Montana Field Guide

Forests within this group are dominated by Engelmann Spruce and Subalpine Fir, either in mixed stands or individually. They occur frequently on both sides of the Continental Divide in the upper montane and subalpine zones. This group occurs at the drier end of the Spruce-fir forest type and site characteristics and the understory vegetation should reflect that in relation to G218 Mesic Spruce-Fir. Other conifers are often present in these stands, typical species include Lodgepole Pine, Douglas-fir or Whitebark Pine. The forest understory may be composed of low shrubs, graminoids and/or forbs. Composition varies widely by geography, site characteristics and association. In some stands the understory will be depauperate and mosses may be prevalent.

Dry to mesic spruce-fir dominated forests occur as low as 3,000 feet west of the Continental Divide, and up to 9,500 feet east of the Continental Divide, particularly in southwestern Montana. Some occurrences are found in locations with cold-air drainage or ponding, or where snowpacks lingers late into the summer, such as north-facing slopes and high-elevation ravines. They can extend down in elevation below the subalpine zone in places where cold-air ponding occurs, especially on north and east aspects. Spruce-fir forests are found on gentle to very steep mountain slopes, high-elevation ridge tops and upper slopes, plateau-like surfaces, basins, alluvial terraces, well-drained benches, and inactive stream terraces. Soils are derived from a variety of parent materials, and are usually rocky or gravelly with good aeration and drainage.

The drier Spruce-fir forests of this group are especially common on steep slopes at upper elevations throughout the eastern Rocky Mountains, whereas the more mesic stands of G218 form substantial cover west of the Continental Divide in the Flathead, Lolo, Bitterroot and Kootenai river drainages.

This Group is equivalent to the Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland Ecological System.

Subalpine Fir (Abies lasiocarpa), Engelmann Spruce (Picea engelmannii) Dominated; Xeric Conifer Forest and Woodlands; Upper Montane and Subalpine Zones; Moderate to Dense Canopies; Moderate to Long Fire Return Intervals, Mixed Severity or Stand Replacing Fires.

In Montana, this Group occurs frequently on both sides of the Continental Divide in the upper montane and subalpine zones. It extends east to the Bears Paw Mountains where it occurs in very limited amounts, the Highwoods Mtns, the Snowy Mtns, and the Pryor and Bighorn Mtns.

In MT, G219 occurs within these Level III Ecoregions: 15 (Northern Rockies), 16 (Idaho Batholith), 17 (Middle Rockies) and 41 (Canadian Rockies).

In Montana, G219 occurs within these Major Land Resource Areas: 43A-Northern Rocky Mountains, 43B - Central Rocky Mountains, 44A - Northern Rocky Mountain Valleys, and 46 - Northern and Central Rocky Mountain Foothills.

Large Patch-Matrix

This group occurs at relatively low to high elevations west of the Continental Divide and mid to high elevations east of the Divide throughout the mountains and island ranges of north-central and west-central Montana. These forests are found on gentle to very steep mountain slopes, high-elevation ridge tops and upper slopes, plateau-like surfaces, basins, alluvial terraces, well-drained benches, and inactive stream terraces. Occurrences are also found 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 can extend down in elevation below the subalpine zone in places where cold-air ponding occurs, especially on north and east aspects. Dry to mesic spruce-fir dominated forests occur as low as 3,000 feet west of the Continental Divide, and up to 9,500 feet east of the Continental Divide, particularly in southwestern Montana. Soils are derived from a variety of parent materials, and are usually rocky or gravelly with good aeration and drainage.

Engelmann spruce and subalpine fir forests comprise a substantial part of subalpine forests in Montana, including the island ranges of north-central and west-central Montana and southern Montana. In the driest mountain ranges east of the Continental Divide (such as the Bull Mountains, Snowy Mountains, Pryor Mountains, and Dillon area), these forests are restricted to cool exposures, usually on north and east facing aspects. The drier Spruce-fir forests of this group are especially common on steep slopes at upper elevations throughout the eastern Rocky Mountains, whereas the more mesic stands of G218 form substantial cover west of the Continental Divide in the Flathead, Lolo, Bitterroot and Kootenai river drainages.

