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A3620 Tsuga mertensiana - Pinus contorta var. murrayana Sierran Forest Alliance

Type Concept Sentence: Tsuga mertensiana is dominant or codominant in the tree canopy with Pinus albicaulis, Pinus contorta var. murrayana, or Pinus monticola. This alliance is found in the Sierra Nevada of California north into the southern Cascades, and west into the Klamath Mountains, where it typically forms stands above lake margins and north-facing aspects with late-lasting snow.

Common (Translated Scientific) Name: Mountain Hemlock - Sierra Lodgepole Pine Sierran Forest Alliance

Colloquial Name: Sierra-Cascade Mountain Hemlock - Lodgepole Pine Forest

Hierarchy Level:  Alliance

Type Concept: This alliance consists of forests where Tsuga mertensiana is dominant or codominant in the tree canopy with Pinus albicaulis, Pinus contorta var. murrayana, or Pinus monticola. Trees are <40 m in height, and the canopy is intermittent to continuous. The shrub and herbaceous layers are sparse to abundant. Many stands have few shrubs or herbs. Trees are shade-tolerant, creating stable, all-aged stands. In addition, Tsuga mertensiana can pioneer on moraines and glaciated surfaces and grow as individuals or in groves. Tsuga mertensiana occurs in the subalpine in the mountains of central and northern California, where it typically forms stands above lake margins and north-facing aspects with late-lasting. It is a slow-growing conifer that attains a height of 30 m and an age of 250 years. Established seedlings grow slowly in partial shade and are drought-intolerant. All stages of the trees can tolerate heavy snow packs. Because Tsuga mertensiana is shallow-rooted, it is very susceptible to windthrow. Plants layer forming krummholz on exposed ridges at timberline. This alliance is found in the Sierra Nevada of California north into the southern Cascades, and west into the Klamath Mountains. Tsuga mertensiana is found as individuals or small, isolated groves at its southern limit near Triple Divide Peak. Stands are common at subalpine elevations on glaciated slopes leading up to the highest mountaintops and ridges. Stands also occur east of the Sierra Crest in the Mammoth region. It is common and extensive at subalpine elevations on all the major volcanic peaks in the southern Cascades. Habitats are subalpine stream benches, slopes, most extensive on north-facing aspects and lake margins. Elevation ranges from 1900-2700 m.

Diagnostic Characteristics: Tsuga mertensiana is dominant or codominant in the tree canopy with Pinus albicaulis, Pinus contorta var. murrayana, or Pinus monticola.

Rationale for Nominal Species or Physiognomic Features: No Data Available

Classification Comments: Based on the mountain hemlock forest alliance of the MCV (Sawyer et al. 2009).

Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: No Data Available

Floristics: This alliance consists of forests where Tsuga mertensiana is dominant or codominant in the tree canopy with Pinus albicaulis, Pinus contorta var. murrayana, or Pinus monticola. Trees are <40 m in height, and the canopy is intermittent to continuous. The shrub and herbaceous layers are sparse to abundant. Many stands have few shrubs or herbs. Trees are shade-tolerant, creating stable, all-aged stands. In addition, Tsuga mertensiana can pioneer on moraines and glaciated surfaces and grow as individuals or in groves (Tesky 1992).

Dynamics:  Tsuga mertensiana is a slow-growing conifer that attains a height of 30 m and an age of 250 years. Established seedlings grow slowly in partial shade and are drought intolerant. All stages of the trees can tolerate heavy snow packs. Because Tsuga mertensiana is shallow-rooted, it is very susceptible to windthrow. Plants layer forming krummholz on exposed ridges at timberline (Tesky 1992).
Environmental Description:  Stands are common at subalpine elevations on glaciated slopes leading up to the highest mountaintops and ridges. Tsuga mertensiana occurs in the subalpine in the mountains of central and northern California, where it typically forms stands above lake margins and north-facing aspects with late-lasting snow (Fites-Kaufman et al. 2007, Sawyer 2007).
Geographic Range: This alliance is found in the Sierra Nevada of California north into the southern Cascades, and west into the Klamath Mountains. Tsuga mertensiana is found as individuals or small, isolated groves at its southern limit near Triple Divide Peak. Stands also occur east of the Sierra Crest in the Mammoth region. It is common and extensive at subalpine elevations on all the major volcanic peaks in the southern Cascades, where it sometimes forms timberline at Antelope Creek Lakes cRNA and Red Butte-Red Fir RNA.

