Invalid Unit Specified
M500 Tsuga heterophylla - Abies grandis - Larix occidentalis Lower Montane Forest Macrogroup

The U.S. National
Vegetation Classification
Type Concept Sentence: Mesic to moist conifer forests and woodlands of the lower montane zone of the central Rocky Mountains and interior Pacific Northwest, including the eastern Cascades. Abies grandis, Larix occidentalis, Pseudotsuga menziesii, Thuja plicata, or Tsuga heterophylla are the major dominants.
Collapse All::Expand All
Common (Translated Scientific) Name: Western Hemlock - Grand Fir - Western Larch Mesic Lower Montane Forest Macrogroup
Colloquial Name: Central Rocky Mountain Mesic Lower Montane Forest
Hierarchy Level: Macrogroup
Type Concept: This macrogroup encompasses mesic conifer forests and woodlands of the lower montane zone of the central Rocky Mountains and interior Pacific Northwest, including the eastern Cascades. Abies grandis, Larix occidentalis, Pseudotsuga menziesii, Thuja plicata, or Tsuga heterophylla are the major dominants. Abies lasiocarpa, Picea engelmannii, Picea engelmannii x glauca hybrids, Picea glauca, Pinus contorta, and Pinus monticola are major associates. Pinus ponderosa may be present but only on the warmest and driest sites. Deciduous hardwood species occur, but typically are not dominant; they include Populus tremuloides and Betula papyrifera. This macrogroup is found in the Rocky Mountains of western Montana west through northern Idaho into northeastern Washington and southern and central British Columbia, and south into the northwestern Blue Mountains of Oregon. Although in a continental climate, these forests are influenced by incursions of mild, wet, Pacific maritime air masses. Snow occurs throughout the macrogroup, but can be modified by warmer Pacific air masses even in the winter, or in the southern range, melted by rain during warm winter storms. Elevations range from 100 to 2195 m (300-7200 feet). In the Cascades, this macrogroup occurs on the upper east slopes in Washington, south of Lake Chelan and south to Mount Hood in Oregon. Occurrences are generally found on all slopes and aspects but grow best on sites with high soil moisture, such as valley bottoms, on benches, well-drained slopes, toeslopes and moist ravines. Sites supporting these forests are typically warmer and moister than the prevailing local climate. However, these are moist, non-flooded or upland sites that are not saturated year-long. At the periphery of its distribution, this macrogroup is confined to moist canyons and cooler, moister aspects. These mesic and productive forests tend to have long fire-return intervals, ranging from 150 to over 500 years for stand-replacing fires, and with moderate-severity fire intervals of 50-100 years. Gap dynamics are important in older stands. Disturbance regimes are not well-documented for the montane white spruce forests, but likely include periodic windthrow as well as fire spreading from adjacent, drier forests and woodlands. Larix occidentalis woodlands are maintained post-establishment by frequent, low-severity surface fires.
Diagnostic Characteristics: These productive and diverse forests dominated by Tsuga heterophylla and/or Thuja plicata in most cases are found in the interior of the Pacific Northwest, in areas under a continental climate but influenced somewhat by incursions of mild, wet, Pacific maritime air masses. Floristic affinities are with the Rocky Mountains. Some of these forests may persist for centuries, having fire-return intervals over 500 years. Other trees present can include Abies lasiocarpa, Picea engelmannii x glauca hybrids, Pinus contorta, Pinus ponderosa, Populus tremuloides, and Pseudotsuga menziesii. Mesic conifer forests of the central Rocky Mountains, where Abies grandis, Pseudotsuga menziesii, or Larix occidentalis are the major dominants.
Rationale for Nominal Species or Physiognomic Features: While Tsuga heterophylla is an important tree in the coastal rainforest regions of North America, its occurrence and dominance of forests in the interior Pacific Northwest is accompanied by floristic affinities with the Rocky Mountains, as represented by Larix occidentalis. The "Douglas-fir - grand fir" zone is well-described in the literature, and Abies grandis is a good name choice. Alternative species for the name could include Thuja plicata or Picea glauca.
