Ecological dynamics

The dominant visual aspect of this site is a grove of shrubby quaking aspen with a heavy understory of shrubs and forbs. This site is composed of one to several quaking aspen clones, each with a common genetic makeup and individual phenological and physiological characteristics. Composition by weight for the entire plant community is approximately 5 percent grass, 10 to 20 percent forbs, and 75 to 85 percent shrubs (the aspen usually do not develop into tree form).

During the last few thousand years, this site has evolved in a climate characterized by cool, moist summers and cold, wet winters. The site has evolved in pockets that accumulate snow. Snow may be present on the site from mid October to late June. This site is typically multi-layered. Sufficient light is able to penetrate the canopy to support abundant understory growth. The aspen stands are un-even in age due to the loss of top growth from disease, insects, age, or breakage from snow loads. As these conditions occur the individual aspen shrubs are then able to replace themselves through rhizomatous reproduction. Understory species that occur near the periphery of an aspen clone are generally shade intolerant. They include basin wildrye, bluebunch wheatgrass, bottlebrush squirreltail, mountain brome, slender wheatgrass, bittercherry, mountain big sagebrush, and common chokecherry.

Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, Rocky Mountain elk, and Shiras moose.

Fire stimulates suckering or root sprouting from the root system. The fire frequency on the site is dependent on the frequency of fire on adjacent range sites and the level of moisture in the fuels on the site. Fire conditions generally need to be severe to carry a fire through this plant community. Often due to higher humidity and fuel moisture within the aspen grove, fire is knocked down once it enters the site. Therefore fire frequency is generally less frequent than on adjacent upland range sites. The normal fire frequency is 75-120 years.

The total annual production is 4000 pounds per acre (4480 kilograms per hectare) in a normal year. In a below normal year production is 3000 pounds per acre (3360 kilograms per hectare). In an above normal year production is 4500 pounds per acre (5040 kilograms per hectare).

Structurally, shrubs are very dominant followed by cool season deep-rooted perennial forbs, followed by perennial grasses being sub-dominant.

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. The Reference Plant Community varies dependent on the normal or average snow depth and its’ duration. With lesser snow depths and shorter durations, shrubs such as mountain snowberry, serviceberry, and Woods’ rose may be more prevalent than Scoulers willow. Sites with deeper snow levels resulting in longer durations will have fewer understory shrubs and have a dominance of aspen. A typical composition for the plant community of Phase 1.1 with a moderate snow depths and durations is listed later under “Reference Plant Community Phase Plant Species Composition”.

Additional data needs to be collected to obtain the species in the Reference Plant Community for snowpockets that have snow depths and durations that differ from this typical situation.

The plant community can go through an herbaceous stage where vegetation is dominated by grasses and forbs under full sunlight. Dominant grasses found in this stage include a mix of shade tolerant and shade intolerant plants. This stage is experienced after a major disturbance such as root-rot, insect damage, or ground fire. Following a major disturbance, the aspen root system gives rise to many root suckers, assuming the root system has remained intact and is still healthy. Most other shrubs in the understory will also sprout from their crowns or root systems following a fire. This stage is shown as Phase 1.2 in the state and transition model. This stage occurs for a short period of time.


FUNCTION:

This site is not well suited for livestock grazing because the plant community is so dense that it is hard for livestock to physically enter it. Typically, they will use the outer edges of the community only. Snowpockets that form with a lower average snow depth and duration may be grazed. This type of snowpocket site is an important area for wildlife. They provide cover, nesting, and food, although it is still often so dense that larger animals find it difficult to enter them. Hunting opportunities are good where the site is isolated from human activity. Severe degradation of adjacent sites will occur prior to this site being degraded.

Impacts on the Plant Community.

