• ABBREVIATION
• SYNONYMS
• NRCS PLANT CODE
• COMMON NAMES
• TAXONOMY
• LIFE FORM
• FEDERAL LEGAL STATUS
• OTHER STATUS
• AUTHORSHIP AND CITATION

ABBREVIATION:

SYNONYMS:

NRCS PLANT CODE [310]:

COMMON NAMES:

TAXONOMY:

LIFE FORM:

FEDERAL LEGAL STATUS:

OTHER STATUS:

AUTHORSHIP AND CITATION:

• GENERAL DISTRIBUTION
• ECOSYSTEMS
• STATES
• BLM PHYSIOGRAPHIC REGIONS
• KUCHLER PLANT ASSOCIATIONS
• SAF COVER TYPES
• SRM (RANGELAND) COVER TYPES
• HABITAT TYPES AND PLANT COMMUNITIES

GENERAL DISTRIBUTION:

Rocky Mountain white fir occurs in the mountains of central and southern Colorado to southeast Idaho and eastern Nevada, south to southeastern California and southern Arizona and New Mexico, with localized populations in northwest Mexico [191]. It is only sparingly distributed in the mountains of the eastern Mojave Desert in California [186]. Rocky Mountain white fir is common on the eastern rim of the Great Basin, with the central Great Basin forming a 200-mile gap between the two varieties of white fir [185].

California white fir occurs primarily in the Sierra Nevada, Klamath and Siskiyou mountains of California, and in western Nevada on the eastern slopes of the Sierra [102]. Some report its distribution into the mountains of southwest Oregon south to northern Baja [191], while others report that in the ranges of southern California and northern Baja, white fir more closely resembles the Rocky Mountain variety [316].

It is planted in rural and urban landscapes across the northern and northeastern United States [185,202], and distribution maps include it in Maine and Massachusetts [309].

ECOSYSTEMS [117]:

STATES:

BLM PHYSIOGRAPHIC REGIONS [43]:

KUCHLER [176] PLANT ASSOCIATIONS:

SAF COVER TYPES [92]:

SRM (RANGELAND) COVER TYPES [274]:

HABITAT TYPES AND PLANT COMMUNITIES:

In higher elevations and mesic sites of the mixed conifer forests of California and southern Oregon, California white fir is common and often dominant, sometimes comprising 80% or more of the large trees in a stand, and may form pure stands [124,178,244,262]. It may also share dominance with incense-cedar (Calocedrus decurrens), ponderosa pine (Pinus ponderosa), lodgepole pine (P. contorta), sugar pine (P. lambertiana), Jeffrey pine (P. jeffreyi), Douglas-fir (Pseudotsuga menziesii), California black oak (Quercus kelloggii), grand fir, Pacific madrone (Arbutus menziesii), and tanoak (Lithocarpus densiflorus) [178,244]. Western juniper (Juniperus occidentalis) may be found on shallow soil inclusions in white fir forests in California and Oregon [77]. Herbaceous cover tends to be sparse (seldom >5%) in white fir forests, except on moist sites where it may approach 100% [40,262]. Understory species diversity is high. Rundel and others [262] list several important understory species found in white fir forests. Riparian communities in California white fir forests include white alder (Alnus rhombifolia), thinleaf alder (A. incana ssp. tenuifolia), bigleaf maple (Acer macrophyllum), red-osier dogwood (Cornus sericea ssp. sericea), western azalea (Rhododendron occidentale), Sierra currant (Ribes nevadense), thimbleberry (Rubus parviflorus), Oregon ash (Fraxinus latifolia), Pacific ninebark (Physocarpus capitatus), black cottonwood (Populus balsamifera ssp. trichocarpa), swamp carex (Carex senta), wild rhubarb (Darmera peltada) and California spikenard (Aralia californica). White fir is also a secondary species in the subalpine woodland represented by whitebark pine (P. albicaulis), limber pine (P. flexilis), mountain hemlock (Tsuga mertensiana), lodgepole pine, western white pine (P. monticola) and foxtail pine (P. balfouriana) [40]. California white fir is one of the coniferous dominants of the California hardwood forests consisting primarily of tanoak, California black oak, giant chinquapin (Chrysolepis chrysophylla), Pacific madrone, California bay (Umbellularia californica), canyon live oak (Q. chrysolepis), and red alder (A. rubra). Its dominance in this type fades in the hardwood forests of the northern Sierra and southern Cascades where it may occur with Pacific madrone, giant chinquapin, and Pacific yew (Taxus brevifolia) [126,206].