Classification Comments: Information on this macrogroup needs to be better integrated across the northwestern U.S., British Columbia and Alberta. The biogeographic line between this macrogroup and Vancouverian Coastal Rainforest Macrogroup (M024) needs to be more clearly determined, as there is a convergence of Rocky Mountain and east-side Cascadian floristics in the East Cascades and north into British Columbia.

Central Rocky Mountain Mesic Grand Fir - Douglas-fir Forest Group (G211) in this macrogroup should be considered for merging with East Cascades Mesic Grand Fir - Douglas-fir Forest Group (G212) in M024; they share a number of floristic similarities, along with some differences. But perhaps those differences would be better handled as alliance-level distinctions. This needs review.

Tsuga heterophylla is a major tree species in the Pacific Northwest, and it is an important species in M024. This macrogroup contains western hemlock and western red-cedar associations that are confined to the interior regions of the Northwest. Certainly, there are some floristic similarities between the Northern Rockies types and those found west of the Cascades. However, there's a distinct "Rocky Mountain" set of species, i.e., Anemone piperi, Aralia nudicaulis, Coptis occidentalis, found in the Rocky Mountains. Further information needs to be included here for interior western hemlock and western red-cedar forests of British Columbia.
Similar NVC Types:
M024 Vancouverian Coastal Rainforest, note: shares some of the dominant tree species (especially the grand fir-Douglas-fir forests of the east Cascades in G212); but associated shrub and herb composition is somewhat different.
M501 Central Rocky Mountain Dry Lower Montane-Foothill Forest, note:
Physiognomy and Structure: Generally, these are productive forests, ranging from closed-canopy to more open "savanna-like" woodlands. Composed of [usually] tall, long-lived, needle-leaved evergreen trees, sometimes composed of just one tree species, but more often are of mixed composition. Deciduous hardwoods intermingle in some occurrences; deciduous conifers are dominant in some areas. Deciduous tall and short shrubs, and perennial graminoids, forbs or ferns often form shrub and herbaceous layers, respectively. Often there is high cover of mosses. Some occurrences may lack the shrub layer. Some of these forests are the most diverse of any Rocky Mountain forest, sometimes approaching or equaling the within-stand diversity of some eastern North American forests, but the diversity resides in the shrub and herb taxa, not the trees.
Floristics: In the grand fir - Douglas-fir zone, Abies grandis is dominant and Pseudotsuga menziesii commonly shares the canopy. Abies lasiocarpa, Larix occidentalis, Picea engelmannii, Pinus contorta, and Pinus monticola are major associates. On most mesic sites, intermediate to older age stands may support some Thuja plicata and Tsuga heterophylla in the overstory. In other locations, Tsuga heterophylla and Thuja plicata are the dominants, while Pseudotsuga menziesii and Abies grandis commonly share the canopy, and Pinus monticola, Pinus contorta, Abies lasiocarpa, and Larix occidentalis are major associates. Picea engelmannii and Abies lasiocarpa may be present but only on the coldest sites, and Pinus ponderosa may be present but only on the warmest and driest sites or mid-seral, post-fire sites. In central British Columbia, Tsuga heterophylla and/or Thuja plicata are the dominants and are generally associated with some Picea glauca x engelmannii, Abies lasiocarpa, or Pseudotsuga menziesii. Deciduous hardwood species occur, but typically are not dominant; they include Populus tremuloides and Betula papyrifera.

