Upland Loam (big sagebrush)

Description

The Reference state has been determined by study of rangeland relic areas, areas protected from excessive disturbance, and areas under outside influences such as domestic livestock grazing and recreational uses.
Literature review, trends in plant communities under a variety of uses, and historical accounts also have been considered.

The reference state represents all plant communities and ecological dynamics of the upland loam Big sagebrush site. This state includes all biotic communities that become on the ecological site if all successional sequences are completed under the natural disturbance regime. This state is dominated by Basin and/or Wyoming big sagebrush with a diverse understory of native perennial grasses and native perennial and annual forbs. The nutrient cycling in native shrub-steppe ecosystems is characteristically ‘‘tight’’ (i.e. net concentrations of plant-available nutrients are low) because the broad spatial and temporal diversity of plants (woody and herbaceous) and soil microbes rapidly exploit nutrients as they are mineralized (Paschke et al., 2000). The primary disturbance mechanisms for this site in reference condition include fire, insect herbivory, and fluctuations in climate, such as drought or wet periods.

Prior to European settlement, fire return intervals were thought to be adequate enough to inhibit the encroachment of Pinyon and Utah juniper into the more productive deeper soils that support shrub steppe communities (Tausch 2002, Romme et al. 2007). However, as the number of years between fire events increases due to reduction in fine fuels or fire suppression, Pinyon and Utah juniper readily invade these communities. The time required to complete the transition of shrub steppe to a closed Pinyon and juniper woodland is variable. The transition is dependant on both the rate of tree establishment and site potential. Woodland presence at the landscape level also influences the rate of encroachment and closure on adjacent open areas

Reference state: Community phases maintained by fire, drought, insect herbivory, and time without disturbances. Indicators: A diverse and productive understory co-existing with a fluctuating canopy of big sagebrush.
Feedbacks: Infrequent, but regular droughts that result in a reduction of sagebrush cover. Higher than average precipitation cycles that maintains the episodic native plant reproductive cycles. Insect infestations and/or a fire regime sufficient enough to inhibit Pinyon and Utah juniper encroachment. Improper grazing that results in a loss of native herbaceous understory, the establishment of non-native invasive plants, and a reduction in the fire return interval.

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. However, plant community 1.3 is most at risk due Pinyon and Utah juniper encroachment.

Trigger: The establishment of non-native invasive plants and/or Increased establishment of Utah juniper and Pinyon to a point where they drive the ecological dynamics of the site.

Submodel

Description

The current potential state is very similar to the reference state in energy capture, nutrient cycling, hydrologic function and disturbance regime. The current potential state may include acclimatized, naturalized, or invasive nonnative species. With proper management, plant communities within the current potential state may be managed and used for various purposes by man without significant alteration in plant community composition or production. It includes all of the plant communities that exist in the reference state, but with the inclusion of nonnative species.
These plant communities with significant portions of invasive annuals are possible within this state. Continuous surface disturbances (improper grazing, off-highway-vehicle (OHV) use, recreational activities, etc.) can stress the native perennial plants and allow the non-natives species to increase. This shift in species composition could invoke another transition to a different state and affect the nutrient cycling, hydrologic function and soil stability. At this time there is no known way to completely remove the non-native plants from the site once they have become established. Therefore, this state is irreversibly altered from the reference state.

Current Potential state: Community phases maintained by fire, insects, drought, and time without disturbances.

Indicators: A diverse and productive understory dominated by native plants with non-native herbaceous plants co- existing under a canopy of big sagebrush.

Feedbacks: Infrequent, but regular droughts that reduce grass cover combined with sufficient moist cycles to maintain episodic reproductive cycles of native plants. Insect herbivory or fire return interval sufficient enough to inhibit Pinyon and juniper encroachment. Improper livestock grazing, that facilitates the loss of herbaceous understory, increasing non-native invasive plants, and causing a lengthened fire return interval).

At-risk community: Community 2.3 is the most at risk when Utah juniper and Pinyon have increase to a point where they drive the ecological dynamics of the site and have suppressed the understory.
Trigger – Increased Utah juniper and Pinyon, lack of understory, and increased erosion.

Submodel

Description

This state is characterized by a dominance of Utah juniper and Pinyon, with some to very little understory depending on which community phase it is in. It typically occurs if there is a long interval between disturbances, accompanied by a nearby source for Pinyon and Utah juniper seeds. This state can persist for long periods of time until extreme conditions needed for wildfire occur or a management treatment is implemented.

Pinyon and Utah Juniper State: Community phases maintained, in a self-sustaining manner, over time without disturbance.
Indicators: A declining understory, coupled with a dense canopy of Pinyon and Utah juniper.
Feedbacks: Surface disturbance and other negative pressures (grazing, drought, etc.) that reduce the herbaceous understory, combined with a lack of disturbances that remove trees from the community. The removal of trees, which facilitates an increase in herbaceous plant production.
At-risk community – Community 3.1 is most at risk when Utah juniper and Pinyon have increased to a point where there is no longer an understory.
Trigger – Removal of trees.
Restoration Pathway – Active vegetation management that facilitates the removal of trees and allows for the reestablishment of desired native and introduced species.

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. Under careful management, native grasses and forbs may reestablish in this plant community over time.
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 the Current Potential State.

Seeded state: Community phases maintained by fire, drought, and time without disturbances.

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

Feedbacks: Infrequent, but regular droughts that reduce grass cover. Moist cycles that maintain perennial bunch grasses. A fire regime sufficient to inhibit Pinyon and Utah juniper encroachment. 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: Community 4.3 is the most at risk when Utah juniper and Pinyon have increased to a point where they drive the ecological dynamics of the site.

Restoration Pathway: proper domestic livestock grazing practices and the removal of trees that facilitates the reestablishment of native and introduced species.

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). Cheatgrass invasion has been shown to alter the timing, distribution, and composition of organic matter inputs, as well as uptake of mineralized nutrients (Evans et al., 2001). 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: Community 5.2 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