Ecological dynamics
An ecological site is not a precise assemblage of species for which the proportions are the same from place to place or from year to year. In all plant communities, variability is apparent in productivity and occurrence of individual species. Spatial boundaries of the communities; however, can be recognized by characteristic patterns of species composition, association, and community structure. The historic climax plant community for this ecological site has been described by sampling relict or relatively undisturbed sites and/or reviewing historic records. The historic climax plant community is the plant community that evolved over time with the soil forming process and long term changes in climatic conditions of the area. It is the plant community that was best adapted to the unique combination of environmental factors associated with the site.
Natural disturbances, such as drought, fire, grazing of native fauna, and insects, are inherent in the development and maintenance of these plant communities. The effects of these disturbances are part of the range of characteristics of the ecological site. Fluctuations in plant community structure and function caused by the effects of natural disturbances help establish the boundaries and characteristics of an ecological site. They are accounted for as part of the range of characteristics of the ecological site. Recognizable plant community phases are identified in the reference state of the ecological site. Some sites may have a small range of variation, while others have a large range. Some plant community phases may exist for long periods of time, while others may only occur for a couple of years after a disturbance.
Deterioration of the plant community, hydrology, or soil site stability on an ecological site can result in crossing a threshold or potentially irreversible boundary to another state, or equilibrium. This can occur as a result of the loss of soil surface through erosion, the loss of the stability of the site due to disturbances that cause active erosion on the site, increases in the amounts and/or patterns or runoff from rainstorms, changes in availability of surface and subsurface water, significant changes in plant structural and functional types, or the introduction of non-native species. When these thresholds are crossed, the potential of the ecological site to return to the historic climax plant community can be lost, or restoration will require significant inputs . There may be multiple states possible for an ecological site, determined by the type and or severity of disturbance.
The known states and transition pathways for this ecological site are described in the state and transition model. Within each state, there may be one or more known plant community phases. These community phases describe the different plant community that can be recognized and mapped across this ecological site. The state and transition model is intended to help land users recognize the current plant community on the ecological site, and the management options for improving the plant community to the desired plant community.
Plant production information in this site description is standardized to the annual production on an air-dry weight basis in near normal rainfall years.
State 1
Tree State
This site has an overstory comprised of pinyon pine (30%) and juniper (70%). The tree canopy cover is generally 40-55%, but can be higher. The understory is comprised of aproximately 60% shrubs, 30% grasses and 5% each small trees and forbs. Understory species include sideoats grama, muttongrass, blue grama, penstemon, Stansbury cliffrose, turbinella oak and desert ceanothus.
Non-native plant species may be present in minor amounts. Once non-native plants are introduced into the plant community, it is very difficult to eliminate these plants from the site.
State 2
Shrub State
n this community the understory is affected by disturbace that reduces the grass component and shrubs increase and become more dominant. Shrub species that can increase are broom snakeweed, mormon tea, big sage and banana yucca.
Non-native plant species may be present in minor amounts. Once non-native plants are introduced into the plant community, it is very difficult to eliminate these plants from the site.
Transition T1
State 1 to 2
Disturbance that reduces perennial grasses, unmanaged grazing, drought, fire suppression.
Restoration pathway R1
State 2 to 1
Brush removal and possibly tree removal in conjunction with grazing management.