Name:
Thuja plicata / Clintonia uniflora - Xerophyllum tenax Forest
Reference:
Western Ecology Working Group of...
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 Thuja plicata 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 Thuja plicata comprising at least 25% of the total. Because seral tree species occupy these sites readily following disturbance, Pseudotsuga menziesii, Larix occidentalis, Pinus contorta, and Picea engelmannii commonly occur across the range of this type, but in northern Idaho Abies grandis often shares dominance with Thuja. Sites transitional to subalpine occasionally have appreciable cover of Abies lasiocarpa. The understory, in which Thuja is 100% constant, gives every indication that these stands will be Thuja-dominated late in the sere. The tall-shrub component is mostly dispersed clumps, and no one species has high constancy, though Acer glabrum, Alnus viridis ssp. sinuata, Amelanchier alnifolia, and Sorbus scopulina may have 5-10 % cover, singly or in the aggregate. The short-shrub layer is dominant with the indicator Vaccinium membranaceum nearly 100% constant and generally exhibiting greater than 15% cover. Other regularly occurring short shrubs include Paxistima myrsinites, Spiraea betulifolia, Rosa gymnocarpa, Rubus parviflorus, and Lonicera utahensis. The dwarf-shrub Linnaea borealis is always present and its cover can approach 20%. Bromus vulgaris is often the only graminoid represented. In the forb layer Clintonia uniflora and Tiarella trifoliata are reflective of relative mesic conditions, whereas Xerophyllum tenax (considered an indicator when having 5% or greater cover) is indicative of Thuja at its cold, dry extremes, transitional to subalpine habitats. In the northwestern portion of this type's distribution, Xerophyllum appears to be sporadically distributed and Vaccinium is relied on as the alternative indicator.
Accession Code:
VB.CC.28190.THUJAPLICATACLI
Plot-observations of this Community Concept:
0
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