Influence of fire:

This site can burn from wildfire. Burning usually occurs from fire spreading from an adjacent range site when the fuel moisture levels are low in these. Since the plant community in this site is dependent on moist soils which allow deep-rooted plants to grow throughout most of the summer, the fuels often are not dry enough to burn. The fire frequency is usually longer than adjacent range sites. Most of this site is associated with the sagebrush steppe where the normal fire frequency is estimated at 20-50 years. A wildfire can damage or kill most of the above ground plant material. Aspen and most of shrubs adapted to the site are root-sprouting plants and regenerate rapidly. In order for this site to remain intact, fire needs to be a component of plant community development since aspen and willows require bare soil conditions to establish seedlings. Conifer invasion is usually not a problem, but if it occurs, fire is needed to maintain the aspen community.

Influence of improper grazing management.

Typically, this site is not well suited to grazing due to the density of the plant community. The outer edges of the plant community are often grazed and can be adversely impacted. Usually, adjacent sites will be severely impacted before this site is degraded.

Proper grazing management that addresses frequency, duration, and intensity of grazing applied to adjacent sites can maintain the integrity of the plant community and the moist soils on which it is dependent. Properly managed ungulate grazing and browsing does not have a detrimental affect on stand development.

Weather influences:

Because of the deep moist soils, the production of this site changes little during wet or dry precipitation years. The overall production can be adversely influenced with prolonged drought. Prolonged drought can lead to more frequent fires. 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 run-off and flooding. An early, hard freeze can occasionally kill some plants and stop the growth of trees and shrubs.

Influence of insects and disease:

Periodic disease and insect outbreaks can affect vegetation health. Aspen is susceptible to injury or mortality from a variety of borers and fungus. It is most susceptible following fire or when the clone becomes older than 60-70 years. An outbreak of a particular insect is usually influenced by weather but no specific data for this site is available.

Influence of noxious and invasive plants:

Annual and perennial invasive species can compete with desirable plants for moisture and nutrients. The result is reduced production and change in composition of the understory. There are several noxious or invasive plant species that are adapted to this site, particularly following fire. As the canopy closes most of the shade intolerant species decline.

Influence of wildlife:

This site is important for many species of mammals and birds for food and life cycles. Total numbers are seldom high enough to adversely affect the plant community. The site is primarily used in the late spring, summer, and fall by big game. Many birds use the site for food, nesting, or brood rearing in the late spring and summer.

Watershed:

When ground cover is at or near potential, the erosion hazard is slight. The largest threat to degradation of this site is improper grazing management on adjacent sites resulting in degradation of the periphery of the site. This plant community, over time, will get smaller and smaller. If improper grazing management continues to remove the aspen suckers, the entire aspen clone can be lost.


Plant Community and Sequence:

Transition pathways between common vegetation states and phases:

State 1.
1.1. Aspen-Scouler willow-shrubs
Plant Community Phase 1.1 to 1.2 (1.1A). Results from fire.
Plant Community Phase 1.1 to 1.4 (1.1B). Results from improper grazing management.
Plant Community Phase 1.1 to 1.3 (1.1C). Results from old age, insects, and disease.
Plant Community Phase 1.2 to 1.1 (1.2A). Results from no fire.
Plant Community Phase 1.3 to 1.2 (1.3A). Results from fire.
Plant Community Phase 1.4 to 1.1 (1.4A). Results from prescribed grazing, particularly on adjacent sites.

State 1, Phase 1.4 to State 2 (T1A). Results from continued improper grazing management, particularly on adjacent sites. This site has crossed the threshold. It is not economically feasible to move this state back to the State 1.

State 2 to State 3, unknown new site (T2.1A). Results from continued improper grazing management, particularly on adjacent sites.


Practice Limitations.

Only slight limitations exist for implementing vegetative management practices and facilitating practices. However, it may be desirable to locate salt and water away from this site to help improve animal distribution and reduce concentration on this site. Severe limitations exist for seeding after a fire due to sprouting shrubs. Prescribed burning may be needed to revitalize decadent stands of aspen. Potential for sheet and rill erosion is moderate to severe if the shrub canopy is removed by a severe, hot fire and where slopes are greater than 15 percent.