Abstract for M035

Vancouverian Flooded & Swamp Forest
Forêts inondées et marécageuses de la région floristique de Vancouver

Within the wet maritime temperate climate of the Pacific coast of North America, M035 describes forests of swamp, floodplain and estuarine sites that are influenced by high subsurface water levels. The Canadian expression of these forests occurs along the southern and central British Columbia (BC) coast and inland from the Alaska panhandle in northwestern BC. Forest canopies can be evergreen coniferous, cold-deciduous broad-leaved or a mixture. At low elevations, floodplain sites that have experienced recent disturbance (e.g., flooding or anthropogenic disturbance) are typically dominated by cold-deciduous broad-leaved trees, including red alder (Alnus rubra), black cottonwood (Populus trichocarpa), Sitka willow (Salix sitchensis), Pacific crabapple (Malus fusca) and/or bigleaf maple (Acer macrophyllum). On more stable sites, including swamps, the conifers Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), western redcedar (Thuja plicata), amabilis fir (Abies amabilis) and/or yellow-cypress (Callitropsis nootkatensis) become prominent. At higher elevations, mountain hemlock (Tsuga mertensiana) is typically present. Floodplain forests are characterized by dense understories of cold-deciduous broad-leaved shrubs, including salmonberry (Rubus spectabilis), red-osier dogwood (Cornus stolonifera) and Devil’s club (Oplopanax horridus). Lady fern (Athyrium filix-femina), three-leaved foamflower (Tiarella trifoliata), western sword fern (Polystichum munitum) and false lily-of-the-valley (Maianthemum dilatatum) are common herb species; the moss layer is poorly developed. Characteristic understory plants in M035 swamps include salmonberry, yellow skunk cabbage (Lysichiton americanum), sedges (Carex spp.), ferns (especially western sword fern) and salal (Gaultheria shallon). The moss layer is often well-developed in swamps, usually including large leafy moss (Rhizomnium glabrescens), lanky moss (Rhytidiadelphus loreus), stairstep moss (Hylocomium splendens), slender beaked moss (Eurhynchium praelongum) and common green peat moss (Sphagnum girgensohnii).

Flooded and estuarine forests 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. M035 forests occur in a maritime temperate climate, with cool summers, mild winters and high annual precipitation. Mean annual temperature varies from approximately 1° to 10° C. Mean annual precipitation is generally high, although locally variable, averaging >2200 mm. Floodplain soils are poorly to moderately developed, mostly Regosols, because of ongoing deposition of silty and sandy alluvium. Swamp soils are typically mineral Gleysols with a peaty surface layer although, depending on local site-scale hydrology, sometimes Organic soils develop.