Abies concolor



INTRODUCTORY

SPECIES: Abies concolor
 
  Young white fir stand in Emigrant Wilderness, CA. Photo by Janet L. Fryer, USFS, Fire Sciences Laboratory.

AUTHORSHIP AND CITATION:
Zouhar, Kris. 2001. Abies concolor. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

ABBREVIATION:
ABICON

SYNONYMS:
Abies lowiana (Gordon) A. Murray [102]

NRCS PLANT CODE [311]:
ABCO

COMMON NAMES:
white fir
California white fir
Rocky Mountain white fir

TAXONOMY:
The currently accepted scientific name of white fir is Abies concolor (Gord. & Glend.) Lindl. ex Hildebr. (Pinaceae) [71,89,144,145,146,158,178,191,334,336]. Two varieties are recognized [71,144,185,186,191,310] based on differences in morphological and chemical characteristics [124,178,191]:

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 [146,178,186,347,348,349]. Under controlled conditions, white fir has successfully been crossed with other firs. Fertile hybrids were produced with the following crosses [278,283]:

Abies concolor var. lowiana X Abies grandis
Abies concolor var. concolor X Abies religiosa

LIFE FORM:
Tree

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Abies concolor

GENERAL DISTRIBUTION:
White fir occurs from Oregon in the Blue Mountains and southern Cascade range, south throughout California and into the San Pedro de Mátir in northern Baja, California; west through parts of southern Idaho, to Wyoming; and south throughout the Colorado Plateau and southern Rocky Mountains in Utah and Colorado, and into the isolated mountain ranges of southern Arizona, New Mexico and northern Mexico [145,310].The U.S. Geological Survey provides a distributional map of white fir.

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 Sierras [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 [317].

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 [310].

ECOSYSTEMS [117]:
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES26 Lodgepole pine
FRES28 Western hardwoods
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES37 Mountain meadows

STATES:

AZ CA CO ID ME MA
NV NM OR UT WY
MEXICO

BLM PHYSIOGRAPHIC REGIONS [43]:
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
11 Southern Rocky Mountains
12 Colorado Plateau

KUCHLER [176] PLANT ASSOCIATIONS:
K001 Spruce-cedar-hemlock forest
K002 Cedar-hemlock-Douglas-fir forest
K003 Silver fir-Douglas-fir forest
K004 Fir-hemlock forest
K005 Mixed conifer forest
K007 Red fir forest
K008 Lodgepole pine-subalpine forest
K010 Ponderosa shrub forest
K012 Douglas-fir forest
K018 Pine-Douglas-fir forest
K019 Arizona pine forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K022 Great Basin pine forest
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K029 California mixed evergreen forest
K030 California oakwoods
K031 Oak-juniper woodland
K032 Transition between K031 and K037
K034 Montane chaparral
K037 Mountain-mahogany-oak scrub

SAF COVER TYPES [92]:
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
207 Red fir
209 Bristlecone pine
210 Interior Douglas-fir
211 White fir
213 Grand fir
216 Blue spruce
217 Aspen
218 Lodgepole pine
219 Limber pine
220 Rocky Mountain juniper
222 Black cottonwood-willow
224 Western hemlock
227 Western redcedar-western hemlock
228 Western redcedar
229 Pacific Douglas-fir
230 Douglas-fir-western hemlock
231 Port-Orford-cedar
234 Douglas-fir-tanoak-Pacific madrone
235 Cottonwood-willow
237 Interior ponderosa pine
238 Western juniper
239 Pinyon-juniper
243 Sierra Nevada mixed conifer
244 Pacific ponderosa pine-Douglas-fir
245 Pacific ponderosa pine
246 California black oak
247 Jeffrey pine
249 Canyon live oak
256 California mixed subalpine

SRM (RANGELAND) COVER TYPES [275]:
107 Western juniper/big sagebrush/bluebunch wheatgrass
109 Ponderosa pine shrubland
110 Ponderosa pine-grassland
203 Riparian woodland
209 Montane shrubland
210 Bitterbrush
216 Montane meadows
235 Cottonwood-willow
409 Tall forb
411 Aspen woodland
412 Juniper-pinyon woodland
413 Gambel oak
415 Curlleaf mountain-mahogany
418 Bigtooth maple
419 Bittercherry
420 Snowbrush
421 Chokecherry-serviceberry-rose
422 Riparian
504 Juniper-pinyon pine woodland

HABITAT TYPES AND PLANT COMMUNITIES:
White fir is named as a dominant, indicator or climax species in series, habitat, and community type descriptions in the following publications, by state:

Arizona [15,18,19,41,82,101,156,187,188,225,232,295,299,339]
California [147,151,217,244,258,263,269,307,340]
Colorado [15,17,18,37,81,83,156]
Idaho [143]
Nevada [230]
New Mexico [12,13,15,18,19,41,81,82,83,85,101,156,187,188,225,247,295]
Oregon [29,31,64,75,111,130,131,143,149,150,174,220,325]
Utah [15,18,156,201,230,231,345]
Wyoming [236]

