Abies bifolia

Sub-alpine fir

Pinaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Pinaceae (pines). Genus - Abies Mill. Species - Abies bifolia A. Murray bis

Abies bifolia has been, and often still is, included in synonymy under A . lasiocarpa or A . subalpina since about 1890, and A . subalpina under A . lasiocarpa since about the 1920s. Abies bifolia is distinct from A . lasiocarpa, however, in chemical tests on wood (H.S. Fraser and E.P. Swan 1972), lack of crystals in the ray parenchyma (R.W. Kennedy et al. 1968), lack of lasiocarpenonol (J.F. Manville and A.S. Tracey 1989), and distinct terpene patterns (R.S. Hunt and E.von Rudloff 1979). Abies bifolia also tends to have slightly shorter and fewer prominently notched leaves than A . lasiocarpa. The two are clearly separated by the color of their periderm and by the shape of their basal bud scales. These firs may be more distinct than the pairs A . balsamea -- A . fraseri and A . procera -- A . magnifica. A north-south transect, however, from south central Yukon to northern Washington yielded introgressed trees possessing characteristics of both A . lasiocarpa and A . bifolia, recalling the interior spruce (Canadian Forestry Service 1983), which has characteristics of both Picea glauca and P . engelmannii.

Ecology: In the Rocky Mountains, subalpine fir is a shade-tolerant climax species favored by long fire-free intervals. Its seedlings outcompete spruces, lodgepole pine, and Douglas-fir when light intensities are less than 50 percent of full sunlight, but cannot compete with these conifers under brighter light. In Montana and Idaho and in the mountains of eastern Washington and eastern Oregon, subalpine fir often forms pure stands at climax, but it may also mix with Engelmann spruce, which, although considered to be seral to subalpine fir, outlives it and persists to climax. In the Rocky Mountains north and south of Montana and Idaho, Engelmann spruce and subalpine fir may codominate at climax. Throughout much of the Cascade Mountains subalpine fir grows as a shade-intolerant, seral species and is gradually replaced by more shade-tolerant associates such as Pacific silver fir, grand fir, and mountain hemlock. It often invades recently disturbed areas with lodgepole pine. It also pioneers harsh sites on raw geologically young surfaces such as lava flows and talus slopes and on climatically harsh sites near timberline.

Identification

Trees to 30m; trunk to 0.45m diam.; crown spirelike. Bark gray, thin, smooth, with age somewhat furrowed and scaly (toward southern end of range bark is corky [corkbark fir]). Branches diverging from trunk at right angles, stout, stiff; twigs opposite to whorled, grayish, pubescence sparse, light brown; fresh leaf scars with light brown periderm. Buds exposed, brown, globose, small, resinous, apex rounded; basal scales long, narrow, isosceles triangular to spatulate, glabrous, resinous or not resinous, margins entire to rarely crenate, apex sharp-pointed or rounded. Leaves 1.1--2.5cm × 1.25--1.5mm, spiraled and turned upward, flexible; cross section flat, grooved adaxially, sometimes only slightly so; odor camphorlike; abaxial surface with 3--5 stomatal rows on each side of midrib; adaxial surface light green to bluish green, usually glaucous, with 3--6 stomatal rows at midleaf, rows usually continuous to leaf base, usually more numerous toward leaf apex; apex slightly notched to rounded; resin canals large, ± median, away from margins and midway between abaxial and adaxial epidermal layers. Pollen cones at pollination purplish. Seed cones cylindric, 5--10 ´ 3--3.5cm, dark purple-blue to grayish purple, sessile, apex rounded; scales ca. 1.5 ´ 2.5cm, densely pubescent; bracts included. Seeds 5--7 ´ 2--3mm, body brown; wing about 1.5 times as long as body, grayish brown; cotyledons 3--6.

Threats

Fire effects: Subalpine fir bark is thin, especially on young trees, and lower limbs persist after death. Subalpine fir is very fire sensitive and generally suffers high mortality even from low intensity fires. It relies on wind-dispersed seeds which readily germinate on fire-prepared seedbeds to colonize burned areas. In subalpine habitats, scattered subalpine fir trees often escape fire because of discontinuous fuels, broken and rocky terrain, and the moist and cool environment.

Pests and pathogens: Subalpine fir is attacked by several insects. In spruce-fir forests, the most important insect pests are the western spruce budworm (Choristoneura occidentalis) and western balsam bark beetle (Dryocoetes confusus). The silver fir beetle (Pseudohylesinus sericeus) and the fir engraver (Scolytus ventralis) may at times be destructive locally. In the Cascades, the balsam woolly adelgid (Adelges piceae), introduced from Europe, is the most destructive insect pest. This insect has caused significant mortality to subalpine fir, virtually eliminating it from some stands in Oregon and southern Washington.

Other: Subalpine fir is susceptible to windthrow. Although, this tendency is generally attributed to a shallow root system, soil depth, drainage, and stand conditions influence the development of the root system. The kind and intensity of cutting and topographic exposure to wind also influence the likelihood of trees being windthrown.

Reproduction

Flowering and Fruiting - Subalpine fir flowers are monoecious. Male flowers, usually abundant, are borne in pendulous clusters from the axils of the needles on the lower branchlets. Female flowers are fewer, borne erect and singly on the uppermost branchlets of the crown. Male flowers ripen, and pollen is wind-disseminated, during late spring and early summer. Cones are indigo blue when they open in mid-August to mid-October.

Seed Production and Dissemination - Subalpine fir may begin to produce cones when trees are 1.2 to 1.5 m tall and 20 years old, but under closed-forest conditions, seed production is not significant until trees are older and taller.

Seedling Development - Under natural conditions, fir seeds lie dormant under the snow and germinate the following spring. Although germination and early survival of subalpine fir are generally best on exposed mineral soil and moist humus, the species is less exacting in its seedbed requirements than most of its common associates. Subalpine fir has been observed to germinate and survive on a wide variety of other seedbed types including the undisturbed forest floor, undecomposed duff and litter, and decaying wood. Subalpine fir also invades and establishes on severe sites such as recent bums, lava flows, talus slopes, avalanche tracks, and climatically severe regions near timberline.

Vegetative Reproduction - Subalpine fir frequently reproduces by layering where the species is a pioneer in developing forest cover on severe sites such as lava flows and talus slopes or near timberline. Under closed-forest conditions, reproduction by layering is of minor importance.

Species Distribution

Citation

USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97. Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.