Ecological dynamics

The dominant visual aspect of this site is an overstory of silver sagebrush with Idaho fescue in the understory. Composition by weight is approximately 55 to 65 percent grass and grass-like species, 10 to 20 percent forbs, and 20 to 30 percent shrubs.

During the last few thousand years, this site has evolved in a cool climate characterized by dry summers and cold, moist winters. Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, Rocky Mountain elk, and lagomorphs.

Fire has historically occurred on the site at intervals of 20 - 40 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 dominated by silver sagebrush and Idaho fescue. Tufted hairgrass and some wetland sedges such as wooly sedge can occur in the plant community where the water table is within 12 inches of the surface. A variety of dryland sedges, grasses, and forbs occur in minor amounts. A few other shrubs are present that include Woods’ rose and shrubby cinquefoil occur in minor amounts. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

Total annual production is 2400 pounds per acre (2688 kilograms per hectare) in a normal year. Production in a favorable year is 3000 pounds per acre (3360 kilograms per hectare). Production in an unfavorable year is 1800 pounds per acre (2016 kilograms per hectare). Structurally, cool season deep-rooted perennial grasses and grass-like species are more dominant than shrubs followed by perennial forbs.

FUNCTION:

The site provides food, cover, and brood raising habitat for waterfowl and other birds. Big game animals use the site in the late spring, summer, and fall. Livestock use is best in the summer and fall when the soil surface is drier. The site has some aesthetic, picnicking, and hunting value.

The site is resistant to degradation due to high production and available soil moisture, but can be degraded with improper grazing management and the lowering of the water table.

Impacts on the Plant Community.

Influence of fire:

In the absence of normal fire frequency and ungulate grazing, Idaho fescue can become decadent. This is apparent by dead centers in the crowns. Silver sagebrush can also become decadent. Forbs will be maintained in the community.

When fires become more frequent than historic levels (20-40 years), Idaho fescue can be reduced in the plant community. With continued short fire frequency, these species can be completely eliminated along with some forbs. Silver sagebrush usually will increase under frequent fire intervals because it sprouts from the crown, lateral roots, and rhizomes. The understory species may be replaced by a variety of annual and perennial forbs including noxious and invasive species. These fine fuels can cause fires to become more frequent. Kentucky bluegrass may invade the site. Woods’ rose will usually be maintained in the plant community due to sprouting. Shrubby cinquefoil will be maintained in the community with low intensity fires but can be killed with high intensity or hot fires.

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 reduced vigor of the grass and grass-like species. With reduced vigor, recruitment of these species declines. As these species decline, an increase in silver sagebrush can occur and noxious and invasive plants will invade. Kentucky bluegrass may invade the site Forbs will increase.

Continued improper grazing management influences fire frequency by increasing fine fuels. As annuals increase, 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. A planned grazing system can be developed to intentionally accumulate fine fuels in preparation for a prescribed burn. Prescribed burns on this site, however, need extremely careful planning due to the elevation and the species involved.

Weather influences:

Above normal precipitation in May and June can increase total annual production of the plant community but a majority of the available soil moisture for plant growth is predominantly from the water table. Temperatures often drive forage and seed production more than precipitation, although precipitation can indirectly influence water tables. Overall plant composition is normally not affected when perennials have good vigor.

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:

Outbreaks can affect vegetation health. 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:

Big game animals will use this site in the late spring, summer, and fall. Their numbers are seldom high enough to adversely affect the plant community.

Watershed:

Decreased infiltration and increased runoff occur with a decrease in perennial bunchgrasses. 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 no fire.
Phase A to C. Develops with fire.
Phase B to A. Develops with prescribed grazing.
Phase C to A. Develops with prescribed grazing and no fire.

State 1, Phase B or C to State 2. Develops through frequent fire and/or continued improper grazing management and lowering of the water table. This site has crossed the threshold. It is economically impractical to return this plant community to State 1 with accelerating practices.

State 2 to State 3. Develops through rangeland seeding.

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 economically impractical 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 practices. Excessively wet periods may bring the water table at or near the soil surface. Grazing management should take into account this situation and should avoid grazing on wet soils. Slight to moderate limitations exist for implementing facilitating practices on this site. Fences, especially those having set wooden posts in the water table, may move around with winter freezing. There are moderate limitations for mechanical preparations of a seedbed for rangeland seeding due to wet soils.