Ecological dynamics

The dominant visual aspect of this site is black greasewood along with some basin big sagebrush and spiny hopsage with a scattered grass understory. The amount and distribution of the understory grasses is quite variable and is dependent upon the degree of salinity. Composition by weight is 60 percent grasses, 5 percent forbs, and 35 percent shrubs.

The Historic Climax Plant Community (HCPC), the Reference State (State 1), moves through many phases depending on the natural and man-made forces that impact the community over time. State 1, described later, indicates some of these phases. The Reference Plant Community Phase is Phase A. This plant community is dominated by basin wildrye and black greasewood. Subdominants include Indian ricegrass, inland saltgrass, and spiny hopsage. Basin big sagebrush is usually present in small amounts. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

During the last few thousand years, this site has evolved in a semi-arid climate characterized by warm, dry summers and cold, wet winters. Herbivory has historically occurred on the site at low levels of utilization. Herbivores primarily include lagomorphs and small rodents. Infrequent use is made by mule deer and pronghorn antelope. Fire has historically occurred on this site every 80 to 100 years. Fire occurs only in years with above normal precipitation. Total annual production is 850 pounds per acre (944 Kg/ha) in a normal year. Production in a favorable year is 1200 pounds per acre (1333 Kg/ha). Production in an unfavorable year is 650 pounds per acre (722 Kg/ha). Structurally, cool season deep rooted perennial bunchgrasses are very dominant, followed by medium height shrubs being more dominant than perennial forbs while shallow rooted bunchgrasses are subdominant.


FUNCTION:

This site is suited for grazing by domestic livestock in the late spring and early summer. Due to easy access by livestock and the relatively low precipitation on the site, degradation can occur if the plant cover is reduced. Wildlife uses the site in very low numbers. Recreational opportunities are very limited.

Because of the gentle topography, infiltration is normally high and runoff low. Runoff, when it does occur is non-erosive except during high intensity convection storms. Snow accumulates on the site due to the presence of tall shrubs.

Impacts on the Plant Community.

Influence of fire:

In the absence of normal fire frequency, black greasewood and basin big sagebrush increases. Grasses and forbs decrease as shrubs increase.

When fires become more frequent than historic levels (80-100 years), black greasewood, basin big sagebrush, and spiny hopsage are reduced significantly. The reduction is temporary however, since black greasewood and spiny hopsage re-sprout after light to moderate intensity fires. Basin wildrye and inland saltgrass will generally increase after fire. With continued short fire frequency, basin big sagebrush can be completely eliminated along with many of the desirable understory species. These species may be replaced by cheatgrass and medusahead, along with a variety of annual and perennial forbs including noxious and invasive plants. These fine fuels will increase the fire frequency. Root sprouting shrubs such as rabbitbrush and littleleaf horsebrush may increase.

Influence of improper grazing management:

Season-long grazing and/or excessive utilization can be very detrimental to this site. This type of management leads to reducing vigor of the bunchgrasses. With reduced vigor, recruitment of these species declines. As these species decline, the plant community becomes susceptible to an increase in black greasewood and noxious and invasive plants. As cheatgrass and medusahead increase along with other annuals, fires become more frequent. Continued improper grazing management influences fire frequency by increasing fine fuels.

Continuous spring grazing can significantly reduce the vigor of basin wildrye. Excessive utilization during the spring is even more detrimental. The growing points of basin wildrye are several inches above the soil surface. Utilization during the growing season should allow for a 10-12” stubble height by the end of the grazing period.

Proper grazing management that addresses frequency, duration, and intensity of grazing can also keep fine fuels from developing, thereby reducing fire frequency. This can lead to gradual increases in basin big sagebrush. Proper grazing management will also help maintain the integrity of the plant community.


Weather influences:

Above normal precipitation in April, May, and June can dramatically increase total annual production of the plant community. These weather patterns can also increase viable seed production of desirable species to provide for recruitment. Likewise, below normal precipitation during these spring months can significantly reduce total annual production and be detrimental to viable seed production. Overall plant composition is normally not affected when perennials have good vigor.

Below normal temperatures in the spring can have an adverse impact on total production regardless of the precipitation. An early, hard freeze can occasionally kill some plants.

Prolonged drought adversely affects this plant community in several ways. Vigor, recruitment, and production are usually reduced. Mortality can occur. Prolonged drought can lead to a reduction in fire frequency.

Influence of insects and disease:

An outbreak of a particular insect is usually influenced by weather but no specific data for this site is available. Mormon cricket and grasshopper outbreaks occur periodically. Outbreaks seldom cause plant mortality since defoliation of the plant occurs only once during the year of the outbreak.

Influence of noxious and invasive plants:

Many of these species add to the fine-fuel component and lead to increased fire frequency. Many of the annual and perennial invasive species with deep root systems compete with desirable plants for moisture and nutrients. The result is reduced production and change in composition of the understory.

Influence of wildlife:

Big game animals use this site sparingly. Since their use is so light, the influence on the site is minimal. Population explosions of black-tailed jackrabbits occur occasionally. These high populations can affect the plant community. However, the effect is usually temporary since population die-offs normally occur within a year or two.

Watershed:

Decreased infiltration and increased runoff occur with the increase in black greasewood. Desired understory species can be reduced. The increased runoff also causes sheet and rill erosion. This composition change can affect nutrient and water cycles. Abnormally short fire frequency also gives the same results, but to a lesser degree. The long-term effect is a transition to a different state.


Plant Community and Sequence:

Transition pathways between common vegetation states and phases:

State 1.
Phase A to B. Develops with improper grazing management and in the absence of fire.
Phase A to C. Develops with fire.
Phase B to A. Develops with prescribed grazing and brush management.
Phase C to A. Develops with prescribed grazing and no fire.

State 1 to State 2. Develops through frequent fire and improper grazing management. This site has crossed the threshold. It is generally economically impractical to move this state back across the threshold with accelerating practices.
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State 2 to unknown site. Excessive soil loss and changes in the hydrologic cycle caused by continued improper grazing management and/or frequent fire cause this state to cross the threshold and retrogress to a new site with reduced potential. It is economically impractical to return this site to State 1 with accelerating practices.
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Practice Limitations.

Due to the relatively low production potential, soil texture problems, wet soil periods from run-on, and the saline or alkaline conditions, it is generally not economically feasible to seed or use brush management on this site.

No physical limitations exist for seeding on this site except for periods of run-on. The silty clay and strongly saline or alkaline conditions may present specific challenges for seedbed preparation and seeding.