Montana Field Guide

This ecological system, composed of highly variable montane conifer forests, is found throughout Montana. It is associated with a submesic climate regime with annual precipitation ranging from 250 to 1,000 millimeters (10-39 inches), with most precipitation occurring during winter, and April through June. Winter snowpacks typically melt off in early spring at lower elevations. Elevations range from valley bottoms to 1,676 meters (5,500 feet) in northwestern Montana and up to 2,286 meters (7,500 feet) on warm aspects in southern Montana. In northwestern and west-central Montana, this ecosystem forms a forest belt on warm, dry to slightly moist sites. It generally occurs on gravelly soils with good aeration and drainage and a neutral to slightly acidic pH. In the western part of the state, it is seen mostly on well drained mountain slopes and valleys from lower treeline to up to 1,676 meters (5,500 feet). Immediately east of the Continental Divide, in north-central Montana, it occurs at montane elevations. Douglas-fir (Pseudotsuga menziesii) is the dominant conifer both as a seral and climax species. West of the Continental Divide, occurrences can be dominated by any combination of Douglas-fir and long-lived, seral western larch (Larix occidentalis), grand fir (Abies grandis), ponderosa pine (Pinus ponderosa) and lodgepole pine (Pinus contorta). Aspen (Populus tremuloides) and western white pine (Pinus monticola) have a minor status, with western white pine only in extreme western Montana. East of the Continental Divide, larch is absent and lodgepole pine is the co-dominant. Engelmann spruce (Picea engelmannii), white spruce, (Picea glauca)or their hybrid, become increasingly common towards the eastern edge of the Douglas-fir forest belt.

montane elevations, mixed coniferous forests, Abies grandis, ustic soils

Douglas-fir is the dominant conifer; west of the Continental Divide, occurrences are dominated by a mix of Douglas-fir and long-lived, seral western and other species, including lodgepole pine and western white pine. East of the Continental Divide, larch is absent and lodgepole pine is the co-dominant. Engelmann spruce or white spruce, or their hybrid, becomes increasingly common towards the eastern edge of the Douglas-fir forest belt. Grand fir may occur in this forest type, but is typically confined to relatively warm and moister sites in northwestern and west-central Montana.

Undergrowth is dominated by graminoids, such as bluebunch wheatgrass (Pseudoroegneria spicata), Columbia brome(Bromus vulgaris),blue wildrye (Elymus glaucus), pinegrass (Calamagrostis rubescens), Geyer’s sedge (Carex geyeri), and Ross’ sedge (Carex rossii). Common forbs that occur in the understory include American pathfinder (Adenocaulon bicolor), heartleaf arnica (Arnica cordifolia), queen’s cup beadlily (Clintonia uniflora), twinflower (Linnaea borealis), and beargrass (Xerophyllum tenax). The shrub understory contains a variety of shrubs, such as Rocky mountain maple (Acer glabrum), kinnikinnick (Arctostaphylos uva-ursi), common juniper (Juniperus communis), oceanspray (Holodiscus discolor), mallow ninebark(Physocarpus malvaceus), common snowberry (Symphoricarpos albus), birch leaf spiraea (Spiraea betulifolia), dwarf bilberry (Vaccinium caespitosum) or mountain huckleberry (Vaccinium membranaceum)on colder, more mesic sites. In the western part of the state, the Douglas-fir/mountain huckleberry association is the most common type found in the Lolo, Bitteroot and Flathead Mountain ranges on relatively cold sites up to 2,073 meters (6,800 feet) (Pfister et al, 1977).

