White Fir - Abies concolor

White Fir - Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.
Family: Pinaceae.
Also commonly called concolor fir.

This Concolor fir is a Morton Arboretum specimen.

Long considered undesirable for timber, white fir (Abies concolor) is finally being recognized as a highly productive, valuable tree species. White fir reaches its best development and maximum size in the central Sierra Nevada of California, where the record specimen is 58.5 m (192 ft) tall and measures 271 cm (106.6 in) in d.b.h. Large but not exceptional specimens, on good sites, range from 40 to 55 m (131 to 180 ft) tall and from 99 to 165 cm (39 to 65 in) in d.b.h. in California and southwestern Oregon and to 41 m (134 ft) tall and 124 cm (49 in) in d.b.h. in Arizona and New Mexico.

Needle form and terpene content vary sufficiently across the wide range of the species to warrant definition of two varieties: the typical var. concolor, white fir, often called Rocky Mountain white fir, occupies the eastern and southwestern part of the range; var. lowiana (Gord.) Lemm., California white fir, grows in the western range.

Rocky Mountain white fir grows on high mountains, typically with long winters, moderate to heavy snowpacks, and short growing seasons. California white fir grows in cold, high elevations and in warm-to-hot low elevations. Throughout its natural range, white fir grows on a variety of soils developed from almost every kind of parent material. These materials include recent volcanic and igneous rocks of nearly all compositions, large areas of intrusives (mostly granites), and various metamorphics, including serpentine. Sedimentary materials range from limestone, sandstone, and shale to unconsolidated Pleistocene lake deposits.

Conifer, evergreen, 30-50 ft (9-15 m), conical and branched to base, upper branches tend to point upward whereas lower branches are horizontal or directed down. Leaves curve outwards and upwards on branches, 3.8-6.5 long and 2 mm wide, flattened, glaucous on both sides and more or less bluish green (concolor: uniform color, refers to both needle surfaces) Cones are stalked and 8-13 cm long, pale green with a purplish bloom, finally brown.
Sun. Best in deep, rich, moist, well-drained soil, poor on heavy clay. Withstands heat, drought, and cold. A good fir for the east and midwest.
Hardy to USDA Zone 3 Native to Colorado, southern Oregon to southern California and Mexico.

White fir is generally tolerant of a wide range of soil conditions, nutrient availability, and pH values. It seems to be more dependent on moisture availability and temperature than on soil series. In at least one area of summer-dry Mediterranean climate, productive stands of white fir may utilize water obtained from shattered or otherwise porous bedrock well below the maximum soil depth. California white fir is moderately sensitive to excess soil moisture and invades high-elevation meadows by growing near older lodgepole pine, taking advantage of relatively dry ground created by the pine roots. A similar pattern of meadow invasion can develop where radiational heat loss on clear, cold nights is significant. In these situations, the frost-sensitive fir is protected by the pine foliage.

At low elevations California white fir is an aggressive, tolerant species that appears to have been held in check by frequent natural fires. Extensive fire control efforts, however, have reduced fire frequency. As a result, white fir is becoming a major stand component in California at elevations and on sites where originally it was minor. Dense fir regeneration beneath older stands of less tolerant trees is common and threatens a major change in species composition. In many places, especially with giant sequoia, such changes are undesirable, and control measures, including reintroduction of fire, are necessary.

Flowering and Fruiting- White fir is monoecious (that is, both male and female cones are present on each tree). The reddish male strobili (cones) are generally less than 1.6 cm (0.6 in) 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. California white fir flowers in May or June and fertilization occurs shortly thereafter. Flowering of Rocky Mountain white fir at the higher elevations may be delayed and extend into July. Female cones reach full size, 7.5 to 13 cm (3 to 5 in) long, in late summer and turn from greenish or purplish to brown when mature. Cone specific gravity is about 0.85 when mature. The seed matures in September, up to 3 weeks before seedfall.

Damaging Agents- White fir saplings and poles are susceptible to fire damage or kill, but trees become more resistant to both with age and size. White fir is considered more fire resistant than its associated species at high elevations, but less resistant than its associates at low elevations. Fire scars, commonly found in old-growth stands, provide an entry court for a variety of disease and decay organisms.

