Cedar - Hemlock Forest
Global Name:
Central Rocky Mountain-Interior Cedar - Hemlock Forest
Global Rank:
G4G5
State Rank:
S4
(see reason below)
External Links
State Rank Reason
These habitats are restricted in range and extent and some decrease in extent has likely occurred. Primary threats are limited to increases in severe wildfires and climate change, especially increased temeperatures and drought.
General Description
This National Vegetation Classification Group is composed of mesic, upland forests dominated by western red cedar (Thuja plicata) and/or western hemlock (Tsuga heterophylla). These are our most mesic forested sites outside of some riparian and wetland sites. Western red cedar and western hemlock dominated riparian and wetland sites are classified as part of either G505 Montane Forested Wetland or G506 Montane - Subalpine Riparian Forest. This group occurs almost entirely west of the Continental Divide with a small amount east of the divide in Glacier National Park. It is most common in the very northwest part of the state but it occurs as far south and east as the Swan Valley, along drainages just west of Missoula and along some drainages in the Bitterroot Mountains. Occurrences are found on all slopes and aspects but grow best on sites with high soil moisture, such as toeslopes and bottomlands. At the periphery of its distribution, sites are confined to moist stream bottoms and northerly aspects. Sites occur from 2,000-5,000 feet in elevation with average annual precipitation of 25 inches or more. Western red cedar occurs more extensively than western hemlock in the state. Isolated stands of western hemlock occur as far south and east as the Swan Valley, but it is most commonly found in the vicinity of Libby and Thompson Falls, west to the Idaho border.
This group includes the wettest plant associations of the Rocky Mountain Mesic Montane Mixed Conifer Forest Ecological System.
Diagnostic Characteristics
Western Redcedar (Thuja plicata), Western hemlock (Tsuga heterophylla); Mesic Conifer Forests; Montane Zone; Dense Canopies; Long Fire Return Intervals.
Similar Systems
Range
This group occurs almost entirely west of the Continental Divide with a small amount east of the divide in Glacier National Park. It is most common in the very northwest part of the state, but it occurs as far south and east as the Swan Valley, along drainages just west of Missoula and along some drainages in the Bitterroot Mountains.
In MT, G217 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), and 41 (Canadian Rockies).
In Montana, G217 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains, and 44A - Northern Rocky Mountain Valleys.
Density and Distribution
Based on 2025 land cover layer. Grid on map is based on USGS 7.5 minute quadrangle map boundaries.
Mapped Distribution by County
Flathead, Glacier, Lake, Lewis and Clark, Lincoln, Mineral, Missoula, Pondera, Powell, Sanders
Based on 2025 land cover layer.
Spatial Pattern
Large Patch
Environment
Cedar-Hemlock forests are found in cool, mesic sites, particularly in areas which receive more maritime influenced air masses. Occurrences may be found on all slopes and aspects but grow best on sites with high soil moisture, such as toeslopes and bottomlands. At the periphery of its distribution, this group is confined to moist bottomlands where soils may be vernally saturated. Sites occur from 2,000-5,000 feet and have an average annual precipitation of 25 inches or more.
Vegetation
These forests are dominated by western hemlock and/or western red cedar and are typically densely forested. Grand fir is a common component of some sites. Other tree present may include Douglas-fir (Pseudotsuga menziesii), western white pine (Pinus monticola), lodgepole pine (Pinus contorta), western larch (Larix occidentalis) and paper birch (Betula papyrifera). Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) may be present on the coldest sites. Both western red cedar and western hemlock are shade-tolerant conifers that occur in similar mesic environments; however, western red cedar extends onto slightly drier sites and occurs further south and east in Montana. The forest floor is typically shaded or receives dappled sunlight except in forest openings. Thus, the understory is composed of moisture-loving, shade tolerant species. In densely forested sites, understory vegetation may be very sparse with the forest floor being almost entirely covered by duff and litter.
Common shrubs in these habitats include mountain boxwood (Paxistima myrsinites), thinleaf alder (Alnus incana), Rocky Mountain maple (Acer glabrum), birch leaf spiraea (Spiraea betulifolia), common snowberry (Symphoricarpos albus), bunchberry dogwood (Cornus canadensis), thimbleberry (Rubus parviflorus), rusty leaf menziesia (Menziesia ferruginea), and mountain huckleberry (Vaccinium membranaceum). Pacific yew (Taxus brevifolia) can occur as a small tree on some sites in extreme western Montana and as a common shrub in occurrences in the Swan Valley.
