Montana Field Guide

These forests are similar to Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland (4242), but occur in locations with cold-air drainage or ponding, or where snowpacks linger late into the summer, such as north-facing slopes and high-elevation ravines. They are distinguished by their occurrence on mesic to wet microsites within the matrix of the drier (and warmer) subalpine spruce-fir or lodgepole pine forests. The microsites include north-facing slopes, swales or ravines, toeslopes, cold pockets, and other locations where available soil moisture is higher or lasts longer into the growing season. This system can extend down in elevation below the subalpine zone in places where cold-air ponding occurs, especially on north and east aspects. Elevations range from 884 to 1,981 meters (2,900-6,500 feet) west of the Continental Divide, and 1,585 to 2,682 meters (5,200-8,800 feet) east of the Continental Divide. Spruce is usually associated with subalpine fir and occurs either as a climax co-dominant or as a persistent, long-lived seral species in most upper elevation subalpine fir stands. Mountain hemlock (Tsuga mertensiana) occurs as small patches within the matrix of this mesic spruce-fir system, but only in the most maritime of environments of northwestern Montana, in the coldest and wettest sites. The shrub understory contains many ericaceous species such as rusty leaf menziesia (Menziesia ferruginea), dwarf huckleberry (Vaccinium caespitosum), mountain huckleberry (Vaccinium membranaceum), bilberry (Vaccinium myrtillus), grouse whortleberry (Vaccinium scoparium), pink mountain heath (Phyllodoce empetriformis), black twinberry honeysuckle (Lonicera involucrata), gooseberry (Ribesspecies) and thimbleberry (Rubus parviflorus). The herbaceous understory contains mesic forbs, graminoids, and ferns and fern allies on the wettest sites. Moss cover is often high. Stand-replacing fires are less common in mesic spruce-fir forests than in dry-mesic forests.

Forest and woodlands, acidic and udic soils, very long disturbance intervals, long persistence (>500years), Picea engelmannii, Abies lasiocarpa

This system occurs is distinguished by its occurrence on mesic to wet microsites within the matrix of the drier (and warmer) subalpine spruce-fir or lodgepole pine forests. The microsites include north-facing slopes, swales or ravines, toeslopes, cold pockets, and other locations where available soil moisture is higher or lasts longer into the growing season. Engelmann spruce and subalpine fir mesic forests comprise a substantial part of the subalpine forests of the northwestern Montana Rocky Mountains. In Montana, these mesic to wet forests are very common west of the Continental Divide in the Flathead and Kootenai river drainages. The wetter habitat types such as subalpine fir/ devil’s club (Abies lasiocarpa/Oplopanax horridum) and Engelmann spruce/ horsetail (Picea engelmannii/Equisetum arvense) associations are found locally in the Flathead Valley and along Sheep Creek north of White Sulphur Springs.

Tree canopy characteristics are relatively uniform, with Picea and Abies dominating either mixed or alone. Engelmann spruce is more tolerant of extreme environmental conditions than subalpine firs, and is usually more dominant in the drier and wettest occurences within this system. Mountain hemlockoccurs as small to large patches within the matrix of this mesic spruce-fir system but only in the most maritime of environments of northwestern Montana, in the coldest and wettest sites.

The understory of Picea -Abies forests in northwestern Montana often supports diverse stands of ericaceous plants, such as rusty leaf menziesia, dwarf huckleberry mountain huckleberry, bilberry and mountain heath. Grouse whortleberry and Labrador tea (Ledum glandulosum) are common on mesic sites.Cascade azalea (Rhododendron albiflorum) occurs in association with mountain hemlock and subalpine fir in some occurrences in northwestern Montana.Other common shrubs include Rocky Mountain maple (Acer glabrum), serviceberry (Amelanchier alnifolia), black twinberry honeysuckle, currant (Ribes species), thimbleberry, shortfruit willow (Salix brachycarpa) and greyleaf willow (Salix glauca). In the wettest subalpine fir forests in northwestern Montana, devil’s club is a major shrub associate. These sites are usually restricted to ravine bottoms near streams and seeps where the water table remains near the surface all year. The herbaceous layer is typically diverse. Smooth woodrush (Luzula glabrata var. hitchcockii), bluejoint reedgrass (Calamagrostis canadensis), and pinegrass (Calamagrostis rubescens) are the most commonly associated graminoids. On moist sites with seeps or adjacent to running water, a lush herbaceous understory is present. Forb species includebaneberry (Actaea rubra), marsh marigold (Caltha leptosepala), queen’s cup beadlily (Clintonia uniflora), bunchberry dogwood (Cornus canadensis),starry Solomon’s seal (Maianthemum stellatum), sidebellswintergreeen (Orthothilla secunda), arrowleaf groundsel (Senecio triangularis), clasp-leaf twisted stalk (Streptopus amplexifolius), foamflower (Tiarella trifoliata), western meadow rue (Thalictrum occidentale), Sitka valerian (Valeriana sitchensis), green false hellebore (Veratrum viride), and beargrass (Xerophyllum tenax). Ferns and fern allies such ashorsetail (Equisetum species), oakfern (Gymnocarpium dryopteris) and ladyfern (Athyrium species) form dense cover, inespecially wet spruce habitats on flat sites with poor drainage. Moss cover is often high within these forests.