White fir is sensitive to spring and fall frosts. Spring frosts can kill developing buds as well as foliage. Damage to established trees, other than Christmas trees, is not usually significant. On some sites, repeated damage to new fir growth can give a competitive advantage to more resistant species. Cold damage to mature trees takes the form of frost cracks and ring shake. Frost cracks are associated with some rot and decay loss.

Sudden rises in temperature during May and early June can cause damage nearly identical to that of spring frosts. Sun-scalding following thinning is rare in mature trees, although young, thin-barked trees are susceptible. When white fir boles are injured, recovery is slow.

Compared to its associated species, white fir is moderately susceptible to ozone damage. although fir grows faster than associated species in southern California, diameter growth is affected by oxidant damage as much as that of Ponderosa pine. White fir is more resistant to fluoride damage than Douglas-fir or ponderosa pine.

As intensive management of this productive species increases, so will the importance of mechanical injury. Studies in Oregon and California have shown that conventional logging techniques for thinning or partial cutting damaged 22 to 50 percent of the residual stand. Seventy-five percent of these wounds were at ground level, where infection by some decay-causing fungus is almost certain.

Two parasitic plants, white fir mistletoe (Phoradendron bolleanum subsp. pauciflorum), a true mistletoe, and white fir dwarf mistletoe (Arceuthobium abietinum f. sp. concoloris), cause major damage to white fir. In Arizona, Mexico, and the central to southern Sierra Nevada of California, white fir mistletoe is a serious problem on large old trees. Heavy infections cause spike tops, loss of vigor, and increased susceptibility to bark beetle attack. Dwarf mistletoe is a major problem from the southern Sierra Nevada north into Oregon. It is found elsewhere throughout the native range of white fir in coastal and southern California, Nevada, and Arizona.

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. Because of reduced vigor, infected trees are more susceptible to bark beetle attack and various diseases. Heart rots, entering through open mistletoe stem cankers, increase mortality of old-growth trees through stem breakage.

Changes in wood structure in the large stem bulges caused by dwarf mistletoe infections reduce the strength of lumber produced. Current lumber grading practices, however, are not adequate to identify the affected wood.

Dwarf mistletoe need not be a problem in young managed stands because three factors make damage subject to silvicultural control. The parasite is host specific: white fir can be infected only by A. abietinum f. sp. concoloris, which in turn can parasitize only one other fir, grand fir. Small trees (less than 1 m [3.3 ft] tall) are essentially free from infection even in infested stands. Infected young firs free from new overstory infection outgrow the spread of mistletoe if height growth is at least 0.3 m (1 ft) per year.

Annosus root rot (Heterobasidion annosum) is present in all conifer stands and may become a major disease problem as management of white fir increases. Once established, the disease affects trees within a slowly expanding, circular infection center. Spread from tree to tree is through root contacts. New infection centers begin by aerial spread of spores and infection of basal wounds and freshly cut stumps. In true fir, annosus root rot usually does not kill directly but produces considerable moisture stress and loss of vigor that predispose the tree to attack by bark beetles, notably Scolytus. Direct damage resulting from infection is restricted primarily to heart rot of butt and major roots, leading to windthrow and stem breakage. Some degree of control is available through silvicultural means and use of borax on freshly cut stumps.

Other rots of major significance include the yellow cap fungus (Pholiota limonella), Indian paint fungus (Echindontium tinctorium), and white pocket rot (Phellinus pini). Yellow cap fungus causes heavy losses from butt rot and enters through fire scars and basal wounds. Indian paint fungus is a major heart rot organism. This fungus probably infects fir in the same manner it does western hemlock. Entry is through branchlets less than 2 mm (0.08 in) in diameter. The fungus can remain dormant for up to 50 years before being activated by injury to the tree. Rot commonly extends 3 m (11 ft) below and 6 m (20 ft) above each characteristic fruiting body (4). No effective control is known although trees less than 40 years old are relatively free of rot because they have so little heartwood. In the white fir-grand fir complex of Idaho, the fungus was found in 97 percent of the trees that had decay. Almost 80 percent of the decay in old-growth grand fir-white fir stands of eastern Oregon and Washington is caused by Indian paint fungus; in California, it is much less common.