The center of distribution of California white fir is the mixed-conifer forest of the Sierra Nevada Mountains, where it may share or shift dominance with incense-cedar, ponderosa pine, sugar pine, Jeffrey pine, and Douglas-fir. Subdominant trees may include California black oak, Pacific dogwood (C. nuttallii), bigleaf maple, canyon live oak, and tree forms of curlleaf mountain-mahogany (Cercocarpus ledifolius). The shrub canopy is represented by the genera Arctostaphylos, Ceanothus, Chamaebatia, Chrysolepis, Lithocarpus, Prunus, Quercus, Ribes, Symphoricarpos, and Vaccinium. Common genera in the herb layer include Adenocaulon, Clintonia, Disporum, Galium, Iris, Lupinus, Osmorhiza, Pteridium, Pyrola, Maianthemum, and Viola [40]. California white fir stands are common on mesic sites at upper elevations in the Sierra, in what may be called the white fir zone [40,262]. Near its upper elevational limits and on the eastern slope of the Sierra, California white fir shares its climax status with California red fir (A. magnifica) in extensive pure fir forests [40,124,178,185,262]. Here ponderosa pine and incense-cedar are less common and may be absent [40]. Where California white fir occurs on the lower-west-side of the Sierra, ponderosa pine usually dominates, and associates include incense-cedar, sugar pine, and Douglas-fir. California white fir is less common on these xeric sites, although its density has increased since the turn of the century, especially in the smaller size classes in the understory [262]. White fir is a major component of giant sequoia (Sequoiadendron giganteum) groves along the west slope of the central Sierra Nevada, where California hazelnut (Corylus cornuta var. californica) and Pacific dogwood may also be found [40,178,185,262,330]. California white fir is an important component in Jeffrey pine communities on the east slope of the Sierra, where associates include incense-cedar, California black oak, black cottonwood, greenleaf manzanita (Arctostaphylos patula), Sierra mountain misery (Chamaebatia foliolosa), bigleaf maple, California black oak, canyon live oak, and ceanothus [40,178,185,262]. The most significant understory component in many of these forests may be the dense thickets of white fir and incense-cedar saplings with common coverages of 5-10% and 30% or more not being unusual [262]. California white fir occurs with varying degrees of dominance on drier sites in the northern Sierra, with sugar pine, Jeffrey pine, ponderosa pine, California black oak, incense-cedar, western juniper, singleleaf pinyon (P. monophylla), big sagebrush (Artemisia tridentata), ceanothus, greenleaf manzanita, antelope bitterbrush (Purshia tridentata), Utah snowberry (Symphoricarpos oreophilus var. utahensis), chokecherry (Prunus virginiana), and rabbitbush (Ericameria bloomeri) as possible associates [40,262,316]. More detailed descriptions of the Sierran montane and subalpine conifer forests can also be found in Pase [241,242].

In the Cascade Range, the white fir zone occurs at elevations above 4,900 feet (1500 m) where white fir is clearly dominant in nearly pure stands with Douglas-fir, sugar pine, ponderosa pine, western white pine, and lodgepole pine as associates [111]. Atzet and McCrimmon [29] recognize 18 white fir associations in the Cascades with the following codominant species: lodgepole pine, western serviceberry (Amelanchier alnifolia), mountain hemlock, Pacific rhododendron (R. macrophyllum), twinflower (Linnaea borealis), California red fir, prince's pine (Chimaphila umbellata), Pacific silver fir (A. amabilis) [140], Oregon-grape (Mahonia repens), vine maple (A. circinatum), western hemlock (T. heterophylla), vanillaleaf (Achlys triphylla), big huckleberry (Vaccinium membranaceum), salal (Gaultheria shallon), Rocky Mountain maple (A. glabrum), anemone (Anemone spp.), California hazelnut, poison oak (Toxicodendron diversilobum), and incense-cedar. The white fir zone in the Cascades grades into red fir forest at upper elevations, where white fir remains an important component along with western white pine, lodgepole pine, mountain hemlock and currant [111,220]. On the western slopes of the Cascades, white fir is found at mid-elevations and on mesic sites above the ponderosa pine forests in mixed conifer stands in mixed dominance with sugar pine, ponderosa pine, incense-cedar, Douglas-fir and California black oak. Here it may also be associated with western hemlock, Pacific dogwood, Pacific yew, pacific madrone, vine maple, twinflower, and shrubs such as snowbrush ceanothus (C. velutinus), giant chinquapin, bush chinquapin (C. sempervirens), bitter cherry (P. emarginata), sharpleaf snowberry (S. acutus), baldhip rose (Rosa gymnocarpa), Sierran gooseberry (Ribes roezlii), snow raspberry (Rubus nivalis), common whipplea (Whipplea modesta), and pinemat manzanita (A. nevadensis) [111,207,208,220,262]. It is found less commonly on the east side of the Cascade Range [262]. In the Silver Lake area of southern Oregon, white fir occurs in association with ponderosa pine and Idaho fescue (Festuca idahoensis), along with antelope bitterbrush, greenleaf manzanita and Oregon-grape [75].

