Print Report

A3379 Tsuga heterophylla - Pseudotsuga menziesii / Holodiscus discolor Dry Forest Alliance

Type Concept Sentence: This is a dry-mesic conifer-dominated forest alliance that is characterized by a mixed overstory canopy of Tsuga heterophylla and Pseudotsuga menziesii. Other common tree associates include Abies amabilis, Abies grandis, Picea sitchensis, and Thuja plicata. A subcanopy of Acer macrophyllum and/or Taxus brevifolia may also be present. It occurs at low elevations (0-1500 m) within the maritime-influenced region of the Pacific Northwest on the lower slopes of the coastal ranges that feature high precipitation, long frost-free periods, and low fire frequencies.


Common (Translated Scientific) Name: Western Hemlock - Douglas-fir / Oceanspray Dry Forest Alliance

Colloquial Name: Western Hemlock - Douglas-fir / Oceanspray Dry Forest

Hierarchy Level:  Alliance

Type Concept: These coniferous forests are characterized by a mixed overstory canopy of Tsuga heterophylla and Pseudotsuga menziesii. Other common tree associates include Abies amabilis, Abies grandis, Picea sitchensis, and Thuja plicata. A subcanopy of Acer macrophyllum, and/or Taxus brevifolia may also be present. The moderately dense shrub layer is commonly composed of Amelanchier alnifolia, Acer circinatum, Chimaphila menziesii, Chimaphila umbellata, Gaultheria shallon, Holodiscus discolor, Linnaea borealis, Mahonia nervosa, Paxistima myrsinites, Rosa gymnocarpa, Rubus ursinus, and Vaccinium parvifolium. The herbaceous layer is dominated by drought-tolerant and shade-tolerant forbs and ferns, including Achlys triphylla, Calamagrostis rubescens, Goodyera oblongifolia, Oxalis oregana, Orthilia secunda, and Pteridium aquilinum. An upper tree canopy dominated by Tsuga heterophylla and Pseudotsuga menziesii and dry-site conditions are diagnostic of this alliance. This coniferous forest alliance occurs at low elevations (0-1500 m) within the maritime-influenced region of the Pacific Northwest, from north coastal California to the northern coast of Vancouver Island, British Columbia. Stands are best represented on the lower slopes of the coastal ranges that feature high precipitation, long frost-free periods, and low fire frequencies. 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 steeper slopes and warmer aspects, on well-drained sites, and are quite dry throughout the year. The associations in this alliance are found throughout the range and represent the driest forested stands of the ~North Pacific Maritime Douglas-fir - Western Hemlock Rainforest Group (G240)$$. The associations are recognized as consistently the driest expressions of these forests throughout their range by local ecologists.

Diagnostic Characteristics: An upper tree canopy dominated by Tsuga heterophylla and Pseudotsuga menziesii and dry site conditions are diagnostic of this alliance.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This is the driest microsite alliance of this group. Stands are well-drained and the understory species are tolerant of warm and dry conditions during the growing season.

Similar NVC Types: No Data Available
note: No Data Available

Physiognomy and Structure: This is a dry-mesic conifer-dominated forest alliance that is characterized by a mixed overstory canopy of evergreen needle-leaved trees.

Floristics: These coniferous forests are characterized by a mixed overstory canopy of Tsuga heterophylla and Pseudotsuga menziesii. Other common tree associates include Abies amabilis, Abies grandis, Picea sitchensis, and Thuja plicata. A subcanopy of Acer macrophyllum, and/or Taxus brevifolia may also be present. The moderately dense shrub layer is commonly composed of Amelanchier alnifolia, Acer circinatum, Chimaphila menziesii, Chimaphila umbellata, Gaultheria shallon, Holodiscus discolor, Linnaea borealis, Mahonia nervosa, Paxistima myrsinites, Rosa gymnocarpa, Rubus ursinus, and Vaccinium parvifolium. The herbaceous layer is dominated by drought-tolerant and shade-tolerant forbs and ferns, including Achlys triphylla, Calamagrostis rubescens, Goodyera oblongifolia, Oxalis oregana, Orthilia secunda, and Pteridium aquilinum.

Dynamics:  No Data Available

Environmental Description:  This coniferous forest alliance occurs at low elevations (0-1500 m) within the maritime-influenced region of the Pacific Northwest, from north coastal California to the northern coast of Vancouver Island, British Columbia. Stands are best represented on the lower slopes of the coastal ranges that feature high precipitation, long frost-free periods, and low fire frequencies. 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 steeper slopes and warmer aspects, on well-drained sites, and are quite dry throughout the year. The associations in this alliance are recognized as consistently the driest expressions of these forests throughout their range by local ecologists.

Geographic Range: This alliance is found in the northern California Coast Ranges north to the northern end 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 A3379 Western Hemlock - Douglas-fir / Oceanspray Dry Forest Alliance A3379 1.B.2.Nd.3.c
Association CEGL000067 Douglas-fir - Western Hemlock / Oceanspray Forest CEGL000067 1.B.2.Nd.3.c
Association CEGL000097 Western Hemlock / Cascade Barberry / Twinflower Forest CEGL000097 1.B.2.Nd.3.c
Association CEGL000483 Western Red-cedar - Western Hemlock / Redwood Sorrel Forest CEGL000483 1.B.2.Nd.3.c
Association CEGL002614 Douglas-fir - Western Hemlock / California Huckleberry Forest CEGL002614 1.B.2.Nd.3.c
Association CEGL002615 Douglas-fir - Western Hemlock / Pacific Rhododendron - California Huckleberry Forest CEGL002615 1.B.2.Nd.3.c
Association CEGL005531 Douglas-fir / Salal - Oceanspray Forest CEGL005531 1.B.2.Nd.3.c
Association CEGL005532 Douglas-fir / Salal - Red Huckleberry Forest CEGL005532 1.B.2.Nd.3.c
Association CEGL005533 Douglas-fir / Oceanspray / Trailing Snowberry Forest CEGL005533 1.B.2.Nd.3.c
Association CEGL005537 Douglas-fir - Western Hemlock / Salal - Oceanspray Forest CEGL005537 1.B.2.Nd.3.c
Association CEGL005539 Douglas-fir - Western Hemlock / Salal - Red Huckleberry Forest CEGL005539 1.B.2.Nd.3.c
Association CEGL007365 Douglas-fir / Salal - Cascade Barberry / Western Swordfern Forest CEGL007365 1.B.2.Nd.3.c

Concept Lineage: A.NCCN-043 (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: No Data Available

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

  • Faber-Langendoen, D., J. Drake, M. Hall, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, M. Russo, K. Schulz, L. Sneddon, K. Snow, and J. Teague. 2013-2019b. Screening alliances for induction into the U.S. National Vegetation Classification: Part 1 - Alliance concept review. NatureServe, Arlington, VA.