Ecological dynamics

This site ranges from poor to rich fens. Poor fens are characterized by a pH of 4.0 to 5.5. Bryophytes (Sphagnum) are dominant followed by vascular species (sedges and ericads). Rich fens are slightly acid to 7.0. They are dominated by sedges, other graminoids, and true mosses.

Composition by weight is 80-90 percent grass and grass-likes, 10-20 percent mosses and forbs, and 0-2 percent shrubs.

This site has evolved in a montane climate characterized by cool summers and cold, wet winters. A fen is formed by a stable discharge of groundwater. It requires wet, anaerobic soils, carbon accumulation from vigorous plant growth, low soil temperatures, and thousands of years to form the characteristic organic soil.

Fens form at low points in the landscape or near slopes where ground water intercepts the soil surface. Ground water inflows maintain a fairly constant water level year-round, with water at or near the soil surface. Constant high water levels lead to accumulation of organic material. In addition to peat accumulation and perennially saturated soils, some fens have distinct soil and water chemistry properties with high levels of one or more minerals. The surrounding landscape may be ringed with other wetland sites (see Wet meadow, Meadow, and Dry Meadow ESD’s) or a variety of upland sites from grasslands to forest.

Herbivory has historically occurred on this site at low levels of utilization. Herbivores include mule deer, white-tail deer, bighorn sheep, Shira’s moose, and Rocky Mountain elk.

Fire has had little or no influence on the development of the site. Wildfires are rare.

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 a mosaic of grass/ grass-like species. Forbs and shrubs are minor components of the plant community. Some of these species may be dominant in small areas due to soil and water variations as stated above. Small areas within the fen site may be dominated by either Carex aquatilis, Carex atherodes, Carex rostrata, Carex vesicaria, Eleocharis quinqueflora, Eleocharis palustris, Calamagrostis canadensis or any of the grass/grass-like species listed in the Reference Plant Community Phase Plant Species Composition table. Sphagnum species may occur in most of these plant communities. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

The total annual production is 1500 pounds per acre (1666 kilograms per hectare) in a normal year. Production in a favorable year is 2000 pounds per acre (2222 kilograms per hectare). Production in an unfavorable year is 1000 pounds per acre (1111 kilograms per hectare). Structurally, cool season deep-rooted perennial sedges and grasses are very dominant, followed by perennial forbs being more dominant than shrubs.


FUNCTION:

Due to the rarity of this site and fragile nature of the peat layer, grazing by large herbivores should be discouraged. Wet soils can limit grazing opportunities, particularly early in the year.

Due to the permanent saturation at the soil surface, recreational opportunities are limited. Hunters and fisherman may cross the site. Motorized vehicles can be very detrimental to the site because of the saturated surface soils.

Site degradation is usually the result of the stable discharge of water being changed. This can occur with down cutting of adjacent stream channels or significant run-off following prolonged drought. This can result from on-site improper grazing or off-site conditions in the upper watershed. Once adjacent streams down-cut, concentrated flows change the hydrology of the site.

Other threats to the site may include inundation, peat mining, livestock grazing, and invasive species.


Impacts on the Plant Community:

Influence of fire:

This site usually does not burn from wildfire. If a fire occurs, it usually does not adversely affect the plant community. Most plants including shrubs sprout back the next growing season.

Influence of improper grazing management:

Livestock grazing should be avoided on this site due to the potential of de-stabilizing the normal groundwater discharge. Livestock can cause soil damage due to trampling.

Weather influences:

Because of the deep soils, the influence of groundwater discharge at the surface, seasonal flooding and run-on, the production of this site changes little during wet or dry precipitation years. Below normal temperatures in the spring have little impact on 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 plant community. The plants that grow on this site are very competitive potentially invasive species. The growing season and associated environment limit the potential for the introduction of undesirable plants.

Influence of wildlife:

Large and small mammals are occasional users of the site. Waterfowl and shore birds use the site for food, nesting, or brood raising in the late spring, summer, and fall. Total numbers are seldom high enough to adversely affect the plant community.

Watershed:

The largest threat to degradation of this site is the de-stabilization of the ground water discharge to the soil surface. Off-site conditions can affect the gradient of adjacent stream channels that can affect the hydrologic function. If the perennial 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. These events may be triggered by massive wildfires or poor forest/ rangeland health. As the hydrologic function is changed, site potential is lost. Eventually the water table is below the root zone of the adapted perennial grasses, sedges, and rushes. These are ultimately replaced by perennial forbs and shallow rooted grasses and grass-likes. Extreme down cutting and lowering of the water table can move the site across a threshold to a new, less productive site. Severe down-cutting can result in a plant community that resembles an upland site.


Plant Community and Sequence:

Transition pathways between common vegetation states and phases:

State 1 to State 2. Develops through permanently modifying the discharge of ground water to the surface. This can occur with grazing, down-cutting of the adjacent stream channel, or changes in the hydrologic function of the upper watershed.


Practice Limitations:

There are severe seeding limitations on this site due to difficulty in preparing an adequate seedbed in saturated soils. Restoration of fens is thought to be difficult or impossible due to their reliance on groundwater and snowmelt hydrology. Fens are delicate systems that form in situ over thousands of years, requiring highly stable conditions. Once damaged, recovery is slow and the resulting hydrologic alterations may result in permanent degradation. Elimination of existing vegetation prior to planting should not be attempted. Grade stabilization structures or other bioengineering practices may be needed to prevent further down-cutting of the channel. Fencing of the site for livestock exclusion might also be a consideration.