Name:
Thuja plicata / Clintonia uniflora - Xerophyllum tenax Forest
Reference:
NatureServe Biotics 2019
Description:
This is a small- to large-patch forested community found in the northern Rocky Mountains of western Montana west into northeastern Washington. This type generally occupies the highest elevation <i>Thuja plicata</i> communities, representing relatively cold and dry environments. Its known elevational range is 790 to 1675 m (2600-5500 feet). This type is very heterogeneous, occurring across a broad range of habitat conditions; it occurs from toeslope positions to the tops of ridges and on all degrees of slope and all aspects. Parent materials are variable, with loess and ash caps deposited over glacial outwash and till in some areas. The upper soil horizons are well- to excessively drained and coarse-textured (in some areas sandy soils predominate). Glacial compression is invoked as the reason many of the soil profiles have a compacted subsoil, which results in shallow rooting and accounts in part for the more xeric nature of these sites. The canopy cover of this forest type is usually in excess of 60%, with <i>Thuja plicata</i> comprising at least 25% of the total. Because seral tree species occupy these sites readily following disturbance, <i>Pseudotsuga menziesii, Larix occidentalis, Pinus contorta</i>, and <i>Picea engelmannii</i> commonly occur across the range of this type, but in northern Idaho <i>Abies grandis</i> often shares dominance with <i>Thuja</i>. Sites transitional to subalpine occasionally have appreciable cover of <i>Abies lasiocarpa</i>. The understory, in which <i>Thuja</i> is 100% constant, gives every indication that these stands will be <i>Thuja</i>-dominated late in the sere. The tall-shrub component is mostly dispersed clumps, and no one species has high constancy, though <i>Acer glabrum, Alnus viridis ssp. sinuata, Amelanchier alnifolia</i>, and <i>Sorbus scopulina</i> may have 5-10 % cover, singly or in the aggregate. The short-shrub layer is dominant with the indicator <i>Vaccinium membranaceum</i> nearly 100% constant and generally exhibiting greater than 15% cover. Other regularly occurring short shrubs include <i>Paxistima myrsinites, Spiraea betulifolia, Rosa gymnocarpa, Rubus parviflorus</i>, and <i>Lonicera utahensis</i>. The dwarf-shrub <i>Linnaea borealis</i> is always present and its cover can approach 20%. <i>Bromus vulgaris</i> is often the only graminoid represented. In the forb layer <i>Clintonia uniflora</i> and <i>Tiarella trifoliata</i> are reflective of relative mesic conditions, whereas <i>Xerophyllum tenax</i> (considered an indicator when having 5% or greater cover) is indicative of <i>Thuja</i> at its cold, dry extremes, transitional to subalpine habitats. In the northwestern portion of this type's distribution, <i>Xerophyllum</i> appears to be sporadically distributed and <i>Vaccinium</i> is relied on as the alternative indicator.
Accession Code:
urn:lsid:vegbank.org:commConcept:34583-{2A346A03-F1A8-4C49-8891-91C0AECE085F}
Plot-observations of this Community Concept:
0
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