The Klamath Mountains in northwestern California and southwestern Oregon have the greatest concentration of conifer species on earth, with white fir among them [300]. Here white fir is considered an indicator of the lower elevational limit of montane forest vegetation, which blends into Douglas-fir-hardwood forests below on the west side and into ponderosa pine-California black oak on the east side. On the west side white fir occurs primarily with Douglas-fir as a codominant, and on the east side with Pinus spp. and California red fir. Westside associates also include sugar pine, ponderosa pine, incense-cedar, Port-Orford-cedar (Chamaecyparis lawsoniana), Pacific yew, giant chinquapin, prince's pine, bigleaf maple, canyon live oak, Pacific madrone, Pacific trillium (Trillium ovatum), and American vetch (Vicia americana). Eastside associates include Douglas-fir, incense-cedar, sugar pine, ponderosa pine, Pacific dogwood, canyon live oak, California black oak, bigleaf maple, Pacific yew, giant chinquapin, Mahala mat (Ceanothus prostratus), and dwarf Oregon-grape (Berberis nervosa), with an understory of mainly sclerophyllous shrubs in dense patches, or of nonsclerophylls such as baldhip rose, and creeping snowberry (S. mollis). Herbs are uncommon except for prince's pine, and bracken fern (Pteridium aquilinum). At higher elevations, white fir grades into red fir with which it shares dominance on some sites. At still higher elevations, white fir may be found with western hemlock, western white pine, and lodgepole pine [268]. The white fir series in the Siskiyou Mountains of southern Oregon and northern California is divided into several associations with codominants including: California red fir, currant, baldhip rose, creeping snowberry, prince's pine, sandler oak, Oregon boxwood (Paxistima myrsinites), dwarf Oregon-grape, giant chinquapin, Alaska-cedar (C. nootkatensis), brewer spruce (Picea breweriana), big huckleberry, salal, tanoak, Pacific yew, Port-Orford-cedar, Douglas-fir, Rocky Mountain maple, oceanspray (Holodiscus discolor), ponderosa pine, western hemlock, vine maple and Jeffrey pine [31,136,305]. Mixed conifer associates in the Siskiyou Mountains include Douglas-fir, ponderosa pine, sugar pine, incense-cedar, western hemlock, vine maple, Pacific yew, twinflower, snow raspberry, common whipplea, and pinemat manzanita [111,220]. Some characteristic understory species of white fir forests in the Siskiyou Mountains are given by Franklin and Dyrness [111].

In the South Warner Mountains of northeastern California, the white fir series occurs in three habitat types and is codominant with tailcup lupine (Lupinus caudatus), sweet cicely (Osmorhiza claytonii), and whiteveined wintergreen (Pyrola picta) [257]. White fir is important in closed forest stands on the Modoc Plateau in association with incense-cedar, ponderosa pine, quaking aspen, and western juniper [262,316]. In northeastern California, white fir is increasingly influenced by grand fir [124]. In southeastern Oregon, white fir occurs in the ponderosa pine forest zone with grand fir, western larch (Larix occidentalis), Douglas-fir, lodgepole pine, western white pine, mountain-mahogany, common snowberry (S. albus), mountain snowberry (S. oreophilus), antelope bitterbrush, mountain big sagebrush (A. tridentata ssp. vaseyana), elk sedge (C. geyeri), Idaho fescue, pinegrass (Calamagrostis rubescens), Wheeler bluegrass (Poa nervosa), and bluebunch wheatgrass (Pseudoroegneria spicata). In the true fir forest zone of southeastern Oregon, white fir occurs with grand fir, ponderosa pine, lodgepole pine, western larch, Douglas-fir, western white pine, Pacific yew, thimbleberry, twinflower, big huckleberry, grouse whortleberry (V. scoparium), western oakfern (Gymnocarpium dryopteris), oneleaf foamflower (Tiarella trifoliata var. unifoliata), and drops of gold (Disporum hookeri) [64,130]. Further north, white fir grades into the grand fir zone, with the two species hybridizing where they intergrade [64,111]. In this zone of genetic overlap, it is impossible to visually tell the two species and their hybrids apart [103].

In the mountain ranges of southern California, dominance shifts from ponderosa to Jeffrey pine to white fir with increasing elevation. White fir is also a major component of the subalpine forest type in this area. California black oak stands, montane meadows and chaparral are interspersed throughout the area where white fir is dominant, and sugar pine, incense-cedar, and western juniper are secondary components in many stands [287]. In the San Bernardino Mountains white fir is codominant with ponderosa pine, Jeffrey pine or with sugar pine on north aspects, with incense-cedar and California black oak as common associates and a wealth of herbaceous species mixed with a considerable understory of shrubs. It may also be codominant with sugar pine in more open stands, with Jeffrey pine, canyon live oak and some timberland chaparral species as understory, and no herbaceous species present [151,217]. In the Transverse and Peninsular ranges of southern California, white fir occurs at upper elevations and mesic slopes with ponderosa pine, Jeffrey pine, sugar pine, and incense-cedar. Here white fir and sugar pine form a community on moister slopes with incense-cedar, lodgepole pine, Sierra currant, Sierran gooseberry, thimbleberry, Sitka willow (Salix sitchensis), and blue elderberry (Sambucus cerulea). It may also be found with bigcone Douglas-fir (P. macrocarpa) in this area [204]. Scattered and gnarled specimens of white fir may also be found in the western juniper woodland, lodgepole pine, or limber pine forest [306]. In the Clark and Kingson mountains of the Mojave Desert, and other southern California populations as far north as the Tehachapi Mountains, white fir more closely resembles the Rocky Mountain variety, and is found with singleleaf pinyon, Colorado pinyon (P. edulis), Utah juniper (J. osteosperma), Rocky Mountain maple, Utah serviceberry (A. utahensis), singleleaf ash (Fraxinus anomala), bush oceanspray (H. dumosus), canyon live oak, shrub live oak (Q. turbinella), wax currant (R. cereum), desert gooseberry (R. velutinum), and common elderberry (S. nigra ssp. canadensis) [124,316]. In the Sierra San Pedro Mártir, white fir and incense-cedar are restricted to the most mesic sites in an open forest dominated by Parry pinyon (P. quadrifolia) and Jeffrey pine from 4,600 to 7,900 feet (1400-2400 m) [40].

