JD Droughty Clayey North 9-12 PZ

Description

The Historical Reference State is representative of the natural range of variability for the site under pristine conditions. The reference state is a 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Current potential plant communities mirror those of the above Historical Reference (State 1) yet with the addition of a low level of invasive exotic plant invasion and influences of livestock herbivory.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's bluegrass) and shrubs, among other changes.

Description

Within this state, site resources are primarily controlled by shrub species and western juniper. Native perennial grass composition has been reduced considerably. Sprouting and non-sprouting shrubs as well as western juniper are present. Exotic herbaceous species are often present.

Multiple plant community phases are likely within this state, influenced by livestock herbivory and fire. Sprouting species such as rabbitbrush and broom snakeweed as well as non-sprouting species such as shadscale may be dominant but will be outcompeted by western juniper overtime as canopy closure and moisture competition progresses. Invasive annual grasses such as cheatgrass and medusahead are likely.

Juniper encroachment can decrease cover of grasses and shrubs by reducing light availability and altering site hydrology through increased interception of precipitation, reduced infiltration and increased erosion. Bare ground will increase and erosion may be increased rendering the site at risk of transitioning to an eroded state (State 6).

Description

Within this state, site resources are primarily controlled by exotic annual and perennial herbaceous species. Native perennial grass composition has been greatly diminished. Shrub species and western juniper may also be present.

Multiple plant communities are possible within this state, all of which are dominated by invasive annual grasses such as cheatgrass and medusahead as well as invasive annual and perennial forbs, such as prickly lettuce, or Russian thistle (Salsola tragus). Native invader shrub species such as broom snakeweed may also be common

Overtime, with increasing invasion by annuals, soil stabilizing perennial root biomass will be decreased, and bare ground may increase outside of the growing season, elevating potential for erosion and rendering the site at risk of transitioning to an eroded state (State 6).

Description

Within this state, site resources are primarily controlled by introduced range grasses such as crested wheatgrass (Agropyron cristatum). Multiple community phases may occur within this state and will include different compositions of native and invasive shrub and grass species and western juniper. Plant composition will be dependent on seeded species mixes used and the effectiveness of the revegetation effort. Similar to the ecological dynamics within other states of this site, shrub species and western juniper will increase with greater time since fire and herbivory pressure. While introduced range grasses may provide some analogous ecological functions to native perennial grasses, they may competitively exclude native grasses in the long-term.

Description

This state is characterized by the loss of soil through wind and water erosion. Low herbaceous cover is available to stabilize the soil and renders the soil surface vulnerable to raindrop impacts, runoff and entrainment of soil particles by wind. The potential for a shift to this state is greatly increased toward the steeper 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 and western juniper are likely. Rehabilitation of this state is unknown but would likely pose significant challenges due to degradation of abiotic function of the site.