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.
Forest and Woodland, ustic and acidic soils, long persistence, Picea engelmannii, Abies lasiocarpa
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).
Major disturbances include occasional blowdown, insect outbreaks (30-50 years), mixed-severity fire, and stand-replacing fire (150-500 years). The more summer-dry climatic areas also have occasional high-severity fires. Insects and diseases can play a major role in the successional direction of these forests. Throughout Montana, subalpine fir and spruce are affected by spruce budworm attacks, and large stands of these subalpine forests can be killed following several years of drought or unusually mild winters.
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. 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.
Post-fire restoration strategies will depend largely 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, pearlyeverylasting (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 mostly colonizes sites with some organic matter.
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. 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.
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