Common shrubs include Acer glabrum, Amelanchier alnifolia, Cornus nuttallii, Mahonia nervosa, Menziesia ferruginea, Paxistima myrsinites, Rosa gymnocarpa, Rubus parviflorus, Spiraea betulifolia, Symphoricarpos albus, Symphoricarpos hesperius, Taxus brevifolia, and Vaccinium membranaceum. Oplopanax horridus is common in the understory in depressional areas with high water tables. Composition of the herbaceous layer reflects local climate and degree of canopy closure; it is typically highly diverse in all but closed-canopy conditions. Aralia nudicaulis, Clintonia uniflora, Linnaea borealis, Tiarella trifoliata, Viola orbiculata, Cornus canadensis, and Xerophyllum tenax are common forbs in these forests. Other forbs include Actaea rubra, Adenocaulon bicolor, Anemone piperi, Arnica latifolia, Coptis occidentalis, Galium triflorum, Goodyera oblongifolia, Orthilia secunda, Prosartes hookeri (= Disporum hookeri), Streptopus amplexifolius, Thalictrum occidentale, and Trillium ovatum. In the eastern Cascades, Acer circinatum, Achlys triphylla, Anemone deltoidea, Chrysolepis chrysophylla, and Vancouveria hexandra are more common. Graminoids usually form a very minor component and typically include Bromus vulgaris and minor amounts of Carex deweyana, Carex geyeri, Elymus glaucus, Festuca subulata, and Oryzopsis asperifolia. Ferns and fern allies also form an important component of the understory in many occurrences and commonly include Athyrium filix-femina, Botrychium spp., Dryopteris filix-mas, Dryopteris expansa (= Dryopteris assimilis), Equisetum spp., and Gymnocarpium dryopteris. Under closed-canopy conditions, a dense moss layer can form on the forest floor.

This macrogroup also includes woodlands or "savannas" of the deciduous conifer Larix occidentalis. Important low-growing shrubs include Arctostaphylos uva-ursi, Spiraea betulifolia, and Vaccinium cespitosum; taller shrubs can include Acer glabrum, Ceanothus velutinus, Physocarpus malvaceus, Rubus parviflorus, Shepherdia canadensis, or Vaccinium membranaceum. Herbaceous species include Calamagrostis rubescens, Clintonia uniflora, Linnaea borealis, or Xerophyllum tenax.
Dynamics: These mesic and productive forests tend to have long fire return-intervals, ranging from 150 to over 500 years for stand-replacing fires, and with moderate-severity fire intervals of 50-100 years. Gap dynamics are important in older stands. Larix occidentalis woodlands are maintained post-establishment by frequent, low-severity surface fires.

Abies grandis forests include many sites dominated by Pseudotsuga menziesii and Pinus ponderosa which were formerly maintained by wildfire, and may now be dominated by Abies grandis (a fire-sensitive, shade-tolerant species) due to fire exclusion (Lillybridge et al. 1995, Chappell et al. 1997). Pre-European settlement fire regimes of grand fir - Douglas-fir forests were typically of frequent, low-intensity surface fires, maintaining relatively open stands of a mix of fire-resistant species. With the advent of effective fire suppression, longer fire-return intervals are now the rule, and mixed-stature stands with Abies grandis in various size classes now create ladder fuels making these forests more susceptible to high-intensity, stand-replacing fires (Cooper et al. 1987, Lillybridge et al. 1995).

Larix occidentalis is a long-lived species (in excess of 700 years in the northern Rocky Mountains), and thus stands of western larch are themselves persistent. However, the life of Larix-dominated stands probably rarely exceeds 250 years due to various mortality sources and the in-growth of shade-tolerant species, especially on mesic sites. Occurrences of Larix occidentalis stands are generated by stand-replacing fire, the fire-return interval for which is speculated to be approximately 80 to 200 years (Cooper et al. 1987), but are maintained by a higher frequency, surface-fire regime. Fire suppression has led to invasion of the more shade-tolerant tree species Abies grandis, Abies lasiocarpa, Picea engelmannii, or Tsuga spp. and loss of much of the single-story canopy woodlands. Larix occidentalis communities occur in settings where low-intensity, high-frequency fires create open larch woodlands. These sites may be maintained in a seral status for hundreds of years since Larix occidentalis is a long-lived species and the understory is often dominated by Pseudotsuga, which will grow into the upper canopy. The potential dominants, typically Abies lasiocarpa, Picea engelmannii, and/or Abies grandis or rarely Tsuga heterophylla or Thuja plicata, establish and grow on these sites, presenting the distinct probability, given the fire-return intervals for this type, that the "climax" (long-term stable) condition is never attained. It has been noted in northern Idaho that, following disturbance (particularly logging) in some mesic-site occurrences, Larix occidentalis does not necessarily replace itself, the first tree-dominated successional stages being dominated by Pseudotsuga menziesii, Pinus contorta, or less frequently by more shade-tolerant species (Cooper et al. 1987); this response is a consequence of the episodic nature of favorable cone crop years in Larix occidentalis.

