Mountain Loam Gunnison Basin LRU
Scenario model
Current ecosystem state
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Management practices/drivers
Select a transition or restoration pathway
- Transition T1A More details
- Transition T1B More details
- Restoration pathway R2A More details
- Transition T2A More details
- Restoration pathway R3A More details
- Transition T3A More details
- Restoration pathway R4B More details
- Restoration pathway R4A More details
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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
Grass and minor amounts of woody plants such as sagebrush and several forbs make up most of the vegetative cover of this state. The site is treeless; however, trees commonly are in the general vicinity. The dominant grass is Arizona fescue, but subdominant grasses include muttongrass, Letterman’s needlegrass, and pine needlegrass. Sandberg bluegrass, elk sedge, Geyer’s sedge, and bottlebrush squirreltail also are present. The principal forbs are germander beardtongue, flowery phlox, sulphur-flower buckwheat, and hollyleaf clover. Flowery phlox is replaced by Hood’s phlox (spiny phlox) at the lowest elevations. The major shrubs are mountain big sagebrush and yellow rabbitbrush. This state is in areas where proper grazing management has been used over a long period. Proper grazing management allows for the establishment of understory species and increased vigor of stressed plants. Sagebrush may become dominant if the understory species are over-defoliated.
This state represents the community and function of the site prior to European settlement. Two dominant plant community phases are in the reference state. Fire and drought are natural disturbances that drive the pathways between the community phases. The site is subject to frequent periods of drought and fires of mixed intensity and frequency. The fire return interval (FRI) is 10 to 70 years in the more arid sagebrush areas (Wyoming big sagebrush) (Howard, 1999), and it is 15 to 40 years in the wetter mountain big sagebrush areas (Johnson, 2000). Sagebrush species less than 50 years old are easily killed by fire. Most forb species that re-sprout from a caudex, corm, bulb, rhizome, or rootstock recover rapidly following fire, and suffrutescent, low-growing or mat-forming forbs such as pussytoes or buckwheat may be severely damaged by fire (Miller and Eddleman, 2001).
Recurring fires less than 10 years apart maintain the grassland and prevent mountain big sagebrush from becoming established. Five to ten years are needed for mountain big sagebrush to establish and 15 to 20 years for it to return to pre-burn density and canopy cover (Nelle, 2000). Severe fires can slow re-establishment of mountain big sagebrush and extend the period needed for it to become dominant (Nelle et al., 2000). Total production of grass herbage reaches its maximum 2 to 5 years after burning, but the period of increased grass cover is short lived. It begins to decline as the abundance of sagebrush and other shrub species increases. The forb cover has greater biomass 5 to 15 years after burning (Nelle et al., 2000).
When the density and canopy cover of sagebrush are near maximum for several decades, sagebrush can become competitive with the understory forbs and grasses. Grazing can accentuate the competitiveness of sagebrush. Sagebrush has tap, lateral, and tertiary roots that give it a competitive advantage. Thinning of sagebrush crowns may be necessary for establishment of the understory. Treatment methods should be adapted to the specific needs of the site. Sagebrush recruitment is episodic in 7- to 9-year cycles, and sagebrush seeds have limited viability after the second year (Winward, 2004). Resting or deferring grazing after shrub management promotes the establishment of grasses and slows the establishment of sagebrush. Grazing by species that prefer grasses and forbs will speed up the establishment of sagebrush. Needle and thread (Bunting, 1985), Indian ricegrass, and muttongrass are very palatable and can be over-defoliated. Mountain big sagebrush, western wheatgrass, yellow rabbitbrush, Sandberg bluegrass (Bunting, 1985), prairie Junegrass (Bunting, 1985), blue grama, and pine needlegrass are less palatable and can increase in abundance unless burned or defoliated by browsing or grazing. The species most likely to increase in abundance are rabbitbrush and snakeweed.
Submodel
State 2
Mature Sagebrush State
Description
State 2 is a sagebrush-dominant community. It has more shrub cover and less understory cover as compared to state 1. State 2 is an even-structured, single-aged stand. It has more Sandberg bluegrass and western wheatgrass and less prairie Junegrass as compared to State 1.
The abundance of low shrubs such as yellow rabbitbrush and spineless horsebrush is higher and that of herbaceous plants in the understory is lower as compared to state 1. State 2 also has a lower diversity of species. Improper grazing management that decreases the abundance of deep-rooted understory species can lead to compaction of the soil, erosion, decreased organic matter in the soil, and increased exposure due to a reduction in the amount of litter.
