Abstract for M020

Rocky Mountain Subalpine - High Montane Forest
Forêts subalpines et des montagnes de haute altitude des Rocheuses

M020 describes North American continental, temperate subalpine and high montane treed vegetation of the Western Cordillera. The Canadian expression includes mid- to high-elevation forests and woodlands of southern and central British Columbia (BC), southern and west-central Alberta, and southwestern Saskatchewan. Canopies are usually evergreen coniferous, although some cold-deciduous broad-leaved species are found in mid-elevation montane forests and local occurrences of cold deciduous conifer species are found in southern parts of the Canadian range. Stands of M020 vary from closed forests to very open short-statured woodlands, becoming more open and patchy with higher elevation and often occurring as tree islands or ribbons in a matrix of grasslands, meadows or shrublands at elevational treeline. At the highest elevations or on the sites most exposed to wind, trees can be “flagged” or damaged by blowing snow and ice crystals as well as severe cold. Avalanches, windthrow, insect infestations and stand-replacing fires are the most widespread forms of natural disturbance. Dominant tree species include subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta var. latifolia) and interior spruce (Picea engelmannii x glauca). Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) and trembling aspen (Populus tremuloides) are common in mid-elevation montane forests, especially on warm aspects. Mountain hemlock (Tsuga mertensiana), limber pine (Pinus flexilis), whitebark pine (Pinus albicaulis), subalpine larch (Larix lyalli) and western larch (L. occidentalis) are characteristic trees in some areas. Understory species composition is highly diverse and varies with environmental conditions. The ericaceous species mountain huckleberry (Vaccinium membranaceum), white-flowered rhododendron (Rhododendron albiflorum), grouseberry (V. scoparium) and false azalea (Menziesia ferruginea) are common and often dominant. Characteristic herbs include arnicas (Arnica cordifolia, A. latifolia), five-leaved dwarf bramble (Rubus pedatus), three-leaved foamflower (Tiarella trifoliata), Sitka valerian (Valeriana sitchensis), single-flowered clintonia (Clintonia uniflora), oak fern (Gymnocarpium dryopteris) and green false hellebore (Veratrum viride). Mosses and liverworts include red-stemmed feathermoss (Pleurozium schreberi), broom mosses (Dicranum spp.), ragged mosses (Brachythecium spp.) and leafy liverworts (Barbilophozia spp.).

In Canada, M020 occurs within the mountains and high plateaux of interior British Columbia, in the Rocky Mountains, in the foothills of southwestern Alberta and in the Cypress Hills of southeastern Alberta and southwestern Saskatchewan. Elevations extend from approximately 850 mASL to 2300 mASL, depending on location. The macroclimate is dry to subhumid, temperate and continental, with cold, snowy winters and short, cool summers. However, subregional orographic effects create highly variable climatic regimes: mean annual temperatures vary from -1°C to +3°C; annual precipitation varies from 400 mm to >2000 mm, much of it falling as snow. All parts of the range experienced Pleistocene glaciation; soils are mostly Luvisols, Brunisols and Podzols developed in glacial surficial materials.

Three subtypes characterize regional variation in the Canadian range of M020. Subtype CM020a [Dry Rocky Mountain Mid-Montane Forest] characterizes montane forests that occur at mid-elevations in relatively drier, warmer climates of southern BC, western Alberta and southwestern Saskatchewan. CM020b [Dry Rocky Mountain High Montane & Subalpine Forest] occurs at higher elevations in the drier climates of southern BC and southwestern Alberta. CM020c [Humid Rocky Mountain High Montane & Subalpine Forest] occurs over much of the range of M020 in BC and west-central Alberta at higher elevations in more humid climates.