The western red-cedar - western hemlock forests are very productive forests which have been priority stands for timber production. Typically, stand-replacement fire-return intervals are 150-500 years in the Cascades, or 150-500 years in the Northern Rockies, with moderate-severity fire-return intervals of 50-100 years. Thuja and Tsuga are capable of remaining dominant within these forests due to their longevity and Thuja's ability to regenerate vegetatively. In the absence of disturbance, both species continue to regenerate under shaded conditions. Under closed-canopy conditions, both species favor vegetative reproduction over sexual reproduction, thus intermediate and young trees are found under these conditions.
Environmental Description: These forests occur in areas of continental climate that are influenced somewhat by incursions of mild, wet, Pacific maritime air masses. Snow occurs throughout the macrogroup, but can be modified by warmer Pacific air masses even in the winter, or in the southern range, melted by rain during warm winter storms. Elevations range from as low as 400 m in southeastern British Columbia and 100 m along the Skeena River in northwestern British Columbia to 2195 m (2000-7200 feet). In the Cascades, it occurs on the upper east slopes in Washington, south of Lake Chelan and south to Mount Hood in Oregon. Elevations in the Cascades range from 610 to 1220 m (2000-4000 feet) in a very restricted range occupying less than 5% of the forested landscape in the East Cascades. Occurrences generally are found on all slopes and aspects but grow best on sites with high soil moisture, such as valley bottoms, on benches, well-drained slopes, toeslopes and moist ravines. However, these are moist, non-flooded or upland sites that are not saturated yearlong. At the periphery of its distribution, this macrogroup is confined to moist canyons and cooler, moister aspects. This macrogroup differs from those found west of the Cascades in having lower overall precipitation, warmer summer and colder winter temperatures, and more frequent fire (Goward and Spribille 2005).

Climate: This forest macrogroup is found in areas of continental temperate climate that are influenced to varying degrees by incursions of mild, wet, Pacific maritime air masses. Snow occurs throughout the macrogroup, but can be modified by warmer Pacific air masses even in the winter, or in the southern range, melted by rain during warm winter storms. In the eastern Cascades, these forests are associated with a submesic climate regime with annual precipitation ranging from 100 to 200 cm (40-80 inches) and maximum winter snowpacks that typically melt off in spring at lower elevations. This macrogroup also includes montane forests along rivers and slopes, and in mesic "coves" which were historically protected from wildfires. Further east in the Central Rockies, annual precipitation tends to be lower, averaging around 75 cm. Cooper et al. (1987) report that the interior hemlock-cedar forests require at least 20 cm of precipitation during the warm season.

Soil/substrate/hydrology: Parent materials are non-calcareous materials, predominately sedimentary rock and argillite. Intermittent shallow A horizons overlying a dominant B horizon indicate that volcanic ash and loess deposits have significant contribution to soil development, resulting in higher fertility and moisture-holding capacity required for supporting the dominant species. These forests occur on gravelly loams and silts with good aeration and drainage and a neutral to slightly acidic pH.
Geographic Range: This forest and woodland macrogroup occurs in the interior lower montane regions of the Pacific Northwest, east of the Cascade Range south along the eastern Cascades from Lake Chelan south to Mount Hood in Oregon; from interior British Columbia south to eastern Washington, eastern Oregon, northern Idaho and western Montana east to the Continental Divide (DellaSala et al. 2011). In British Columbia, it occurs in the lee of the Coast Mountains in the northwest, and extensively in the mountain valleys of the southeast.
