Abstract for M179

North American Northern Boreal Woodland
Terres boisées boréales nordiques de l'Amérique du Nord

M179 describes northern boreal upland treed vegetation, typically exhibiting woodland physiognomy (<25% cover in the tree layer) with ground cover of lichens. The Canadian range extends from the Alaska – Yukon border to the coast of Labrador and, in northern Alberta, including the highest elevations of the Cameron Hills and Caribou Mountains. Tree species are overwhelmingly evergreen coniferous, but small components of deciduous coniferous and cold-deciduous broad-leaved species occur. Stands of M179 are predominantly open continuous woodlands but vary from closed forests, on the most favourable sites in southern parts of the range, to very open patchy stands of short statured trees near the continental treeline. On wind-exposed sites, especially near treeline, woodlands often occur as tree islands or ribbons in a matrix of shrub tundra; trees develop a krummholtz growth form in response to physical damage by extreme cold and blowing snow and ice crystals. Frequent stand-replacing fires create a diverse landscape mosaic, especially in the southern portion of the range; regional fire cycles are shorter to the west of Hudson Bay. Black spruce (Picea mariana) and white spruce (P. glauca) are the main tree species, sometimes with small amounts of tamarack (Larix laricina), jack pine (Pinus banksiana), balsam poplar (Populus balsamifera) and/or balsam fir (Abies balsamea). Understories are dominated by patches of conifer regeneration, cold-deciduous broad-leaved low shrubs and prostrate dwarf shrubs. A continuous lichen layer, sometimes with patches of feathermosses, characterizes most woodland stands. Common understory species throughout the range include bog bilberry (Vaccinium uliginosum), shrub birches (mainly arctic dwarf birch [Betula nana] and glandular birch [B. glandulosa]), willows (Salix spp.), green alder (Alnus viridis), common Labrador tea (Rhododendron groenlandicum), lingonberry (V. vitis-idaea) and black crowberry (Empetrum nigrum). The most common mat-forming lichen species are reindeer lichens (Cladina spp.); stairstep moss (Hylocomium splendens) and red-stemmed feathermoss (Pleurozium schreberi) are the most prominent feathermosses.

M179 occurs in northern boreal and subarctic climates, characterized by very long, cold winters and short, cool to moderately warm summers. Although maritime influences are pronounced on the Labrador coast, a continental climate is the norm for most of the range. A strong west to east precipitation gradient divides the range into a subhumid portion, in Northwest Territories and Yukon, and a humid portion near and east of Hudson Bay. Mean annual temperatures vary from approximately -4°C to -10°C. With the exception of a few areas in the Cordillera, elevations are <800 mASL. M179 occupies portions of the Arctic Coastal Plain, Cordilleran, Interior Plains and Precambrian Shield physiographic regions. Except for northern Yukon, all parts of the range experienced late Pleistocene glaciation; soils are mostly Brunisols and Luvisols developed in glacial surficial materials, with Cryosols occurring sporadically. Discontinuous permafrost occurs in peatlands and some wet mineral soils throughout the range; continuous permafrost occurs in fine- and medium-textured soils in some northern portions of the range.

Two subtypes distinguish northern boreal woodlands from western Canada, CM179a [Alaskan-Yukon Northern Boreal Woodland], and from east-central Canada, CM179b [East-Central Northern Boreal Woodland].