Abstract for M500

Central Rocky Mountain Mesic Lower Montane Forest
Forêts mésiques des montagnes de faible altitude du centre des Rocheuses

M500 describes lower montane forests in warm to cool, moist to wet, temperate climates in the North American Western Cordillera. In Canada, M500 forests occur in the northwestern and southeastern portions of the British Columbia (BC) interior. These are typically evergreen coniferous forests dominated by western hemlock (Tsuga heterophylla) and/or western red cedar (Thuja plicata), often consisting of tall, long-lived trees in stands that may persist for centuries. Stand-replacing fires occur less frequently than in other forests of the BC interior; gap dynamics driven by pathogens, insects and windthrow prevail. Common tree species associates include subalpine fir (Abies lasiocarpa), Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), lodgepole pine (Pinus contorta var. latifolia) and hybrids of white spruce (interior spruce [Picea engelmannii x glauca]; Lutz spruce [P. x lutzii]). In the warmest parts of the Canadian range, western white pine (Pinus monticola), western larch (Larix occidentalis), ponderosa pine (Pinus ponderosa) and grand fir (Abies grandis) also occur. Trembling aspen (Populus tremuloides) and paper birch (Betula papyrifera) commonly occur following disturbance. Common understory shrubs include black huckleberry (Vaccinium membranaceum), falsebox (Paxistima myrsinites), western thimbleberry (Rubus parviflorus), devil’s club (Oplopanax horridus), oval-leaved blueberry (Vaccinium ovalifolium), Rocky Mountain maple (Acer glabrum) and saskatoon (Amelanchier alnifolia). Typical herb/dwarf shrub species include single-flowered clintonia (Clintonia uniflora), bunchberry (Cornus canadensis), three-leaved foamflower (Tiarella trifoliata), twisted-stalks (Streptopus spp.), five-leaved dwarf bramble (Rubus pedatus), common pipsissewa (Chimaphila umbellata), wild sarsaparilla (Aralia nudicaulis) and twinflower (Linnaea borealis). Ferns often constitute an important component of the herb layer, especially common oak fern (Gymnocarpium dryopteris) and common lady fern (Athyrium filix-femina). Frequently occurring mosses are red-stemmed feathermoss (Pleurozium schreberi), knight’s plume moss (Ptilium crista-castrensis), stairstep moss (Hylocomium splendens), pipecleaner moss (Rhytidiopsis robusta) and electrified cat’s-tail moss (Rhytidiadelphus triquetrus).

In Canada, M500 occurs within a continental temperate climate with warm summers, cool winters and high annual precipitation. These forests grow best on well to imperfectly drained sites with high soil moisture. Mean annual precipitation is highly variable throughout the Canadian range, typically 700 to 1400 mm on average. Where precipitation is lower, sites rely on moisture inputs from snowmelt and stands often occur on lower/toe slopes or on cool aspects. Mean annual temperatures vary from approximately 2.5° to 8° C, depending on latitude and elevation; soils typically don’t freeze in the winter. M500 forests occupy the low to mid-elevations (up to approximately 1500 mASL) in mountains and highlands in southeastern and northwestern BC, wherever precipitation levels are sufficient. All parts of the range experienced Pleistocene glaciation; soils are mostly Podzols, Luvisols and Brunisols developed in glacial surficial materials. Three subtypes characterize regional variation in the Canadian range of M500: CM500a [Southern Mesic Rocky Mountain Low Montane Forest] describes forests in southeastern BC near the international border; CM500b [Typic Mesic Rocky Mountain Low Montane Forest] is the typical condition for the main portion of the Canadian range in southeastern BC; CM500c [Northern Mesic Rocky Mountain Low Montane Forest] describes forests in northwestern BC in the lee of the Coast Mountains.