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Montana Field Guides

Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland

Provisional State Rank: S3

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General Description

Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) make up a substantial part of the montane and lower subalpine forests of the Montana Rocky Mountains and mountain island ranges of north-central and west-central Montana. Spruce is usually associated with fir and occurs as either a climax co-dominant or as a persistent, long-lived seral species in most upper elevation fir habitat types. Dry to mesic spruce-dominated forests range from 884-1,585 meters (2,900-5,200 feet) west of the Continental Divide, and 1585-2,073 meters (5,200-6,800 feet) east of the Continental Divide in the northern and central portions of the state. This system can be found at elevations up to 2,896 meters (9,500 feet) in southwestern Montana. 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. Tree canopy characteristics are relatively uniform. In northern Montana, Engelmann spruce hybridizes with its boreal counterpart, white spruce (Picea glauca). Douglas-fir (Pseudotsuga menziesii), lodgepole pine (Pinus contorta), and western larch (Larix occidentalis) (west of the Continental Divide) are seral but often present in these forests. The understory is comprised of a mixture of shrubs, forbs and graminoids tolerant of warmer and drier soil conditions than those found on the more mesic to wet spruce-fir system. The drier occurrences of this system are especially common on steep slopes at upper elevations throughout the eastern Rocky Mountains, whereas the more mesic occurrences form substantial cover west of the Continental Divide in the Flathead, Lolo, Bitteroot and Kootenai river drainages.


Diagnostic Characteristics

Forest and Woodland, ustic and acidic soils, long persistence, Picea engelmannii, Abies lasiocarpa


Similar Systems

Range
Engelmann spruce and subalpine fir forests comprise a substantial part of the subalpine forests of the Montana Rocky Mountains, 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 habitats within this system are especially common on steep slopes at upper elevations throughout the Montana Rocky Mountains. The more mesic habitats within this system are very common west of the Continental Divide in the Flathead, Lolo, Bitteroot, and Kootenai river drainages.

Ecological System Distribution
Approximately 12,387 square kilometers are classified as Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland in the 2016 Montana Land Cover layers.  Grid on map is based on USGS 7.5 minute quadrangle map boundaries.



Montana Counties of Occurrence
Beaverhead, Big Horn, Broadwater, Carbon, Cascade, Deer Lodge, Fergus, Flathead, Gallatin, Glacier, Golden Valley, Granite, Jefferson, Judith Basin, Lake, Lewis and Clark, Lincoln, Madison, Meagher, Mineral, Missoula, Park, Pondera, Powell, Ravalli, Sanders, Silver Bow, Stillwater, Sweet Grass, Teton, Wheatland

Spatial Pattern
Matrix

Environment
This system forms a belt at relatively low to high elevations west of the Continental Divide and mid to high elevations east of the Divide throughout the Montana Rocky Mountains and island ranges of north-central and west-central Montana. Soils are derived from a variety of parent materials, and are usually rocky or gravelly with good aeration and drainage, but are usually acidic. Occurrences are typically 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-dominated forests range from 884 to 1,585 meters (2,900-5,200 feet) west of the Continental Divide, and 1585 to 2,073 meters (5,200-6,800 feet) east of the Continental Divide in the northern and central portions of the state. They can be found at elevations up to 2,896 meters (9,500 feet) in southwestern Montana.

Vegetation

Tree canopy characteristics are relatively uniform, with Engelmann spruce and subalpine fir dominating, either mixed or alone. In northern Montana, Engelmann spruce hybridizes with its boreal counterpart, white spruce. Spruce is more tolerant of extreme environmental conditions than subalpine fir, and is usually more dominant in the drier and wettest habitats within this system. Douglas-fir, lodgepole pine, and western larch (west of the Continental Divide) are seral but often present in these forests. Mountain hemlock (Tsuga mertensiana) occurs as small to large patches within the matrix of this mesic spruce-fir system, but only in the coldest and wettest environments of northwestern Montana.

