Rocky Mountain Alpine Meadow

This widespread ecological system occurs above upper treeline throughout the Rocky Mountain cordillera, including alpine areas of ranges in Utah and Nevada, and isolated alpine sites in the northeastern Cascades. It is found on gentle to moderate slopes, flat ridges, valleys, and basins, where the soil has become relatively stabilized and the water supply is more or less constant. Vegetation in these areas is controlled by snow retention, wind desiccation, permafrost, and a short growing season. This system is characterized by a dense cover of low-growing, perennial graminoids and forbs. Rhizomatous, sod-forming sedges are the dominant graminoids, and prostrate and mat-forming plants with thick rootstocks or taproots characterize the forbs. Dominant species include Artemisia arctica, Carex elynoides, Carex siccata, Carex scirpoidea, Carex nardina, Carex rupestris, Festuca brachyphylla, Festuca idahoensis, Geum rossii, Kobresia myosuroides, Phlox pulvinata, and Trifolium dasyphyllum. Many other graminoids, forbs, and prostrate shrubs can also be found, including Calamagrostis purpurascens, Deschampsia cespitosa, Dryas octopetala, Leucopoa kingii, Poa arctica, Saxifraga spp., Selaginella densa, Sibbaldia procumbens, Silene acaulis, Solidago spp., and Trifolium parryi. Although alpine dry tundra is the matrix of the alpine zone, it typically intermingles with alpine bedrock and scree, ice field, fell-field, alpine dwarf-shrubland, and alpine/subalpine wet meadow systems.

The vegetation of this system is characterized by moderate to dense cover of low-growing, perennial graminoids and forbs. Rhizomatous, sod-forming sedges are the dominant graminoids, and prostrate and mat-forming plants such as Geum rossii with thick rootstocks or taproots characterize the forbs. Dominant species include Artemisia arctica, Carex elynoides, Carex siccata, Carex scirpoidea, Carex nardina, Carex rupestris, Festuca brachyphylla, Festuca idahoensis, Geum rossii, Kobresia myosuroides, Phlox pulvinata, and Trifolium dasyphyllum. Many other graminoids, forbs, and prostrate shrubs can also be found, including Carex scirpoidea, Calamagrostis purpurascens, Deschampsia cespitosa, Dryas octopetala, Leucopoa kingii, Poa arctica, Saxifraga spp., Selaginella densa, Sibbaldia procumbens, Silene acaulis, Solidago spp., and Trifolium parryi. Cushion plants are more common on shallow rocky soils near transition zones with alpine fell-fields. Relatively mesic species such as Carex haydeniana, Carex siccata, Leucopoa kingii, Potentilla diversifolia, Polygonum bistortoides, and Zigadenus elegans are found in mesic depressions and slopes below snowfields. Some species typical of lower-elevation grasslands, such as Festuca idahoensis, Poa fendleriana, Poa lettermanii, and Pseudoroegneria spicata, dominate some stands.

Although alpine dry tundra is the matrix of the alpine zone, it typically intermingles with alpine bedrock and scree, ice field, fell-field, alpine dwarf-shrubland, and alpine/subalpine wet meadow systems. The vegetation description is based on several references, including Cox (1933), Schwan and Costello (1951), Bamberg (1961), Willard (1963), Bamberg and Major (1968), Lewis (1970), Thilenius (1975), Komarkova (1976, 1980), Douglas and Bliss (1977), Baker (1980a), Hess (1981), Meidinger and Pojar (1991), Zwinger and Willard (1996), Cooper et al. (1997), Ecosystems Working Group (1998), Reid et al. (1999), Neely et al. (2001), NCC (2002), and NatureServe (2011).

This widespread ecological system occurs above upper treeline throughout the Rocky Mountain cordillera, including alpine areas of ranges in Utah and Nevada, and isolated alpine sites in the northeastern Cascades. It is found on gentle to moderate slopes, flat ridges, valleys, and basins, where the soil has become relatively stabilized and the water supply is more-or-less constant. Vegetation in these areas is controlled by snow retention, wind desiccation, permafrost, and a short growing season. Stands in Great Basin ranges are often less extensive and sometimes patchy because of more xeric conditions. Adjacent systems include Rocky Mountain Alpine Bedrock and Scree (CES306.809) and Rocky Mountain Alpine Fell-Field (CES306.811) with Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland (CES306.828) or Rocky Mountain Subalpine-Montane Limber-Bristlecone Pine Woodland (CES306.819) near treeline. Inclusions of the small-patch Rocky Mountain Alpine-Montane Wet Meadow (CES306.812) occur in wet areas below snow deposition areas and alpine basins. The environmental description is based on several references, including Cox (1933), Schwan and Costello (1951), Bamberg (1961), Willard (1963), Bamberg and Major (1968), Lewis (1970), Thilenius (1975), Komarkova (1976, 1980), Douglas and Bliss (1977), Baker (1980a), Hess (1981), Meidinger and Pojar (1991), Zwinger and Willard (1996), Cooper et al. (1997), Ecosystems Working Group (1998), Reid et al. (1999), Neely et al. (2001), NCC (2002), and NatureServe (2011).