These forests are dominated by Engelmann Spruce and Subalpine Fir, either in mixed stands or individually. Other conifers are often present and typically may include Lodgepole Pine, Douglas-fir or Whitebark Pine, with Lodgepole Pine more typical of earlier successional stands, Douglas-fir at lower elevations and Whitebark Pine at higher elevations. This group occurs at the drier end of the Spruce-fir forest type and site characteristics and the understory vegetation should reflect that in relation to G218 Mesic Spruce-Fir.

The forest understory may be composed of low shrubs, graminoids and/or forbs. Composition varies widely by geography, site characteristics and Association. Common shrubs in these drier Spruce-fir forests include Grouse Whortleberry (Vaccinium scoparium), Dwarf Huckleberry (Vaccinium cespitosum), Common Juniper (Juniperus communis), Ninebark (Physocarpus malvaceus), Canada Buffaloberry (Shepherdia canadensis), Spiraea (Spiraea betulifolia), Creeping Oregon-grape (Berberis repens) and Snowberry (Symphoricarpos albus). Common forbs include Arnica (Arnica cordifolia, Arnica latifolia), Clematis (C. columbiana, C. occidentalis), Fragrant Bedstraw (Galium triflorum) and Twinflower (Linnaea borealis). Graminoids are generally few with Pinegrass (Calamagrostis rubescens), Geyer’s sedge (Carex geyeri), and Ross’ sedge (Carex rossii) the common components on these drier sites. Moss may be common in some depauperate understories. Non-native species are typically absent or uncommon in these communities.

In Montana, this group is represented by 15 Associations grouped into 3 Alliances within the National Vegetation Classification, though 2 Alliances only have 1 Association each. These likely represent the diversity of types within this group in Montana.

Major disturbances include occasional blowdown, insect outbreaks (30-50 years), and fire. Fire return intervals average approximately 130 years and are either mixed severity or stand replacing (U.S. Department of Agriculture 2012). Fires in this system are generally more frequent and less intense than those in G218 Mesic Spruce-Fir Forest and Woodland. 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). Following fire, spruce is more successful at establishing on mineral soils. Subalpine fir, in contrast, is better at establishing in the shade and on organic substrates. Post-fire, subalpine fir establishment may be immediate if nearby seed sources exist and seral lodgepole pine is not present. In forests undisturbed by fire or subjected to spruce budworm attacks, subalpine fir assumes greater dominance. Over a period of 500 years, subalpine fir will largely replace spruce on most of these sites.

Insects and disease can play a major role in the successional direction of these forests. Throughout Montana, subalpine fir and spruce are affected by western spruce budworm (Choristoneura occidentalis) attacks. 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, may also contribute to increases in beetle populations within a region (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).

Historically, spruce beetle outbreaks have been related to drought conditions as drought weakens spruce resistance mechanisms to beetle attack (DeRose and Long 2012; Jenkins et al. 2014). Drought has additionally been found to have lag effects on mortality for spruce, subalpine fir and lodgepole pine, with drought having the most substantial and long-lasting effects on subalpine fir, and the smallest impact on lodgepole pine (Bigler et al. 2007). 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).

In the absence of natural fire, periodic prescribed burns can be used to maintain this system. Maintaining historic fire return intervals 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 overmature individuals that are vulnerable to attack. Moderate to severe fires change the age structure of a stand thereby decreasing susceptibility to future beetle 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 reduce potential for future beetle outbreak (Jenkins et al. 2014).

Post-fire restoration strategies will be largely dependent on the severity of the fire. Because lightly burned areas recover quite quickly from fire, reseeding is usually not necessary if an intact, native understory was present before the fire. Early successional stages may be dominated by fireweed, arnica, aster, pearly everlasting (Anaphalis margaritacea), mountain hollyhock (Iliamina rivularis) and other forbs, and small amounts of forest graminoids. Both dominant species 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 colonizes sites with both 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 (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 on 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 will be greatest when spring and early summer conditions are relatively moist and late summer drought is not intense (Alexander and Shepperd 1990).

K.A. Schulz 2013

S. Mincemoyer, L. Vance, T. Luna, M. Hart

12/4/2024