Ecological dynamics

This site occurs on fan remnants, alluvial fans, benches and hillslopes. Grasses with few forbs and shrubs dominate this plant community. Fluctuations in species composition and relative production may change from year to year dependent upon abnormal precipitation or other climatic factors. Bluebunch wheatgrass is well adapted to this site and is the predominant plant if the plant community is in high ecological condition.

Range in Characteristics: Thurber’s needlegrass increases on the shallower soils with gravelly surfaces, especially on the lower end of the precipitation zone within this site.

Response to Disturbance: Improper grazing will cause a decrease in bluebunch wheatgrass and Thurber’s needlegrass while Sandberg bluegrass increases. If deterioration continues Sandberg bluegrass will decline with an increase in annual grasses, weeds, and invasive brush species. The potential for cheatgrass or Medusahead invasion is increased as the site deteriorates.

Multiple pathways of change exist from the Juniper Sagebrush Steppe phase of State 1. If fire is suppressed juniper will continue to expand and out-compete both the bunchgrass and sagebrush understory. When fine fuels are reduced to the point where fire no longer will carry, the site will cross a threshold and transition to Juniper Sagebrush Steppe. With a canopy fire the Juniper Sagebrush Steppe has the potential to transition to cheatgrass. Maturation of the juniper community leads to a juniper woodland with no more than a trace amount of sagebrush and deep-rooted perennial bunchgrasses. The potential for soil erosion increases as the juniper woodland matures and the understory plant community cover declines. The risk of a transition over an abiotic threshold to the Juniper Woodland erosional phase increases with increasing slope and increasing bare ground.

With no fire, improper grazing and/or severe drought within the Juniper Sagebrush Steppe phase of State 1, the perennial bunchgrasses will continue to decline while cheatgrass increases and sagebrush matures further facilitating the decline in bunchgrass. This feedback continues until sagebrush and annual grasses control ecological processes. Frequent fire transitions this community to a cheatgrass dominated state. The risk of a transition over an abiotic threshold to the erosional state increases with increasing slope and increasing bare ground.

Abusive improper grazing can cause seeded phases to transition either to a decadent sagebrush cover or a juniper dominated system. With improper grazing and fire the seeded rangeland has the potential to convert to annual grasses or an eroded state.

Treatment Response: Much of this site occurs towards the 12 inch end of the precipitation zone rather than the 9 inch giving this site greater resistance and resilience to disturbance than other sites in this precipitation zone. One repair pathway indicates potential exists for rehabilitation of the juniper controlled plant community. Potential for success is dependent upon climatic factors and the existence of annual grasses. If annual grasses are present it will require long term treatment. Mechanical treatment of junipers will provide soil cover to facilitate microsites for seedling establishment of seeded adapted native and/or introduced species.

Fire is not a recommended tool of rehabilitation due to the increased risk presented by the presence of annual grasses.

The repair pathway of the sagebrush cheatgrass phase requires chemical or mechanical control of the sagebrush and annual grasses along with seeding. The potential for failure of rehabilitation projects increases with the increased presence of annual grasses. Every effort should be made to prevent the establishment of annual grasses.

Reference Plant Community

State 1 – Reference State

Three plant community phases occur in the Reference State. They are phase 1.1, the Reference Plant Community Phase (RPCP) which is the perennial grass and forb phase, phase 1.2, the sagebrush phase and phase 1.3, sagebrush dominate or the juniper-sagebrush phase.

Phase 1.1. Reference Plant Community Phase (RPCP) is the perennial grass phase. This plant community is strongly dominated by bluebunch wheatgrass with Sandberg bluegrass and Thurber needlegrass being common and lesser amounts of other perennial grasses and a small amount of forbs. Basin big sagebrush and broom snakeweed are common. Grasses compose 80 % of the community, forbs and shrubs 10% each and Juniper less than 1%. Energy capture, nutrient cycling and water use are controlled by the perennial grasses.

Phase 1.2. Sagebrush phase. The sagebrush phase results with prescribed grazing with normal fire frequency of 40-60 years (1.1A). The composition of sagebrush within the plant community will increase as the length of time between fires gets longer. 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 plant 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 dominate or the juniper-sagebrush plant phase.

Phase 1.3. The sagebrush or juniper-sagebrush communities are dominated by either juniper or basin big sagebrush, bluebunch wheatgrass, Thurber’s needlegrass and Sandberg bluegrass. The plant community 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) or State 3 (IRT1B) with the continued lack of fire and improper grazing or drought. With frequent fire this plant community can transition to State 4 (IRT1C).

State 2. Juniper dominated state. This State is dominated by juniper which controls all of the ecological processes. Initially, Phase 2.1, the Juniper-sagebrush phase is occupied by juniper, basin big sagebrush, bluebunch wheatgrass, Thurber’s needlegrass and Sandberg bluegrass with a trace of cheatgrass. If fire continues to be suppressed and severe improper grazing continues, juniper will continue to increase and out compete both the sagebrush and bunchgrass understory. When fine fuels are reduced and will no longer carry fire (fire proof), the site transitions to a juniper woodland community (Phase 2.2). The potential for soil erosion increases as the juniper woodland matures and the understory plant community declines. If a crown fire occurs, State 2 will transition (IRT 2A) to State 4. The risk of an irreversible transition (IRT2B) over an abiotic threshold to the juniper woodland erosional phase of State 5 increases with increasing slope and increasing bare ground. The repair pathway (RP2) from State 2 back to State 1 is generally not economically feasible and would require mechanical treatment of the junipers and seeding to adapted native grasses, forbs and shrubs.

State 3. Sagebrush dominated state. This state is dominated in the understory by cheatgrass and in the overstory by decadent basin big sagebrush (Phase 3.1). This state has developed as a result of continued improper grazing or drought in the absence of fire (IRT 1B). If fire occurs, the plant community transitions to State 4 (IRT 3A) a cheatgrass, Sandberg bluegrass, broom snakeweed and rabbitbrush plant community. The risk of an irreversible transition (IRT3B) to the eroded conditions of State 5 is paramount with severe improper grazing in combination with fire. The repair pathway (RP3) from State 3 back to State 1 is generally not economically feasible and requires mechanical and/or chemical treatment of the basin big sagebrush and rabbitbrush, as well as the cheatgrass and reseeding of adapted native grasses, forbs, and shrubs. Ecological processes in this state are controlled by the sagebrush.

State 4. Cheatgrass dominated state. This state is dominated by cheatgrass and shallow-rooted grasses in the understory with broom snakeweed and/or rabbitbrush (4.1) in the overstory. This state is recognized as the cheatgrass phase and is a result of fire and improper grazing. The ecological processes in this state are controlled by cheatgrass.


State 5. Eroded state. This is the eroded state and is recognized by the soil erosion that is occurring or has occurred on site. Since this state has occurred through either widespread erosion or through severe improper grazing in combination with or without fire all of the other states can transition to this State. The increase in bare ground facilitates the susceptibility of the site to an 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.

State 6. Seeded state. As in State 1, three plant community phases occur in the seeded state. They are 6.1, seeded grass phase; 6.2 Sagebrush seeded grass phase; and 6.3 Sagebrush and/or Juniper seeded grass phase. These three plant communities respond to improper grazing, fire or no fire the same as the plant community phases in State 1. As in 1.3, phase 6.3 is the “at risk” plant community in this state. The seeded state with introduced species is a common occurrence on this ecological site. Improper grazing of the seeded rangeland can cause a reduction in deep rooted perennial grasses in favor of Sandberg’s bluegrass, cheatgrass, sagebrush and or juniper. State 6 can transition to any of the other states, except State 1, with improper grazing and/or fire.