Abies concolor

White 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 concolor (Gord. & Glend.) Lindl. ex Hildebr.

The currently accepted scientific name of white fir is Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (Pinaceae). Two varieties are recognized based on differences in morphological and chemical characteristics. Abies concolor var. concolor Rocky Mountain white fir Abies concolor var. lowiana (Gord.) Lemm. California white fir. California white fir naturally hybridizes with grand fir (Abies grandis) in a belt extending from north-west California, across Oregon, and into central Idaho. Under controlled conditions, white fir has successfully been crossed with other firs. Many populations of Abies concolor have long been isolated geographically and genetically. A geographic cluster of populations in Utah has shorter leaves and slightly different terpene patterns than a similar cluster of populations in Colorado and northern New Mexico (J.W. Wright et al. 1971; E.Zavarin et al. 1975). Another large geographic cluster, in southern New Mexico and Arizona, seems to be strongly linked chemically to Colorado populations (E.Zavarin et al. 1975) and morphologically to southern California populations (J.L. Hamrick and W.J. Libby 1972). Northern California populations with pubescent twigs and notched leaves are unique, as are the Baja California populations with very short, thick leaves and about 18 adaxial stomatal rows. In Los Padres National Forest of coastal southern California and in the Cascades of northern California, apparent introgression with A . lowiana (E.Zavarin et al. 1975; J.L. Hamrick and W.J. Libby 1972) has occurred. Many consider A . lowiana (given specific rank in this treatment) as a synonym of A . concolor or place it in an infraspecific rank under that species.

Ecology: Abies concolor is a native coniferous tree species abundant in many forests of western North America. It is a widespread species, occuring in a wide variety of habitats at elevations ranging from 900 to 3,400 m. The Utah Forest Dynamics Plot (UFDP) is at 3,000 m, near the high end of its range. Abies concolor is uncommon in the UFDP, found mostly on open slopes. In the Yosemite Forest Dynamics Plot (YFDP), Abies concolor is by far the most abundant stem, but is matched in basal area by Pinus lambertiana. After the California Rim fire in 2013, Abies concolor in the YFDP experienced high levels of mortality, especially in the smallest diameter classes.

Identification

Trees to 40m; trunk to 0.9m diam.; crown spirelike. Bark gray, thin, smooth, with age thickening (to 18cm) and breaking into deep longitudinal furrows, often revealing yellowish inner periderm, appearing "corky." Branches diverging from trunk at right angles, the lower often spreading and drooping in age; twigs mostly opposite, glabrous or with yellowish pubescence. Buds exposed, either yellowish and nearly conic (when large) or brownish and nearly globose (when small), resinous, apex rounded to pointed; basal scales equilaterally triangular, glabrous, not resinous, margins entire, apex sharp-pointed. Leaves 1.5--6cm ´ 2--3mm, mostly 2-ranked, flexible, proximal portion ±straight; cross section flat, sometimes slightly grooved adaxially; odor pungent, frequently camphorlike; abaxial surface glaucous, with 4--7 stomatal rows on each side of midrib; adaxial surface grayish green, glaucous, with (7--)12(--18) stomatal rows at midleaf, these usually fewer toward leaf apex; apex usually rounded, sometimes acute or notched; resin canals small, near margins and abaxial epidermal layer. Pollen cones at pollination ± red, purple, or ± green. Seed cones cylindric, 7--12 ´ 3--4.5cm, olive-green, sessile, apex round; scales ca. 2.5--3 ´ 3--3.5cm, pubescent; bracts included. Seeds 8--12 × 3mm, body tan; wing about twice as long as body, tan with rosy tinge; cotyledons 5--7.

Threats

Fire effects: White fir seedlings, saplings and poles are thin-barked and resin blistered and are highly susceptible to fire damage and kill. Additionally, young trees have low-growing branches that can easily ignite from burning undergrowth, providing a fuel ladder into the crown. Consequently, young white fir are usually killed by even low-intensity, surface fires. As trees mature and bark thickens, and some self-pruning of lower branches occurs, they become more resistant to fire. However, the tendency to retain some low branches, the moderately shallow roots, and heavy lichen growth on the branches of white fir make it only moderately fire resistant. In larger trees, mortality results from crown scorch, girdled stems from cambial heating, or damage to moderately shallow roots from soil heating.

Pests and pathogens: Two parasitic plants, white fir mistletoe (Phoradendron bolleanum subsp. pauciflorum), a true mistletoe, and white fir dwarf mistletoe (Arceuthobium abietinum subsp. concoloris), cause major damage to white fir. One-third of the white fir stands in California are severely infested by dwarf mistletoe and the parasite is present in other forest types that contain white fir. Heavily infected trees suffer significant growth losses and are prone to attack by Cytospora abietis, a fungus that kills branches and further reduces growth.

Reproduction

Flowering and Fruiting -White fir is monoecious. The reddish male strobili (cones) are generally less than 1.6 cm long and are densely grouped on the underside of 1-year-old twigs about midcrown. Female cones are borne erect on 1-year-old branches, usually in the uppermost crown although both male and female cones are occasionally found on the same branch.

Seed Production and Dissemination -White fir trees can begin bearing cones when only 40 years old and continue beyond 300 years. Because cones are borne almost exclusively in the uppermost part of the crown, any top damage caused by insects, diseases, or mechanical agents (for example, wind and snow) directly reduces cone production. Seeds are released as cones disintegrate on the tree. The white fir seed has a relatively short, broad wing for its weight and falls more rapidly than a pine or spruce seed. Because most dissemination is by wind, the distance of seed spread is more limited than that of many associated species.

Seedling Development - White fir seeds germinate in the spring immediately following snowmelt or, where snowpacks are deep, in, on, and under the snow. In general, white fir becomes established best in partial shade, but once established grows best in full sunlight. It is less tolerant of shade than associated true firs (except red fir), is slightly more tolerant than Douglas-fir, and is much more tolerant than pines or oaks. Because white fir can survive and grow beneath heavy brush cover and eventually overtop the brush and dominate the site, many pure stands exist in otherwise mixed conifer areas.

Vegetative Reproduction -White fir shows no tendency to reproduce by sprouting or layering, but cuttings can be rooted with or without hormones. The relative ease with which cuttings from juvenile material can be rooted provides an opportunity to produce genetically selected planting stock at relatively low cost.

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.