Nations: CA, US
States/Provinces: BC, ID, MT, OR, WA
US Forest Service Ecoregions (2007)
Domain Name:
Division Name:
Province Name: Southern Rocky Mountain Steppe - Open Woodland - Coniferous Forest - Alpine Meadow Province
Province Code: M331    Occurrence Status: Predicted or probable
Section Name: Yellowstone Highlands Section
Section Code: M331A     Occurrence Status: Predicted or probable
Omernik Ecoregions:
Plot Analysis Summary:
Confidence Level: Moderate
Confidence Level Comments:
Grank: GNR
Greasons:
Concept Lineage:
Predecessors:
Obsolete Names:
Obsolete Parents:
Synonomy: > Picea glauca series (Hoffman and Alexander 1987)
> Cedar-hemlock-pine forest (Thuja-Tsuga-Pinus) (Küchler 1964)
>< Grand Fir: 213 (Eyre 1980) [Grand fir stands are an important component of this group.]
> Grand fir-Douglas fir forest (Abies-Pseudotsuga) (Küchler 1964)
>< Western Hemlock: 224 (Eyre 1980) [Moist western slopes of the northern Rocky Mountains, in northern ID, northwest MT, and northeast WA.]
> Western Larch: 212 (Eyre 1980)
>< Western Redcedar - Western Hemlock: 227 (Eyre 1980) [NW MT, N ID]
>< Western Redcedar: 228 (Eyre 1980)
>< Western White Pine: 215 (Eyre 1980)
Concept Author(s): A.W. Küchler (1964)
Author of Description: M.S. Reid, K.A. Schulz, D. Meidinger, and D. Faber-Langendoen
Acknowledgements:
Version Date: 09Jun2015
References:
  • Achuff, P. L., and H. A. Dudynsky. 1984a. Chapter III. Vegetation. Pages 43-131 in: P. L. Achuff, W. D. Holland, G. M. Coen, and K. Van Tighem, editors. Ecological land classification of Kootenay National Park, British Columbia. Volume I: Integrated resource description. Alberta Institute of Pedology Publication No. M-84-10.
  • Achuff, P. L., and I. G. W. Corns. 1982. Chapter III. Vegetation. Pages 71-156 in: W. D. Holland and G. M. Coen, editors. Ecological (biophysical) land classification of Banff and Jasper national parks. Volume II: Soil and vegetation resources. Alberta Institute of Pedology. Publication No. SS-82-44.
  • Achuff, P. L., R. L. McNeil, M. L. Coleman, C. Wallis and C. Wershler. 2002. Ecological land classification of Waterton Lakes National Park, Alberta. Volume I: Integrated resource description. Parks Canada, Waterton Lakes National Park, Alberta. 226 pp.
  • Agee, J. K. 1993. Fire ecology of Pacific Northwest forests. Island Press, Washington, DC. 493 pp.
  • Chappell, C., R. Crawford, J. Kagan, and P. J. Doran. 1997. A vegetation, land use, and habitat classification system for the terrestrial and aquatic ecosystems of Oregon and Washington. Unpublished report prepared for Wildlife habitat and species associations within Oregon and Washington landscapes: Building a common understanding for management. Prepared by Washington and Oregon Natural Heritage Programs, Olympia, WA, and Portland, OR. 177 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]
  • Daubenmire, R. F., and J. B. Daubenmire. 1968. Forest vegetation of eastern Washington and northern Idaho. Washington State University Agricultural Experiment Station Technical Bulletin No. 60. 104 pp.
  • DellaSala, D. A., P. Alaback, L. Craighead, T. Goward, P. Paquet, and T. Spribille. 2011. Temperate and boreal rainforests of inland northwestern North America. Pages 82-110 in: D. A. DellaSala. Temperate and Boreal Rainforests of the World: Ecology and Conservation. Island Press, Washington, DC.