Rocky Mountain white fir is found in nearly all the major mountain ranges in the southwest [84,188]. The white fir series in the southwest can have any mixture of white fir with Douglas-fir, Engelmann spruce (P. engelmannii), blue spruce (P. pungens), subalpine fir (A. lasiocarpa), ponderosa pine, and southwestern white pine (Pinus strobiformis), depending on the moisture and temperature relationships of the site, and the stage of succession. The more successful reproduction of white fir is diagnostic of the white fir series [188,232]. White fir grades into blue spruce at cooler moister sites at the same elevation, into the subalpine fir series (Engelmann spruce and corkbark fir (A. lasiocarpa var. arizonica)) at higher elevations, and Douglas-fir or ponderosa pine at lower elevations with complex ecotones [16,57,83,188]. At its northern limit in the Rocky Mountains, white fir is replaced by Douglas-fir as the indicated climax on montane forest sites [201]. Rocky Mountain white fir is a dominant or climax component of several habitat types and series in Arizona, New Mexico, Utah and Colorado. Codominant species are listed below:

In Utah, the white fir series occurs throughout the higher mountain ranges of the northwestern region, is found locally in the Uinta Mountains, and increases in importance through southern Utah. On exposed, lower elevation sites white fir occurs either as scattered individuals or groups with quaking aspen (Populus tremuloides) and Douglas-fir as dominant seral associates, and abundant brush or woodland species, such as bigtooth maple and Gambel oak in the interspaces. Western serviceberry, paxistima, and chokecherry are common associates [201]. Undisturbed forest sites in the subalpine zone of Utah are dominated by Engelmann spruce, blue spruce, subalpine fir and white fir with a diverse herbaceous component. These subalpine forests are intermixed with meadows, stringers of limber and bristlecone pines, and open woodlands of aspen or lodgepole pine in areas that have been disturbed by fire in recent times [38]. White fir is a seral species in the subalpine fir series and occurs as scattered individuals in the Douglas-fir series and limber and ponderosa pine habitat types [201,344]. Where Rocky mountain white fir is codominant with quaking aspen, associates include mountain snowberry, Kentucky bluegrass (Poa pratensis), and greenleaf manzanita [230]. Carex spp. are common understory components in some white fir habitat types in Utah [201,230].

The white fir series is the most widespread mixed conifer series in southern Colorado and northern New Mexico. Here it is often co-climax with Douglas fir. Other tree associates include blue spruce, limber pine, ponderosa pine, Engelmann spruce, subalpine fir, quaking aspen, and Rocky Mountain juniper. It is also found in several subalpine fir community types, and blue spruce, Douglas fir, and limber pine habitat types [16,83].

The white fir-Douglas-fir-Ponderosa pine series is the most widespread and one of the most varied types in Arizona and New Mexico [82]. In New Mexico mixed conifer forest, white fir shares climax status with Douglas fir, and the white fir/Gambel oak habitat type is the most widespread [93,142,223]. White fir types grade into Engelmann spruce, blue spruce, and subalpine fir types at higher elevations with mixtures of corkbark fir, Douglas-fir, southwestern white pine, and quaking aspen. At lower elevations, white fir types grade into Douglas-fir and ponderosa pine types [20,178,225,294]. Additional tree associates include Chihuahua pine (P. leiophylla var. chihuahuana), Rocky Mountain lodgepole pine (P. contorta var. latifolia), Mexican pinyon (P. cembroides), New Mexico locust, limber pine, and boxelder (Acer negundo) [188]. South of Mogollon rim, white fir is found with Douglas-fir, southwestern white pine, quaking aspen, Rocky Mountain maple, Gambel oak, fringed brome (Bromus ciliata), muhly (Muhlenbergia spp.), sprucefir fleabane, woodland strawberry (Fragaria americana), Richard's geranium (Geranium richardsonii), Parry's goldenrod (Oreochrysum parryi) and groundsel (Senecio spp.) with a high understory cover of Arizona fescue [82].

In the Madrean region, on mesic slopes, Douglas-fir is often codominant with or is successional to white fir [225,245]. These two species join with spruce and southwestern white pine on cool sites and with ponderosa pine on warm sites. At higher elevations and northern aspects Douglas-fir is replaced by Engelmann spruce and corkbark fir with southwestern white pine in low densities, and occasional stands of quaking aspen [349]. In the Animas Mountains of southern New Mexico and the Sierra Los Ajos in Sonora, Mexico, white fir is found at upper elevations and on north aspects in association with Douglas-fir, quaking aspen, Gambel oak, silverleaf oak (Q. hypoleucoides) and madroño (Arbutus arizonica) [321]. A more detailed description of Rocky Mountain and Madrean montane conifer forests are given by Pase and Brown [243].

White fir is found in riparian communities throughout the west. It is widespread in riparian communities in Zion [135] and Great Basin [278] national parks, and elsewhere in Utah, where it occurs with boxelder and narrowleaf cottonwood (P. angustifolia); and in Wyoming, where it occurs with blue spruce and lodgepole pine [201,236]. In Colorado, Arizona and New Mexico, white fir is found as a dominant species along with blue spruce, narrowleaf and black cottonwood, and/or Rocky Mountain maple in many riparian areas [12,16,37,83,298].

