Common (Translated Scientific) Name: Western Red-cedar - Western Hemlock / Devil''s-club Rocky Mountain Swamp Forest

Colloquial Name: No Data Available

Hierarchy Level:  Association

Type Concept: 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 Thuja plicata or Tsuga heterophylla 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 Thuja plicata or Tsuga heterophylla dominate a nearly closed-canopy forest often with Picea engelmannii (or Picea x albertiana) or Abies grandis trees. In Montana Tsuga heterophylla is present in all occurrences, but Thuja plicata is often codominant. Abies lasiocarpa, Populus balsamifera ssp. trichocarpa, and Pseudotsuga menziesii are also occasionally present in the overstory, but typically with very low cover. Tsuga heterophylla, Thuja plicata, Pseudotsuga menziesii, and Abies lasiocarpa 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 Oplopanax horridus shrubs, which is a rhizomatous species; at least 5% cover of Oplopanax is diagnostic for this type. Other species that infrequently occur in the shrub layer include Acer glabrum or Taxus brevifolia. The shrub layers are typically low in diversity. Herbaceous diversity is typically high, primarily composed of forbs. Athyrium filix-femina and Gymnocarpium dryopteris can be prominent members of the luxuriant herbaceous layer along with Tiarella trifoliata var. unifoliata, Clintonia uniflora, Actaea rubra, Asarum caudatum, Streptopus amplexifolius, Maianthemum stellatum, Viola orbiculata, or Osmorhiza berteroi.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This association is defined as a PNV vegetation type. If it were renamed as a dominance type the species would include Thuja plicata and Tsuga heterophylla. This association (CEGL000479) is distinguished from ~Tsuga heterophylla - (Pseudotsuga menziesii) / Oplopanax horridus / Polystichum munitum Forest (CEGL000497)$$ which has "maritime" character species such as Alnus rubra, Polystichum munitum, Achlys triphylla, Acer circinatum, and Vaccinium parvifolium of the Cascades and west and is more upland/riparian in habitat. Whereas, the association discussed here has the presence/relative abundance of inland species, such as more Abies grandis (in U.S.), Picea engelmannii, Acer glabrum, and Osmorhiza berteroi in Canadian Rocky Mountains. This association tends to be more a wetland/riparian community. This type also needs to be compared to the several other associations already in the USNVC occurring in the Pacific Northwest coastal ranges that have both Tsuga heterophylla and Oplopanax horridus in their names.

As defined here, this association allows for either Tsuga or Thuja to be the dominant in the canopy, alone or in combination with the other; it is recognized however, that most documented stands have both species at least present. This type was previously described by Pfister et al. (1977) and Cooper et al. (1987) as part of the Thuja plicata / Oplopanax horridum Habitat Type. In those treatments, Thuja plicata was given greater weight than Tsuga heterophylla, regardless of the abundance of Tsuga.

The difference between Tsuga and Thuja dominance of the upper canopy in this association 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 that of Thuja, argues for considering the dual designation (Thuja plicata - Tsuga heterophylla) as appropriate; 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 indisputable observation that either of these species can be strongly dominant, with the other occurring only 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