowing establishment of junipers (often Rocky Mountain juniper, common juniper, creeping juniper, or perhaps eastern red cedar) particularly when adjacent or close to well-established juniper sites. This transition has become more frequent following European settlement when the historic fire regime was markedly reduced.
Constraints to recovery
The extended fire interval may make recovery doubtful due to the abundance of exotic cool-season grasses and lack of native grasses. Fire intensity along with consumption of available fuels may cause incomplete or patchy burns. Ladder fuel and/or fuel loading are required for successfully controlling ponderosa pine (crown vs. ground fire). Continued recruitment of seeds (juniper and pine) from adjacent sites will hamper site restoration.
Constraints to recovery include reticence to undertake tree removal and the perception that trees may be a desirable vegetation component for wildlife habitat, carbon sequestration, aesthetics, etc. Managing the site for mule deer, big horn sheep, livestock, or grassland nesting birds will need to consider the intensive management required to restore and maintain the site in State 2. The disturbance regime necessary to restore this site to State 2: Native/Invaded State is very labor intensive and costly; therefore, addressing woody removal earlier in the encroachment phase is the most cost-effective treatment for woody control.
Mechanism
This restoration from State 3: Invaded State to State 2: Native/Invaded State multi-year drought, may be accomplished with mechanical brush control followed by a range planting/transplanting. Mechanical brush control, perhaps coupled with chemical control, may be necessary before planting or transplanting to complete the restoration.
Mechanical/chemical treatments will break up the Kentucky bluegrass sod, followed by seeding and/or transplanting shade-tolerant native herbaceous species, chokecherry, and possibly snowberry. Prescribed fire may be needed to stimulate sprouting of the shrubs. Once well-established, the shrubs will help with snow catchment and provide protection for young green ash (which may also have to be transplanted). Transplanting green ash trees more than 6-7 feet tall would allow them to avoid much of the browsing pressure. The most likely result of this pathway is a return to Plant Community Phase 2.3.
Context dependence
Fire intensity along with consumption of available fuels may cause incomplete or patchy burns. Ladder fuel and/or fuel loading are required for successfully controlling ponderosa pine (crown vs. ground fire). Continued recruitment of seeds (juniper and pine) from adjacent sites will hamper site restoration. Intensive management is required to restore and maintain the site in State 3: Invaded State.
The method or methods of herbaceous weed treatment will be site specific to each situation; but generally, the goal would be to apply the pesticide, mechanical control, or biological control (either singularly or in combination) in a manner that shifts the competitive advantage from the targeted species to the native grasses and forbs. The control method(s) should be as specific to the targeted species as possible to minimize impacts to non-target species.
Mechanism
This restoration from State 4: Invaded Conifer State to State 3: Invaded State results from a stand replacing fire and/or mechanical treatment. This results in the site becoming dominated by exotic cool-season species along with remnant chokecherry, western snowberry, and forbs some of which may be noxious weeds (e.g., leafy spurge, Canada thistle, hounds tongue, absinthium wormwood).
Context dependence
Fire intensity along with consumption of available fuels may cause incomplete or patchy burns. Ladder fuel and/or fuel loading are required for successfully controlling ponderosa pine (crown vs. ground fire). Continued recruitment of seeds (juniper and pine) from adjacent sites will hamper site restoration. Intensive management is required to restore and maintain the site in State 2: Native/Invaded State.
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