Print Report

A3378 Tsuga heterophylla - Pseudotsuga menziesii / Cornus unalaschkensis Mesic Forest Alliance

Type Concept Sentence: This alliance occurs in all the maritime-influenced regions of the Pacific Northwest, from north coastal California to the northern coast of Vancouver Island, British Columbia. Throughout the range of this alliance, much of the annual precipitation occurs as rain. Where snow does occur, it can generally be melted by rain during warm winter storms. In all settings, this alliance occurs where environmental conditions are moderated by the marine influence, with moderate drought and frost. The overstory canopy is dominated by Pseudotsuga menziesii and Tsuga heterophylla. Understory species such as Mahonia nervosa, Vaccinium membranaceum, and Gaultheria shallon are intolerant of drought.

Common (Translated Scientific) Name: Western Hemlock - Douglas-fir / Western Cordilleran Bunchberry Mesic Forest Alliance

Colloquial Name: Western Hemlock - Douglas-fir / Western Cordilleran Bunchberry Mesic Forest

Hierarchy Level:  Alliance

Type Concept: This is a heavily forested alliance. The overstory canopy is dominated by Pseudotsuga menziesii and Tsuga heterophylla. Understory species such as Mahonia nervosa, Vaccinium membranaceum, and Gaultheria shallon are intolerant of drought. Other common tree associates include Thuja plicata, Abies amabilis, and Abies grandis. Rarely, Picea sitchensis may appear, and Callitropsis nootkatensis has been documented with up to 28% cover, but neither are typically present. Shrub species are variable and include Acer circinatum, Chimaphila umbellata, Gaultheria shallon, Linnaea borealis, Mahonia nervosa, Menziesia ferruginea, Vaccinium alaskaense, and Vaccinium parvifolium. The herbaceous layer is highly variable. The following species each occur in about one-third of documented stands: Achlys triphylla, Blechnum spicant, Clintonia uniflora, Cornus unalaschkensis, Goodyera oblongifolia, Polystichum munitum, Tiarella trifoliata, and Trillium ovatum. This alliance occurs in all the maritime-influenced regions of the Pacific Northwest, from north coastal California to the northern coast of Vancouver Island, British Columbia. Throughout the range of this alliance, much of the annual precipitation occurs as rain. Where snow does occur, it can generally be melted by rain during warm winter storms. In all settings, this alliance occurs where environmental conditions are moderated by the marine influence, with moderate drought and frost. Stands of the alliance generally occur on all slopes and aspects, on well-drained mesic sites that do not become very dry by summer''s end. The associations in this alliance are found throughout the range. Although associations may be more moist in the north and more mesic in the south, all are generally in the mid-range of moisture settings, and are never considered consistently very dry or very wet by local ecologists. Soils typically remain moist year-round, but are not subirrigated or saturated. The diagnostic characteristic of this alliance is an overstory of both Pseudotsuga menziesii and Tsuga heterophylla, with an understory that is neither wet nor dry throughout the growing season.

Diagnostic Characteristics: The diagnostic characteristic of this alliance is an overstory of both Pseudotsuga menziesii and Tsuga heterophylla, with an understory that is neither wet nor dry throughout the growing season.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: These are mesic forests that are neither overly wet or dry throughout the growing season.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Forests within this alliance are characterized by a tall canopy of evergreen needle-leaved trees which can exceed 50 m in height, ranging from 60-100% cover. Understory trees are usually broad-leaved deciduous or evergreen species. A short- to tall-shrub stratum of cold-deciduous or broad-leaved evergreen shrubs is often present, but may be sparse. The herbaceous understory is often very lush, and characterized by shade-tolerant forbs and ferns. Late-successional stands have very large trees, huge amounts of woody debris including large snags and logs, and better developed understories. However, young stands are often dense-stemmed and the understory depauperate.

