The mountain forests of British Columbia and the American northwest: Floristic patterns and syntaxonomy

Abstract

An overview of the montane and subalpine forests of Abies lasiocarpa, Picea engelmannii, Abies amabilis and Tsuga mertensiana of northwestem North America is provided based on 541 releves of forest vegetation from coastal and inland British Columbia, Washington and northwestern Montana. A new classification is proposed based on an examination of the floristic patterns across these communities. Owing to their broadscale floristic similarities, coastal subalpine Abies amabilis-Tsuga mertensiana forests and inland forests of Abies lasiocarpa, Picea engelmannii, P. glauca, Thuja plicata and Tsuga heterophylla are combined into a single order, Thujetalia plicatae. The floristic patterns within this order in turn support the recognition of four alliances. These are (1) Tsugion mertensianae, including coastal and inland subalpine forests of Tsuga mertensiana, Abies amabilis, A. lasiocarpa and Picea engelmannii, with deep winter snowpacks and an often luxuriously developed shrub layer; (2) Abieti-Tsugion heterophyllae all. nov., including mesic inland montane Thuja plicata-Tsuga heterophylla and Abies lasiocarpa-Picea engelmannii forests and related southern boreal Abies lasiocarpa-Picea glauca communities; (3) Gymnocarpio-Abietion lasiocarpae, including moist coastal and inland forests dominated by a fern-rich understory and Oplopanax horridus; and (4) Lysichito-Chamaecyparidion nootkatensis, which includes wet coastal subalpine forests with Lysichiton americanum. A total of five new associations are described, bringing the number of recognized associations within the order to twenty-five. An extensive synonymy and crosswalk to other classification systems is provided.