• WOOD PRODUCTS VALUE
• IMPORTANCE TO LIVESTOCK AND WILDLIFE
• PALATABILITY
• NUTRITIONAL VALUE
• COVER VALUE
• VALUE FOR REHABILITATION OF DISTURBED SITES
• OTHER USES AND VALUES
• MANAGEMENT CONSIDERATIONS

WOOD PRODUCTS VALUE:

IMPORTANCE TO LIVESTOCK AND WILDLIFE:

In the southwest, desert bighorn sheep and white-tailed deer occasionally browse white fir [183,276]. In the Rocky Mountains, red squirrels cache white fir cones during late summer and fall before the cones are fully mature [106,114,185]. Some white fir habitat types in the Southwest and Utah provide habitat for black bears and cougars and have high cover value for wildlife [190,294]. In riparian woodlands in the Southwest, white fir is often a codominant species with hardwoods such as maples. These woodlands tend to be small in area, but provide unique and critical habitat for many species of wildlife such as the Arizona gray squirrel, river otter, zone-tailed hawk, common black hawk, American dipper, summer tanager, bullock oriole, yellow warbler, Arizona alligator lizard, Sonoran mud turtle, and canyon tree frog [12,101,294]. At the southern end of its range in the Madrean region, white fir occurs in "island" habitats at the uppermost elevations of isolated mountain ranges, providing small areas of geographically unique habitat for wildlife. An example are the wildlife species present in the Rincon Mountains of Saguaro National Monument, Arizona, presented by Davis and Sidner [73]. The highly variable stand structure with multi-storied shrub layers in some southwestern white fir habitat types provides increased microhabitat diversity for birds [101,294]. White fir forests in the Southwest provide habitat for Mexican spotted owls in Arizona, New Mexico [116,194], and Utah [341]; goshawks in Arizona [70,196,255]. Thick-billed parrots, reintroduced in the mountains of southeastern Arizona, occur in mixed-conifer forests with white fir [279]. Several species of amphibians and reptiles may be found in white fir montane mixed conifer forests such as that at upper elevations in Saguaro National Monument [193]. Two species of endangered salamanders (Jemez Mountains salamander and Sacramento Mountain salamander) in New Mexico are found in mixed conifer forests dominated by white fir [250].

PALATABILITY:

NUTRITIONAL VALUE:

COVER VALUE:

VALUE FOR REHABILITATION OF DISTURBED SITES:

OTHER USES AND VALUES:

MANAGEMENT CONSIDERATIONS:

• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

The crown of young trees is symmetrical and sharp-pointed, becoming irregular and rounded at the summit [162]. California white fir has a narrow, cylindrical, almost spire-like crown [185,186]. Rocky mountain white fir tends to have a broader crown [185]. White fir branches are short and stout, with leaves 1.2 to 2.8 inches (3-7 cm) long and generally curved upward. Branches are arranged in whorls of 4 or 5, which are repeatedly branched in one plane to form flat, horizontal sprays. Buds are blunt and resinous [71]. In Arizona white fir stands, braches reach nearly to the ground if the trees are widely spaced, and in more dense stands, half or more of the trunk is often bare [162].

The rooting habit of white fir is usually fairly shallow, but appears to be adaptable to local conditions: deep and intensive where soil conditions permit, to shallow and widespread where rocks or seasonal water tables limit effective soil depth. There is no strong tendency to maintain a single deep taproot although rapid taproot development is critical for survival of new germinants in a dry summer climate. White fir is susceptible to wind throw following partial cutting. Root diseases may contribute to lack of wind firmness. Root grafting between firs is common and is a factor in the spread of root rots [178]. Effects of mycorrhizal associations have been explored and appear to be important in white fir, especially for establishment and early growth on poor sites. It appears that bare mineral soils promote the association [22,178].

White fir is thought to be a slow growing species [157,178,219]. It can survive for exceptionally long periods as a suppressed tree and still respond to release by increasing growth dramatically. White fir may reach ages of 300-400 years. Old growth characteristics in Southwest are given by Steuver and Hayden [294]. Information on productivity of white fir is available [178,201,262].

The varietal differences in California and Rocky Mountain white fir are based on differences in morphological and chemical characteristics, such as needle tip shape and stomatal arrangement [40,133] and terpene content [124,178]. 

RAUNKIAER [253] LIFE FORM:

REGENERATION PROCESSES:

Cone and seed production: Cone and seed production vary with tree size, age and dominance. White fir trees can begin bearing cones at 40 years and continue beyond 300 years [178]. The best producers are mature, healthy dominants in the 12 to 35 inch (30-89 cm) d.b.h. range [120,178]. Cone production is higher on trees near openings [119] and on trees following release [178]. Immature trees can produce heavy seed crops, but their production is more erratic than that of mature trees [119,178]. Pole-sized trees in dense stands will not produce cones unless their leaders reach full sunlight. In mixed conifer forests of California only 4% of understory white fir between 3.6 and 7.5 inches (9.1-19 cm) in diameter produce cones [105]. In Oregon and California, heavy seed crops in white fir are borne on a 3- to 9- year cycle, with fair to good crops occurring every 2 to 5 years, and bumper crops every 5 to 9 years [178]. In the Rocky Mountains, medium to heavy seed crops are produced every 2 to 4 years [105]. Cone production patterns may be different on extreme sites [110,120,157,178]. Because cones are borne on the uppermost part of the crown, any top damage caused by insects, diseases or mechanical agents (e.g. wind and snow) directly reduces cone production. Cones produce about 185 to 295 seeds apiece [105,119]. Seed numbers can reach 600,000/acre (1.5 million/ha) or more where white fir is a site dominant [112,178], and as many as 220,000 where white fir is a minor overstory component [181].