  • 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, S. Gawler, M. Hall, C. Josse, G. Kittel, S. Menard, C. Nordman, M. Pyne, M. Reid, L. Sneddon, K. Schulz, J. Teague, M. Russo, K. Snow, and P. Comer, editors. 2010-2019a. Divisions, Macrogroups and Groups for the Revised U.S. National Vegetation Classification. NatureServe, Arlington, VA. plus appendices. [in preparation]
  • Goward, T., and T. Spribille. 2005. Lichenological evidence for the recognition of inland rain forests in western North America. Journal of Biogeography 32:1209-1219.
  • Hessburg, P. F., B. G. Smith, R. B. Salter, R. D. Ottmar, and E. Alvarado. 2000. Recent changes (1930s-1990s) in spatial patterns of interior northwest forests, USA. Forest Ecology and Management 136(1-3):53-83.
  • Hessburg, P. F., B. G. Smith, S. C. Kreiter, C. A. Miller, R. B. Salter, C. H. McNicoll, and W. J. Hann. 1999. Historical and current forest and range landscapes in the interior Columbia River Basin and portions of the Klamath and Great Basins. Part 1: Linking vegetation patterns and landscape vulnerability to potential insect and pathogen disturbances. General Technical Report TNW-GTR-458. USDA Forest Service, Pacific Northwest Research Station, Portland, OR. 357 pp.
  • Hoffman, G. R., and R. R. Alexander. 1987. Forest vegetation of the Black Hills National Forest of South Dakota and Wyoming: A habitat type classification. Research Paper RM-276. USDA Forest Service, Rocky Mountain Forest and Range Experiment Station, Fort Collins, CO. 48 pp.
  • Johnson, C. G., and R. R. Clausnitzer. 1992. Plant associations of the Blue and Ochoco mountains. R6-ERW-TP-036-92. USDA Forest Service, Pacific Northwest Region, Wallowa-Whitman National Forest. 163 pp. plus appendices.
  • Johnson, C. G., Jr., and S. A. Simon. 1987. Plant associations of the Wallowa-Snake Province Wallowa-Whitman National Forest. Technical Paper R6-ECOL-TP-255A-86. USDA Forest Service, Pacific Northwest Region, Wallowa-Whitman National Forest. 399 pp. plus appendices.
  • Küchler, A. W. 1964. Potential natural vegetation of the conterminous United States. American Geographic Society Special Publication 36. New York, NY. 116 pp.
  • Leavell, D. 2000. Vegetation and process of the Kootenai National Forest. Ph.D. dissertation, University of Montana, Missoula. 508 pp.
  • Lillybridge, T. R., B. L. Kovalchik, C. K. Williams, and B. G. Smith. 1995. Field guide for forested plant associations of the Wenatchee National Forest. General Technical Report PNW-GTR-359. USDA Forest Service, Pacific Northwest Research Station, Portland, OR. 335 pp.
  • Pfister, R. D., B. L. Kovalchik, S. F. Arno, and R. C. Presby. 1977. Forest habitat types of Montana. General Technical Report INT-34. USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, UT. 174 pp.
  • Steele, R., R. D. Pfister, R. A. Ryker, and J. A. Kittams. 1981. Forest habitat types of central Idaho. General Technical Report INT-114. USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, UT. 138 pp.
  • Topik, C. 1989. Plant associations and management guide for the Abies grandis zone Gifford Pinchot National Forest. R6-ECOL-TP-006-88. USDA Forest Service, Pacific Northwest Region, Portland, OR. 110 pp.
  • Topik, C., N. M. Halverson, and T. High. 1988. Plant associations and management guide of the ponderosa pine, Douglas-fir, and grand fir zone, Mt. Hood National Forest. R6-ECOL-TP-004-88. USDA Forest Service, Pacific Northwest Region, Portland, OR. 136 pp.
  • Williams, C. K., B. F. Kelly, B. G. Smith, and T. R. Lillybridge. 1995. Forest plant associations of the Colville National Forest. General Technical Report PNW-GTR-360. USDA Forest Service, Pacific Northwest Region, Portland, OR. 140 pp.