Submodel
Description
This state is characterized by sagebrush removal due to fire or shrub management treatments, which may include chaining, disking, and mowing. The community dynamics are similar those of the reference state. This state could persist for long periods. Sagebrush will start to re-establish when the conditions are favorable. This site historically has been seeded to perennial species such as crested wheatgrass and Russian wildrye.
Due to changes in soil properties and the presence of seeded plants, this state is not likely to return to the reference state unless restoration practices are applied.
Submodel
Description
State 4 consists dominantly of sagebrush. This state has more shrub cover and less understory cover. The community is an even-structured, single-aged stand. Less introduced species are in this state. The abundance of low shrubs such as yellow rabbitbrush and spineless horsebrush is increased, replacing some of the herbaceous component in the understory. This state has minimal diversity of species. Improper grazing management leads to a decrease in the abundance of deep-rooted plants in the understory.
Submodel
Mechanism
Improper grazing for extended periods during the growing season can reduce the amount of fine fuel in the understory, which favors sagebrush encroachment. Lack of fire over time can cause this transition (McIver et al., 2010). Extended periods of drought and lack of insect and pathogen activity can result in a single-aged stand of sagebrush. This transition is characterized by a decrease in the understory and an increase in the amount of bare ground between the shrubs and other evidence of soil erosion. The depletion of fine fuel due to improper grazing shifts the fire regime from relatively frequent fires of low to mixed severity (10- to 50-year mean fire return interval) to less frequent fires of high severity (more than 50-year mean fire return interval) (McIver et al., 2010). Short-term drought in winter and early in spring facilitates and increase in the understory. Grasses respond quicker to moisture received in midsummer and late in summer than do shrubs. Loss of topsoil and a reduction in the water-holding capacity in the upper part of the soil occur when the understory is not sufficient to prevent runoff.
Mechanism
Historically, this transition has resulted from a catastrophic wildlife but it can be induced by human activity (shrub management or prescribed burning). Introduced species are seeded. Short-term loss of topsoil and a reduction in the water-holding capacity in the upper part of the soil occurs, and the diversity of species is decreased.
Mechanism
This transition is caused by catastrophic fire or other natural disturbances or by human activity (shrub management or prescribed burning). Native species are seeded.
Mechanism
This transition is caused by human activity (shrub management or prescribed burning) or a catastrophic wildfire. Introduced species are seeded.
Mechanism
This site may be restored to resemble the Arizona fescue and mountain big sagebrush community of the reference state by seeding commercial mixtures of native grasses, forbs, and shrubs. Selective removal of introduced species also may be needed. If properly managed, a semblance of the diversity and complexity of the reference state can be restored.
Mechanism
Improper grazing for extended periods during the growing season can reduce the amount of fine fuel in the understory, which favors sagebrush encroachment. Lack of fire over time can cause this transition (McIver et al., 2010). Extended periods of drought and lack of insect and pathogen activity can result in a single-aged stand of sagebrush. This transition is characterized by a decrease in the understory and an increase in the amount of bare ground between the shrubs and other evidence of soil erosion. The depletion of fine fuel due to improper grazing shifts the fire regime from relatively frequent fires of low to mixed severity (10- to 50-year mean fire return interval) to less frequent fires of high severity (more than 50-year mean fire return interval) (McIver et al., 2010). Short-term drought in winter and early in spring facilitates an increase in the understory. Grasses respond quicker to moisture received in midsummer and late in summer than do shrubs. Loss of topsoil and a reduction in the water-holding capacity in the upper part of the soil occur when the understory is not sufficient to prevent runoff.
Mechanism
The site may be restored to resemble the western wheatgrass and mountain big sagebrush community in the reference state by seeding commercial mixtures of native grasses, forbs, and shrubs. Selective removal of introduced species also may be needed. If properly managed, a semblance of the diversity and complexity of the reference state can be restored. This restoration pathway is intensive if attempted on a large scale.
Mechanism
Fire and wet periods can cause the mature, single-aged shrub communities to transition to grassland if proper grazing is implemented and sufficient seed is in the seedbank to regenerate the understory species. If sufficient seed or mature plants are not available, reseeding may be needed. Shrub management practices such as prescribed burning and prescribed grazing can be used to assist in restoring state 4 to state 3.
Model keys
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The Ecosystem Dynamics Interpretive Tool is an information system framework developed by the USDA-ARS Jornada Experimental Range, USDA Natural Resources Conservation Service, and New Mexico State University.