Print Report

A3604 Tsuga heterophylla - Picea sitchensis / Rhytidiadelphus loreus Forest Alliance

Type Concept Sentence: This alliance covers forests of the Pacific Northwest dominated by Picea sitchensis and Tsuga heterophylla on well-drained, fresh to moist, nutrient-poor sites with thin soils, usually directly facing the ocean. The understory is variable but species are indicators of nutrient-poor soils, such as Rhytidiadelphus loreus.

Common (Translated Scientific) Name: Western Hemlock - Sitka Spruce / Gooseneck Moss Forest Alliance

Colloquial Name: North Pacific Western Hemlock - Sitka Spruce Forest

Hierarchy Level:  Alliance

Type Concept: This alliance consists of forests of the Pacific Northwest dominated by Picea sitchensis and Tsuga heterophylla on well-drained, fresh to moist, nutrient-poor sites with thin soils, usually directly facing the ocean. The understory is variable, but species are indicators of nutrient-poor soils, such as Rhytidiadelphus loreus. Forests included in this alliance are dominated by Picea sitchensis, but Tsuga heterophylla and Pseudotsuga menziesii may codominate the canopy. Common understory species include Blechnum spicant, Calamagrostis nutkaensis, Eurhynchium oreganum, Eurhynchium oreganum, Gaultheria shallon, Maianthemum dilatatum, Polystichum munitum, Rhizomnium glabrescens, Rhytidiadelphus loreus, Tiarella trifoliata, and Trisetum canescens. This alliance is found within the maritime climate-influenced region of the Pacific Northwest, from northern Oregon to southern Alaska, usually within 50 km of tidewater and below 1000 m in elevation. Stands typically occur on coastal terraces, but extend up river valleys and seaward slopes of coastal mountains. Stands occur on moderate to steep slopes with shallow to moderately deep soils.

Diagnostic Characteristics: Forests dominated by Picea sitchensis or having at least 25% cover of that species with other conifers, and open understory growth, on thin nutrient-poor soils.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: This alliance comes mostly from Del Meidinger, British Columbia ecologist.

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Forests of this alliance are typified by a dense to moderately open multi-aged canopy of needle-leaved evergreen trees on average exceeding 50 m in height. Broad-leaved cold-deciduous trees may form a scattered subcanopy, particularly in canopy gaps. The next stratum is usually a broad-leaved evergreen or, less commonly, a broad-leaved, cold-deciduous tall-shrub layer. A low-shrub layer of clambering cold-deciduous shrubs is very common.

Floristics: Forests included in this alliance are dominated by Picea sitchensis, but Tsuga heterophylla and Pseudotsuga menziesii may codominate the canopy. Common understory species include Blechnum spicant, Calamagrostis nutkaensis, Eurhynchium oreganum, Eurhynchium oreganum, Gaultheria shallon, Maianthemum dilatatum, Polystichum munitum, Rhizomnium glabrescens, Rhytidiadelphus loreus, Tiarella trifoliata, and Trisetum canescens.

Dynamics:  Fires tend to be infrequent in stands of this alliance due to high average humidities and low lightning frequencies. When they do burn, these forests are susceptible to high-intensity crown fires. Windthrow resulting from intense winter storms is a common, and occasionally catastrophic, agent of disturbance which can result in forest turnover. Alnus rubra and Rubus spectabilis, in particular, can form semi-persistent communities on disturbed sites. Regeneration and growth of Picea sitchensis can be severely limited in such early-seral stands. In mature Picea sitchensis forests, regeneration often occurs on downed "nurse logs" on the forest floor.
Environmental Description:  This alliance occurs within the maritime climate-influenced region of the Pacific Northwest, from northern Oregon to southern Alaska, usually within 50 km of tidewater and below 1000 m in elevation. Stands of this alliance are best represented in the relatively mild, wet climates along the coast. Although this alliance is usually associated with coastal terraces, these forests may extend up river valleys and seaward slopes of coastal mountains. Annual precipitation ranges from 65-550 cm, with the majority falling as rain. Winter rains can be heavy. Summer rain decreases to the south, but coastal fog events and drizzle are characteristic throughout the range and minimize drought stress. Stands occur on moderate to steep slopes with shallow to moderately deep soils. Best forest development is on deep, moist, well-aerated soils with abundant calcium and magnesium and moderate acidity (Burns and Honkala 1990a).
Geographic Range: This alliance is found in coastal mountains and along immediate coastlines of southern Alaska, British Columbia, Washington and Oregon.

Nations: CA,US

States/Provinces:  AK, 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.f Western Hemlock - Sitka Spruce North-Central Pacific Rainforest Group G751 1.B.2.Nd.3.f
Alliance A3604 Western Hemlock - Sitka Spruce / Gooseneck Moss Forest Alliance A3604 1.B.2.Nd.3.f
Association CEGL005523 Sitka Spruce / Pacific Reedgrass Forest CEGL005523 1.B.2.Nd.3.f
Association CEGL005524 Sitka Spruce / Salal Forest CEGL005524 1.B.2.Nd.3.f
Association CEGL005525 Sitka Spruce / False Lily-of-the-Valley Forest CEGL005525 1.B.2.Nd.3.f
Association CEGL005526 Sitka Spruce - Douglas-fir / Salal Forest CEGL005526 1.B.2.Nd.3.f
Association CEGL007306 Sitka Spruce / California Huckleberry Forest CEGL007306 1.B.2.Nd.3.f
Concept Lineage: No Data Available

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: >< Picea sitchensis-Tsuga heterophylla Forests (Chappell et al. 1997)
>< Sitka Spruce Series (Henderson et al. 1989)
>< Sitka Spruce Series (Sawyer and Keeler-Wolf 1995)
>< Sitka Spruce: 223 (Eyre 1980)
>< Western Hemlock - Sitka Spruce: 225 (Eyre 1980)
>< Western Needleleaf Forests: 1: Spruce-Cedar-Hemlock Forest (Picea-Thuja-Tsuga) (Küchler 1964)
Concept Author(s): D. Meidinger, in Faber-Langendoen et al. (2013)

Author of Description: G. Kittel

Acknowledgements: No Data Available

Version Date: 09-26-14
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