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 [124,178,244,263]. 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% [40,263]. Understory species diversity is high. Rundel and others [263] 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 Sierras, in what may be called the white fir zone [40,263]. Near its upper elevational limits and on the eastern slope of the Sierras, California white fir shares its climax status with California red fir (A. magnifica) in extensive pure fir forests [40,124,178,185,263]. 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 Sierras, 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 [263]. 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 [40,178,185,263,331]. California white fir is an important component in Jeffrey pine communities on the east slope of the Sierras, 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 [40,178,185,263]. 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 [263]. California white fir occurs with varying degrees of dominance on drier sites in the northern Sierras, 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 [40,263,317]. 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) [111,207,208,220,263]. It is found less commonly on the east side of the Cascade Range [263]. 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 [301]. 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 [269]. 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 [31,136,306]. 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) [258]. White fir is important in closed forest stands on the Modoc Plateau in association with incense-cedar, ponderosa pine, quaking aspen, and western juniper [263,317]. 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 [288]. 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 [307]. 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) [124,317]. 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:

Codominant species State References
ninebark (P. malvaceus) UT [201,345]
mountain sweetroot (Osmorhiza chilensis) UT [201]
Oregon-grape UT, AZ, NM [201,295,345]
mountain snowberry UT [345]
quaking aspen UT, NV [230]
common juniper UT [231,345]
mountain snowberry UT [231,295]
Rocky Mountain maple UT, CO, NM, AZ [16,83,178,225,295,345]
curlleaf mountain-mahogany UT
greenleaf manzanita UT [345]
Gambel oak (Q. gambelii) UT, AZ, CO, NM [16,83,178,225,295,345]
bearberry (Arctostaphylos uva-ursi) CO, NM, AZ
bush oceanspray AZ, CO, NM
dwarf bilberry (V. myrtillus) AZ, CO, NM
sprucefir fleabane (Erigeron eximius) AZ, CO, NM [16,83,295]
sweetscented bedstraw (Galium triflorum) CO, NM [16,83]
bigtooth maple (A. grandidentatum) AZ, NM
screwleaf muhly (Muhlenbergia virescens) AZ, NM
dryspike sedge (C. foenea) AZ, NM [295]
Arizona fescue (F. arizonica) AZ, NM [178,225,225,295]
Arizona walnut (Juglans major) AZ, NM
Nevada peavine (Lathyrus lanszwertii var. leucanthus) AZ, NM
beardless wildrye (Leymus triticoides) AZ, NM
New Mexico locust (Robina neomexicana) AZ, NM
burnet ragwort (Packera sanguisorboides) AZ, NM [295]
Douglas-fir NM [178,225]

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 [201,345]. 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 [93,142,247]. 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 [20,178,225,295]. 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 [350]. 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) [322]. 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 [279] 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 [12,16,37,83,299].


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Abies concolor

GENERAL BOTANICAL CHARACTERISTICS:
White fir is a large, native, coniferous tree. Mature white fir trees in the central Sierra Nevada are 140 to 180 feet (43-55 m) tall, and 40 to 80 inches (1-2 m) dbh, but may grow larger [104,186]. Rocky mountain white fir rarely exceeds 125 feet (38 m) tall or 3 feet (0.9 m) in diameter [104]. Bark on young trunks is smooth, gray and blistered with resin vesicles, becoming thick, hard and deeply furrowed into scaly ridges with age [71,162].

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 [295]. Information on productivity of white fir is available [178,201,263].

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 [254] LIFE FORM:
Phanerophyte (undisturbed)

REGENERATION PROCESSES:
White fir reproduction is by seed, and it shows no tendency to reproduce by sprouting or layering. Cuttings can, however, be rooted with or without hormones [178]. White fir is monoecious. The male strobili are 0.2 to 0.4 inches (6-9 mm) long and are densely grouped on the underside of 1-year-old twigs about mid-crown. Female cones are 3 to 5 inches (7-12 cm) long and borne erect on 1-year-old branches, usually in the uppermost crown.

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 [104]. 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 [104]. 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 [104,119]. 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:
Because of its wide distribution, white fir is subjected to very different climates, soils, animals, plant associates and other environmental factors from place to place [186].

