Ecological dynamics

The dominant visual aspect of this site is Idaho fescue and threetip sagebrush. Composition by weight is approximately 50 to 70 percent grasses, 10 to 20 percent forbs and 20 to 30 percent shrubs.

NOTE: This site may be R012XYO48ID, NORTH SLOPE DEEP LOAMY 12-16” ARTRV/FEID that has burned more frequently than the historic intervals sometime in the past. This may have created a fire disclimax with threetip sagebrush becoming the dominant shrub. This theory needs to be field tested.

During the last few thousand years, this site has evolved in an 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, Rocky Mountain elk, pronghorn antelope, big horn sheep and lagomorphs. Fire has historically occurred on the site at intervals of 50 to 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 A. This plant community is dominated by threetip sagebrush and Idaho fescue. Mountain big sagebrush is a subdominant shrub species and a variety of other shrubs can occur. Subdominant herbaceous species include bluebunch wheatgrass, milkvetch and arrowleaf balsamroot. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

Total annual production is 600 pounds per acre (670 kilograms per hectare) in a normal year. Production in a favorable year is 900 pounds per acre (1008 kilograms per hectare). Production in an unfavorable year is 450 pounds per acre (504 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:
This site is best suited for summer and fall grazing by livestock. This site is valuable as habitat for mule deer, Rocky Mountain elk, big horn sheep, pronghorn antelope and raptors. It is used by wildlife in the summer and fall. It is also suited for recreationAL use in the summer and fall. It is used for hunting, hiking and photography.

Due to the limited access on steeper slopes and relatively high production, most areas of this site are not easily degraded. Lower footslopes in proximity to bottoms or drainages are most likely to degrade due to access by animals from these adjoining lands. Infiltration is good where the plant community has a good shrub component. A mixed stand of shrubs and perennial grasses is necessary to reach the potential of the site.

Impacts on the Plant Community.

Influence of fire:
Three-tip sagebrush exhibits variable sprouting abilities following fire. The specific response may depend on ecotypic differences, fire severity, soil moisture or a combination of these factors. Generally, it re-sprouts vigorously after fire, but may be a weak sprouter in some areas. It is considered a strong sprouter for this site. Three-tip sagebrush sprouts from shallow lateral roots or the root crown. It can also layer. Nearly pure stands can develop after the site burns.

In the absence of normal fire frequency, three-tip sagebrush 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. If a Utah juniper seed source is in the proximity, juniper can invade the site. See “Influence of Juniper Invasion” below. An increase in tall shrubs generally leads to an increase in juniper by providing bird perches and “nursery” sites for juniper establishment.

When fires occur more frequently than historic levels (50-70 years), three-tip sagebrush is reduced significantly. Rabbitbrush can increase slightly. Three-tip sagebrush may re-sprout vigorously after burning. With a continued short fire frequency, three-tip sagebrush can be completely eliminated along with many of the desirable understory species such as bluebunch wheatgrass and Idaho fescue. These species may be replaced by Sandberg bluegrass along with a variety of annual and perennial forbs including noxious and invasive plants. Cheatgrass can invade the site at lower elevations. These fine fuels will increase the fire frequency.

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 Idaho fescue and bluebunch wheatgrass and other bunchgrasses. With reduced vigor, recruitment of these species declines. As these species decline, the plant community becomes susceptible to increase in three-tip sagebrush, annuals and noxious and invasive plants.

Continued improper grazing management influences fire frequency by increasing these fine fuels. The site then becomes susceptible to an invasion of noxious and invasive plants and soil erosion. If cheatgrass and/or medusahead increase due to improper grazing management and become 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 three-tip sagebrush. A planned grazing system can be developed to intentionally accumulate fine fuels in preparation for a prescribed burn. Any brush management should be carefully planned, as a reduction in shrubs without a suitable understory of perennial grasses, can increase cheatgrass and/or medusahead which leads to more frequent fire intervals.

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 changes in fire frequency.

Influence of insects and disease:
Outbreaks can affect vegetation health. 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.

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 the spring, summer and fall. Their numbers are seldom high enough to adversely affect the plant community.

Watershed:
Decreased infiltration and increased runoff occur with an increase in three-tip 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.

Influence of juniper invasion:
The following discussion deals with Utah juniper.

In plant communities that are invaded by juniper, the species has a competitive advantage for the following reasons:
• Juniper is very drought tolerant.
• It has the ability to extract soil moisture from a wide range of soil depths.
• Juniper has high evapo-transpiration rates.
• The species intercepts rain and snow before it reaches the soil surface.
• It has the ability to grow as long as there is soil moisture and the temperature is above freezing.
• Juniper has a relatively rapid growth rate and is long-lived. It can readily over-top shade intolerant species which leads to mortality.
• Nutrient cycling is reduced.
• As the canopy closes, juniper gains control of energy capture.

As juniper extracts water, other plants are unable to acquire sufficient water and nutrients to sustain growth and reproduction, thus reducing cover and biomass in the interspaces. After the canopy closes, there is sufficient soil moisture available for shallow-rooted, shade tolerant species to persist directly under the tree.

The following hydrological impacts occur on sites invaded by juniper:
• Infiltration in the interspaces is reduced.
• Run-off increases resulting in increased sheet and rill erosion with elevated sediment loads.
• Soil temperatures increase in the interspaces which results in accelerated drying of the soil surface.
• Increased bare ground in the interspaces.
• Soil moisture storage is reduced.

As bare ground and interconnectiveness of bare ground increases, flow rates are accelerated (reduction of flow sinuosity) and run-off out of the area increases.

Degradation of these systems can result in the formation of a feedback cycle in which greater juniper cover and density results in greater plant and soil disturbance between the canopies.

In summary, a closed juniper community takes control of the following ecological processes: (1) hydrology, (2) energy capture and (3) nutrient cycling. The changes are primarily driven by the hydrological processes. The development of a closed juniper canopy always results in a transition across the threshold to a different state. Generally, when juniper canopy cover nears 20%, the plant community is approaching the threshold.

Plant Community and Sequence:
Transition pathways between common vegetation states and phases:

State 1.
Phase A to B. Develops in the absence of fire and improper grazing management. There is a Utah juniper seed source present in the vicinity near the site.
Phase A to C. Results from a fire.
Phase A to D. Results from improper grazing management and no fire. There is no Utah juniper seed source present in the vicinity.
Phase B to C. Results from a wildfire or brush management.
Phase B to A. Occurs with prescribed grazing and brush management or prescribed burning.
Phase C to A. Results from prescribed grazing and no fire.
Phase D to A. Occurs with prescribed grazing.
Phase D to C. Occurs with fire or prescribed burning and prescribed grazing.
Phase C to D. Occurs with no fire and improper grazing management.

State 1 Phase C and D to State 2. Develops through frequent fire and improper grazing
management. This site has crossed the threshold. It is economically practical to return this plant community to State 1 with accelerating practices.

State 1, Phase B to State 3. Develops with improper grazing management and no fire from a juniper invaded phase of State 1. This site has crossed the threshold. It is economically impractical 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 improper grazing management and no fire 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 plant community to State 1 with accelerating practices.

State 3 to unknown site. Continued lack of fire or improper grazing management cause this state to cross the threshold and retrogress to a new site with reduced potential due to significant soil loss and changes in hydrology. It is economically impractical to return this plant community to State 1 with accelerating practices.

Practice Limitations:
Moderate limitations exist for vegetative management practices due to slope. Severe limitations exist on the site for implementing facilitating and accelerating practices due to steep slopes.