Seed predation: Insects that feed on cones and seeds may seriously reduce yield. Seed chalids typically destroy 8 to 10% of white fir seeds and have destroyed up to 60% of a crop [108]. Cone moths, cone midges, and cone maggots also reduce yields [119]. In California and Oregon, the Douglas squirrel cuts and caches cones, but generally takes less than 1% of the cone crop [106].

Seed dispersal: White fir seeds are released and disseminated by wind as the cone disintegrates on the tree in the fall. Because white fir seed has a short, broad wing relative to its weight, if falls more rapidly and travels a shorter distance from the tree than many of its associated species. Downwind seed spread into an opening is about 1.5 to 2 times the height of the tree [119,178,203]. A small percentage of seeds may be transported greater distances by strong or gusty winds [218].

Germination: After release in the fall, white fir seeds overwinter in or under the snow. This cold, moist stratification is required for germination [108]. Germination of white fir seeds occurs in the spring immediately following snowmelt. Where snowpack is deep, seeds may germinate in, on, and under the snow [157,178]. Of white fir seeds sown in November in white and red fir stands in the Sierra Nevada, 82 to 86% of all germination occurred by May 9, and 96 to 98% by May 22 [39]. Only a small proportion (20-50%) of seeds are viable [178]. Thus, germination is low, averaging about 37% . Under controlled conditions, white fir seeds may be stored for 5 or 6 years, but under natural conditions seeds do not remain viable over 1 year [108].

Seedling establishment and survival: White fir seeds that germinate in the snowpack, above the ground, rarely survive, therefore, seeds that fall before the permanent snow cover are more likely to produce seedlings [119]. Germination and early growth are best on bare mineral soil, though seedlings may establish in soils covered by a litter layer [71,100]. Root systems developed in mineral soil without organic layers are longer, heavier, and have more mycorrhizal root tips than those grown in soil with organic layers [22,178]. Seedlings generally establish best in partial shade, and can establish easily under a closed canopy in dense shade [178]. Shade favors seedling survival in white fir because seedlings are very sensitive to soil drying and heating. Damping off fungi, cutworms, drought, heat, trampling and browsing are responsible for most seedling mortality [39,119]. White fir seedlings are more susceptible to spring frost damage and deer browse than many associated species [157,178,219].

Growth: Once established, white fir grows best in full sun [178]. Shade-tolerant white fir saplings can, however, endure decades of suppression under a closed canopy or in dense brushfields. Leader growth is very slow under these conditions, and suppressed plants may be only 3 feet (0.9 m) tall at 50 years [91]. White fir dramatically increases in diameter and height growth when canopy openings are created, or when its height surpasses surrounding vegetation [100,181].

SITE CHARACTERISTICS:

Rocky Mountain white fir grows on high mountains with precipitation ranging from 20 to 35 inches (510-890 mm). California white fir grows in cold, high elevations and warm-to-hot low elevations with precipitation ranging from 35 to 75 inches (890-1900 mm), but grows best in the southern Cascades and western Sierra Nevada, where precipitation is between 39 and 49 inches (990-1240 mm) [178]. Within the mixed conifer forests of the Sierra Nevada, white fir tends to occupy the more mesic sites, such as northern exposures, at lower elevations, and the more xeric sites at upper elevations [111,262]. In Utah, white fir typically occupies cool and dry northern exposures [201,344]. In the Southwest, white fir occupies numerous topographical settings, and local conditions can vary from cold and moist to warm and dry [83]. Winter snowpack provides the majority of the moisture at high elevations, with fall and early spring rains providing most of the moisture at lower elevations [178]. The upper latitudinal limit of white fir may coincide with a mean maximum January temperature of about 30 to 32 degrees Fahrenheit (-1 to 0 °C) [201]. White fir is sensitive to both frost damage and, occasionally sun scald [178]. White fir is also moderately susceptible to ozone damage [157]. White fir 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 [157,178,219].

California white fir occurs in a wide elevational range, as low as 3,000 feet (900 m) in the North Coast Ranges to over 10,000 feet (3000 m) in the San Bernardino Mountains and the Sierra San Pedro Mártir of Baja, California [186]. Pure white fir forests are common in Oregon and California and they occupy a narrow elevational band from about 4,600 to 5,250 feet (1400-1600 m) in the southern Cascades and from 5,400 to 5,900 feet (1650-1800 m) in the Siskiyou Mountains of northwestern California [111]. In the Sierra Nevada, white fir is a major component of mixed conifer forests occurring between 4,100 to 7,200 feet (1250-2200 m) [262]. Rocky Mountain white fir is found most frequently at elevations ranging from 6,900 to 8,900 feet (2100-2700 m) [178]. In the mountains of southern Arizona, it occupies the highest elevations [188]. Generalized elevational and precipitation ranges are as follows, by state:

White fir grows on a variety of slightly to strongly acid soils from almost every type of parent material [14,105,111,178,186,201]. It is generally tolerant of a wide range of soil conditions, nutrient availability and pH values. Growth and development are best on moderately deep and well-drained sandy-loam to clay-loam soils, regardless of parent material. California white fir is moderately sensitive to excess soil moisture [178]. White fir is usually found on frigid soil temperature regimes or the warmest of the cryic regimes [223,294]. In the arid Organ Mountains of southern New Mexico white fir occurs as a topo-edaphic climax on the cool upper eastern slopes [84].

