Semidesert Very Steep Stony Loam (Two-Needle Pinyon, Utah Juniper)

Description

This Reference State was determined by the study of rangeland relic areas and areas protected from excessive disturbance and influences such as grazing and recreation. Literature review, historical accounts and observations of trends in plant community dynamics under a variety of sites has also been considered. Community phases, community pathways, other states, transitions, and thresholds, have been determined through similar studies and experience.

This state represents the natural range of variability that historically dominated the dynamics of this ecological site. This state includes the biotic communities that would have been expressed on the ecological site if all successional sequences were completed without interferences by man under the present environmental conditions; natural disturbances are inherent in its development. This state is dominated by a very sparse canory of two-needle pinyon and Utah juniper with a well developed understory of native shrubs, perennial grasses and perennial and annual forbs. The primary disturbance mechanisms for this site in the reference condition include drought and insects.

Reference state: Community phases maintained by drought and insect pathogen cycles.

Indicators: A well developed shrub and grass understory co-existing with a canopy of Utah juniper and Two-needle pinyon.

Feedbacks: Infrequent, but regular droughts that reduce tree cover.

At-risk Community Phase: All communities are at risk when plants in the understory are stressed, and nutrients become available for invasives to establish.

Trigger: The introduction of invasive plants into the understory.

Submodel

Description

This state is very similar to the reference state, except that invasive grasses and/or forbs are present in all phases. The primary disturbance mechanisms for this state include natural and human caused disturbances; however, due to steep slopes there are very little man induced disturbances. Drought and insects may influence the community shifts. Trailing of livestock to water and some minor recreational activities (i.e. hiking) are the most common and have very little impact on the site other than introduction of invasive grasses and forbs. The shift in species composition could affect nutrient cycling, hydrology and soil stability. At this time there is no known way to effectively remove invasive plants from the site once they have become established. Therefore, this site is often irreversibly altered from the reference state

Current Potential State: Community phases maintained by drought and insect herbivory cycles.

Indicators: A shrub and grass understory co-existing with a canopy of Utah juniper.

Feedbacks: Infrequent, but regular droughts to reduce tree cover. Establishment of invasive plant species such as cheatgrass.

Submodel