The understory of these forests often supports diverse stands of ericaceous shrubs, such as rusty leaf menziesia (Menziesia ferruginea), dwarf huckleberry (Vaccinium caespitosum), mountain huckleberry (Vaccinium membranaceum), dwarf bilberry (Vaccinium myrtillus) and mountain heath (Phyllodoce species). Grouse whortleberry (Vaccinium scoparium) is common on mesic sites. Cascade azalea (Rhododendron albiflorum) occurs in association with mountain hemlock and subalpine fir in some mesic occurrences in northwestern Montana.Other common shrubs include Rocky Mountain maple (Acer glabrum), serviceberry (Amelanchier alnifolia),Utah honeysuckle (Lonicera utahensis), ninebark (Physocarpus malvaceus),currant (Ribesspecies), thimbleberry (Rubus parviflorus), birch leaf spiraea (Spiraea betulifolia) and common snowberry (Symphoricarpos albus). On the driest sites in the Bighorn Mountains,big sagebrush (Artemisia tridentata) may be present.Smooth woodrush (Luzula glabrata var. hitchcockii)is the most common graminoid on mesic sites at higher elevations. Pinegrass (Calamagrostis rubescens), Geyer’s sedge (Carex geyeri), and Ross’ sedge (Carex rossi) are common on drier sites. Forb diversity varies depending on moisture conditions. Species includebaneberry (Actaea rubra), arnica (Arnica species),Columbia clematis (Clematis occidentalis), queen’s cup beadlily (Clintonia uniflora), bunchberry dogwood (Cornus canadensis), fragrant bedstraw (Galium triflorum), twinflower (Linnaea borealis), clasp-leaf twisted stalk (Streptopus amplexifolius), western meadow rue (Thalictrum occidentale) and beargrass (Xerophyllum tenax).


National Vegetation Classification Switch to Full NVC View

Adapted from US National Vegetation Classification

A3614 Abies lasiocarpa - Picea engelmannii Rocky Mountain Moist Forest Alliance
CEGL000311 Abies lasiocarpa / Picea engelmannii - Galium triflorum Forest
CEGL000315 Abies lasiocarpa / Picea engelmannii - Linnaea borealis Forest
CEGL000319 Abies lasiocarpa / Picea engelmannii - Menziesia ferruginea Forest
CEGL000337 Abies lasiocarpa / Picea engelmannii - Symphoricarpos albus Forest
CEGL000338 Abies lasiocarpa / Picea engelmannii - Thalictrum occidentale Forest
CEGL000340 Abies lasiocarpa / Picea engelmannii - Vaccinium caespitosum Forest
CEGL000341 Abies lasiocarpa / Picea engelmannii - Vaccinium membranaceum Rocky Mountain Forest
CEGL000346 Abies lasiocarpa - Xerophyllum tenax Forest
CEGL000406 Picea (engelmannii x glauca, engelmannii) - Clintonia uniflora Forest
CEGL002174 Picea engelmannii - Galium triflorum Forest
CEGL002689 Picea engelmannii - Linnaea borealis Forest
A3615 Abies lasiocarpa - Picea engelmannii Southern Rocky Mountain Moist Forest Alliance
A3640 Abies lasiocarpa - Picea engelmannii - Pinus flexilis Dry-Mesic Rocky Mountain Krummholz Alliance
CEGL000985 Abies lasiocarpa / Picea engelmannii Krummholz
A3643 Abies lasiocarpa - Picea engelmannii Rocky Mountain Dry-Mesic Forest Alliance
CEGL000298 Abies lasiocarpa / Picea engelmannii - Arnica cordifolia Forest
CEGL000299 Abies lasiocarpa / Picea engelmannii - Arnica latifolia Forest
CEGL000301 Abies lasiocarpa / Picea engelmannii - Calamagrostis rubescens Forest
CEGL000304 Abies lasiocarpa / Picea engelmannii - Carex geyeri Forest
CEGL000344 Abies lasiocarpa / Picea engelmannii - Vaccinium scoparium Forest
CEGL000368 Picea engelmannii - Hypnum revolutum Forest
CEGL000381 Picea engelmannii - Vaccinium scoparium Forest
CEGL000919 Abies lasiocarpa / Picea engelmannii - Juniperus communis Woodland
CEGL005925 Picea engelmannii - Juniperus communis Forest
A3644 Abies lasiocarpa - Picea engelmannii Dry-Mesic Scree & Talus Woodland Alliance
CEGL000925 Abies lasiocarpa Scree Woodland
A3948 Valeriana sitchensis - Luzula glabrata var. hitchcockii - Xerophyllum tenax Subalpine Mesic Meadow Alliance
CEGL005856 Chamerion angustifolium Rocky Mountain Meadow
*Disclaimer: Alliances and Associations have not yet been finalized in the National Vegetation Classification (NVC) standard.  A complete version of the NVC for Montana can be found here.

Dynamic Processes

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 the Rocky Mountain Subalpine Mesic Spruce-Fir Forest and Woodland system. 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 within most habitats of this system.

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 in this system, 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).


Management

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).


Restoration Considerations

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).


