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A3763 Tsuga heterophylla - Thuja plicata / Ledum glandulosum Treed Bog Alliance

Type Concept Sentence: This alliance consists of deep peat, organic, treed fens and bogs dominated in the upper canopy by Tsuga heterophylla and/or Thuja plicata. These are open woodlands with trees that are at least 5 m tall, but the canopy layer can be very open (10-20%). Thick sphagnum moss species cover the ground, and a low-shrub layer may or may not be present. Ledum glandulosum is often a dwarf-shrub layer component. This alliance is found in southern British Columbia coastal areas, coastal Oregon and the Puget Lowlands of Washington.

Common (Translated Scientific) Name: Western Hemlock - Western Red-cedar / Western Labrador-tea Treed Bog Alliance

Colloquial Name: Western Hemlock - Western Red-cedar / Western Labrador-tea Treed Bog

Hierarchy Level:  Alliance

Type Concept: This alliance consists of deep peat, organic, treed fens and bogs dominated in the upper canopy by Tsuga heterophylla and/or Thuja plicata. Pseudotsuga menziesii and Abies grandis may also share the upper tree canopy, and cold-deciduous trees, including Alnus rubra and Acer macrophyllum, often form a subcanopy layer. Acer circinatum, Menziesia ferruginea, Oplopanax horridus, Rubus spectabilis, and Vaccinium spp. are the most common shrubs. The herbaceous layer is dominated by wetland and moist forest species. These are open woodlands with trees that are at least 5 m tall, but the canopy layer can be very open (10-20%). Thick sphagnum moss species cover the ground, and a low-shrub layer may or may not be present. Ledum glandulosum is often a dwarf-shrub layer component. This alliance is found in southern British Columbia coastal areas, coastal Oregon and the Puget Lowlands of Washington. These forests occur on stream terraces, in depressions adjacent to streams, as impounded wetlands, and on subirrigated soils with an impermeable layer near the surface. Perennially saturated sites occur at or below the water table, and may have artesian springs. The soils are organic and saturated for part of the growing season.

Diagnostic Characteristics: Fens or bogs dominated by Tsuga heterophylla and/or Thuja plicata with or without a dwarf-shrub layer.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Treed bogs and fens of British Columbia, Washington and Oregon.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Stands of this alliance typically have a somewhat open (50-70% cover) canopy of needle-leaved evergreen trees approaching 50 m or more in height. There is often a sparse to moderately dense layer of cold-deciduous or broad-leaved evergreen shrubs. In the wettest communities, shrubs are mostly confined to higher microsites such as root wads, rotten logs, and buttress roots of trees. Wetter sites usually have mud-bottomed openings between the shrubs, with a sparse vegetation of hygrophytic vascular plants and mosses. Large logs are common and serve as nurse logs for tree regeneration.

Floristics: Vegetation is characterized by a somewhat open forest canopy dominated by Tsuga heterophylla, which is usually confined to higher microsites such as buttress roots, stumps and nurse logs. Thuja plicata is a typical associate in these stands. Pseudotsuga menziesii and Abies grandis may also share the upper tree canopy, and cold-deciduous trees, including Alnus rubra and Acer macrophyllum, often form a subcanopy layer. In Cascade or Coast ranges stands, Acer circinatum, Menziesia ferruginea, Rubus spectabilis, and Vaccinium spp. are the most common shrubs. Oplopanax horridus is common in coastal stands. The herbaceous layer is dominated by wetland and moist forest species, including Asarum caudatum, Athyrium filix-femina, Blechnum spicant, Lysichiton americanus, Polystichum munitum, Senecio triangularis, Tiarella trifoliata var. laciniata, Trientalis borealis ssp. latifolia (= Trientalis latifolia), and Trillium ovatum. Mosses are abundant and average 35-40% in ground cover. Large logs are common and serve as nurse logs for Tsuga heterophylla.

Dynamics:  Due to waterlogged soils, these forests may be somewhat open, with tree regeneration occurring only on elevated microsites and surfaces, such as fallen logs and root-ball hummocks. Following disturbance, Alnus rubra vigorously colonizes sites previously supporting stands of this alliance, creating a short-lived deciduous forest. The organic soils in these forests are susceptible to erosion and oxidation following physical disturbance, making reforestation difficult. These forests typically occur as small patches in the upland forest matrix. This spatial structure allows them to function as refugia and foraging stations for wetland dependent fauna (Topik et al. 1986).
Environmental Description:  Vegetation within this alliance occurs in marine-influenced regions of mountains of the coastal and interior Pacific Northwest. Near the coast, much of the annual precipitation occurs as rain, but at higher elevations winter snows do occasionally occur. Snow can be melted by rain during warm winter storms. Annual precipitation is 300 cm or more in the coastal ranges of Oregon and Washington. These forests occur on stream terraces, in depressions adjacent to streams, as impounded wetlands, and on subirrigated soils with an impermeable layer near the surface. Perennially saturated sites occur at or below the water table, and may have artesian springs. The soils are organic and saturated for part of the growing season. These forests are often transitional to non-forested wetlands. Adjacent plant communities are usually on riparian or depressional wetlands, and dominated by Salix, Alnus, or Carex spp. at the wetter margin and moist upland forests of Tsuga heterophylla or Thuja plicata at the drier edges.
Geographic Range: This alliance is found in southern British Columbia coastal areas, coastal Oregon and the Puget Lowlands of Washington.

Nations: CA,US

States/Provinces:  BC, OR, WA


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 2 Shrub & Herb Vegetation Class C02 2
Subclass 2.C Shrub & Herb Wetland Subclass S44 2.C
Formation 2.C.2 Temperate to Polar Bog & Fen Formation F016 2.C.2
Division 2.C.2.Na North American Bog & Fen Division D029 2.C.2.Na
Macrogroup 2.C.2.Na.3 Beach Pine / Bog Labrador-tea / Cusick''s Sedge North Pacific Bog & Fen Macrogroup M063 2.C.2.Na.3
Group 2.C.2.Na.3.c Beach Pine / Bog Labrador-tea / Peatmoss species Wooded Bog & Poor Fen Group G610 2.C.2.Na.3.c
Alliance A3763 Western Hemlock - Western Red-cedar / Western Labrador-tea Treed Bog Alliance A3763 2.C.2.Na.3.c
Association CEGL000477 Western Hemlock / Western Labrador-tea / Slough Sedge - American Skunk-cabbage Treed Bog CEGL000477 2.C.2.Na.3.c
Association CEGL003339 Western Hemlock - (Western Red-cedar) / Bog Labrador-tea / Peatmoss species Treed Bog CEGL003339 2.C.2.Na.3.c
Association CEGL003417 Western Hemlock - (Western Red-cedar) / Peatmoss species Treed Bog CEGL003417 2.C.2.Na.3.c
Concept Lineage: No Data Available

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: >< Tsuga heterophylla-Thuja plicata Coniferous Wetlands (Chappell et al. 1997)
>< Western Hemlock: 224 (Eyre 1980)
>< Western Redcedar - Western Hemlock: 227 (Eyre 1980)
Concept Author(s): G. Kittel, in Faber-Langendoen et al. (2013)

Author of Description: G. Kittel

Acknowledgements: No Data Available

Version Date: 12-18-14
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