Abstract for M024

Vancouverian Coastal Rainforest
Forêts pluviales côtières de la région floristique de Vancouver

M024 describes the low to mid-elevation coastal forests of Pacific maritime temperate climates in western North America. The Canadian expression includes forests of the southern and central British Columbia (BC) coast. Most of these forests are rainforests comprising stands of large trees that are hundreds of years old. Canopies are typically evergreen coniferous, although cold-deciduous broad-leaved species are sometimes present in the tree stratum following disturbance. Stand-replacing fires occur occasionally in drier parts of the range, otherwise gap dynamics driven by pathogens, insects and windthrow is the prevailing disturbance regime. Western hemlock (Tsuga heterophylla) is the characteristic tree species. In Canada, other common trees include Pacific silver fir (Abies amabilis), western red cedar (Thuja plicata), coast Douglas-fir (Pseudotsuga menziesii var. menziesii), Sitka spruce (Picea sitchensis), yellow-cypress (Callitropsis nootkatensis), grand fir (Abies grandis), red alder (Alnus rubra) and big-leaved maple (Acer macrophyllum). Shore pine (Pinus contorta var. contorta) is dominant on some very dry sites. Western white pine (Pinus monticola) and mountain hemlock (Tsuga mertensia) occur occasionally. The understory is typically dominated by broad-leaved shrubs, conifer regeneration, ferns and a well-developed moss layer. Common shrubs include oval-leaved blueberry (Vaccinium ovalifolium), red huckleberry (V. parvifolium), salal (Gaultheria shallon), false azalea (Menziesia ferruginea) and, in drier climate areas, Cascade barberry (Berberis nervosa). Deer fern (Blechnum spicant) is the most widespread herb; others include foamflowers (Tiarella spp.) and western sword fern (Polystichum munitum). Lanky moss (Rhytidiadelphus loreus), stairstep moss (Hylocomium splendens) and Oregon beaked moss (Kindbergia oregana) predominate in the moss layer.

In Canada, M024 forests occur between sea level and approximately 1000 mASL in a maritime temperate climate, with cool summers, mild winters and high annual precipitation. Mean annual precipitation varies between approximately 1200 and 4300 mm, the majority falling as rain in winter months; snow is only a minor proportion and localized within the range. Mean annual temperatures vary from approximately 3°to 10° C, depending mostly on latitude and elevation; soils typically don’t freeze in winter. Growing degree days above 5° C (GDD) vary between approximately 1000 and 2200 across the Canadian range. All parts of the Canadian range experienced Pleistocene glaciation; soils are mostly Podzols developed in glacial surficial materials. Mor humus forms predominate.

Three subtypes characterize regional variation in the Canadian range of M024. CM024a [Drier Vancouverian Rainforest] primarily occurs in drier climatic areas where there is a history of fire. Coast Douglas-fir co-dominates in the canopy. Conversely, CM024c [Northern Vancouverian Rainforest] describes the Canadian expression of Pacific coastal rainforests at the northern edge of their global range. These forests are dominated by western hemlock and Sitka spruce and notable for the absence of Pacific silver fir and coast Douglas-fir. CM024b [Typic Vancouverian Rainforest] is the predominant condition occurring over most of the Canadian range.