The herbaceous layer may be depauperate in closed stands to diverse and abundant in more open stands. Queen’s cup beadlily (Clintonia uniflora), western foamflower (Tiarella trifoliata), pioneer violet (Viola glabella), Canadia violet (Viola canadensis), roundleaf violet (Viola orbiculata) and beargrass (Xerophyllum tenax) are most the most common forbs in these forests. Other forbs include baneberry (Actaea rubra), pathfinder (Adenocaulon bicolor), false sarsaparilla (Aralia nudicaulis), arnica (Arnica cordifolia), fragrant bedstraw (Galium triflorum), rattlesnake plantain orchid (Goodyera oblongifolia), twinflower (Linnaea borealis), wintergreen (Pyrola asarifolia) and western trillium (Trillium ovatum). In extreme northwestern Montana, wild ginger (Asarum caudatum) is a component on mesic sites with a mild temperature regime.
Ferns and fern allies also form an important component of the understory particularly in the more mesic sites. Species include American ladyfern (Athryium filix-femina), western swordfern (Polystichum munitum), male fern (Dryopteris filix-mas), oak fern (Gymnocarpium dryopteris) and horsetails (Equisetum species). Bracken fern (Pteridium aquilinum) can occur in relatively high coverage (20% or greater) in mature stands, however it can form dense (up to 100%) cover in early seral stands, retarding forest regeneration. Graminoids may be absent or form a very minor component, and may include forest brome (Bromus vulgaris), fringed brome (Bromus ciliatus), blue wildrye (Elymus glaucus), and rough leaf ricegrass (Oryzopsis asperifolia).
In Montana, this group is represented by 2 Alliances and 9 Associations. These likely represent the diversity of vegetation types within this group. 2 additional Alliances and 4 Associations of western redcedar-western hemlock dominated vegetation types are found in the riparian and wetland habitat groups of G505 and G506.
National Vegetation Classification
Download the complete NVC hierarchy for Montana
TT2 B02 Temperate-Boreal Forest and Woodland
TT2.b S92 Cool Temperate Forest and Woodland
TT2.b3 F112 Temperate Continental Conifer Forest and Woodland
TT2.b3.Nb D337 Rocky Mountain Foothills and Montane Forest and Woodland
TT2.b3.Nb.2 M500 Central Rocky Mountain-Interior Moist Montane Forest
TT2.b3.Nb.2.b G217 Central Rocky Mountain-Interior Cedar - Hemlock Forest
A3612 Tsuga heterophylla - Thuja plicata Cool-Mesic Central Rocky Mountain Forest Alliance
CEGL005930 Thuja plicata / Clintonia uniflora - Xerophyllum tenax Forest
A3613 Tsuga heterophylla - Thuja plicata Warm-Mesic Central Rocky Mountain Forest Alliance
CEGL000471 Thuja plicata / Aralia nudicaulis Forest
CEGL000472 Thuja plicata / Asarum caudatum Forest
CEGL000474 Thuja plicata / Clintonia uniflora Forest
CEGL000488 Tsuga heterophylla / Aralia nudicaulis Forest
CEGL000490 Tsuga heterophylla / Asarum caudatum Forest
CEGL000491 Tsuga heterophylla / Athyrium filix-femina Forest
CEGL000493 Tsuga heterophylla / Clintonia uniflora Forest
CEGL000494 Tsuga heterophylla / Gymnocarpium dryopteris Forest
*Disclaimer: Some Alliances and Associations are considered provisional. Some require further documentation to verify their occurrence in the state
and some may be modified or deleted in future revisions after collection of additional data and information.
Dynamic Processes
Western red cedar and western hemlock are highly shade-tolerant and long-lived. In the absence of fire, both species can reproduce vegetatively (Pfister et al 1977; Minore 1990). Closed-canopy conditions generally favor vegetative reproduction, and this strategy is common in old-growth stands (Tesky 1992b). Western red cedar can reproduce vegetatively by branch layering, rooting of fallen branches, and by branch development on fallen trees (Parker 1979). Trees of this species have reached 2,000 years in northern Idaho (Parker 1986); trees in northwestern Montana have attained ages of at least 500 years. Disturbed sites can and occasionally do return directly to dominance by the climax tree species, but other stands are often a mixture of the climax species with other seral tree species.
Typically, stand-replacement fire-return intervals are 150-500 years, with moderate-severity fire intervals ranging from 50 to 100 years (Arno 1979). Western red cedar, western hemlock and grand fir are characterized by having thin bark, shallow root systems, low dense branching habits, and heavy lichen growth, making these species susceptible to fire damage (Fischer and Bradley 1987). All but the largest trees are typically killed in fires of moderate intensity. With vigorous fire suppression, longer fire-return intervals are now common, and multi-layered stands of conifers provide fuel "ladders," making these forests more susceptible to high-intensity, stand-replacing fires.
