Ecological dynamics

The site occurs as a mosaic of small barren or nearly barren areas in association with other sites. The visual aspect of the site is the small barren areas in association with Wyoming big sagebrush sites, usually Loamy 8-10” or Loamy 10-12”. The site itself is either barren or nearly devoid of vegetation. The nearly barren areas may be from 2 to 15 feet across. The dominant species on the site are Wyoming big sagebrush and small amounts of perennial bunchgrasses such as Thurber’s needlegrass, bluebunch wheatgrass, Sandberg bluegrass, or bottlebrush squirreltail. Composition by weight is approximately 55 to 65 percent grasses, 10 to 20 percent forbs, and 20 to 30 percent shrubs.

During the last few thousand years, this site has evolved in a semi-arid climate characterized by dry summers and cold, wet winters. Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, pronghorn antelope, lagomorphs, and small rodents.

Fire history is related to the associated sites as the site itself has very low production and low amounts of fine fuels. Associated sites historically burned at intervals of 50-70 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 1.1. This plant community is rarely dominated by any one species but bluebunch wheatgrass, Thurber’s needlegrass, Sandberg bluegrass, and bottlebrush squirreltail can occur in variable amounts in the understory. Scattered Wyoming big sagebrush plants occur in the overstory. The dominant forbs include pepperweed and Hoods phlox with a variety of other forbs and shrubs in small amounts. The plant species composition of Phase 1.1 is listed later under “Reference Plant Community Phase Plant Species Composition”.

Total annual production is 75 pounds per acre (84 kilograms per hectare) in a normal year. Production in a favorable year is 100 pounds per acre (112 kilograms per hectare). Production in an unfavorable year is 25 pounds per acre (28 kilograms per hectare). Structurally, cool season deep rooted perennial bunchgrasses are dominant, followed by tall shrubs being more dominant than perennial forbs while shallow rooted perennial bunchgrasses are subdominant.


FUNCTION:

The site is normally too small a component in the association to have any values of its own.

This site has very little value for livestock grazing due to the sparse vegetation. The use is related to the use of the associated sites that are usually suited to spring and fall grazing.

The site has limited value for wildlife but is used incidentally by wildlife using adjacent associated sites.

The recreation values for this site are usually an extension of the other sites with which it is associated.

The site can be easily degraded with improper grazing management due to low potential production and ease of access, although the site and its associated sites often have limited livestock water.


Impacts on the Plant Community.

Influence of fire:

Fire has little influence on the site itself due to the low production and lack of fine fuels. In the absence of normal fire frequency in the associated Wyoming big sagebrush sites, a small increase of shrubs can occur. Grasses and forbs decrease as shrubs increase. With the continued absence of fire, Wyoming big sagebrush can displace most of the primary understory species, particularly since lateral shrub roots from the adjacent sites can extend into this site.

When fires become more frequent than historic levels (50-70 years), Wyoming big sagebrush is reduced significantly. Rabbitbrush can increase slightly. With continued short fire frequency, Wyoming big sagebrush can be completely eliminated along with many of the desirable understory species such as bluebunch wheatgrass and Thurber’s needlegrass. These species may be replaced by bottlebrush squirreltail 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:

The site is used with the associated sites. Season-long grazing and/or excessive utilization can be very detrimental to this site. This type of management leads to reduced vigor of the bunchgrasses. With reduced vigor, recruitment of these species declines. As these species decline, the plant community becomes susceptible to increases in Wyoming big sagebrush 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 Wyoming big sagebrush. Any brush management should be carefully planned, as a reduction in shrubs without a suitable understory of perennial grasses can increase cheatgrass which will lead to more frequent fire intervals.

Weather influences:

Above normal precipitation in March, April, and May 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 reduction in fire frequency.

Influence of Insects and disease:

Outbreaks can affect vegetation health. The sagebrush defoliator moth (Aroga websterii) causes mortality in relatively small patches. It seldom kills the entire stand. 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.
Annual and perennial 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:

Wildlife’s use of this site is incidental to their use of associated sites. Big game animals associated use of this site occurs in the spring, summer, fall, and in moderate winters. Their numbers are seldom high enough to adversely affect the plant community. Burrowing rodents can alter soil profiles and allow invasion of undesirable plants.

Watershed:

Decreased infiltration and increased runoff occur with an increase in Wyoming big sagebrush. 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 1.1 to 1.2. Develops with improper grazing management.
Phase 1.1 to 1.3. Develops with fire.
Phase 1.2 to 1.1. Develops with prescribed grazing.
Phase 1.3 to 1.1. Develops with prescribed grazing and no fire.

State 1 to State 2. Develops through frequent fire and continued improper grazing management. The site has crossed the threshold. It is generally not economically feasible to move this state back to State 1 with accelerated 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 generally not economically feasible to move this state back to State 1 with accelerated practices.

Practice Limitations:

Only slight limitations exist on this site for implementing vegetative management and facilitating practices. The ability to implement these practices would be influenced by the limitations of the associated sites.

Because this site occurs as a small percentage of any given area, no accelerating practices would be applied specifically to this site. The application would be incidental to the practice applied on associated sites. Severe limitations for implementation of accelerated practices exist on this site because of the high sodium content of the soils and the shallow depth to the heavy clay or silty clay layers.