Abstract for M496

West-Central North American Boreal Forest
Forêts boréales du Centre-ouest de l'Amérique du Nord

M496 describes the low elevation upland boreal and Rocky Mountain foothill forests in west-central Canada, ranging from southeastern Yukon and southern Northwest Territories to northwestern Ontario. Forest canopies can be coniferous, broad-leaved cold-deciduous or a conifer–broad-leaved mixture. These forests are maintained on the landscape by stand-replacing fire, with most parts of the range experiencing short (<100 years) to intermediate (100-270 years) regional fire cycles. Dominant tree species include trembling aspen (Populus tremuloides), white spruce (Picea glauca), black spruce (Picea mariana), lodgepole pine (Pinus contorta var. latifolia) and jack pine (Pinus banksiana). Balsam poplar (Populus balsamifera) occurs on nutrient-rich, usually moist sites. Paper birch (Betula papyrifera) is an early seral species that becomes more common eastward in the range. At higher elevations or in fire-sheltered locations, fir species (Abies lasiocarpa or A. balsamea) co-occur with white spruce in late seral stands. Understories vary from dense, species-rich shrub and herb conditions to poorly developed shrub and herb layers with continuous feathermoss and/or lichen ground cover. Common understory species include prickly rose (Rosa acicularis), squashberry (Viburnum edule), common Labrador tea (Rhododendron groenlandicum), fireweed (Chamerion angustifolium), tall bluebells (Mertensia paniculata), downy lymegrass (Leymus innovatus), bluejoint reedgrass (Calamagrostis canadensis), lingonberry (Vaccinium vitis-idaea), red-stemmed feathermoss (Pleurozium schreberi) and stairstep moss (Hylocomium splendens).

M496 occurs within a subhumid continental boreal climate, with long, cold winters and short, mild summers. Continental effects are modified in the Cordilleran portion of the range (CM496b), where higher elevations and mountain influences mitigate temperature extremes and generate greater precipitation than in the northern and eastern parts of the range. Mean annual temperature varies from about -5°C at the northern limit in the Northwest Territories to about +2°C in the southern Alberta foothills. Annual precipitation varies between approximately 300 and 750 mm across the geographic range of M496, depending on latitude, longitude and elevation. Elevations are generally <500 mASL in the eastern portion of the range (i.e., northwestern Ontario to central Saskatchewan), increasing gradually westward to approximately 800 mASL in northern Alberta, and extending to the lower boundary of the high montane/subalpine zone in Cordilleran portions of western Alberta, British Columbia, Yukon and Northwest Territories. Regional geologic and topographic features of the Cordilleran, Interior Plains and western Precambrian Shield physiographic regions produce an array of local site conditions. Essentially, all parts of the range experienced Pleistocene glaciation; soils are mostly Brunisols and Luvisols developed in surficial glacial materials.

Two subtypes distinguish Central boreal forests (CM496a [Central Boreal Forest]) in Alberta, Saskatchewan, Manitoba and northwestern Ontario from low elevation boreal and foothills forests in the Cordilleran region of Alberta, British Columbia, southeastern Yukon and southwestern Northwest Territories (CM496b [Cordilleran Boreal Forest]).