Species Associated with this Ecological System
  • Details on Creation and Suggested Uses and Limitations
    How Associations Were Made
    We associated the use and habitat quality (common or occasional) of each of the 82 ecological systems mapped in Montana for vertebrate animal species that regularly breed, overwinter, or migrate through the state by:
    1. 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, Foresman 2012, Adams 2003, and Werner et al. 2004);
    2. Evaluating structural characteristics and distribution of each ecological system relative to the species' range and habitat requirements;
    3. Examining the observation records for each species in the state-wide point observation database associated with each ecological system;
    4. Calculating the percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system 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, and species that only migrate through Montana were only evaluated for migratory habitat use.  In general, species were listed as associated with an ecological system if structural characteristics of used habitat documented in the literature were present in the ecological system or large numbers of point observations were associated with the ecological system.  However, species were not listed as associated with an ecological system if there was no support in the literature for use of structural characteristics in an ecological system, even if point observations were associated with that system.  Common versus occasional association with an ecological system was assigned based on the degree to which the structural characteristics of an ecological system matched the preferred structural habitat characteristics for each species as represented in scientific literature.  The percentage of observations associated with each ecological system relative to the percent of Montana covered by each ecological system was also used to guide assignment of common versus occasional association.  If you have any questions or comments on species associations with ecological systems, please contact the Montana Natural Heritage Program's Senior Zoologist.

    Suggested Uses and Limitations
    Species associations with ecological systems 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 (this information can be requested at: http://mtnhp.org/requests/default.asp) or systematic surveys for species and evaluations of habitat at a local site level by trained biologists.  Users of this information should be aware that the land cover data used to generate species associations is based on imagery from the late 1990s and early 2000s and was only intended to be used at broader landscape scales.  Land cover mapping accuracy is particularly problematic when the systems 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 ecological system within its known geographic range, portions of that ecological system 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.
    • 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.
    • 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.

Original Concept Authors
R. Crawford and M.S. Reid, mod. C. Chappell and G. Kittel (NatureServe ed. date 25Jan2007)

Montana Version Authors
L.K. Vance, T. Luna, M.Hart

Version Date
1/1/2017

References
  • Classification and Map Identifiers

    Cowardin Wetland Classification: Not applicable

    NatureServe Identifiers:
    Element Global ID 28663
    System Code CES306.828, Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland

    National Land Cover Dataset:
    42: Evergreen Forest

    ReGAP:
    4242: Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland


  • Literature Cited AboveLegend:   View Online Publication
    • Alexander, R.R. and W.D. Shepperd. 1990. Picea engelmannii Parry ex Engelm. Silvics of North America 1:187-203.
    • Bebi, P., D. Kulakowski, and T.T. Veblen. 2003. Interactions between fire and spruce beetles in a subalpine Rocky Mountain forest landscape. Ecology 84(2):362-371.
    • Bigler, C., D.G. Gavin, C. Gunning, and T.T. Veblen. 2007. Drought induces lagged tree mortality in a subalpine forest in the Rocky Mountains. Oikos 116(12):1983-1994.
    • DeRose, R.J. and J.N. Long. 2012. Factors influencing the spatial and temporal dynamics of Engelmann spruce mortality during a spruce beetle outbreak on the Markagunt Plateau, Utah. Forest Science 58(1): 1-14.
    • Jenkins, M.J., E.G. Hebertson, and A.S. Munson. 2014. Spruce beetle biology, ecology and management in the Rocky Mountains: an addendum to spruce beetle in the rockies. Forests 5(1):21-71.
    • Kulakowski, D. and T.T. Veblen. 2006. The effect of fires on susceptibility of subalpine forests to a 19th century spruce beetle outbreak in western Colorado. Canadian Journal of Forest Research 36(11):2974-2982.
    • Lindemann, J.D. and W.L. Baker. 2001. Attributes of blowdown patches from a severe wind event in the Southern Rocky Mountains, USA. Landscape Ecology 16(4):313-325.
    • U.S. Department of Agriculture, Forest Service, Missoula Fire Sciences Laboratory. 2012. Information from LANDFIRE on Fire Regimes of Rocky Mounatin Subalpine Mixed-Conifer Communities. In: Fire Effects Information System, [Online]. U.S. Department of Agr
    • Uchytil, R.J. 1991. Abies lasiocarpa. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Arno, S. F. 1980. Forest fire history in the northern Rockies. Journal of Forestry 78(8):460-465.
    • Pfister, R. D., B. L. Kovalchik, S. F. Arno, and R. C. Presby. 1977. Forest habitat types of Montana. USDA Forest Service. General Technical Report INT-34. Intermountain Forest and Range Experiment Station, Ogden, UT. 174 pp.

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Citation for data on this website:
Rocky Mountain Subalpine Dry-Mesic Spruce-Fir Forest and Woodland.  Montana Field Guide.  Retrieved on , from