Major disturbances include occasional blowdown, insect outbreaks (30-50 years), and fire. Fire return intervals are longer in this system than in the drier Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland system and range between 170 to more than 300 years (U.S. Department of Agriculture, 2012). The majority of fires in this system are stand replacing, although mixed severity fires also occur (U.S. Department of Agriculture, 2012). The cool and moist environment of this system favors greater fuel loading and infrequent fires, however when dry conditions persist over long periods, these characteristics promote intense, stand-replacing fires (Reinhardt and Holsinger, 2010). Both subalpine fir and Engelmann spruce are highly susceptible to fire, in part due to their shallow roots, thin bark, and dense stand growth habits (Alexander and Shepperd, 1990; Uchytil, 1991). Mountain hemlock is also highly susceptible to fire due to its low-hanging branches, although its bark is relatively thick and may provide some protection to low-intensity burning (Tesky, 1992). Following fire, spruce is more successful at establishing on mineral soils while subalpine fir is comparatively better at establishing in the shade and on organic substrates. Both mountain hemlock and spruce are generally slow to establish after fire (Alexander and Shepperd, 1990; Tesky, 1992). In Montana, subalpine fir will often form pure stands with lesser dominance by Engelmann spruce, although Engelmann spruce often outlives subalpine fir in this system (Uchytil, 1991). Over time, in the absence of fire or in the presence of spruce budworm attacks, subalpine fir will largely replace spruce within most habitats of this system, with the exception of the wettest sites.

Insects and disease influence species composition and successional direction of this system. Throughout Montana, subalpine fir and spruce are affected by western spruce budworm (Choristoneura occidentalis) attacks. Spruce and subalpine fir in this system may be comparatively less vulnerable to spruce budworm outbreak than those in the Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland system due to higher energy reserves associated with trees on more mesic sites that increase defense potential against spruce budworm attack (Dupont et al., 1991). The spruce beetle (Dendroctonus rufipennis) also causes extensive damage to spruce in this system. Severe wind events that cause extensive blowdown are often followed by spruce beetle outbreaks as downed trees provide an abundant food supply and are favored by the beetles (Lindemann and Barker, 2001). Other disturbances that cause an abundance of downed material, including landslides and avalanches, also contribute to increases in local beetle populations (Jenkins et al., 2014). When outbreak conditions occur, or when downed material is unavailable, spruce beetles will also attack live trees, favoring large size classes and overmature individuals (Alexander and Shepperd, 1990). Beetle outbreaks have implications for watershed function, wildlife habitat, recreation, and stand species composition (Jenkins et al., 2014). Large stands of these subalpine forests can be killed following several years of drought or unusually mild winters.

Spruce broom rust (Chrysomyxa arctostaphyli) also occurs in this system causing deformation and increased vulnerability to windbreak (Alexander and Shepperd, 1990). Subalpine fir is additionally affected by western balsam bark beetle (Dryocoetes confuses), balsam wooly adelgid (Adelges piceae), and the fir engraver beetle (Scolytus ventralis). Root and wood rots also affect the dominant species in this system by weakening their defenses to insect attack and increasing vulnerability to windfall (Jenkins et al., 2014). Root decay is especially problematic for mature subalpine fir in the Northern Rockies (Uchytil, 1991).

In the absence of natural fire, periodic prescribed burns can be used to maintain this system, however, fire return intervals are generally quite long where site conditions are more mesic. Maintaining historic fire return intervals in this system may decrease stand susceptibility to spruce beetle outbreak (Bebi et al, 2003; Kulakowski and Veblen, 2006). Old stands have a greater abundance of downed material and mature individuals that are vulnerable to attack. Moderate to severe fires change the age structure of a stand thereby decreasing susceptibility to future attack (Kulakowski and Veblen, 2006).

All species in this system are vulnerable to windthrow. Mechanical thinning for silvicultural or fire risk reduction purposes should therefore consider stand blowdown as a potential result of thinning treatment. Risk of windfall increases in stands with shallow soils and poor drainage, high degree of root and wood rot, and old, dense stand structure (Alexander and Shepperd, 1990). Alternatively, thinning may be useful to promote natural regeneration and reduce abundance of overmature individuals in a stand, altering stand age structure, and thereby decreasing susceptibility to future spruce beetle outbreaks. However, logging residue may contribute to beetle population increases, and downed woody material may therefore need to be removed from the site to prevent beetle population growth. In general, increasing forest heterogeneity limits beetle spread and extent of outbreak (Jenkins et al., 2014).

The wetter habitat types characteristic of this system are usually not subjected to frequent stand-replacing fires. However, crown fires do occur when large, stand-replacing fires in adjacent drier forests travel into these habitats. The dominant species in this system are good seed producers and are capable of regenerating well following fire. Spruce is capable of regenerating well on bare mineral soils if adequate moisture is present during the first two years of growth. Subalpine fir and mountain hemlock colonize both sites with mineral soil and those with some organic matter. At the higher elevation occurrences of this system, seedling survival may be greater where duff seedbeds are present as they protect seedlings from harsh climatic conditions, whereas at lower elevations, mineral seedbeds may be more conducive to seedling establishment (Uchytil, 1991).

Large, prescribed, stand-replacement fires are not recommended in areas where spruce is in severe decline. Small-scale prescribed burning during late fall after several hard frosts can facilitate regeneration and increase stand heterogeneity in terms of age structure and species composition, thereby decreasing susceptibility to insect outbreaks (Jenkins et al., 2014). In some cases, nursery stock may be used to expedite regeneration of severely burned areas if seed rain from adjacent stands is not likely to occur, or if bare mineral soil following severe insect outbreak is limited (Jenkins et al., 2014). When supplemental planting is required, cold, moist stratification is necessary for germination of subalpine fir and spruce (Uchytil, 1991). Success of seedling establishment may be greater than in the Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland system due this system’s tendency to occur on north aspects with cool air ponding where seedling establishment is favored and droughty conditions are less likely to occur (Alexander and Shepperd, 1990).