Ecological dynamics
State 1
Reference State
The reference state was determined by literature review, historical accounts and observations of trends in plant community dynamics. Relic areas not influenced by grazing were not located within this site and may not exist. Community composition data were inferred from State 2.
The reference state represents the plant communities and ecological dynamics of this ecological site under pre-settlement conditions and a natural disturbance regime. The plant communities of the reference state were likely similar to the climate induced plant communities of the interpretive state (State 2), and were characterized by a relatively sparse shrub cover of valley saltbush with Indian ricegrass and James’ galleta. Indian ricegrass and valley saltbush cover were likely higher in the reference state. James’ galleta often increases under grazing due to loss of less grazing tolerant species. Annual forbs were likely sparse and a minor component of the vegetation communities, highly dependent on precipitation timing and amount. The primary disturbances included fluctuations in precipitation and native ungulate browsing. Plant community composition likely changed during wet and dry periods, fluctuating between community phases 1.1 and 1.2.
Reference State: Plant communities influenced by climate fluctuations between wet and dry periods.
Indicators: Communities dominated by valley saltbush, with Indian ricegrass and James’ galleta important perennial grasses. No invasive species present.
Feedbacks: Natural fluctuations in climate allow for a self-sustaining sparse shrub community with shrub and grass components.
At-risk Community Phase: Community 1.2 is particularly susceptible to damage from livestock grazing, invasion by non-native species, and erosion.
Trigger: Improper livestock grazing in an arid system that did not evolve with large herbivores, which reduced plant cover and disturbed soils, and concomitant invasion of non-native plants that permanently altered ecological dynamics.
Community 1.1
Valley saltbush /Indian ricegrass – James’ galleta shrubland
Data for this community phase does not exist, but the community composition was likely similar to community phase 2.1, except with higher vegetative cover and production, fewer forbs, and a greater importance of Indian ricegrass and less importance of James’ galleta. Species composition in the below table was interpreted from Community Phase 2.1.
Community 1.2
Valley saltbush /James’ galleta – Indian ricegrass shrubland
Data for this community phase does not exist, but the community composition was likely similar to community phase 2.2, except with higher vegetative cover and production and fewer forbs. James’ galleta may naturally have been a more dominant grass in this phase due to higher drought tolerance than Indian ricegrass.
Pathway 1.1a
Community 1.1 to 1.2
This pathway occurs when a dry climatic phase triggers mortality and dieback in valley saltbush, Indian ricegrass, and other shallow-rooted shrubs and herbaceous species. James' galleta may be impacted with severe drought, but is generally more tolerant of drought conditions than the other dominant species.
Pathway 1.2a
Community 1.2 to 1.1
This pathway occurs with wetter than normal, or a return to normal precipitation periods and time, that allow for recruitment and growth of valley saltbush and Indian ricegrass.
State 2
Current Potential
This state represents the current potential of this ecological site, and the dynamics include disturbance by livestock and invasive species in addition to the climate fluctuations that influenced the reference state. This state will naturally fluctuate between community phases 2.1 and 2.2, and will shift to community phase 2.3 with abusive livestock use. Continued abusive use, especially if coupled with drought, could cause a transition to a degraded state (State 3), or a forb dominated state (State 4).
Current Potential State: Plant communities influenced by climate fluctuations between wet and dry periods, livestock grazing, and invasive plants.
Indicators: Communities dominated by valley saltbush with Indian ricegrass and James’ galleta important perennial grasses. Invasive species including cheatgrass and redstem stork’s bill (Erodium cicutarium) are typically present but not abundant.
Feedbacks: Natural fluctuations in climate allow for a self-sustaining sparse shrub community with shrub and grass components. Improper livestock use that damages soils, reduces vegetative cover and promotes establishment of non-native species.
At-risk Community Phase: Community phases 2.2 and 2.3 are at risk of transitioning to a degraded or forb dominated state with continued abusive livestock grazing use, especially in combination with drought.
Trigger: Continuous improper livestock grazing, or severe drought with invasive plant invasion.
Community 2.1
Valley saltbush /Indian ricegrass – James’ galleta shrubland
This phase is characterized by shrub dominance, with valley saltbush being dominant shrub. Secondary shrubs are of minor importance. Common species may include green molly (Bassia americana), greasewood (Sarbotus vermiculatus), and broom snakeweed (Gutierrezia sarothrae). Perennial grasses are an important component of this phase, with Indian ricegrass, squirreltail (Elymus elymoides), and James’ galleta important species. Cheatgrass may be present. The forb component of this community is highly variable, with composition and amounts of forbs varying from year to year and site to site. The non-native annual forb redstem stork’s bill may be present.
Community 2.2
Valley saltbush /James’ galleta shrubland
This community phase is characterized by valley saltbush, with minor secondary shrubs as in community phase 2.1. James’ galleta is the dominant grass in this phase. Squirreltail and Indian Ricegrass are the sub-dominant grass cover. Cheatgrass may be present at low amounts. Forbs may be more diverse in this phase, due to reduced competition with shrubs. The below table lists commonly forb encountered species. Redstem stork’s bill may be present at low amounts.
Community 2.3
Valley saltbush
Community composition data were not collected for this phase. This community phase is characterized by dominance of bare ground, almost no herbaceous cover, and greatly reduced shrub cover. This phase is at high risk of erosion and invasive species dominance.
Pathway 2.1a
Community 2.1 to 2.2
This pathway occurs when a dry climatic phase triggers mortality and dieback in valley saltbush, Indian ricegrass, and other shallow-rooted shrubs and herbaceous species. James' galleta may be impacted with severe drought, but is generally more tolerant of drought conditions than the other dominant species.