A variety of biotic disturbance agents may impact these habitats. Defoliation of western hemlock by the western hemlock looper (Lambdina fiscellaria lugubrosa) causes mortality in mature and old growth stands, with previous looper outbreaks increasing risk of future defoliation (Tesky 1992a; McCloskey et al. 2009). Warmer and drier growing season conditions may increase stand susceptibility to looper attack, and outbreaks are expected to be increasingly frequent and severe in the future (McCloskey et al. 2009). Western blackheaded budworm (Acleris gloverana) and hemlock sawfly (Neodiprion tsugae) also cause western hemlock defoliation and may cause severe damage to even-aged juvenile stands (Nealis and Turnquist 2010). The gall midge (Mayetiola thujae) infects western redcedar, causing damage to their seeds. Fungi attack western redcedar in the form of root and trunk rots. In the eastern portion of western redcedar’s range in northwestern Montana, Poria asiatioa and Phellinus weiri are most damaging, and are increasingly common in old-growth stands. Roots injured by fire may be more vulnerable to fungal infection (Tesky 1992b).
Windthrow can occur during unusually intense wind storms as both species typically possess shallow, spreading root systems. Trees are particularly susceptible to uprooting in areas with shallow soils or a high water table (Tesky, 1992a). Individual trees that have been damaged by root diseases are especially prone to windthrow. Frost damage also affects western hemlock in northwestern Montana (Tesky 1992a).
Management
In the absence of natural fire, periodic prescribed burns can be used to maintain these habitats. Fire is generally infrequent in this group due to moist conditions, however, intense summer drought may lead to severe burning as this group is highly productive with heavy fuel loading (Fischer and Bradley 1987). Prescribed burning will therefore be most effective following summer drought when fuels are driest. Burning may be a valuable strategy to control dwarf mistletoe outbreaks (Tesky 1992a), promote nutrient cycling and species diversity, and create mineral seedbeds that favor natural regeneration of the species in this group (Fischer and Bradley 1987). However, fire may also have consequences when root damage occurs, leading to chronic stress, growth loss, and increased susceptibility to fungal infection (Tesky 1992b).
When thinning is utilized for silvicultural or fire risk reduction purposes, increased risk of windthrow should be considered. Both dominant species in this group are vulnerable to blowdown, in part due to their shallow rooting systems. Maintaining windfirm borders when thinning is necessary to avoid widespread blowdown (Tesky 1992a). Thinning may likewise increase susceptibility to insect defoliation, particularly for stands dominated by western hemlock, and vulnerability to insect attack should be considered prior to thinning (Nealis and Turnquist 2010).
Invasive weeds have not been a major problem in these habitats. However, orange and meadow hawkweeds may be problematic at some sites especially following disturbance.
Restoration Considerations
Post-fire restoration strategies will depend largely on the severity of the fire. Early successional stages may be dominated by fireweed (Chamerion angustifolium) and other forbs, graminoids and understory shrubs. If seed trees are present, both dominant species are good seed producers and are capable of regenerating well following fire. However, of all conifers in the northern Rocky Mountains, western red cedar and western hemlock seedlings have the slowest growth rates and are highly susceptible to drought. Both species are capable of regenerating well on bare mineral soils if adequate moisture is present during the first two years of growth. Drought and high soil temperatures damage seedlings growing in full sunlight, with western red cedar being particularly sensitive (Tesky 1992a; Tesky 1992b).
Intense fires that occur during summer months cause considerable damage to native perennial grasses, forbs and shrubs, and may completely destroy existing seed banks, especially on steep facing slopes. In some cases, severely burned sites will require replanting with seedlings. In the Northern Rocky Mountain region, containerized nursery stock is out-planted in the spring. Generally, larger container volume of nursery stock results in higher outplanting success than bareroot nursery stock, especially if spring and early summer precipitation patterns are unpredictable, and exposed mineral soil temperatures are high during the first year of establishment. Generally, 6-8 cubic inch container stock types are used on milder sites with good site preparation, and 10, 15 or 20 cubic inch container stock is used on the hotter, drier aspects or sites. Conifer stocking rates must be developed on a site-by-site basis to meet management objectives.
Species Associated with this Community
- How Lists Were Created and Suggested Uses and Limitations
Animal Species Associations
Please note that while all vertebrate species have been systematically associated with vegetation communities, only a handful of invertebrate species have been associated with vegetation communities and invertebrates lists for each vegetation community should be regarded as incomplete. Animal species associations with natural vegetation communities that they regularly breed or overwinter in or migrate through were made by:
- Using personal observations and reviewing literature that summarize the breeding, overwintering, or migratory habitat requirements of each species (Dobkin 1992, Hart et al. 1998, Hutto and Young 1999, Maxell 2000, Werner et al. 2004, Adams 2003, and Foresman 2012);
- Evaluating structural characteristics and distribution of each vegetation community relative to the species' range and habitat requirements;
- Examining the observation records for each species in the state-wide point observation database associated with each vegetation community;
- Calculating the percentage of observations associated with each vegetation community relative to the percent of Montana covered by each vegetation community to get a measure of "observations versus availability of habitat".