Floristics: The overstory canopy is dominated by Pseudotsuga menziesii and Tsuga heterophylla. Understory species such as Mahonia nervosa, Vaccinium membranaceum, and Gaultheria shallon are intolerant of drought. Other common tree associates include Thuja plicata, Abies amabilis, and Abies grandis. Rarely, Picea sitchensis may appear, and Callitropsis nootkatensis (= Chamaecyparis nootkatensis) has been documented with up to 28% cover, but neither are typically present. Shrub species are variable and include Acer circinatum, Chimaphila umbellata, Gaultheria shallon, Linnaea borealis, Mahonia nervosa, Menziesia ferruginea, Vaccinium alaskaense, and Vaccinium parvifolium. The herbaceous layer is highly variable. The following species each occur in about one-third of documented stands: Achlys triphylla, Blechnum spicant, Clintonia uniflora, Cornus unalaschkensis, Goodyera oblongifolia, Polystichum munitum, Tiarella trifoliata, and Trillium ovatum.

Dynamics:  These forests have a high- or moderate-severity fire regime with natural return intervals of 100-600 years. Pseudotsuga menziesii colonizes vigorously and is favored with logging and/or fire disturbance to these forests. With increasing time since disturbance, Tsuga heterophylla or Thuja plicata become more abundant in the canopy, due to their ability to regenerate under closed-canopy conditions. At drier sites, Pseudotsuga menziesii is able to regenerate under the relatively open canopy. Logging often results in conversion to deciduous or mixed forest with Alnus rubra or Acer macrophyllum.
Environmental Description:  Throughout the range of this alliance, much of the annual precipitation occurs as rain. Where snow does occur, it can generally be melted by rain during warm winter storms. In all settings, this alliance occurs where environmental conditions are moderated by the marine influence, with moderate drought and frost. Stands of the alliance generally occur on all slopes and aspects, on well-drained mesic sites that do not become very dry by summer''s end. The associations in this alliance are found throughout the range. Although associations may be more moist in the north and more mesic in the south, all are generally in the mid-range of moisture settings, and are never considered consistently very dry or very wet by local ecologists. Soils typically remain moist year-round, but are not subirrigated or saturated.
Geographic Range: This alliance occurs from north coastal California to the northern coast of Vancouver Island, British Columbia.

