Name:
Thuja plicata - Tsuga heterophylla / Oplopanax horridus Rocky Mountain Swamp Forest
Reference:
NatureServe Biotics 2019
Description:
This is a linear, small-patch association located within moist and mild climatic regimes in the northern Rocky Mountains of Washington, Idaho and Montana. This is a saturated to seasonally flooded wetland forest community usually found in a mosaic with other wetland or riparian <i>Thuja plicata</i> or <i>Tsuga heterophylla</i> types. Ranging in elevation from 455 to 1311 m (1500-4300 feet), it is found on seep toeslopes and along riparian zones on wet streambank terraces. Landforms include lower benches, valleys, lower stream terraces, wet bottoms, and toeslope seepage areas. High water tables and cold-air drainage are characteristic of these sites. The water table is typically shallow, and soils are loams and sandy loams. Either <i>Thuja plicata</i> or <i>Tsuga heterophylla</i> dominate a nearly closed-canopy forest often with <i>Picea engelmannii</i> (or <i>Picea x albertiana</i>) or <i>Abies grandis</i> trees. In Montana <i>Tsuga heterophylla</i> is present in all occurrences, but <i>Thuja plicata</i> is often codominant. <i>Abies lasiocarpa, Populus balsamifera ssp. trichocarpa</i>, and <i>Pseudotsuga menziesii</i> are also occasionally present in the overstory, but typically with very low cover. <i>Tsuga heterophylla, Thuja plicata, Pseudotsuga menziesii</i>, and <i>Abies lasiocarpa</i> saplings are common in the subcanopy, with the latter being most common in higher elevation occurrences in Montana. The understory has a patchy to dense layer of tall <i>Oplopanax horridus</i> shrubs, which is a rhizomatous species; at least 5% cover of <i>Oplopanax</i> is diagnostic for this type. Other species that infrequently occur in the shrub layer include <i>Acer glabrum</i> or <i>Taxus brevifolia</i>. The shrub layers are typically low in diversity. Herbaceous diversity is typically high, primarily composed of forbs. <i>Athyrium filix-femina</i> and <i>Gymnocarpium dryopteris</i> can be prominent members of the luxuriant herbaceous layer along with <i>Tiarella trifoliata var. unifoliata, Clintonia uniflora, Actaea rubra, Asarum caudatum, Streptopus amplexifolius, Maianthemum stellatum, Viola orbiculata</i>, or <i>Osmorhiza berteroi</i>.
Accession Code:
urn:lsid:vegbank.org:commConcept:29388-{1DC061A4-C518-4AFF-B53D-8FC0CDFB8FE0}
Plot-observations of this Community Concept:
3
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