Subalpine Avalanche Rocky Mountain maple-Redosier dogwood Acer glabrum-Conus sericea ssp. sericea-Amelanchier alnifolia

Description

This ecological site is defined by active disturbance of the force of the avalanche within the chute and the lower run out zone. The frequency and severity of disturbance can vary, but the impact on the vegetation community favors species that can withstand the force of the avalanche. Rigid trunked conifer species rarely are able to withstand the force of the avalanche in the center of the chute, and will either snap at the trunk or have broken tops, or be stunted. If trees are found in the chute, they generally are lower down in elevation in the flatter runout zone, the area with least force of the avalanche. They can be either deciduous resprouting species like quaking aspen or black cottonwood, or conifer species with a maximum 20 percent cover in the lower elevation, lower impact runout zone, and young (25 years old) growing between disturbance events. Shrub species that basally resprout after disturbance or are able to lie prostrate and sprout multiple stems are preferred. The most common species found in avalanche chutes is Rocky Mountain maple. While shrub monocultures can exist, especially of the tall shrubs Sitka alder (Alnus viridis ssp. sinuata) and Rocky Mountain maple (Acer glabrum), a mix of shrubs is more prevalent. Depending upon the vegetation originally at the site and the severity of the disturbance, the post disturbance vegetation can be dominated by herbaceous species as well. This is particularly pertinent in high elevation alpine areas, bedrock areas within the chute or in very moist runout areas of the chute. Montane and subalpine areas with high adjacent conifer cover, will have conifer encroachment along the edges of the avalanche chute. Under low frequency and low severity disturbance regimes, the chute may partially infill. The repetitious disturbance by avalanches does not allow for the establishment of a forested overstory within the chute, but seedlings of tree species such as Douglas-fir (Pseudotsuga menziesii), subalpine fir (Abies lasiocarpa), and western larch (Larix occidentalis) may encroach along the edges. Low elevation runout areas may have up to 20 percent cover of stunted conifer trees with an understory of resprouting shrubs developed between disturbance events. These chutes will return to shrub or herbaceous vegetation with disturbance. There is a mix of shrub species found at this site including the resprouting mesophytic species Rocky Mountain maple, Sitka alder, Saskatoon serviceberry (Amelanchier alnifolia), common snowberry (Symphoricarpos albus), Greene’s mountain ash (Sorbus scopulina), red elderberry (Sambucus racemosa), thimbleberry (Rubus parviflorus), prickly currant (Ribes lacustre), and rose species. The most commonly found tall shrub species are Sitka alder and Rocky Mountain maple. Monocultures of various shrub species do occur including Sitka alder and Drummond’s willow (Salix drummondii). Herbaceous species commonly found are Rainier pleated gentian (Gentiana calycosa), green needlegrass (Nassella viridula), and splitleaf Indian paintbrush (Castilleja rhexifolia). Chutes with aspen (Populus tremuloides) originally present, may become thickets of aspen with a mix of other resprouting shrubs present. Quaking aspen is a prolific resprouter and in certain situations with low disturbance or low frequency of disturbance or lower in the runout zone of the chute, may be able to survive.

This ecological site is important forage and browse for wildlife species and livestock due to the high production and diversity of species. Hansen et al. (1995) found that Saskatoon serviceberry and common snowberry are fair to good forage palatability for sheep, cattle, and horses. Serviceberry has good palatability for sheep. Rocky mountain maple and thimbleberry are poor forage for cattle and horses, but fair for sheep. These species are considered medium to low in energy and protein values in fall and winter seasons. All are considered fair to poor value for elk, whitetail and mule deer for thermal or feeding cover value, but good value for bird species. Serviceberry is considered good food value for whitetail and mule deer and antelope, but fair for bird species. Common snowberry is considered fair food values for elk, deer, antelope, and bird species. Rocky Mountain maple is good for mule deer, but fair for whitetail deer and antelope and also fair for bird species. Thimbleberry is poor food value for elk, deer, and antelope, and fair for bird species. Redosier dogwood (Cornus sericea) is a faculatative wetland designated species, with medium energy value and low protein value (poor retention of digestible protein value during fall and winter). It is fair for cattle and sheep forage palatability, but poor for horses. It is rated as good food value for mule and whitetail deer (readily to moderately available in the plant’s range and consumed to a high degree). It is fair for antelope and poor for elk (readily to moderately available in the plant’s range but consumed only to a moderate degree). It is fair food value for upland game birds, waterfowl, small non-game birds, and small mammals. It is fair cover value for elk, mule deer, whitetail deer, upland game bird, waterfowl, small non-game birds, and small mammals.

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