White fir grows from canyon bottoms and ravines up to ridgetops on gentle, moderate, and steep slopes of all aspects. It develops best on gentle slopes and level ground [178]. In the Rocky Mountains, white fir, along with blue spruce and Douglas-fir, often replaces the dominant deciduous species near middle elevation streams passing through sheltered valleys or canyons [245].

Botanical associates of white fir that may affect its growth include snowbrush ceanothus, which contains allelopathic chemicals in its foliage that suppress radicle growth of white fir [66,178]. Mycorrhizal associations are thought to protect white fir roots from allelopathic chemicals produced by bracken fern [178].

SUCCESSIONAL STATUS:

The white fir series in the Southwest can have varying mixtures of white fir, with conifer associates dependent on moisture and temperature relationships of the site and stage of succession. The more successful reproduction of white fir is diagnostic of the white fir series [188,232]. Mosaics of contrasting successional stages are considered to be the result of both insects and past fires [223]. Within the mixed conifer type, white fir tends to achieve climax dominance on moist sites [111,327] and in localized areas with long fire-free intervals that give white fir the chance to mature to a point where it is moderately fire-tolerant. In mixed conifer forests with a natural fire regime of low-intensity surface fires, white fir is kept from attaining climax dominance because it is more fire sensitive than its coniferous associates [2,13]. Thus, many white fir habitat types are in mid-successional stages, with various seral species dominating the overstory and white fir dominating the reproductive size classes [40,111]. Seral associates that often dominate a site include ponderosa pine [83,115,185,223,294], Douglas-fir [83,115,185,294], southwestern white pine [185], Gamble oak, New Mexico locust [294], California black oak [113], quaking aspen [40,153,178,223,230,245], and lodgepole pine [245].

White fir will seed into the understory of ponderosa pine stands or in mixtures of ponderosa pine, Douglas-fir, quaking aspen, and southwestern white pine [185]. Many habitat types in the white fir series in the Southwest are dominated by Douglas-fir and ponderosa pine in mid-seral stages, with white fir steadily gaining dominance as succession proceeds [83,294]. Lodgepole pine is a common seral species in the white fir type, with seedlings of white fir in the understory that are less than a meter in height but in excess of 100 years old. Both aspen and ponderosa pine are present at sites where high intensity fires have occurred or where ground fires have slowed or prevented replacement by white fir and Douglas- fir [223]. With fire suppression, white fir is able to mature in the understory with a concurrent decrease in pine reproduction and eventually begins to replace the pines as they succumb to root diseases and bark beetles, resulting in a gradual change in structure and composition in white fir habitat types [27,40,113,115,184,186,257]. White fir will eventually dominate if the fire-free interval is sufficiently long to allow trees to grow to a fire-resistant size, unless another disturbance event gets them. In a Jeffrey pine forest in South Lake Tahoe, California, a disease outbreak killed the Jeffrey pine overstory, releasing the small white firs in the understory which went on to become the predominant species on the site. They then suffered extreme moisture stress form drought and succumbed to a fir engraver attack causing them to die rapidly [269].

It appears that white fir may be an early colonizer of disturbed sites, gradually increasing in dominance over time [34,139,262]. In northeastern California, overgrazing in big sagebrush- steppe communities allowed for the invasion and establishment of white fir in an unusually xeric setting for white fir [257]. White fir may also be a pioneering species in upper elevation meadows within its type where it has been observed to invade by growing near older lodgepole pine [111,178]. White fir is an early seral species at the lowest elevations of the subalpine forest in New Mexico [223].

Following overstory removal (logging or stand-replacement fires) in mixed conifer or white fir forests of the southern Cascades and Sierra Nevada, sites are often dominated by montane chaparral shrubs, primarily ceanothus and manzanita, but also mountain whitethorn, currant and gooseberry (Ribes spp.), chinquapins, and some oaks [65,105,111,149,178]. Seeds of some species may lie dormant in the forest floor for as long as 300 years and germinate following removal of overstory. Sierra mountain misery and grasses may also assume significant roles [178]. Given a nearby seed source and absence of further burning, white fir seedlings can establish under shrubs within about 10 to 20 years [65,218]. A 30 year delay in tree recruitment was observed after a stand-replacement fire in the Lake Tahoe Basin [263]. Given the continued absence of fire, white fir will eventually overtop the shrubs and dominate the site, creating pure stands in otherwise mixed conifer areas [65].

Following overstory removal in mixed conifer or white fir forests in the Southwest, herbaceous species usually dominate the vegetation for the first few years of succession, and diminish in late seral conditions as shading inhibits their growth [83,101,134,157,223,294]. Seral shrubs and trees that follow herbs include aspen, New Mexico locust, Rocky Mountain maple, bush oceanspray, and Gambel oak, and may dominate the site for the next 40 to 100 or more years [83,101,134,153,157,223]. Gradually tree seedlings, including white fir, become established, although growth is slow under the canopy. Scattered conifers emerge above the shrubs after 50 to 100 years. This stage persists for another 50 or more years, with a closed stand of replacement conifers not fully developed until 100-200 years after the fire, the time depending on numerous factors such as shrub density, climatic conditions, availability of tree-seed sources, soil conditions, livestock, wildlife, and human use. Old growth is characterized by conifer overstory and low shrubs in the understory, with possible sparse herbaceous cover [134,157,223]. White fir may establish quickly on mesic sites and dominate early seral stages, while conifers such as southwestern white pine, limber pine and ponderosa pine may dominate the early seral stages on xeric sites [13,225,294].

