Semidesert Sandy Loam (4-Wing Saltbush)

Description

The reference state is determined by study of rangeland relic areas, i.e. areas protected from excessive disturbances and influences, such as improper livestock grazing and damaging recreational activities. Literature reviews, trends in plant community dynamics, and historical accounts are also considered.

This reference state represents the plant communities and ecological dynamics of the semidesert sandy loam, fourwing saltbush site. This state includes the biotic communities that become established on this ecological site if all successional sequences are completed under the natural disturbance regime. This state is dominated by perennial warm and cool season grasses, where fourwing saltbush, winterfat, and Cutler's jointfir make up the shrub canopy. In this state, both warm and cool season grass species occur; however, typically one cool and one warm season species dominates the site. Utah juniper can naturally invade on the moderately deep soil components when this site is in close proximity to juniper dominated ecological sites. Due to the aggressive competitive nature of Utah juniper to out compete understory species, blow-out areas are common where this species occurs; however, these instances occur on a small scale at the margins of the site, and thus far a juniper dominated state has not been observed. Primary disturbance mechanisms include infrequent fire, insect herbivory, weather fluctuations, and native herbivore grazing. Timing of these natural disturbances dictates the ecological dynamics that can occur. The reference state is self sustaining and resistant to change due to its high resistance to natural disturbances and high resilience following natural disturbances. When natural disturbances do occur, the rate of recovery is relatively rapid due to niches being filled with highly adapted native vegetation.

Reference State: Plant communities influenced by infrequent fire, insects, native herbivore grazing, and climate fluctuations.

Indicators: A well developed perennial cool and warm season grass understory with winterfat and/or fourwing saltbush forming the dominant visual aspect.

Feedbacks: Infrequent but regular fires to maintain the perennial grass understory and the establishment of shrubs.

At-risk Community Phase: All communities are at risk when native plants are stressed and nutrients become available for invasive plants to establish, particularly 1.3 where the native perennial bunchgrass understory is limited and nutrients may be available for the establishment of invasive species; however non-native invasive species have been known to establish into intact perennial plant communities with little to no disturbances.

Trigger: Improper livestock grazing and the establishment of non-native invasive plant species.

Submodel

Description

This state is similar to the reference state except that non-native plants are now present in all plant community phases. A shift in species composition will affect the nutrient cycling, soil-water relationships, hydrology, and soil stability. Dominant grasses include both warm and cool season species; however heavy spring grazing will generally remove the cool season grasses such as Indian ricegrass, and heavy late summer and early fall grazing will remove the warm season grasses such as black grama and James’ galleta. Utah juniper is still a common invader of shallower soil components, creating blowout areas and increasing erosion. This state is losing resistance to disturbances and resilience after disturbance. Invasive plants are beginning to fill available niches and become established on the site.

Current Potential State: Plant communities influenced by both natural and man influenced events, including rodent activity, OHV overuse, improper livestock grazing, insect herbivory, fire, time without disturbances, and climatic fluctuations.

Indicators: A perennial cool and warm season grass understory with fourwing saltbush, and/or winterfat forming the dominant visual aspect, when present. Non-native species are now present in all plant communities.

Feedbacks: Extended drought, improper livestock grazing, or other disturbance that change the ecological dynamics of the site. Infrequent but regular fires or properly managed domestic livestock grazing to maintain the understory and the establishment of shrubs.

At-risk Community Phase: All communities are at risk; however plant community 2.3 is most at risk due to its limited understory.

Trigger: Disturbance that facilitates the dominance of invasive forbs and/or grasses.

Submodel

Description

This state is characterized by the dominance of invasive forbs/shrubs. These species may include, but are not limited to Russian thistle, cheatgrass, tansy mustard, broom snakeweed, annual stickseed, and annual Cryptantha. One or more invasive species has increased to a point where they influence or drive the disturbance regime and nutrient cycle. Russian thistle and/or cheatgrass are the most likely species to establish and dominate. Russian thistle is a prolific reproducer; one plant can produce up to 250,000 seeds, which are dispersed by the wind when the dead plant “tumbles” across the landscape. While generally considered an unwanted weed, Russian thistle may actually help disturbed sites recover more quickly. If topsoil is present, Russian thistle roots are invaded by mycorrhizal fungi, and because this plant does not form associations with these fungi, both the plant and root are killed. This causes increased mycorrhizal fungi in the soil and an increased chance for other plants to establish through the aid of these fungi associations. Land managers however, must be aware that without proper management, other invasive annuals, such is cheatgrass, may become established instead of the desirable native species. If topsoil is missing, mycorrhizal fungi and Russian thistle can persist for relatively long periods of time (Howard 1992). The competitiveness of these invasive species and their ability to quickly establish after a disturbance, makes this state extremely resistance to change and resilient after a disturbance.

Invasive Forb State: Community phases influenced by improper grazing and weather cycles.

Indicators: A complete understory of invasive forbs and/or broom snakeweed where native perennial shrubs, grasses, and forbs are minimally present.

Feedbacks: Improper livestock grazing and weather cycles that maintain the dominance of invasive forbs/shrubs with minimal decrease in native perennial grasses, shrubs, and forbs. Increased occurrence of cheatgrass, decreasing the fire return interval. Flooding and alluvial deposits that facilitate the establishment of sand sagebrush.

Trigger: The increased establishment of cheatgrass, caused by a decrease in the fire return interval, which facilitates the continued removal of other grasses, shrubs, and forbs.

Submodel

Description

This state’s ecological processes are driven by the dominance of cheatgrass, where native and invasive plant species may also be present. Cheatgrass dramatically affects the soil/plant/water relationships of a site. After cheatgrass has invaded a site, the fundamental nutrient cycling processes, root pores, mycorrhizal associations, microbial species, and soil organic material change (Chapin et al. 1997, Belnap and Phillips 2001). These alterations may eventually create ecologically impoverished sites that are very difficult to restore to functionally diverse perennial herbaceous and woody communities. The competitiveness of cheatgrass and its ability to quickly establish after a disturbance make this state extremely resistance to change and resilient after a disturbance.

Annual Grass State: Community phases maintained, in a self-sustaining manner, by frequent fire.

Indicators: A site where ecological processes are driven by cheatgrass.

Feedbacks: A self sustaining disturbance regime of frequent fire.

Submodel