Name:
Tsuga heterophylla - Pseudotsuga menziesii / Cornus unalaschkensis Mesic Forest Alliance
Reference:
NatureServe Biotics 2019
Description:
This is a heavily forested alliance. The overstory canopy is dominated by <i>Pseudotsuga menziesii</i> and <i>Tsuga heterophylla</i>. Understory species such as <i>Mahonia nervosa, Vaccinium membranaceum</i>, and <i>Gaultheria shallon</i> are intolerant of drought. Other common tree associates include <i>Thuja plicata, Abies amabilis</i>, and <i>Abies grandis</i>. Rarely, <i>Picea sitchensis</i> may appear, and <i>Callitropsis nootkatensis</i> has been documented with up to 28% cover, but neither are typically present. Shrub species are variable and include <i>Acer circinatum, Chimaphila umbellata, Gaultheria shallon, Linnaea borealis, Mahonia nervosa, Menziesia ferruginea, Vaccinium alaskaense</i>, and <i>Vaccinium parvifolium</i>. The herbaceous layer is highly variable. The following species each occur in about one-third of documented stands: <i>Achlys triphylla, Blechnum spicant, Clintonia uniflora, Cornus unalaschkensis, Goodyera oblongifolia, Polystichum munitum, Tiarella trifoliata</i>, and <i>Trillium ovatum</i>. This alliance occurs in all the maritime-influenced regions of the Pacific Northwest, from north coastal California to the northern coast of Vancouver Island, British Columbia. Throughout the range of this alliance, much of the annual precipitation occurs as rain. Where snow does occur, it can generally be melted by rain during warm winter storms. In all settings, this alliance occurs where environmental conditions are moderated by the marine influence, with moderate drought and frost. Stands of the alliance generally occur on all slopes and aspects, on well-drained mesic sites that do not become very dry by summer's end. The associations in this alliance are found throughout the range. Although associations may be more moist in the north and more mesic in the south, all are generally in the mid-range of moisture settings, and are never considered consistently very dry or very wet by local ecologists. Soils typically remain moist year-round, but are not subirrigated or saturated. The diagnostic characteristic of this alliance is an overstory of both <i>Pseudotsuga menziesii</i> and <i>Tsuga heterophylla</i>, with an understory that is neither wet nor dry throughout the growing season.
Accession Code:
urn:lsid:vegbank.org:commConcept:38665-{2BD394E1-5CEC-4BCD-91BE-2FDAF5E8763A}
Plot-observations of this Community Concept:
0
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