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A3617 Tsuga mertensiana Rocky Mountain Forest Alliance
Type Concept Sentence: The forests are known from the middle and northern Rocky Mountains and are characterized by a canopy dominated by Tsuga mertensiana.
Common (Translated Scientific) Name: Mountain Hemlock Rocky Mountain Forest Alliance
Colloquial Name: Rocky Mountain Hemlock Forest
Hierarchy Level: Alliance
Type Concept: These forests are characterized by a canopy of Tsuga mertensiana, a needle-leaved evergreen tree which can approach 35 m in height. Other conifers that may be present include Abies grandis, Abies lasiocarpa, Picea engelmannii, and Pinus monticola. The understory is often sparse due to dense canopy shading. Characteristic understory shrubs may include Lonicera utahensis, Menziesia ferruginea, Paxistima myrsinites, Rhododendron albiflorum, Taxus brevifolia, and Vaccinium membranaceum. Herbaceous species include Asarum caudatum, Athyrium filix-femina, Clintonia uniflora, Coptis occidentalis, Gymnocarpium dryopteris, Maianthemum stellatum, Prosartes hookeri, Tiarella trifoliata, Trillium ovatum, Viola orbiculata, and Xerophyllum tenax. This forest alliance occurs in the middle and northern Rocky Mountains in Idaho, Montana, and eastern Washington. It occurs in cold, snowy subalpine environments and is generally associated with areas of incursions of maritime air masses, which moderate temperatures and produce deep winter snowpacks. Although this alliance typically occurs in subalpine habitats, it may occur in montane forest environments, such as slope benches or canyon bottoms, which are prone to cold-air drainage. Most soils can be characterized as loose, coarse-textured, and well-drained.
Diagnostic Characteristics: Forests of the subalpine zones of the northern Rocky Mountains with canopies dominated by Tsuga mertensiana in association with other conifer species.
Rationale for Nominal Species or Physiognomic Features: No Data Available
Classification Comments: This alliance is now defined for mountain hemlock forests of the subalpine zones of the Rocky Mountains and was formerly included with associations found further north. Very little descriptive material exists for associations in this alliance and further review will be required to adequately describe its attributions.
Similar NVC Types: No Data Available
note: No Data Available
Physiognomy and Structure: Associations in this alliance are characterized by a dense canopy of needle-leaved evergreen trees, resulting in low light intensities at the forest floor and low understory cover. Trees are often large and widely spaced, with an open understory of occasional shrubs. When present, the shrub layer is often composed of low ericaceous shrubs which are sparsely scattered. An herbaceous layer of graminoids is occasionally present.
Floristics: These forests are characterized by a canopy of Tsuga mertensiana, a needle-leaved evergreen tree which can approach 35 m in height. Other conifers that may be present include Abies grandis, Abies lasiocarpa, Picea engelmannii, and Pinus monticola. The understory is often sparse due to dense canopy shading. Understory shrubs are largely ericaceous, including Lonicera utahensis, Menziesia ferruginea, Paxistima myrsinites, Rhododendron albiflorum, Taxus brevifolia, and Vaccinium membranaceum. Herbaceous species include Asarum caudatum, Athyrium filix-femina, Clintonia uniflora, Coptis occidentalis, Gymnocarpium dryopteris, Maianthemum stellatum (= Smilacina stellata), Prosartes hookeri (= Disporum hookeri), Tiarella trifoliata, Trillium ovatum, Viola orbiculata, and Xerophyllum tenax.
Dynamics: Tsuga mertensiana is a slow-growing, long-lived conifer, which can regenerate under its own canopy. Forests dominated by this species can be seral to forests dominated by other shade-tolerant conifers, such as Tsuga heterophylla or Callitropsis nootkatensis at the lower or northern edges of its range, respectively.
Environmental Description: This alliance occurs in cold, snowy subalpine environments of the northern Rocky Mountains. It is generally associated with areas of incursions of maritime air masses, which moderate temperatures and produce deep winter snowpacks. Although this alliance typically occurs in subalpine habitats, it may occur in montane forest environments, such as slope benches or canyon bottoms, which are prone to cold-air drainage. Most soils can be characterized as loose, coarse-textured, and well-drained.
Geographic Range: This alliance occurs in the subalpine zones of the central and northern Rocky Mountains.
Nations: US
States/Provinces: ID, MT, OR, WA
Plot Analysis Summary:
http://vegbank.org/natureserve/ELEMENT_GLOBAL.2.899675
Confidence Level: Low
Confidence Level Comments: No Data Available
Grank: GNR
Greasons: No Data Available
Concept Lineage: No Data Available
Predecessors: No Data Available
Obsolete Names: No Data Available
Obsolete Parents: No Data Available
Synonomy: >< Mountain Hemlock: 205 (Eyre 1980)
>< Western Needleleaf Forests: 4: Fir-Hemlock Forest (Abies-Tsuga) (Küchler 1964)
>< Western Needleleaf Forests: 4: Fir-Hemlock Forest (Abies-Tsuga) (Küchler 1964)
- Atzet, T., and D. L. Wheeler. 1984. Preliminary plant associations of the Siskiyou Mountains Province, Siskiyou National Forest. USDA Forest Service, Pacific Northwest Region, Portland, OR.
- Atzet, T., and L. A. McCrimmon. 1990. Preliminary plant associations of the southern Oregon Cascade Mountain Province. USDA Forest Service, Pacific Northwest Region, Siskiyou National Forest, Grants Pass, OR. 330 pp.
- Cooper, S. V., K. E. Neiman, R. Steele, and D. W. Roberts. 1987. Forest habitat types of northern Idaho: A second approximation. General Technical Report INT-236.USDA Forest Service, Intermountain Research Station, Ogden, UT. 135 pp. [reprinted in 1991]
- Eyre, F. H., editor. 1980. Forest cover types of the United States and Canada. Society of American Foresters, Washington, DC. 148 pp.
- 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.
- Küchler, A. W. 1964. Potential natural vegetation of the conterminous United States. American Geographic Society Special Publication 36. New York, NY. 116 pp.