SR Very Shallow Rockland 12-16 PZ

Description

The Reference State is representative of the natural range of variability for the site under pristine conditions. The reference state is a low productivity, bunchgrass shrubland. State dynamics are maintained by interactions between climatic patterns and disturbance regimes. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These are maintained by ecosystem processes and structural elements such as the presence of all structural and functional plant groups, the retention of organic matter and the maintenance of plant community cover. Plant community phase changes are primarily driven by infrequent fire and/or periodic drought.

Submodel

Description

This state is similar to the Reference State. Ecological function has not changed fundamentally, however the resiliency of the site has been reduced by the presence of invasive plants. Additionally, livestock herbivory may be present as a disturbance process and changes in climate may be altering ecological dynamics. Non-native plant species may increase in abundance but will not become dominant or control ecological processes within this state. These species can be highly flammable and can promote fire where historically fire had been infrequent. Negative feedbacks enhance ecosystem resilience and contribute to the stability of the state. These are maintained by ecosystem processes and structural elements such as the presence of all structural and functional groups, and retention of organic matter and nutrients. Positive feedbacks driven by plant community invasion decrease ecosystem resilience and stability of the state. These include exotic plant species' high seed output, persistent seed bank, rapid growth rate, ability to cross pollinate, and adaptations for seed dispersal. Plant community phase changes are primarily driven by infrequent fire, periodic drought and ungulate herbivory.

Current potential plant communities also mirror those of the above Historical Reference (State 1) yet with the addition of a low level of invasive exotic plant invasion and influences of livestock herbivory. Livestock herbivory may result in decreases in deep rooted perennial grasses, and related increases in shallow-rooted perennial grasses (such as Sandberg bluegrass), unpalatable forbs and shrubs.

Description

Within this state, site resources are primarily controlled by exotic annual herbaceous species. Native perennial grass and forb composition has been greatly diminished. Fire frequency may be increased by higher fine fuel loads, potentially having significant ecological consequences for this otherwise fuel limited site. Rehabilitation of this state will be extremely difficult due to thin soils, high potential for invasive annual grass encroachment, susceptibility of soils to erosion and damaging frost heaving, and mechanical limitations due to areas of rock outcrop.

Multiple plant communities are possible within this state, all of which are dominated by invasive annual grasses such as cheatgrass, ventenada and medusahead and potentially invasive annual and perennial forbs. Subshrub and shrub species may also be present. Overtime, with increasing invasion, soil stabilizing perennial root biomass will be decreased. Bare ground will increase, potentially increasing erosion of these thin soils and risking a transition to an eroded state.

Description

This state is characterized by significant soil loss through wind and water erosion. Most herbaceous cover has been lost and soil stabilizing microbiotic soil crusts are degraded. Loss of these components reduces soil stabilization and renders the soil surface vulnerable to raindrop impacts, runoff and entrainment of soil particles by wind. Extensive areas of erosion pavement are common. The potential for a shift to this state is greatly increased toward the steeper end of the slope range of this site. Positive feedbacks develop as low vegetative cover leads to decreased litter and organic matter production, higher soil temperature variability, and decreased nutrient cycling, further destabilizing soil and decreasing potential plant establishment. Grass and forb vegetative cover is low yet invasive annual plants are likely and some shrubs and subshrubs may remain where soil persists in areas of fractured bedrock. Potential for rehabilitation of this state is unknown but would likely pose significant challenges due to degradation of abiotic function of the site, the susceptibility of soils to erosion and damaging frost heaving, and mechanical limitations due to areas of rock outcrop.