Ecological dynamics

Range in Characteristics:

Coarse fragments in the surface layer or a decrease in clay in the subsoil will favor the presence of Thurber’s needlegrass in the stand. Similarly, big sagebrush increases with a decrease in clay in the surface layer. Western juniper will increase in the absence of fire, particularly at the upper end of the precipitation range. As this site deteriorates the soils with higher clay content in the surface will favor the invasion of medusahead and those with more loam in the surface will be more favorable to cheatgrass invasion.

Response to Disturbance:

If the condition of the site deteriorates as a result of overgrazing, bluebunch wheatgrass, and Thurber’s needlegrass decrease while broom snakeweed increases and annuals invade. In the absence of periodic fire, western juniper will increase. Under deteriorated conditions bare soil interspaces increase and excessive erosion reduces the site productivity.

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 annual grasses. 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 and/or medusahead abundance 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 an annual grass 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 type 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:

This site has low resilience to disturbance due to the low annual precipitation of less than 12 inches. 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 incorporate methods to provide soil cover to provide microsites for seedling establishment along with seeding of adapted native and/or introduced species.

Fire is not a recommended tool of rehabilitation when significant amounts of annual grasses are present due to the increased risk of rapid increase in the annual grasses that can control the ecological processes on the site.

The repair pathway of the sagebrush annual grass 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 presence of annual grasses. Every effort should be made to prevent the establishment of annual grasses.

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 steppe phase.

Phase 1.1. Reference Plant Community Phase (RPCP) is the perennial grass phase. This plant community is strongly dominated by bluebunch wheatgrass and Thurber’s needlegrass with basin wildrye and Sandberg bluegrass being common and lesser amounts of other perennial grasses and a small amount of forbs. Basin big sagebrush is common. Grasses compose 90 % of the community, forbs and shrubs 5% each. 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 and normal fire frequency of 40-60 years (1.1A). This transition would be accelerated with improper grazing. The composition of sagebrush within the plant community will increase as the length of time between fires gets longer. 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 plant community. 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 dominant plant communities.

Phase 1.3. Sagebrush or juniper-sagebrush is dominated by either juniper or basin big sagebrush, bluebunch wheatgrass, Thurber’s needlegrass and Sandberg bluegrass. This 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 and/or medusahead 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. 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, with minor amounts of 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 fire will no longer carry (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 state, 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 of adapted native grasses, forbs and shrubs. Seeding with introduce species will move the site to State 6.

State 3. This state is dominated in the overstory by decadent basin big sagebrush (Phase 3.1) with cheatgrass and/or medusahead in the understory. Ecological processes in this state are controlled by the sagebrush. This state has developed as a result of continued improper grazing or drought in the absence of fire (IRT1B). If fire occurs, the plant community transitions to State 4 (IRT3A) a cheatgrass and/or medusahead dominated plant community. The risk of an irreversible transition (IRT3B) to the eroded conditions of State 5 occurs 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, rabbitbrush, and annual grasses and reseeding of adapted native grasses, forbs, and shrubs. Seeding with introduce species will move the site to State 6.

State 4. This state is dominated by cheatgrass and/or medusahead with few other shallow-rooted grasses in the understory but may have some broom snakeweed and/or rabbitbrush (4.1) in the overstory. This state is recognized as the annual grass phase and is a result of fire and improper grazing. Continued improper grazing and fire will transition this state to the eroded state 5. The ecological processes in this state are controlled by cheatgrass and/or medusahead.

State 5. This is the eroded state and is recognized by the soil erosion that is occurring or has occurred on site. Since this state occurs through widespread erosion as a result of 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 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. 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, annual grasses, sagebrush and/or juniper. State 6 can transition to any of the other states, except State 1, with improper grazing and/or fire.