Douglas-fir and all associated seral species in this system regenerate well following fire, and all, with the exception of lodgepole pine, tolerate repeated low intensity surface fires due to thick bark and deep roots. In the absence of disturbance, the longevity and fire resistance of western larch and Douglas-fir lead to their co-dominance in many areas of western Montana. Douglas-fir and grand fir continue to regenerate under shaded conditions, and these too may become dominant in undisturbed stands. In eastern Montana, lodgepole pine is most often co-dominant with Douglas fir. Presettlement fire regimes may have been characterized by frequent, low-intensity ground fires that maintained relatively open stands of a mix of fire-resistant species. Under present conditions, the fire regime is mixed severity and more variable with stand-replacing fires more common, resulting in increasing forest homogeneity. Fire return intervals vary between approximately 40 and 80 years, with intervals being shortest in stands in which Douglas-fir and western larch are co-dominant, and longest where Douglas-fir and lodgepole pine are co-dominant (U.S. Department of Agriculture, 2012). In Glacier National Park, this forest type historically experienced fire return intervals of 36 years at dry sites, and 46 years at relatively mesic sites, with stand replacing fires occurring at intervals of approximately 140-180 years (Barrett et al., 1991). 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. Both western larch and lodgepole pine are aggressive colonizers after major disturbances. These are very productive forests which have been priorities for timber production.

The species in this system vary in their susceptibility to biotic vectors. Western larch is generally resistant to damage from pathogens and insects (Scher, 2002). However, in western larch stands in the Bitterroot Mountains of western Montana where fire has been suppressed and regeneration is limited, dwarf mistletoe infects trees and impacts stand persistence (McCune, 1983). In contrast to western larch, grand fir, Douglas-fir, lodgepole pine, and ponderosa pine are susceptible to a variety of insects and pathogens. Both grand fir and Douglas-fir are affected by western spruce budworm (Choristoneura occidentalis) and Douglas-fir tussock moth (Orgyia pseudotsugata), while the western balsam bark beetle (Dryocoetes confuses) and fir engraver beetles (Scolytus ventralis) further affect grand fir (Howard and Aleksoff, 2000; Steinberg, 2002). The Douglas-fir bark beetle (Dendroctonus pseudotsugae) causes abundant damage to Douglas-fir in this system and fire-affected stands tend to be more vulnerable to attack (Negron et al., 1999; Hood and Bentz, 2007; Six and Skov, 2009). Both lodgepole pine and ponderosa pine are highly susceptible to mountain pine beetles. Elevated temperature and increasing drought severity combine to favor beetle population growth and weaken lodgepole and ponderosa pine defense mechanisms, increasing susceptibility to beetle attack (Raffa et al., 2008).

In the absence of natural fire, periodic prescribed burns can be used to maintain this system. Low-severity burning decreases fuel loading, probability of stand-replacing fires, and increases available nutrients in the soil (Arno et al., 1995). Prescribed fire is particularly important when management goals include the maintenance of western larch and/or ponderosa pine within this system (Habeck, 1992; Scher, 2002). Burning exposes a mineral seedbed which is preferred for germination by all species in this system. The timing of prescribed burning in this system is important and fall burning following dry summers is typically most effective. Removing seedlings and duff from the bases of western larch and ponderosa pine may be necessary to prevent fire damage to roots and the spread of surface fires to tree crowns (Scher, 2002; Kolb et al., 2007). The varying vulnerability of species in this system to windthrow should be considered when thinning is applied to reduce fire risk. Western larch has deep roots and moderate to high windthrow resistance, ponderosa pine and douglas fir are moderately susceptible, and lodgepole pine is highly susceptible to windthrow due to its shallow root system (Scher, 2002; Anderson, 2003).

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. Dominant species such as Douglas-fir, lodgepole pine and western larch regenerate well following fire and mineral soil seedbeds that result from burning favor germination by these species. However, prolonged drought conditions and high soil temperatures on bare mineral soils can impede natural regeneration and may require supplemental planting post-disturbance (Scher, 2002).

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 and ridgetops. Steep slopes may require reseeding with native grasses to prevent soil erosion. In some cases, severely burned sites will require replanting with conifer seedlings. Generally, larger container volume of nursery stock results in higher outplanting success than bareroot nursery stock, especially where spring and early summer precipitation patterns are unpredictable, or where 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 and to meet management objectives.

Prescribed fire may be an additionally valuable restoration strategy in stands with high levels of dwarf mistletoe if all infected individuals are eliminated (Hawksworth et al., 2002). High severity burning controls dwarf mistletoe by eliminating infected trees and promoting regeneration of uninfected individuals (Alexander and Hawksworth, 1976). However, when utilizing prescribed burning as a restoration strategy, the effects of fire on local insect populations should be considered as vulnerability to attack may increase post fire (e.g. Hood and Bentz, 2007).