Abstract for M034

Rocky Mountain-Great Basin Montane Riparian & Swamp Forest
Forêts montagnardes, riveraines et marécageuses des Rocheuses et du Grand Bassin

M034 describes forests and woodlands of riparian and permanently saturated sites in the continental temperate climate of the Western Cordillera of North America. The Canadian expression of these forests occurs east of the Coast Mountains in southern, central and northwestern British Columbia (BC), and in the Rocky Mountains and foothills of southern and west-central Alberta. Forest canopies can be evergreen coniferous, cold-deciduous broad-leaved or a mixture. Floodplain sites that have experienced recent disturbance (e.g., flooding or anthropogenic disturbance) are typically dominated by cold-deciduous broad-leaved species, including black cottonwood (Populus trichocarpa), paper birch (Betula papyrifera), trembling aspen (Populus tremuloides), mountain alder (Alnus incana ssp. tenuifolia) and willows (Salix spp.). On more stable sites at lower elevations, including swamps, interior spruce (Picea glauca x engelmannii) or sometimes western red cedar (Thuja plicata) often dominate, while at higher elevations subalpine fir (Abies lasiocarpa) and Engelmann spruce (P. engelmannii) become prominent tree species. Stands usually have complex structure of tree, shrub and herb layers. Shrub species include willows (Salix spp.), red-osier dogwood (Cornus stolonifera), water birch (Betula occidentalis), bracted honeysuckle (Lonicera involucrata), mountain huckleberry (Vaccinium membranaceum), and various gooseberries or currants (Ribes spp.). Horsetails (especially Equisetum arvense and E. pratense) are characteristic in the herb layer, accompanied by a wide diversity of other species, including common lady fern (Athyrium filix-femina), bluejoint reedgrass (Calamagrostis canadensis), bunchberry (Cornus canadensis), naked mitrewort (Mitella nuda), arctic sweet coltsfoot (Petasites frigidus), dwarf raspberry (Rubus pubescens), three-leaved foamflower (Tiarella trifoliata), common oak fern (Gymnocarpium dryopteris), soft-leaved sedge (Carex disperma), five-leaved dwarf bramble (Rubus pedatus) and arrow-leaved ragwort (Senecio triangularis). The moss layer is often well-developed in swamps and stabilized floodplain communities, usually including a variety of leafy mosses (Mnium spp., Rhizomnium spp. and Plagiomnium spp.) along with red-stemmed feathermoss (Pleurozium schreberi), stairstep moss (Hylocomium splendens) and/or glow moss (Aulacomium palustre).

Riparian forests and woodlands are subject to floodplain dynamics, including erosion of banks, removal of established vegetation, channelization, scouring and sediment deposition. Treed swamps are generally small stable ecosystems that are maintained by persistently high local water tables. M034 occurs in a continental temperate climate, with warm summers, cool winters and highly variable annual precipitation within its range. Mean annual temperature varies from approximately -1° to 9° C, depending on latitude and elevation. Mean annual precipitation varies from 350 mm in drier areas to >2000 mm in wetter subregional climates. Soils on actively flooded sites are poorly to moderately developed, mostly Regosols, because of ongoing deposition of silty and sandy alluvium; better soil development is present on older stabilized fluvial ‘benches’. Swamp soils are typically mineral Gleysols with a peaty surface layer, although sometimes Organic soils develop.