Abstract for M299

North American Boreal Conifer Poor Swamp
Marécages pauvres à conifères boreaux de l'Amérique du Nord

M299 describes nutrient-poor to medium wetland forests and woodlands throughout the boreal region of North America. These include bog and fen woodlands as well as poor to intermediate swamps, usually developed on peat deposits. This vegetation is characterized by black spruce (Picea mariana) and/or tamarack (Larix laricina) in the tree layer, overwhelming dominance of ericaceous species in the understory and ground cover of Sphagnum mosses. Typical understory species include common Labrador tea (Rhododendron groenlandicum), leatherleaf (Chamaedaphne calyculata), blueberries (Vaccinium spp.), shrub willows (Salix spp.), shrub birches (Betula spp.), bog laurel (Kalmia polifolia), three-leaved false Solomon’s seal (Maianthemum trifolium), cloudberry (Rubus chamaemorus), small cranberry (V. oxycoccus) and bog rosemary (Andromeda polifolia). Sheep laurel (K. angustifolia) and rhodora (Rhododendron canadense) often replace R. groenlandicum in Atlantic Canada. Peat mosses (Sphagnum spp.) dominate the ground cover, but feathermosses (esp. red-stemmed feathermoss [Pleurozium schreberi] and stairstep moss [Hylocomium splendens]) are common on dry microsites (e.g., peat hummocks). These are generally stable ecosystems that are maintained by persistently high water tables within a cold climate. M299 occurs in boreal and subarctic climates, characterized by long, cold winters and short, cool to moderately warm summers. Mean annual temperatures in the Canadian range vary from approximately -10°C in Inuvik, Northwest Territories to >3.5°C in parts of insular Newfoundland. Mean annual precipitation generally follows a west to east gradient, increasing from <300 mm in the western subarctic to as high as 1800 mm in parts of Nova Scotia and insular Newfoundland. Substrates are usually Sphagnum-derived peats with nutrient regimes ranging from poor to medium, depending on local site-scale hydrology. Within a stand, hummocky microtopography associated with the growth of certain Sphagnum spp. provides a range of micro-scale moisture and nutrient gradients. Permafrost is a feature of subarctic and some northern boreal peatlands.