Ecological dynamics

Ecological Dynamics of the Site:

The dominant visual aspect of this site is a plant community dominated by Nevada bluegrass, alpine timothy, and meadow barley. Shrubs are normally not present, however several willow species can be found in small amounts. Composition by weight is approximately 80-90 percent grasses and grass-likes and 10-20 percent forbs. Typically, the soil surface of the site is slightly undulating causing small depressions and high spots with variable soil moisture regimes. This site is commonly found in complex with the following sites:

1. Marsh site. Deeper depressions with water at or near the surface or slightly above the surface for the entire growing season. This site is dominated by broadleaf cattail, hardstem bulrush, and common threesquare.

2. Wet Meadow site. Shallow depressions with the water table at or near the surface for the entire growing season. This site is dominated by Carex and Juncus.

3. Meadow site. Slightly higher areas that are drier during the growing season. The water table is down to a depth of 20-40 inches by the end of the growing season. This site is dominated by tufted hairgrass and Nebraska sedge.


During the last few thousand years, this site has evolved in a semi-arid climate characterized by dry summers and cold, wet winters. Flooding and high water table have also influenced the development of this site. Herbivory has historically occurred on this site at low levels of utilization. Herbivores include pronghorn antelope, mule deer, Rocky Mountain elk, sage grouse, lagomorphs, and small rodents.

Fire has historically occurred on the site at intervals of 20-40 years. Fire has had little influence on the development of the site. This site normally burns in conjunction with an adjacent upland site.

The soils within any complex of meadow sites are highly variable. Factors that affect the determination of the site include depth to water table at end of growing season, micro-topography, and drainage class. Depth to water table and micro-topography are measurable features. Determination of drainage class requires the use of soil interpretation tables. Other interpretive factors that may be used for site determination are the frequency and duration of flooding and the depth, frequency, and duration of ponding.

Micro-topography is a feature that has a dramatic affect on depth to water table and the resulting plant communities. A few inches of change in surface elevation changes species composition and/or production. Slightly undulating topography is common in meadow complexes, therefore, more than one site should be expected.

An infinite number of combinations of factors that influence the ecology of potential plant communities exist. For practical purposes, four (4) plant communities where the depth to the water table drives the vegetative composition have been described. They are:

• Dry meadow Water table at >40” at end of growing season
• Meadow Water table at 20-40” at end of growing season
• Wet meadow Water table at 10-20” at end of growing season
• Marsh Water at surface to <10” at end of growing season

Most wetland species have a wide range of tolerance for variations in soil moisture. Most species occur in more than one site, although most are dominant on just one site.
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 Nevada bluegrass, alpine timothy, and meadow barley. The plant species composition of Phase A is listed later under “Reference Plant Community Phase Plant Species Composition”.

Total annual production is 1400 pounds per acre (1555 kilograms per hectare) in a normal year. Production in a favorable year is 2000 pounds per acre (2222 kg/ha). Production in an unfavorable year is 800 pounds per acre (888 kg/ha). Structurally, cool season deep-rooted perennial grasses are very dominant, followed by perennial forbs.


FUNCTION:

This site is suitable for big game and livestock grazing in the late spring, summer, and fall. Wet soils can limit grazing opportunities, particularly early in the year.

This site can be used for hiking, access to fishing, hunting, viewing wildlife and plants, and horseback riding. The wet soils can limit access. Motorized vehicles can be very detrimental to the site especially when soils are saturated to the surface.

Due to the deep soils, fertility, inherent high productivity, and relatively flat slopes, the site is fairly resistant to disturbances that can potentially degrade it. Site degradation is usually the result of lowering of the water table. 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 lower the water table.


Impacts on the Plant Community.

Influence of fire:

When this site burns, it usually does not adversely affect the plant community. With sufficient moisture, most plants, including shrubs, sprout back during the next growing season. Fires typically occur from mid-summer into fall.

Influence of improper grazing management:

Season-long grazing and/or excessive utilization can be very detrimental to this site. The grasses in the plant community will decline in the stand and sedges, rushes, and forbs will increase. Continued improper grazing management will result in a stand of forbs and Kentucky bluegrass with sedges and rushes. This reduced ability of the community to withstand seasonal flooding results from continued improper grazing management and/or the potential down cutting of adjacent streams. If down cutting or the initiation of headcuts occurs, both will lower the water table level and thus reduce the potential of the site.

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.

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. Ephemeral streams commonly occur on this site. Prolonged drought may adversely affect the frequency of ephemeral streams and the plant community that relies on them. 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.

Influence of Insects and disease:

Periodic disease and insect 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:

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.

Influence of wildlife:

This site is important for many species of mammals for food and life cycles. 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. Sage grouse use the site for brood rearing and forage.
Total numbers are seldom high enough to adversely affect the plant community.

Watershed:

The largest threat to degradation of this site is the lowering of the water table. Off-site conditions can affect the gradient of adjacent stream channels that can affect the water table. If the perennial grass and sedge cover is depleted or the perched watertable is lost, 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. 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.


Plant Community and Sequence:

Transition pathways between common vegetation states and phases:

State 1.
Phase A to B. Develops with improper grazing management.
Phase B to A. Results from prescribed grazing.

State 1 Phase A or B to State 2. Develops through channel down cutting and permanently lowering the late growing season water table to more than 40 inches. This can occur with continued improper grazing management. It may also occur with proper grazing on the site, but channel erosion may continue if poor off-site conditions cause frequent and/or severe flooding. The site has crossed the threshold. This state cannot be returned to State 1 without raising the water table.

State 2 to unknown site. Results from continued lowering of the water table through down cutting of the stream channel. The site crosses the threshold and retrogresses to a new site with reduced potential due to significant loss of available soil moisture from the lowered water table. It occurs with continued improper grazing management or repeated significant run-off events. This state cannot be returned to State 1 without raising the water table.

Practice Limitations.

There are moderate seeding limitations on this site due to difficulty in preparing an adequate seedbed due to water table. Elimination of existing vegetation prior to planting is difficult in wet seasons and high water table periods. There are moderate to severe limitations for brush management using chemicals due to the proximity to water bodies. Grade stabilization structures may be needed to prevent further down-cutting of the channel. Other options for rehabilitation may include application of fertilizer, prescribed grazing, and off-site livestock water development. Fencing of the site for better livestock control might also be a consideration.