Upland Loam (pinyon-Utah juniper)

Description

The Reference state has been determined by study of rangeland relic areas, areas protected from excessive disturbance, and areas under influences such as grazing and recreational uses. Through literature review, historical accounts and observations of trends in plant community dynamics under a variety of uses have been considered.
Community phases, community pathways, states, transitions, thresholds, and restoration pathways 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. It was in a natural dynamic equilibrium with the historic biotic, abiotic, climatic factors at the time of European immigration and settlement. The dominant aspect of this site is Pinyon and Utah Juniper with an understory of big sagebrush and associated grasses. Fluctuations in species compositions and relative production may change from year to year dependant upon abnormal precipitation or other climatic factors. The primary disturbance mechanisms for this site in reference condition include drought, insects, and very rare fire. Because catastrophic disturbances like a crown fire or drought happen with long intervals, these communities have long periods of succession, (i.e. long periods of dense Pinyon and Juniper)—200-400 years. In the semi-arid environment of this ecological site, fine fuels are typically not continuous, reducing the likelihood of short fire return intervals. Typically, fires occurred in late spring through mid summer following several wet years tha allowed the fine fuels to become more contiguous (Baisan and Swetnam, 1990, and Swetnam and Baisan, 1996).
The timing of drought, and fire, coupled with surface disturbance can dictate whether the community can stay within the reference state or if the community transitions into another state

Reference state: Community phases maintained by drought, insects, and infrequent fires. Indicators: A well developed understory co-existing with a canopy of older Pinyon and Utah juniper.
Feedbacks: Infrequent, but regular droughts to reduce tree cover and allow for a productive herbaceous understory. The loss of native herbaceous understory species that results in opportunities for erosion.

At-risk Community Phase: All communities are at risk when native plants in the understory are stressed, and

nutrients become available for non-natives to establish.

Trigger: Decrease of native plants in the understory and the introduction of non-native plants to fill the available niches.

Submodel

Description

This state is very similar to the reference state, except that non-native grasses and/or forbs are present in all phases. The current potential state may include naturalized or invasive non-native species. The primary disturbance mechanisms include all those found in the reference state as well as human induced disturbances, including improper domestic livestock grazing and recreation activities, including off highway vehicle (OHV) overuse. Plant communities within the current potential state are more likely managed and used for various purposes by man, without significant alteration in plant community composition or production. In time, continued surface disturbances, will likely stress the native plant species and allow for non-native species to increase. This shift in species composition could affect nutrient cycling, hydrology, and soil stability. At this time there is no known way to effectively remove the non-native plants from this 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, insects, and infrequent fires, domestic livestock grazing, and vegetation manipulation by man.

Indicators: A well developed understory co-existing with a canopy of older Pinyon and Utah juniper.

Feedbacks: Infrequent, but regular droughts to reduce tree cover and allow for a productive herbaceous understory. Rarely, short fire intervals that result in complete loss of the perennial native shrub and grass community and an increase in non-native invasive annual grasses. Vegetation manipulation by man, such as chaining, burning, seeding, etc.

At-risk Community Phase: All plant communities are at risk for the increased establishment of annual grasses and forbs; however plant community 2.2 is likely most at risk due to its limited understory.

Trigger: Frequent fire return interval that allows for in the complete dominance of annual grasses and forbs. Vegetation manipulation by man.

Submodel

Description

This state is recognized by the predominance of invasive annuals. Invasive annuals have increased to a point where they influence or drive the disturbance regime and the nutrient cycle and energy flow, altering it from the regimes and cycles associated with sagebrush ecosystems. Research has shown that plant species differ substantially in their effects on soil water content and temperature and their effects on the frequency and intensity of disturbance. Once exotic plants like cheatgrass or Russian thistle have invaded a site fundamental nutrient cycling processes are known to change (Chapin et al., 1997). Energy flow in this state is severely suppressed, with photosynthesis occurring only during a brief period in the spring. Cheatgrass invasion has also been shown to

change the composition root pores, mycorrhizal associations, and assemblages of microbial species potentially affecting soil structure and the rate of soil organic matter decomposition (Belknap and Phillips, 2001). The altered disturbance regime and the loss of soil organic matter could create ecologically impoverished sites that are very difficult, if not impossible to restore to functionally diverse perennial herbaceous and woody communities.

Invasive Annuals State: Community phases maintained by fire, drought, livestock grazing; vegetation management, and time without disturbances.

Indicators: An annual grass or forb understory, where big sagebrush may or may not be present

Feedbacks: Short fire intervals, which maintain the annual grass and forb understory. Longer fire intervals, vegetation management, or livestock grazing that allows for the sagebrush overstory to reestablish.

At-risk Community Phase: Community 3.2 is the most at risk when cheatgrass or other annuals completely dominate the site, shortening the fire return interval that maintains the annual grass/forb community.

Submodel

Description

This state results from a significant vegetation manipulation that may include prescribed burning, chaining, disking, mowing, or other technique, with the introduction of non-native perennial grasses such as Crested wheatgrass or Russian wildrye. The dominant understory plant species are the seeded grasses and forbs. The community dynamics are similar to the Current Potential State. Depending on the species used for the reseeding practice, the site could have more resistance to fire as well as better tolerance to grazing pressure. This state may persist for long periods of time. Typically, big sagebrush will reestablish in the seeding to significant proportions within 30 years. Actively manipulating plant communities in the invasive annuals or Juniper invasion states to create a seeded range state is often the first step in assisted succession to restore natural plant communities back to something similar to the Current Potential state.

Seeded State: Community phases maintained by fire, continued vegetation manipulation, insect herbivory, drought, and time without disturbances.

Indicators: A developed perennial herbaceous understory of seeded species, typically non-natives, co-existing with a canopy of big sagebrush.

Feedbacks: Infrequent, but regular droughts that reduce grass cover. Moist cycles that maintain perennial bunch grasses. Fire, insect herbivory, and/or vegetation management that allows for the removal of trees. Improper grazing resulting in a loss of the herbaceous understory, an increase in invasive plants, and an increase in the fire return interval.

At-risk Community Phase: All communities are at risk when non-native invasive annual species increase to a point where they begin to drive the ecological dynamics of the site.

Submodel