Ecological dynamics

The dominant visual aspect of the site is barren ground with very sparse vegetative cover. The site has shadscale saltbush in the overstory with Salmon wildrye and Indian ricegrass in the understory. The composition by weight is 40-60 percent grasses, 10-20 percent forbs and 30-40 percent shrubs.

During the last few thousand years, this site has evolved in an arid climate characterized by dry summers and cold winters. Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, bighorn sheep, lagomorphs and small rodents. Fire has historically occurred on the site at intervals of 80-100 or more years. Fire only occurs in favorable years.

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 Salmon wildrye and Indian ricegrass in the understory and shadscale saltbush in the overstory. Subdominant species include bottlebrush squirreltail, Sandberg bluegrass, Indian ricegrass, bluebunch wheatgrass, Hoods phlox, bud sagebrush and Wyoming big sagebrush. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

Total annual production is 200 pounds per acre (222 kilograms per hectare) in a normal year. Production in a favorable year is 350 pounds per acre (388 kilograms per hectare). Production in an unfavorable year is 75 pounds per acre (83 kilograms per hectare). Structurally, cool season perennial bunchgrasses are dominant, followed by medium shrubs being more dominant than perennial forbs.

FUNCTION:
This site is not well suited for livestock grazing due to the low productivity and fragile soils. This is a very dry site and supports a very small compliment of wildlife. Mule deer spend considerable time on this site on sunny winter days as the slopes are usually free of snow.

This site has a very high natural erosion rate. Due to the steep slopes and fragile soils it can be easily degraded by improper grazing management. This site is naturally relatively barren and arid looking. It is unappealing aesthetically to most viewers and gives one an impression of “badlands”.

Impacts on the Plant Community.

Influence of fire:
In the absence of normal fire frequency, shadscale saltbush can gradually increase on the site. Grasses and forbs decrease as shrubs increase. With the continued absence of fire, these shrubs can displace many of the primary understory species.

When fires become more frequent than historic levels (80-100 years), shadscale saltbush, bud sagebrush and Wyoming big sagebrush are reduced significantly. Green rabbitbrush will generally re-sprout after fire. With continued short fire frequency, these shrubs can be completely eliminated along with many of the desirable understory species such as Salmon wildrye, bluebunch wheatgrass and Indian ricegrass. Sandberg bluegrass will increase along with a variety of annual and perennial forbs including noxious and invasive plants. Cheatgrass will invade the site. These fine fuels will increase the fire frequency.

Influence of improper grazing management:
Season-long grazing and/or excessive grazing can be very detrimental to this site. This type of management leads to reduced vigor of the bunchgrasses and palatable shrubs. With reduced vigor, recruitment of these species declines. As these species decline, the plant community becomes susceptible to an increase in prickly pear, Wyoming big sagebrush, green rabbitbrush and noxious and invasive plants.

Continued improper grazing management influences fire frequency by increasing fine fuels. As cheatgrass increases and becomes co-dominant with Sandberg bluegrass and other annuals, fires become more frequent.

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 prickly pear, Wyoming big sagebrush and green rabbitbrush. A planned grazing system can be developed to maintain the integrity of the plant community on this site.

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:
Mormon crickets and grasshopper outbreaks occur periodically. Outbreaks seldom cause plant mortality since defoliation of the plant occurs only once during the year of the outbreak.

Shadscale saltbush can be heavily impacted by the scale insect, Orthezia annae. It is also called “mealy bug”. This insect is moved by ants from one plant to another and feeds on the roots of shadscale saltbush. It can cause stand mortality especially following a series of drought years.

Influence of noxious and invasive plants:
Many of these species add to the fine-fuel component and lead to increased fire frequency. Perennial and annual invasive species 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 in all seasons. Their numbers are seldom high enough to adversely affect the plant community.

Watershed:
Decreased infiltration and increased runoff occur with an increase in prickly pear, Wyoming big sagebrush and green rabbitbrush. Desired understory species can be reduced. This composition change can affect nutrient and water cycles. Increased runoff also causes sheet and rill erosion. 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 no fire.
Phase C to A. Develops with prescribed grazing and no fire.
State 1 Phase C to State 2. Develops through frequent fire or improper grazing management. This site has crossed the threshold. It is not economically practical to return this plant community to State 1 with accelerating practices.
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 a threshold and retrogress to a new site with reduced potential. It is not economically practical to return this plant community to State 1 with accelerating practices.

Practice Limitations.
Slight to moderate limitations exist on this site for implementing vegetative management and facilitating practices. Severe limitations exist for implementing accelerating practices due to low annual precipitation and low site potential due to soils.