Pathway 2.1b
Community 2.1 to 2.3
This pathway occurs when abusive livestock grazing, often in combination with drought, remove the bulk of herbaceous vegetation, and remove significant shrub cover, leaving a phase dominated by bare ground with low shrub cover.
Pathway 2.2a
Community 2.2 to 2.1
This pathway occurs with wetter than normal, or a return to normal precipitation periods and time, that allow for recruitment and growth of valley saltbush and Indian ricegrass.
Pathway 2.2b
Community 2.2 to 2.3
This pathway occurs when abusive livestock grazing, often in combination with drought, remove the bulk of herbaceous vegetation, and remove significant shrub cover, leaving a phase dominated by bare ground with low shrub cover.
Pathway 2.3a
Community 2.3 to 2.1
This pathway may occur with time in the absence of further disturbance, and will occur more quickly with favorable precipitation conditions. The time necessary for recovery is unknown; one study found an increase in Gardner's saltbush cover after 14 years of rest from grazing. Recovery times will depend on precipitation and the level of degradation.
Pathway 2.3b
Community 2.3 to 2.2
This pathway may occur with rest from grazing and no additional disturbance. James' galleta may recover more quickly, and this pathway may be more likely than pathway 2.3a.
State 3
Degraded
This state is characterized by low vegetative cover with eroded soils and dynamics influenced by halogeton invasion. Reduced vegetative cover in this state has exposed soil to erosion, and soil surfaces have high gravel cover, sometimes approaching a desert pavement appearance. Halogeton alters soil biology and chemistry, which can make soils more hostile for native plant recruitment, and facilitates further halogeton establishment. This state is very vulnerable, and continued abusive use, especially if coupled with drought, or severe drought alone could cause a transition to a forb dominated state (State 4).
Degraded State: Plant communities influenced by abusive livestock grazing, climate fluctuations and halogeton invasion.
Indicators: Low vegetative cover and high cover of bare ground and gravels. Halogeton is significant but not dominant. Forbs are more important and diverse in this state than in the interpretive or reference state.
Feedbacks: Improper livestock use that damages soils, reduces vegetative cover and promotes soil erosion, establishment of non-native species, and an increase in forbs.
At-risk Community Phase: Community phase 3.1 is at high risk of transitioning to a forb dominated state (State 4).
Trigger: Continuous improper livestock grazing, and/or severe drought or other disturbance that removes vegetation.
Community 3.1
Valley saltbush / James’ galleta- Halogeton
This community phase is characterized by low cover of valley saltbush. James’ galleta is the dominant species. Indian ricegrass may be present at low cover. Forbs make a significant contribution to this community phase, although cover and density will vary with precipitation. Halogeton is prevalent in this community phase, but is still at relatively low cover.
State 4
Forb dominated
This state is characterized by dominance by forbs, with halogeton the most important species. Valley saltbush may be eliminated or greatly reduced. James’ galleta is the dominant grass, and Indian ricegrass may be eliminated or greatly reduced. Desert trumpet (Eriogonum inflatum) may be an important species. Reduced vegetative cover in this state has exposed soil to erosion, and soil surfaces have high gravel cover, sometimes approaching a desert pavement appearance. Halogeton alters soil biology and chemistry, which can make soils more hostile for native plant recruitment, and facilitates further halogeton establishment.
Annual dominated State: Plant communities influenced by climate fluctuations between wet and dry periods, livestock grazing, and invasive plants.
Indicators: Communities dominated by forbs, with halogeton the dominant species. Valley saltbush is eliminated or greatly reduced. High cover of bare ground and gravels, and erosion is typically visible.
Feedbacks: Low or absent cover of native perennials, a halogeton seedbank, and altered soils promote the maintenance of a halogeton dominated state.
Community 4.1
Forb dominated
This community phase is characterized by absence or very low cover of valley saltbush and dominance of forbs. Halogeton is the dominant plant, and desert trumpet is an important species. James’ galleta is the most abundant native perennial grass, but is present at much reduced levels relative to more intact states.
Transition T1A
State 1 to 2
Transition from reference state (State 1) to interpretive state (State 2). This transition occurred with pervasive intensive livestock use beginning in the 1880’s. Livestock grazing introduced invasive species such as cheatgrass and halogeton, and increased site susceptibility to continued invasion; once established these species are virtually impossible to remove, thus causing a shift to an altered state. The composition and productivity of the altered state was also likely affected, with reduced cover of palatable, grazing intolerant species and increasing the importance of less palatable, more grazing tolerant species.
Transition T2A
State 2 to 3
Transition from interpretive state (State 2) to degraded state (State 3). This transition may occur with continued heavy grazing that reduces valley saltbush cover and exposes soils to invasion by halogeton and erosion.
Transition T2B
State 2 to 4
Transition T2B Transition from interpretive state (State 2) to forb dominated state (State 4). This transition may occur when severe abusive grazing, often in combination with drought, that eliminates or depletes valley saltbush cover to the extent that halogeton and other forbs dominate.
Transition T3A
State 3 to 4
Transition from degraded state (State 3) to forb dominated state (State 4). This transition may occur with continued abusive grazing, often in combination with drought, that eliminates or depletes valley saltbush cover to the extent that halogeton and other forbs dominate. This transition may occur even if livestock grazing is removed if drought or other disturbance removes valley saltbush cover and provides an opening for halogeton to become dominant.
