Ecological dynamics

Range in Characteristics:

One-spike Danthonia can be expected to be a greater percentage of the species composition in microsites that are intermittently ponded during the late winter and early spring and where the soil surface horizon is shallower. Sandberg bluegrass becomes a greater percentage of the species composition where the site occurs near the lower limits (12 inches) of the precipitation range of occurrence and on the shallower soils. Total production is proportional to surface soil depth, decreasing as the surface soil layer becomes shallower.

Response to Disturbance:

With improper grazing Idaho fescue and bluebunch wheatgrass will decrease. With continued improper grazing onespike danthonia decreases and low sagebrush and Sandberg bluegrass increase. With continued deterioration, annuals invade. Increased bare ground reduces site productivity and contributes to erosion on the steeper portions of the site. The historical fire frequency in State 1 is expected to be 60 to 80 years. This fire frequency minimizes juniper invasion into the site as very few if any juniper survive to maturity. Many occurrences of the site have no juniper.

Treatment Response:

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 low sagebrush phase, phase 1.2 the low sagebrush or juniper low sagebrush phase and phase 1.3, the low sagebrush or juniper low sagebrush dominant phase.

Phase 1.1 is the reference plant community phase (RPCP), the perennial grass and low sagebrush phase which is expressed with normal fire frequency when low sagebrush is significantly reduced and any juniper seedlings and saplings that may be present are eliminated as well as a few of the old growth juniper if present. In this phase the density of low sagebrush and other shrubs are significantly reduced and the dominant visual aspect of the site is perennial grasses with few forbs and low sagebrush. Over time with the absence of fire and proper grazing the low sagebrush and other shrubs reestablish, annual forbs are reduced and the plant community pathway (CP 1.2A) moves back toward the low sagebrush or juniper low sagebrush plant community, Phase 1.2. With normal or reduced fire frequency the plant community pathway (CP1.1B) moves toward phase 1.3. The vegetative composition of the community is approximately 80 percent grasses, 8 percent forbs, and 12 percent shrubs. Any exotic plant species are usually maintained at very low levels by the healthy native plant community.


Phase 1.2, the low sagebrush or juniper low sagebrush phase is dominated by low sagebrush with or without juniper, Idaho fescue, and bluebunch wheatgrass, with Sandberg bluegrass and one-spike danthonia being common. Usually the juniper are widely scattered. A variety of forbs including buckwheat, serrate balsamroot, western yarrow and phlox are present. Fire in this community (1.2A) returns it to phase 1.1. With less than normal fire frequency (1.2B) the low sagebrush and the juniper become dominant, improper grazing accelerates the change to the low sagebrush or juniper low sagebrush dominated phase (1.3).


Phase 1.3, is dominated by low sagebrush with decreased amounts of perennial grasses and if juniper is present there is an increase in juniper seedlings and saplings and a few old growth juniper may be present. This phase is a result of Phase 1.1 having an extended period of time without fire and with or without improper grazing (CP1.1B) or Phase 1.2 being improperly grazed with less than normal fire frequency (CP 1.2B). With fire at normal frequency and proper grazing this phase can be returned to Phase 1.1 by a community pathway CP1.3A. Phase 1.3 is the plant community “at risk” of transitioning across the threshold to another state. With continued improper grazing management and lack of fire, it may transition (IRT1A) to State 2 with abundant juniper seedlings, saplings and a few mature trees. If exotics such as cheatgrass are present in sufficient quantity in Phase 1.3 and fire occurs more often than the expected frequency the plant community may begin a transition (IRT1B) with or without proper grazing to an annual grass dominated state, state 3.

State 2 is a state dominated by low sagebrush and other shrubs and/or western juniper with severely decreased amounts of perennial grasses. The transition (IRT1) from state 1 phase 1.3 is driven by no fire with improper grazing and/or drought as it crosses a biotic threshold where low sagebrush and/or juniper control all of the site’s ecological processes. Over time on the steeper slopes (10-12%), an edaphic threshold can also be crossed. Where juniper is present and it matures it fully occupies the site. The repair pathway (RP1) from state 2 back to state 1 is generally not economically feasible and requires mechanical and/or chemical treatment of sagebrush, other shrubs, juniper and exotic annual grasses and may also require seeding of desired forbs and grasses. The sites’s ecological processes are controlled by the low sagebrush or juniper in this state.

State 3 is a state dominated by exotic annuals such as cheatgrass and/or medusahead and may have a few scattered old growth juniper. This state results from a transition (IRT2A), driven by fires from state 2 crossing a biotic threshold or a transition (IRT1B) from phase 1.3, state 1 by frequent fires with or without proper grazing. The repair pathway (RP2) from state 3 back to state 1 is generally not economically feasible requiring chemical and/or mechanical treatment of annual grasses along with seeding of perennial grasses and shrubs. In this state the ecological processes are controlled by annual grasses.

State 4 is the eroded state resulting from frequent fires in states 2 (IRT 2B) or 3 (IRT3A) that exposes the soil to accelerated erosion. The ecological processes in this state are controlled by abiotic conditions.