White fir, balsam fir, silver fir, white balsam (Peattie 1950), Colorado white fir (Silba 1986), Rocky Mountain white fir (Little 1980), abeto del Colorado, pino real blanco [Spanish]; for var. lowiana, California white fir, Sierra white fir (Hunt 1993).
One variety, Abies concolor var. lowiana (Gordon) Lemmon 1895 (syn.: Picea lowiana Gordon 1862; Abies lowiana (Gordon) A. Murray 1863; A. concolor subsp. lowiana (Gordon) E. Murray 1983).
Abies concolor seems to be one of those unfortunate species (another is Pinus ponderosa) for which the established taxonomic nomenclature does not appear to fairly represent the genetic diversity of the taxon. Conventionally it is assigned to two groups, concolor and lowiana. Some taxonomists (e.g., Hunt (1993)) assign each of these groups to its own species; others treat lowiana as a variety or a subspecies; and others (e.g., Farjon 1998) draw no distinctions. Hunt (1993) sums up the problem when he calls A. concolor "a western catchall species for firs with green seed cones and with glaucous adaxial leaf surfaces," noting the existence of several discrete, more or less geographically isolated population complexes:
Based on this information, I have chosen to treat all of these populations within Abies concolor, noting that the existence of several varieties could probably be supported; of these, however, only var. lowiana has been described.
Trees to 60 m tall and 190 cm dbh; crown spirelike, becoming somewhat flat-topped with age. Bark gray, thin, smooth, with age thickening (to 18 cm) 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, yellow to tan and either nearly conic (when large) or brown and nearly globose (when small), resinous, apex rounded to pointed; basal scales equilaterally triangular, glabrous, resinous or not, margins entire, apex sharp-pointed. Leaves 1.5-6 cm × 2-3 mm, mostly 2-ranked, flexible, proximal portion ±straight; cross section flat, sometimes grooved adaxially; odor pungent; abaxial surface glaucous or not, with 4-8 stomatal rows on each side of midrib; adaxial surface grayish green, glaucous or not, with (5-)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, turning yellow-brown, then darker brown, sessile, apex round; scales ca. 2.5-3 × 2.8-3.8 cm, pubescent; bracts included. Seeds 8-12 × 3 mm, body tan or dull brown; wing about twice as long as body, tan or brown with rosy tinge; cotyledons 5-9. 2n=24" (Hunt 1993).
Hunt (1993) discriminates var. lowiana according to this key:
Adaxial surface at midleaf glaucous, with about (7-)12(-18) rows of stomates; leaves (2-)4-6 cm; leaf apex of lower branches usually rounded; widespread in w US but not in Sierra Nevada.
Adaxial surface at midleaf not glaucous, with about (5-)7(-9) rows of stomates; leaves 2-4(-6) cm; leaf apex of lower branches weakly notched; Sierra Nevada of California and Nevada, north coastal mountains of California.
USA: Idaho, Oregon, California, Nevada, Utah, Colorado, New Mexico, Arizona; Mexico: Baja California Norte, Sonora; at 900-3400 m in conifer forests (Hunt 1993). Occurs in both pure and mixed stands (Little 1980). See also Thompson et al. (1999). Hardy to Zone 4 (cold hardiness limit between -34.3°C and -28.9°C) (Bannister and Neuner 2001, variety not specified).
Var. lowiana is the dominant shade-tolerant species of the Sierra Nevada mixed-conifer forest, which is thought by many to be the finest conifer forest area on Earth. Accordingly, this tree grows to very large sizes, exceeded only by the red fir (A. magnifica) of Northern California and the noble fir (A. procera) of Oregon and Washington. Thanks to over a century of industrious fire suppression, A. lowiana is probably more numerous in these forests than ever before, and has itself become a significant fire hazard as it increases stem densities in the forest and, when dry, is highly flammable.
Var. lowiana boasts the Merced Lake Giant, which is near the trail at the east end of Merced Lake in Yosemite National Park, California, and had a dbh of 223 cm and was 66.1 m tall, with a stem volume of 99 m3 in 1997. Yosemite must be the "sweet spot" for A. lowiana, because it is also home to the second, third, and fourth-largest known specimens, with a fair number of trees over 60 m tall and/or over 200 cm DBH (Van Pelt 2001).
Outside of the Sierra Nevada, the largest known tree is 43 m tall and 184 cm dbh with a crown spread 15 m; it grows in Uinta National Forest, UT (American Forests 1996). The tallest is a tree 49.5 m tall in the Hermosa Creek roadless area, San Juan Mountains, Colorado, discovered and measured in August 2014 (Markworth 2014).
Ages of >300 years are cited in Burns & Honkala (1990). The ITRDB tree-ring chronology CA513 spans 1596-1968, 372 years, and is presumably derived from live-tree material.
I have to recommend the forests of Baja California Norte, atop the Sierra San Pedro Martír. This is one of the most extraordinary forests of large conifers left in North America, because it has not been subject to fire suppression. Consequently, it remains a large area of open, parklike stands of conifers (mostly A. concolor, Pinus coulteri, P. jeffreyi, and Pinus lambertiana). It is most readily accessed by a good quality gravel road ascending the west slope of the range to a national astronomical observatory maintained atop the range crest. The road leaves the Transpeninsular Highway 140 km south of Ensenada and (in 1994) is signed "Observatorio". The forest starts around the park entrance, 75 km from the highway, and continues beyond road's end at the observatory, 20 km further on. Camping is superb but water is scarce.
A comparably impressive forest, still containing fairly large trees, can be seen high on Mt. San Jacinto in southern California, e.g. in the vicinity of the aerial tram station.
As noted above, the largest trees are in Yosemite National Park, with the most spectacular examples at the east end of Merced Lake; along the Tioga Pass Road about a mile east of the turnoff for the Tuolumne grove of giant sequoias (Sequoiadendron giganteum); near the Badger Pass ski area; and in the Little Yosemite Valley (Van Pelt 2001). Giant sequoia groves are a good place to observe how this species, in the absence of fire, can come to dominate the understory of what was formerly an open, park-like forest.
The name "concolor" refers to the fact that both upper and lower needle surfaces are the same color. The winged seeds provide food for songbirds and small mammals; deer eat the foliage, and porcupines the bark (Little 1980).
Markworth, Matt. 2014.08.14. The Leverett White Fir. www.ents-bbs.org/viewtopic.php?f=70&t=6506#p29675, accessed 2014.08.17.
Last Modified 2014-12-05