Abstract for M501

Central Rocky Mountain Dry Lower Montane - Foothill Forest
Forêts sèches des montagnes de faible altitude et du piémont du centre des Rocheuses

M501 describes foothill, lower montane and plateau forests and woodlands of warm, dry, continental temperate climates of the North American Western Cordillera. The Canadian range includes continuous forests as well as woodlands and forest patches of the Cordilleran Dry Forest and Rocky Mountain Foothills Parkland CNVC vegetation zones in south-central British Columbia (BC) and southwestern Alberta. In the warmest and driest areas, the climate is moist enough to support tree growth only under certain conditions and the natural vegetation is often a landscape mosaic comprising patches of grassland or shrub-steppe and groves of forest and woodland (i.e., parkland). In cooler and moister areas, forest cover can be continuous. In parkland landscapes, M501 describes only the treed portion of the vegetation mosaic. In BC, these are primarily coniferous forests and woodlands; in Alberta, cold-deciduous broad-leaved species dominate. In BC, communities are generally dominated or co-dominated by Ponderosa pine (Pinus ponderosa) or Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), although lodgepole pine (Pinus contorta var. latifolia) often occurs with Douglas-fir. In Alberta, most occurrences of M501 are pure stands of trembling aspen (Populus tremuloides), sometimes accompanied by balsam poplar (Populus balsamifera), white spruce (Picea glauca), Douglas-fir and/or lodgepole pine. Understory composition is variable, depending on site conditions and degree of canopy closure. Typical shrubs include saskatoon (Amelanchier alnifolia), snowberries (Symphoricarpos albus; S. occidentalis), holly-leaved barberry (Berberis aquifolium), shiny-leaved meadowsweet (Spiraea lucida), wild roses (Rosa spp.), soapberry (Shepherdia canadensis) and common juniper (Juniperus communis). Grass species are often important in the understory, including pine reedgrass (Calamagrostis rubescens), bluebunch wheatgrass (Pseudoroegneria spicata), mountain rough fescue (Festuca campestris), Idaho fescue (F. idahoensis) and prairie junegrass (Koeleria macrantha). Other common understory species include common yarrow (Achillea millefolium), wild strawberry (Fragaria virginiana), common bearberry (Arctostaphylos uva ursi), arrow-leaved balsamroot (Balsamorhiza sagittata), heart-leaved arnica (Arnica cordifolia) and northern bedstraw (Galium boreale). Red-stemmed feathermoss (Pleurozium schreberi) is the most frequent moss. Fire and insect infestations are the most common forms of natural disturbance, often amplified by drought. The forests and woodlands of M501 are adapted to frequent low- to moderate-intensity surface fires that maintain relatively open stands of fire-resistant species (especially in BC) as well as restricting the size of forest patches in parkland landscapes. With fire suppression, stands have become denser, forest groves have encroached into grasslands, and high intensity stand-replacing fires are more prevalent.

In Canada, M501 occurs in a dry, continental temperate climate with warm summers and cool winters. Mean annual temperature varies from 2° to 9°C, and precipitation typically varies from 350 to 600 mm. Elevations seldom exceed 1400 mASL, and can be as low as 150 mASL. All parts of the range experienced Pleistocene glaciation; soils are mostly Luvisols, Brunisols and, in Alberta, Chernozems, developed in glacial surficial materials. A surface layer of volcanic ash occurs in some areas. Two subtypes distinguish regional variation in the Canadian range of M501: CM501a [Warm Dry Rocky Mountain Low Montane Forest] describes Ponderosa pine – Douglas-fir forests and woodlands in the driest valleys and plateaux of southern BC, and CM501b [Cool Dry Rocky Mountain Low Montane Forest] characterizes forests and woodlands of higher elevations in BC as well as the parkland areas of the Rocky Mountain foothills in southwestern Alberta.