Common (Translated Scientific) Name: Western Red-cedar / Western Oakfern Forest

Colloquial Name: No Data Available

Hierarchy Level:  Association

Type Concept: This Thuja plicata forest association is known from the northern Rocky Mountains of British Columbia, northern Idaho and northwestern Montana. It represents one of the driest Thuja plicata riparian communities, and the driest Thuja type to have a fern layer. It occurs at elevations ranging from 975 to 1370 m (3200-4500 feet). Typical locations include slopes or benches along major mountain streams. Slopes are moderate to steep, and stands are generally located on mid to lower slopes. Parent materials are usually quartzite, sandstone, or schist, often mixed or overlain with volcanic ash. Soils are gravelly loams to silty clay loam to silt. Stands are subirrigated yet well-drained. Duff layers average 8 cm in depth. Late-seral stands have closed canopies and are dominated by Thuja plicata. Stands not in a late-seral stage are more heterogeneous, with a mix of conifers in addition to Thuja. Seral species persisting in these stands include Abies grandis as the most abundant and common. Others include Tsuga heterophylla, Picea engelmannii (or Picea x albertiana), Pinus monticola, Larix occidentalis, and Pseudotsuga menziesii. The shrub layer is typically limited to 10-20% total cover. Highly constant species include Acer glabrum, Lonicera utahensis, Linnaea borealis, Rubus parviflorus, and Taxus brevifolia. The herbaceous layer has mostly ferns and forb species with few to no grasses. Gymnocarpium dryopteris is diagnostic for this type, with at least 1% cover, but is often much more abundant. Athyrium filix-femina or Adiantum pedatum are often present, but with low cover or only on moist microsites. Other highly constant mesic forbs include Clintonia uniflora, Tiarella trifoliata, Coptis occidentalis, Osmorhiza berteroi, Prosartes hookeri, Aralia nudicaulis, and Maianthemum stellatum.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This community, in regard to subcanopy and undergrowth composition, defining abiotic parameters and geographic distribution is virtually indistinguishable from ~Tsuga heterophylla / Gymnocarpium dryopteris Forest (CEGL000494)$$. The difference between Tsuga and Thuja dominance of the upper canopy is quite probably related to historical accident, past disturbance events and subsequent successional patterns. Despite the very long fire-return intervals (200-500 years for stand-replacing fire), the longevity of both species, especially Thuja, argues for considering the dual designation (Thuja plicata - Tsuga heterophylla) as appropriate (i.e., combining these two associations into one); if one or the other species responds to disturbance by attaining canopy dominance, it is unlikely the non-dominant species will become dominant in the average fire-free interval. Others have recognized that quite probably a dominance continuum exists between these two species by naming at least 8 plant associations with the dual designation (Tsuga heterophylla - Thuja plicata /_).

Arguing against this approach is the approach being taken by the USNVC placing emphasis on existing vegetation composition, and it is indisputable that either climax tree species can be strongly dominant with the other species only occurring in the reproductive layers, if at all. In northern Idaho, where these species are sympatric over an extensive range, there are drainages where one or the other species is present and its complement is not (Daubenmire and Daubenmire 1968); this phenomenon has never been satisfactorily explained and again argues for recognizing separate Thuja plicata and Tsuga heterophylla types.

Similar NVC Types: No Data Available

note: No Data Available