Vegetation in these areas is controlled by snow retention, wind desiccation, permafrost and a short growing season. Dry summers associated with major drought years (mean return interval of 100 years) would favor grasses over forbs, whereas wet summers result in a more diverse mixture of forbs and graminoids. Dry turf dominated by graminoids such as Carex elynoides, Carex rupestris, or Kobresia myosuroides is intolerant of deep snow cover and occurs on wind-scoured slopes and ridges (Willard 1963). These species are efficient in obtaining water due to the turf-forming root system. Much of the soil moisture in dry turf is from summer precipitation, whereas mesic alpine slopes and meadows occur on sites with moderate snow accumulation or receive additional moisture from melting snowbeds. Lewis (1970) reports that Carex rupestris can send its roots under the edge of boulderfields and rock channels to obtain additional moisture.

Kobresia myosuroides is a major late-seral community in the alpine (Cox 1933, Willard 1963, Hess 1981, Komarkova 1986). Willard (1963) states that the Kobresia myosuroides stands on Trail Ridge, Colorado, are very old. Osburn (1958b) estimates that a minimum of 100 years are necessary for the formation of 1 inch of humus soil under present alpine conditions in the Front Range of Colorado. This estimate would suggest that some stands on Trail Ridge are 800 to 1300 years old.

Native large herbivores (Rocky Mountain bighorn sheep, mule deer and elk) are common in the alpine but probably do not greatly affect vegetation cover because animals move frequently as they reduce vegetation cover. Willard (1963) and Komarkova (1976) both remark on the abundance of pocket gopher (Thomomys talpoides fossor) activity within stands dominated by Carex elynoides. They state that due to the gophers' grazing, small patches of the plant communities are left isolated. Pocket gophers also dig tunnels beneath the soil surface of Trifolium dasyphyllum and Silene acaulis stands, eating the roots and bulbs of the plants. Pocket gophers kill individual plants in the stands by clipping the roots of the vegetation or smothering the aboveground portion of the plants with soil. The freshly aerated, bare soil is invaded by species from Carex elynoides - Carex rupestris - Kobresia myosuroides Rocky Mountain Alpine Turf Alliance (A3155). Polemonium viscosum stands are short-lived, however, possibly due to the loose soil substrate that is subject to erosion by wind and water (Willard 1963, Marr and Willard 1970, Zwinger and Willard 1996). Meadow voles (Microtus sp.) live in alpine meadows, feeding on the stems and blades of graminoids. When vole populations are high, however, the small mammals also feed on cushion plants, shredding the centers of Silene acaulis and Trifolium nanum. Seedlings from erect-form species, such as Geum rossii, become established in the dead parts of the cushion plants. Once established, the erect-form species shade and outcompete the remaining cushion plants. Willard (1963) suggests that Geum rossii stands may be expanding into adjacent cushion plant communities.

Very small burns of a few square meters (replacement fire) caused by frequent lightning strikes may occur as a rare disturbance where there is enough fuel buildup. Lewis (1970) reports that Carex rupestris can send its roots under the edge of boulderfields and rock channels to obtain additional moisture.

Grazing by domestic sheep used to be more widespread in this high-elevation system, and can still impact some stands where there are sheep ranching operations. Effects of sheep grazing depend on vegetation and vary with stocking rates and management with heavy grazing usually resulting in depletion and increased erosion rates.

Human development has impacted many locations throughout the ecoregion. High- and low-density urban and industrial developments also have large impacts. For example, residential development has significantly impacted locations within commuting distance to urban areas. Impacts may be direct as vegetation is removed for building sites or more indirectly through natural fire regime alteration, and/or the introduction of invasive species. Mining operations can drastically impact natural vegetation. Road building and power transmission lines continue to fragment vegetation and provide vectors for invasive species.

This system occurs above upper treeline throughout the North American Rocky Mountain cordillera, including alpine areas of ranges in Utah and Nevada, central Wyoming, and isolated alpine sites in the northeastern Cascades.