Crane [69] presents successional trends of white fir habitat types in Colorado that appear reasonable for Utah types as well. In Utah, white fir becomes the dominant climax tree on characteristically cool and dry sites that are usually northern exposures [344]. These sites are apparently too warm and dry for subalpine fir and Engelmann spruce. Although white fir reproduces most abundantly under shade, it also invades open slopes within the mountain-brush zone [201]. White fir and Douglas-fir are replacing brush species on some northern exposures, and, in the absence of fire, these sites may develop into conifer forests [63].

SEASONAL DEVELOPMENT:

In New Mexico, white fir growing with Douglas-fir completed bud elongation by May 4, and most of its flush extension by the middle of June, and exhibited about twice the flush growth of Douglas-fir over a 5-year period [56]. Flowering of Rocky Mountain white fir may extend into July at higher elevations. Female cones reach full size in late summer and turn brown when mature. The seed matures in September, up to 3 weeks before seedfall [178,235].

Radial growth begins before height growth in white fir, and lasts longer. Height growth in white fir begins 1 to 1.5 months later than in associated conifers and lasts about 6 weeks [178]. On the west slope of the Sierra Nevada at 5,200 feet (1585 m) within the Stanislaus National Forest, white fir leader growth began on June 24 and was completed by mid-August. New needles emerge from fascicles after height growth begins [104]. Old needles are shed primarily in the fall and winter. In California, most needles drop in October and November [46].

• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

FIRE ECOLOGY OR ADAPTATIONS:

The primary range of white fir is in the mid-elevation, mixed conifer and white fir zones in California and the central and southern Rocky Mountains. These forest types may be characterized by a mixed fire regime, with fires of variable frequency and severity [25], with some sites experiencing frequent surface fires [7], and others experiencing infrequent crown fires. Mean fire intervals are generally intermediate to intervals in understory and stand replacement regimes, ranging between 30 and 100 years [25]. Mean fire intervals in Sierra Nevada mixed conifer forests are estimated to range between 5 and 30 years, and varied in response to ignition source, fuel accumulations, fuel moisture and burning conditions [332]. Any given location within a mixed fire regime could experience some stand-replacement fires and some nonlethal fires along with a number of fires that burned at mixed severities, creating mosaic patterns of stand structure and fuels [25,215,304]. Low severity fires thin understory regenerating trees, while more severe crown fires may knock succession back to herbs and shrubs. Thus, past burn mosaics tended to increase the probability that subsequent fires would also burn in a mixed pattern. Complex mountain topography also contributed to variable fuels and burning conditions that favored nonuniform fire behavior [25]. After decades of fire exclusion, much of the landscape mosaic has aged and advanced successionally, and patches of late successional forests with large accumulations of dead and living fuels have coalesced, increasing likelihood of fires of unusual size and severity [25,54,169,209,285,286,287,315]. This shift toward landscape homogeneity may adversely affect biodiversity, and may also be perpetuated as the probability of large, high-severity fires increases with continued fire suppression [338]. Much of the living fuels in these forests are small white firs and other shade tolerant species, filling in the understories with dense thickets and increasing fuel continuity and fire ladders of resinous foliage, often in cylindrical crowns that may lead to crown fires when they do burn [178,186,223,287]. Fuel loadings in this type may vary widely due to stand history and site productivity [25,330].

There is evidence that a mixed regime may have been important for perpetuation of giant sequoia groves in the Sierra Nevada [25,295]. Giant sequoia groves burned every 2-10 years for the last 3000 years and have not burned in 100-130 years [288,289,295]. The more mesic, mid-elevation, mixed conifer forests of California formerly experienced low to moderate severity wildfires every15 to 30 years [287,332]. Other areas that may have had mixed fire regimes include the Marble Mountains of northern California [304]; the mixed conifer zone in the montane forests of the Madrean borderlands; the Animas Mountains of southwest New Mexico [296]; mixed conifer forests in the Jemez Mountains, New Mexico [307]; the white fir/Rocky Mountain maple habitat type in Arizona and New Mexico [232,294]; the high elevation, white fir/forest fleabane habitat type [294]; the lowest elevations of the subalpine forest in New Mexico [86,157,223]; the mixed conifer zone of the Sandia Mountains, New Mexico [36]; and the white fir zone in the central Siskiyou Mountains, Oregon [3].

White fir is also a component of drier ponderosa and Jeffrey pine habitat types that evolved with an understory fire regime. An understory fire regime is characterized by relatively frequent, low severity fires that result in open, uneven-aged stands consisting primarily of the more fire tolerant species. White fir was not a major component of these stands under this regime, and existed as scattered individuals or small groups that managed to survive to a fire resistant age. Open ponderosa pine, larch and Douglas-fir forests at lower elevations in the west have been extensively harvested and protected from fire resulting in a compositional shift to an unnaturally dense understory of Douglas-fir, grand fir white fir, or incense-cedar [27,185,234]. Areas where this fire regime was important include the ponderosa pine and mixed conifer forests of southern Arizona and New Mexico [33,35,68,115,