Species that breed in Montana were only evaluated for breeding habitat use. Species that only overwinter in Montana were only evaluated for overwintering habitat use. Species that only migrate through Montana were only evaluated for migratory habitat use. In general, species are listed as associated with a vegetation community if it contains structural characteristics known to be used by the species. However, species are not listed as associated with a vegetation community if we found no support in the literature for the species’ use of structural characteristics of the community even if point observations were associated with it. If you have any questions or comments on animal species associations with vegetation communities, please contact the Montana Natural Heritage Program's Senior Zoologist.
Plant Species Associations
Please note that while diagnostic, dominant, or codominant vascular plant species for a vegetation community have been systematically assigned to those communities and vascular plant Species of Concern were systematically evaluated for their associations with vegetation communities, the majority of Montana’s vascular plant species have not been evaluated for their associations with vegetation communities and no attempt has been made to associate non-vascular plants, fungi, or lichens with vegetation communities. Plant species associations with natural vegetation communities were made in a manner similar to that described above for animals, but with review of Lesica et al. (2022) and specimen collection data from the Consortium of Pacific Northwest Herbaria. If you have any questions or comments on plant species associations with vegetation communities, please contact the Montana Natural Heritage Program's Program Botanist.
Suggested Uses and Limitations
Species associations with vegetation communities should be used to generate potential lists of species that may occupy broader landscapes for the purposes of landscape-level planning. These potential lists of species should not be used in place of documented occurrences of species or predicted habitat suitability models (this information can be requested at: https://mtnhp.mt.gov/requests/), or systematic surveys for species and onsite evaluations of habitat by trained biologists. Users of this information should be aware that the land cover data used to generate species associations is based on satellite imagery from 2016 and was only intended to be used at broader landscape scales. Land cover mapping accuracy is particularly problematic when the vegetation communities occur as small patches or where the land cover types have been altered over the past decade. Thus, particular caution should be used when using the associations in assessments of smaller areas (e.g., evaluations of public land survey sections). Finally, although a species may be associated with a particular vegetation community within its known geographic range, portions of that vegetation community may occur outside of the species' known geographic range.
Literature Cited
- Adams, R.A. 2003. Bats of the Rocky Mountain West; natural history, ecology, and conservation. Boulder, CO: University Press of Colorado. 289 p.
- Consortium of Pacific Northwest Herbaria. https://www.pnwherbaria.org/ Last accessed May 30, 2025.
- Dobkin, D. S. 1992. Neotropical migrant land birds in the Northern Rockies and Great Plains. USDA Forest Service, Northern Region. Publication No. R1-93-34. Missoula, MT.
- Foresman, K.R. 2012. Mammals of Montana. Second edition. Mountain Press Publishing, Missoula, Montana. 429 pp.
- Hart, M.M., W.A. Williams, P.C. Thornton, K.P. McLaughlin, C.M. Tobalske, B.A. Maxell, D.P. Hendricks, C.R. Peterson, and R.L. Redmond. 1998. Montana atlas of terrestrial vertebrates. Montana Cooperative Wildlife Research Unit, University of Montana, Missoula, MT. 1302 p.
- Hutto, R.L. and J.S. Young. 1999. Habitat relationships of landbirds in the Northern Region, USDA Forest Service, Rocky Mountain Research Station RMRS-GTR-32. 72 p.
- Lesica P., M. Lavin, and P.F. Stickney. 2022. Manual of vascular plants, 2nd Edition. Brit Press. 779 p.
- Maxell, B.A. 2000. Management of Montana's amphibians: a review of factors that may present a risk to population viability and accounts on the identification, distribution, taxonomy, habitat use, natural history, and the status and conservation of individual species. Report to U.S. Forest Service Region 1. Missoula, MT: Wildlife Biology Program, University of Montana. 161 p.
- Werner, J.K., B.A. Maxell, P. Hendricks, and D. Flath. 2004. Amphibians and reptiles of Montana. Missoula, MT: Mountain Press Publishing Company. 262 p.
- Species of Concern Associated with this Community
Vascular Plants
Mammals
Birds
Reptiles
Amphibians
- Diagnostic, Dominant, or Codominant Plant Species for this Community
Vascular Plants
- Other Native Species Commonly Associated with this Community
Vascular Plants
Original Concept Authors
M.S. Reid
Montana Version Authors
S. Mincemoyer
Version Date
12/4/2024
References
- Literature Cited AboveLegend:
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- Web Search Engines for Articles on "Central Rocky Mountain-Interior Cedar - Hemlock Forest"
