Ecological dynamics

The dominant visual aspect of this site is a variety of willow species with a dominantly sedge understory. This site may occur in complex with dry meadow and meadow range sites in the flood plain. Composition by weight is approximately 30 to 40 percent grass, 5 to 15 percent forbs, and 50 to 60 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. The site has evolved on flood plains that have occasional to frequent and brief to very brief flooding. This flooding scours some areas and deposits sediment in others. This disturbance is necessary to provide exposed, moist mineral soil with full sunlight to germinate willows. Depositional areas can bury parts of limbs and twigs to start new plants. Scouring can also expose existing tree roots that will sprout. A water table near the surface to within 12 inches of depth is necessary to provide season long moisture for the growth of the willow species. Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, moose, Rocky Mountain elk, and beaver.

Fire has played a minimum role in maintaining the plant community. When fire does occur, almost all species resprout from the roots or crowns. Fire can cause some bare soil with full sunlight to germinate seed of willow species. The fire frequency on the site is dependent on the frequency of fire on adjacent range sites and moisture in the fuels on the site. The normal fire frequency is 50 to 100 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 an overstory of a variety of willow species. The herbaceous layer contains a variety of sedges and some tufted hairgrass. A variety of forbs occur on the site in minor amounts. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

The total annual production is 3300 pounds per acre (3696 kilograms per hectare) in a normal year. Production in an unfavorable year is approximately 2800 pounds per acre (3136 kilograms per hectare). In a favorable year, production is approximately 3800 pounds per acre (4256 kilograms per hectare). Structurally, shrubs are very dominant followed by grass-like species which are more dominant than forbs.


FUNCTION:

This site is suited for livestock grazing in late spring, summer, and fall. This site is usually heavily used by livestock, particularly in the summer. Prescribed grazing must be planned to avoid degradation of the site. Special management should be used to protect the adjacent water courses and the associated values. This is an important site for wildlife for cover and food. If the site is associated with perennial streams, a fisheries resource could also be present. The site has high value for recreation such as camping and picnicking. Hunting opportunities are good where the site is isolated from human activity. Degradation of the site can occur with high recreational use, improper grazing management, and down cutting of the adjacent stream course or upper watershed conditions that alter the flood frequency or duration.

Impacts on the Plant Community:

Influence of fire:

This site can burn from wildfire. Burning usually occurs from fire spreading from an adjacent ecological site when the fuel moisture levels are low in this site. Since the plant community in this site is strongly influenced by a water table allowing 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. The normal fire frequency on the site is estimated at 50-100 years. A wildfire can kill most of the above ground plant material. Most of the shrubs adapted to the site are root-sprouting plants and regenerate rapidly. The herbaceous layer is mostly rhizomatous species and will resprout. Fire can provide some areas of exposed mineral soil for willows to establish new plants.

Influence of improper grazing management:

Season-long grazing and/or excessive utilization can be very detrimental to this site. Fall use, year after year, will result in excessive utilization on the willow regeneration. This may lead to a single age class stand of shrubs that are tunneled. Uncontrolled beaver populations may eliminate some willows. Due to improper grazing management grasses, forbs, and shrubs can all decline in the plant community. Shrubs usually increase initially, but with continued improper management, will decline.

Continued improper grazing management will result in a stand of forbs and Kentucky bluegrass with reduced vigor. The ability of the community to withstand seasonal flooding is reduced and down cutting of an adjacent stream channel can result. This down cutting will lower the water table and thereby reduce the potential of the site. This site is particularly difficult to manage because animals seek out the site for shade and it is usually adjacent to water.

Proper grazing management that addresses frequency, duration, and intensity of grazing can maintain the integrity of the plant community and the water table on which it is dependent. Upstream watershed conditions must be maintained to have normal run-off events including moderate flooding.

Weather influences:

Because of the deep soils, the influence of the water table, seasonal flooding, and run-on, the production of this site changes little during wet or dry precipitation years. The overall production can be influenced adversely with prolonged drought. Prolonged drought can increase fire frequency. 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. An early frost can stop the growth on the shrubs. Low temperatures can result in lower total production.

Influence of Insects and disease:

Periodic disease and insect outbreaks can affect vegetation health. 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 plants that are adapted to this site. Some invasive species include whitetop, leafy spurge, dock, Canadian thistle, reed canarygrass, foxtail barley, perennial pepperweed, and teasel. Other invasive species may include meadow foxtail, redtop, and Kentucky bluegrass

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, summer, and fall.

Watershed:

The largest threat to degradation of this site is the lowering of the water table and changes in flooding characteristics either from incised channels or upstream conditions. Off-site conditions can affect the gradient of adjacent stream channels that can affect the water table. If the perennial grass, sedge and shrub cover is depleted, down cutting can be accelerated within the site. High run-off events from the adjacent uplands can severely damage or change the normal stream channel on the site. As the water table is lowered, productive potential is lost. Eventually the water table is below the root zone of the adapted perennial grasses and shrubs. These are ultimately replaced by perennial forbs and shallow rooted grasses. Extreme down cutting and lowering of the water table can move the site across the threshold to a new, less productive site. Severe down-cutting can result in a plant community that resembles an upland site. Reducing the frequency of flooding can adversely effect the regeneration of willows, leading to a decadent or dead overstory of old shrubs with no regeneration.

Plant Community and Sequence:

Transition pathways between common vegetation states and phases:

State 1.
Phase A to B. Develops with much reduced flooding frequency.
Phase A to C. Develops with improper grazing management.
Phase A to D. Develops with wildfire.
Phase A to E. Develops with uncontrolled beaver populations.
Phase B to A. This will occur with normal flooding frequency returning and prescribed grazing.
Phase C to A. This results from prescribed grazing.
Phase D to A. Results from no recent fires and prescribed grazing.
Phase E to A. Results from controlling the beaver population and prescribed grazing.

State 1 to State 2. This results from a deeply incised channel that lowers the water table and significantly reduces the flood frequency. The flood frequency can also be reduced from significant changes in the upper watershed that significantly changes runoff events, such as increased conifers, instream water diversions and prolonged drought. Improper grazing management has continued. Uncontrolled beaver populations can take out all willows and some understory plants. Improper grazing management can cause down cutting which results in a lowered water table. There is reduced scouring and sediment deposition.

The site has crossed the threshold. This state cannot be returned to State 1 without raising the water table and restoring flood frequency. This might be done over time using structures or bio-engineering practices, but the plant community may take many years to approach the plant community in State 1.


Practice Limitations:

Use of equipment is usually not feasible for seeding. Hand seeding or aerial seeding can be considered following a fire or other disturbance. Brush management is not recommended. The shrubs have high value for stream bank stabilization, channel protection, and wildlife habitat. Special management practices need to be used to protect this site from deterioration. There are slight limitations to implement vegetative management practices except for avoidance of grazing on wet soils.