Ecological dynamics

The reference plant community is dominated by Wyoming big sagebrush and bluebunch wheatgrass. Basin big sagebrush and Thurber needlegrass are present. Sandberg bluegrass is the dominant shallow rooted perennial grass. A variety of forbs are common. Vegetative composition of the community is approximately 80 percent grasses, 10 percent forbs and 10 percent shrubs. The approximate ground cover is 70 to 80 percent (basal and crown).


Range in Characteristics:
Bluebunch wheatgrass increases on clayey surfaces. Thurber’s needlegrass increases on loamy surfaces and on droughtier sites. Wyoming big sagebrush is clearly dominant at lower precipitations while basin big sagebrush increases at higher precipitations. Crab apple is associated with sediments including those interlaid with diatomaceous earth. Production increases at the upper end of the precipitation zone.

Response to Disturbance:
When the condition of the site deteriorates as a result of over grazing bluebunch wheatgrass rapidly decreases. Wyoming big sagebrush and Sandberg bluegrass increase. Cheatgrass, medusahead, other annuals, biennial weeds and bulbous bluegrass are strong invaders. With fire and continued disturbance sagebrush is severely impacted, rabbitbrush increases slightly and annuals and noxious biennial forbs continue to invade. Bare ground increases and excessive erosion contributes to downstream sedimentation. The excessive erosion is most pronounced in drainage areas where deep incised gulley’s form.

States: ARTRW/POSE-BRTE; POSE-POBU/biennial forbs or BRTE-TACA8/biennial forbs (following fire on degraded range)

Treatment Response:

The repair pathways located between State 1 and States 2 and 3 indicates potential for rehabilitation. It will require mechanical or chemical treatment of sagebrush and annual grasses along with seeding of native or adapted introduced species in either of these two plant communities. If annual grasses are present in either of them it will require long term treatment. Since the risk of a seeding failure is high, it would be advisable to implement assisted succession by planting an aggressive perennial such as crested wheatgrass and then following up years later with a reintroduction of native species. Every effort should be made to prevent establishment of annual grasses on this site.
Reference Plant Community

State 1 – Reference State

Three plant community phases occur in the Reference State. They are phase 1.1, the perennial grass and forb phase, phase 1.2, the sagebrush grass phase and phase 1.3, the sagebrush dominant phase.

Phase 1.1. The perennial grass and forb phase. This plant community is strongly dominated by bluebunch wheatgrass with Thurber’s needlegrass, basin wildrye and Sandberg bluegrass being common. Lesser amounts of other perennial grasses and a small amount of forbs are also present. Energy capture, nutrient cycling and water use are controlled by the perennial grasses.

Phase 1.2. The Reference Plant Community Phase (RPCP) is the sagebrush grass phase. The sagebrush grass phase results with prescribed grazing and a normal fire frequency of 40-60 years (1.1A). Wyoming big sagebrush and basin big sagebrush are both common. The composition of sagebrush within the plant community will increase as the length of time between fires gets longer. Grasses compose 85 % of the community, forbs 5% and shrubs 10%. A period of improper grazing can accelerate the increase in sagebrush even if the bunchgrass plant community is maintained. Under prescribed grazing and fire the plant community pathway (1.2A) moves back toward Phase 1.1, the perennial grass and forb phase. With the continued absence of fire and improper grazing management or drought (1.2B), the plant community will move towards phase 1.3, sagebrush dominant phase. The ecological processes in this phase are still controlled by the perennial grasses.

Phase 1.3. The sagebrush dominant phase is dominated by Wyoming or basin big sagebrush, and lesser amounts of bluebunch wheatgrass, Thurber’s needlegrass, basin wildrye and Idaho fescue. Sandberg bluegrass has increased in the stand as well as cheatgrass. Big sagebrush controls the ecological processes in this plant community. This phase is a result of the absence of fire with improper grazing or drought and can occur through community pathways 1.1B or 1.2B. This phase is the “at risk” plant community within State 1. As the site deteriorates the potential for cheatgrass invasion increases. With prescribed grazing and fire this phase can be returned to Phase 1.1 by community pathway 1.3A. Since this phase is “at risk” it can transition to State 2 (IRT1A) with the continued lack of fire and improper grazing or drought. With fire, improper grazing and drought this plant community can transition to State 3 (IRT1B).

State 2. This State is dominated by big sagebrush which controls all of the ecological processes. Initially, Phase 2.1, the sagebrush dominant phase is occupied by Wyoming and basin big sagebrush, with minor amounts of bluebunch wheatgrass and Thurber’s needlegrass. Sandberg bluegrass has increased along with cheatgrass. If fire continues to be suppressed and severe improper grazing continues, the sagebrush will become decadent and the cheatgrass will replace the bunchgrass understory. The potential for soil erosion increases as this transition in the plant community occurs. The risk of an irreversible transition (IRT2A) over an abiotic threshold to the Erosional State, State 4, increases with fire, improper grazing or drought.

State 3. This state is dominated by annual grasses with few other shallow-rooted grasses in the understory but may have some rabbitbrush (3.1) in the overstory. This state is recognized as the annual grass phase and is a result of fire, improper grazing and drought. Continued improper grazing and fire will transition this state to the eroded state 4. The ecological processes in this state are controlled by the annual grasses.

State 4. This is the eroded state and is recognized by the soil erosion that is occurring or has occurred on the site in the past. Since this state has occurred through widespread erosion as a result of severe improper grazing in combination with fire all of the other states can transition to this State. The increase in bare ground facilitates the increase in wind and/or water erosion. Abiotic factors control site resources and ecological functions. Rehabilitation of this state may not be practical or possible due to extreme soil loss.