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

Colloquial Name: No Data Available

Hierarchy Level:  Association

Type Concept: This small-patch, hygric (damp) to hydric (wet) community is associated with the inland penetration of a Pacific maritime climatic regime, occurring in the east Cascades and northeastern Washington, east into northern Idaho and northwestern Montana. This type ranges in elevation from 460 to 1430 m (1500-4700 feet). The primary environmental driver is abundant water throughout the growing season; standing water is often present early in the growing season, and water tables are high throughout the year. This is typically a streamside stringer, around seeps, where toeslopes intercept the water table, and some of the most extensive examples are associated with gentle slopes (<20 % inclination) with perched water tables. The stands are often sheltered in valley bottoms. Sites often have considerable microsite variation due to hummocking, and this can be reflected in the within-stand vegetation patterning. Soils are derived primarily from alluvium of various geologic origins. With textures ranging from loamy sands to silt loams and often having an appreciable gravel content, soils are very permeable. The tree canopy is highly variable in cover with dense old-growth Thuja-dominated stands approaching 100% canopy cover and other sites that perhaps have experienced wind throw having less than 50% cover. Thuja plicata dominates both the upper canopy and the reproductive layers; Tsuga heterophylla, Abies grandis and Picea engelmannii are consistent upper canopy components; only Tsuga has appreciable cover in the reproductive layers. In a modal expression of the type a nearly continuous layer of Athyrium filix-femina dominates the undergrowth, concealing a rich diversity of forbs. Some sites have appreciable cover of tall shrubs including Taxus brevifolia, Alnus viridis ssp. sinuata, and Acer glabrum. Incidental individuals or small patches of Oplopanax horridus may be found. The short and dwarf-shrub layers are relatively inconspicuous, a combined cover seldom exceeding 10%. Some consistently present hygric- to hydric-indicating forbs include Senecio triangularis, Trautvetteria caroliniensis, Streptopus amplexifolius, Gymnocarpium dryopteris, Viola glabella, Aconitum columbianum, and Circaea alpina; some have considered the presence of the first four of these forbs to be indicative of the type when the cover of Athyrium is less than 1%.

Diagnostic Characteristics: No Data Available

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: It has been the approach of Inland Northwest U.S. vegetation scientists to consider stands with a mix of Thuja plicata and Tsuga heterophylla (and Abies grandis) or either species alone and occurring on sites sufficiently wet to support at least 5% Oplopanax horridus or Athyrium filix-femina to be classed as Thuja plicata habitat types or plant associations. Daubenmire and Daubenmire (1968) argued, based on their investigations in northern Idaho and eastern Washington, that even where Tsuga constitutes the dominant tree species in a stand, it would not so remain. Ultimately the nurse-logs, from which these trees generated and grew, would decay, favoring Thuja reproduction in these wet environments (Tsuga not establishing well on mineral substrates). The Daubenmires also noted that, if Tsuga / Athyrium or Tsuga / Oplopanax segregates were recognized, they would include few stands and little area; they also demonstrated that there was no floristic differences in the undergrowth between Thuja- and Tsuga-dominated stands. Others have followed suit (Pfister et al. 1977, Lillybridge et al. 1995, Williams et al. 1995) and have included, even as did the Daubenmires, stands from wet environments and having Tsuga and no Thuja within the Thuja series (alliance).

The classification effort underway in Waterton-Glacier International Peace Park (IPP) has chosen to follow the USNVC and its predilection for recognizing actual cover rather than potential. The IPP classification distinguishes Tsuga types when the cover of this species is at least 25% of the upper canopy; the 25% figure is rather arbitrary and corresponds to no intrinsic break in the cover of either tree species. Another problematical distinction is that between the relative indicator values of Oplopanax and Athyrium; some consider these two species to be indicator equivalents (Lillybridge et al. 1995), whereas others (Hansen et al. 1995) are unequivocal in stating that Oplopanax is characteristic of wetter environments. Where the distribution of Athyrium and Oplopanax overlap, from the Clearwater River northward in Idaho, ~Thuja plicata / Athyrium filix-femina Forest (CEGL000473)$$ is considerably more uncommon, these sites being occupied by ~Thuja plicata - Tsuga heterophylla / Oplopanax horridus Rocky Mountain Swamp Forest (CEGL000479)$$ in which Athyrium is 100% constant and its cover frequently exceeds that of Oplopanax. One cannot invoke cold-air drainage and ponding on the latter type (noted by Hansen et al. 1995) as the distinguishing factor because Athyrium is abundantly represented on all Oplopanax sites. At least in northern Idaho Oplopanax sites occurred on coarser-textured soils with greater amounts of gravel (40-60%).

Similar NVC Types: No Data Available

note: No Data Available