Insects from seven genera attack white fir cones and seeds. Two cause damage with considerable loss of seed. Seed maggots (Earomyia spp.) are the most abundant and damaging. The fir cone looper (Eupithecia spermaphaga) covers almost the entire range of white fir and periodically causes considerable local damage.

although many insects feed on white fir foliage, few cause significant damage as defoliators. The most destructive of these is the Douglas-fir tussock moth (Orgyia pseudotsugata). Over most of its range the tussock moth shows equal preference for true fir and Douglas-fir foliage. Epidemic outbreaks, although sporadic, are explosive and damaging. In California, white fir is the preferred host, but outbreaks have not reached the severe levels sustained elsewhere. Occasionally, localized outbreaks result in increased stand growth as mortality of subordinate trees "thin" an overdense stand.

The western spruce budworm (Choristoneura occidentalis) is the most destructive defoliator in western North America, causing serious damage in Canada and the Rocky Mountains and Pacific coast regions of the United States. Some outbreaks are short lived, but some continue for 20 years or more. although initial damage is to new foliage and buds, trees can be completely defoliated in 4 to 5 years. Ultimate damage ranges from minor growth loss to major tree mortality over extensive areas, depending on severity and duration of the outbreak.

A similar species, the Modoc budworm (Choristoneura retiniana [= viridis]), is endemic to the Warner Mountains of northeastern California and southeastern Oregon. Damage to California white fir in the Warner Range has been sporadic and light.

The New Mexico fir looper (Galenara consimilis) is restricted to New Mexico and can be a serious problem locally on white fir. Weevils of the genus Agronus attack foliage of young trees and may cause concern with intensive forest management. Sawflies (Neodiprion spp.) are generally not a problem-but are potentially damaging in dense stands of young fir. In California, a species of Neodiprion sawfly has reached epidemic levels locally on white fir. White fir needleminer (Epinotia meritana) covers the full range of white fir and can cause extensive branch kill predisposing trees to bark beetle (Scolytus) attack.

Cutworms (Noctuidae) can be a problem in nurseries and, more especially, in natural regeneration areas. Cutworms have been responsible for more than 30 percent of the seedling mortality in California.

The most damaging white fir pest is the fir engraver beetle (Scolytus ventralis). This bark beetle is found over the entire range of white fir and causes serious damage nearly everywhere. Mortality equivalent to an estimated 2.4 million m³ (430 million fbm) of growing stock is caused each year in California alone. Losses during epidemics are even larger. The fir engraver can attack any tree, but those suffering from root rot infections or tussock moth attack are especially vulnerable. In general, anything that reduces tree vigor, such as mistletoes, Cytospora, drought, or fire, increases susceptibility to attack. Several other bark beetles-including one species of Pseudohylesinus and two species of Scolytus, the roundheaded borer (Tetropium abietis) and the flatheaded fir borer (Melanophila drummondi)- frequently join the fir engraver in attacking and killing individual trees. In epidemic conditions, however, mortality is primarily caused by the fir engraver. Maintenance of stand health and vigor is the only known control.

Selected varieties:

'Blue Cloak' is a weeping form selected for its blue foliage. Grows to 30 x 15 feet in 30 years.
'Candicans' is one of the bluest forms; fast-growing, conical. Grows to 40 feet.
'Compacta' irregularly rounded and slow-growing. To 2 feet, it is great for a rock garden or as specimen in larger planting.
'Conica': A compact, conical dwarf with steel-blue 1" needles. Leader grows about 1 foot every two years.
'Fagerhult': very blue, slow-growing ground-hugging variety.
'Masonic Broom': a flat-topped bush form with blue needles.
'Wintergold': Green needles turn golden in winter; fast-growing.

White fir is a general, all-purpose, construction-grade wood used extensively for solid construction framing and plywood. A significant portion of the Christmas trees used in California are young white fir. These trees are harvested from natural stands, from regeneration areas where the trees are cultured for as long as 11 years before harvest, and from areas used specifically for Christmas tree production.

Detailed and exact wildlife censuses for large areas do not exist, and any listing of species numbers associated with a major forest type is an approximation. There are, however, about 123 species of birds found in the white fir type of California, 50 of which are associated primarily with mature forests. Perhaps because of the dense nature of most true fir forests in California, there are only 33 species of mammals commonly present and of these only 7 are generally associated with mature forests. Reptiles are represented by 17 species, mostly at lower elevations. Only eight are regularly associated with mature forests.

References:
1. United States Forest Service Silvics Manual Abies concolor

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