Montana Field Guide

This 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.

Western Redcedar (Thuja plicata), Western hemlock (Tsuga heterophylla); Mesic Conifer Forests; Montane Zone; Dense Canopies; Long Fire Return Intervals.

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.

Large Patch

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.

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.

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).

In the absence of natural fire, periodic prescribed burns can be used to maintain these habitats. Fire is generally infrequent in this system due to moist conditions, however, intense summer drought may lead to severe burning as this system 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 system (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 system 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.

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.

M.S. Reid

S. Mincemoyer

12/4/2024