Nations: CA,US

States/Provinces:  BC, CA, OR, WA


Confidence Level: Low

Confidence Level Comments: No Data Available
Grank: GNR

Greasons: No Data Available
Type Name Database Code Classification Code
Class 1 Forest & Woodland Class C01 1
Subclass 1.B Temperate & Boreal Forest & Woodland Subclass S15 1.B
Formation 1.B.2 Cool Temperate Forest & Woodland Formation F008 1.B.2
Division 1.B.2.Nd Vancouverian Forest & Woodland Division D192 1.B.2.Nd
Macrogroup 1.B.2.Nd.3 Western Hemlock - Sitka Spruce - Redwood Rainforest Macrogroup M024 1.B.2.Nd.3
Group 1.B.2.Nd.3.c Douglas-fir - Western Hemlock / Salal Rainforest Group G240 1.B.2.Nd.3.c
Alliance A3378 Western Hemlock - Douglas-fir / Western Cordilleran Bunchberry Mesic Forest Alliance A3378 1.B.2.Nd.3.c
Association CEGL000029 Sierra White Fir - Western Hemlock / Vine Maple Forest CEGL000029 1.B.2.Nd.3.c
Association CEGL000086 Douglas-fir - (Western Hemlock) / Pacific Rhododendron Forest CEGL000086 1.B.2.Nd.3.c
Association CEGL000099 Western Hemlock / Giant Chinquapin Forest CEGL000099 1.B.2.Nd.3.c
Association CEGL000119 Western Hemlock / Thinleaf Huckleberry / Twinflower Forest CEGL000119 1.B.2.Nd.3.c
Association CEGL000120 Western Hemlock / Thinleaf Huckleberry / Common Beargrass Forest CEGL000120 1.B.2.Nd.3.c
Association CEGL000121 Douglas-fir - Western Hemlock / California Huckleberry / Western Swordfern Forest CEGL000121 1.B.2.Nd.3.c
Association CEGL002845 Douglas-fir - (Grand Fir, Western Red-cedar) / Cascade Barberry - Salal Forest CEGL002845 1.B.2.Nd.3.c
Association CEGL005535 Douglas-fir - Western Hemlock / Sweet After Death Forest CEGL005535 1.B.2.Nd.3.c
Association CEGL005538 Douglas-fir - Western Hemlock / Salal - Cascade Barberry Forest CEGL005538 1.B.2.Nd.3.c
Association CEGL005541 Douglas-fir - Western Hemlock / Cascade Barberry Forest CEGL005541 1.B.2.Nd.3.c
Association CEGL005544 Douglas-fir - Western Hemlock / Pacific Rhododendron Forest CEGL005544 1.B.2.Nd.3.c
Association CEGL005545 Douglas-fir - Western Hemlock / Pacific Rhododendron / Western Swordfern Forest CEGL005545 1.B.2.Nd.3.c
Association CEGL005546 Douglas-fir - Western Hemlock / Pacific Rhododendron - California Huckleberry / Western Swordfern Forest CEGL005546 1.B.2.Nd.3.c
Association CEGL005570 Western Hemlock - Douglas-fir / Cascade Barberry - Little Prince''s-pine Forest CEGL005570 1.B.2.Nd.3.c
Association CEGL005571 Western Hemlock - Douglas-fir / Pacific Rhododendron - Alaska Blueberry / Western Cordilleran Bunchberry Forest CEGL005571 1.B.2.Nd.3.c
Association CEGL005631 Douglas-fir - Grand Fir / Vine Maple / Western Swordfern Forest CEGL005631 1.B.2.Nd.3.c
Association CEGL007289 Douglas-fir - Western Hemlock / Pacific Rhododendron - Beaked Hazelnut / Western Swordfern Forest CEGL007289 1.B.2.Nd.3.c
Association CEGL007333 Douglas-fir - Western Hemlock / Salal / Common Beargrass Forest CEGL007333 1.B.2.Nd.3.c
Association CEGL007337 Douglas-fir - Western Hemlock / Threeleaf Foamflower Forest CEGL007337 1.B.2.Nd.3.c
Association CEGL007382 Douglas-fir / (Common Snowberry, Trailing Snowberry) - Saskatoon Serviceberry Forest CEGL007382 1.B.2.Nd.3.c
Association CEGL007396 Douglas-fir - Sierra White Fir / Oceanspray / Western Swordfern Forest CEGL007396 1.B.2.Nd.3.c
Concept Lineage: A.NCCN-042 (This replaces, in part, A.107-Pseudotsuga menziesii - Tsuga heterophylla Forest Alliance.)

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: > Aesculus californica (California buckeye groves) Alliance (Sawyer et al. 2009) [75.100.00]
> Quercus lobata (Valley oak woodland) Alliance (Sawyer et al. 2009) [71.040.00]
>< Douglas fir-western hemlock, # 230 (Küchler 1964)
>< Douglas-fir - Western Hemlock: 230 (Eyre 1980)
>< Sierra Nevada Mixed Conifer: 243 (Eyre 1980)
>< Western Hemlock Series (Sawyer and Keeler-Wolf 1995)
>< Western Hemlock: 224 (Eyre 1980)
>< Western Needleleaf Forests: 2: Cedar-Hemlock-Douglas Fir Forest (Thuja-Tsuga-Pseudotsuga) (Küchler 1964)
>< Western Needleleaf Forests: 5: Mixed Conifer Forest (Abies-Pinus-Pseudotsuga) (Küchler 1964)
Concept Author(s): G. Kittel, in Faber-Langendoen et al. (2013)

Author of Description: G. Kittel

Acknowledgements: No Data Available

Version Date: 09-26-14
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