Nations: US

States/Provinces:  CA, OR


Confidence Level: Moderate

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.4 California Red Fir - Mountain Hemlock - Sierra Lodgepole Pine Forest Macrogroup M025 1.B.2.Nd.4
Group 1.B.2.Nd.4.a California Red Fir - Shasta Red Fir - Mountain Hemlock Forest Group G749 1.B.2.Nd.4.a
Alliance A3620 Mountain Hemlock - Sierra Lodgepole Pine Sierran Forest Alliance A3620 1.B.2.Nd.4.a
Association CEGL000123 Mountain Hemlock / Deer Oak / Sidebells Wintergreen Forest CEGL000123 1.B.2.Nd.4.a
Association CEGL000177 Western White Pine / Common Beargrass Woodland CEGL000177 1.B.2.Nd.4.a
Association CEGL000912 Douglas-fir - Mountain Hemlock / Vine Maple Woodland CEGL000912 1.B.2.Nd.4.a
Association CEGL003132 Whitebark Pine - Mountain Hemlock / Mixed Herbaceous Woodland CEGL003132 1.B.2.Nd.4.a
Association CEGL008622 Western White Pine / Western Needlegrass Forest CEGL008622 1.B.2.Nd.4.a
Association CEGL008685 Mountain Hemlock / Sparse Understory Forest CEGL008685 1.B.2.Nd.4.a
Association CEGL008686 Mountain Hemlock / Pioneer Rockcress Forest CEGL008686 1.B.2.Nd.4.a
Association CEGL008687 Mountain Hemlock - Western White Pine Forest CEGL008687 1.B.2.Nd.4.a
Association CEGL008688 Mountain Hemlock - Sierra Lodgepole Pine Forest CEGL008688 1.B.2.Nd.4.a
Association CEGL008689 Mountain Hemlock - Sierra Lodgepole Pine / Purple Mountain-heath Forest CEGL008689 1.B.2.Nd.4.a
Association CEGL008690 Mountain Hemlock - Sierra Lodgepole Pine / Ross'' Sedge Forest CEGL008690 1.B.2.Nd.4.a
Association CEGL008691 Mountain Hemlock - Sierra Lodgepole Pine - Western White Pine Forest CEGL008691 1.B.2.Nd.4.a
Association CEGL008692 Mountain Hemlock - Sierra Lodgepole Pine - Whitebark Pine Forest CEGL008692 1.B.2.Nd.4.a
Concept Lineage: Includes parts of A.146 and A.531

Predecessors: No Data Available

Obsolete Names: No Data Available

Obsolete Parents: No Data Available
Synonomy: = Tsuga mertensiana (Mountain hemlock forest) Alliance (Sawyer et al. 2009) [84.100.00]
Concept Author(s): M.S. Reid after Sawyer et al. (2009)

Author of Description: M.S. Reid

Acknowledgements: No Data Available

Version Date: 12-18-14
  • 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.
  • Fites-Kaufman, J. A., P. Rundel, N. Stephenson, and D. A. Weixelman. 2007. Montane and subalpine vegetation of the Sierra Nevada and Cascade ranges. Pages 456-501 in: M. Barbour, T. Keeler-Wolf, and A. A. Schoenherr, editors. Terrestrial Vegetation of California, third edition. University of California Press, Berkeley.
  • Sawyer, J. O., T. Keeler-Wolf, and J. Evens. 2009. A manual of California vegetation. Second edition. California Native Plant Society, Sacramento CA. 1300 pp.
  • Tesky, J. L. 1992a. Tsuga mertensiana. In: Fire Effects Information System, [Online]. USDA Forest Service, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). [http://www.fs.fed.us/database/feis/]