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 [111,263]. In Utah, white fir typically occupies cool and dry northern exposures [201,345]. 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) [263]. 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:

State Elevation Range Precipitation Range References
California 3,900-9,800 feet (1200-3000 m) [178]
Oregon 2,000-6,600 feet (600-2000 m) 14-45 inches (350-1150 mm) [64,146]
Utah 5,000-9,200 feet (1500-2800 m) [201,345]
Colorado 7,900-10,200 feet (2400-3100 m) [83]
Arizona 5,500-9,000 feet (1700-2750 m) [162]
New Mexico 6,400-10,200 feet (1950-3100 m) [295]

White fir grows on a variety of slightly to strongly acid soils from almost every type of parent material [14,104,111,178,186,201]. 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 [247,295]. 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:
California white fir is a major climax component throughout the mixed conifer forests within its range [178,225]. White fir reproduces abundantly under conditions of dense shade, and it is an aggressive pioneer species as well [201]. Successional relationships of white fir are complicated by floristic differences over its large range of occurrence [188].

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 [247]. Within the mixed conifer type, white fir tends to achieve climax dominance on moist sites [111,328] 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 [83,115,185,247,295], Douglas-fir [83,115,185,295], southwestern white pine [185], Gamble oak, New Mexico locust [295], California black oak [113], quaking aspen [40,153,178,230,245,247], 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 [83,295]. 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 [247]. 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 [27,40,113,115,184,186,258]. 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 [270].

It appears that white fir may be an early colonizer of disturbed sites, gradually increasing in dominance over time [34,139,263]. 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 [258]. 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 [247].

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 [65,104,111,149,178]. 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 [264]. 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 [83,101,134,157,247,295]. 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 [83,101,134,153,157,247]. 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 [134,157,247]. 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 [13,225,295].

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 [345]. 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:
White fir requires 2 years to complete its reproductive cycle. Cones are initiated in mid-May of the 1st year as microscopic primordia within vegetative buds. Bud differentiation occurs in midsummer and separate seed-cone and pollen-cone buds develop until each becomes dormant in the fall [300]. During the spring of the 2nd year, cone buds resume growth and conelets are recognizable in early May. In Oregon and California, second year reproduction phenology proceeds with flowering in late May to early June, and fertilization occurring shortly thereafter [108,178,235]; cones reaching full size by early to late August [104,235]; and seed dispersal beginning in late September to early October [106,119].

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 [105]. Old needles are shed primarily in the fall and winter. In California, most needles drop in October and November [46].


FIRE ECOLOGY

SPECIES: Abies concolor

FIRE ECOLOGY OR ADAPTATIONS:
White fir occurs in a variety of forest and habitat types that evolved with a variety of fire regimes. Thin-barked and resin blistered, with drooping lower branches, young white fir is highly susceptible to fire, and mature trees are only moderately fire tolerant. White fir is an aggressive, shade-tolerant species that will seed into the understory of low-elevation ponderosa or Jeffrey pine stands or into mixtures of ponderosa pine, Douglas-fir, quaking aspen, and southwestern white pine [185]. On these sites, its numbers were previously controlled by frequent surface fires. With fewer fires in the last century, it is becoming a major stand component at elevations and on sites where historically it was minor [178]. At mid-elevations in the mixed conifer and white fir zones, fires may have burned in a pattern of different severities, including patches where most of the moderately susceptible trees such as white fir, survived [25], and patches where white fir stands were completely destroyed [201]. This type of fire regime creates a forest mosaic of stands with varied structures, species compositions, and seral stages. White fir is also a component of forest communities that evolved with less frequent, stand-replacing fires. The following discussion provides examples from white fir communities that evolved with mixed, understory, and stand-replacement fire regimes.

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 [333]. 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 [25,215,305]. 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 [25,54,169,209,286,287,288,316]. 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 [339]. 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 [178,186,247,288]. Fuel loadings in this type may vary widely due to stand history and site productivity [25,331].

There is evidence that a mixed regime may have been important for perpetuation of giant sequoia groves in the Sierra Nevada [25,296]. Giant sequoia groves burned every 2-10 years for the last 3000 years and have not burned in 100-130 years [289,290,296]. The more mesic, mid-elevation, mixed conifer forests of California formerly experienced low to moderate severity wildfires every15 to 30 years [288,333]. Other areas that may have had mixed fire regimes include the Marble Mountains of northern California [305]; the mixed conifer zone in the montane forests of the Madrean borderlands; the Animas Mountains of southwest New Mexico [297]; mixed conifer forests in the Jemez Mountains, New Mexico [308]; the white fir/Rocky Mountain maple habitat type in Arizona and New Mexico [232,295]; the high elevation, white fir/forest fleabane habitat type [295]; the lowest elevations of the subalpine forest in New Mexico [86,157,247]; 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 [33,35,68,115,297]; the Sacramento and White mountains of New Mexico [224]; and ponderosa pine stands in central Oregon [253,298]. Because of changes in fuels during the last century, these areas may now experience crown fires when they do burn, with high tree mortality [5].

White fir may also be a component in ecosystems with a stand-replacement fire regime such as western subalpine forests and Douglas-fir/western hemlock forests [25]. The more arid Jeffrey pine forests on the Mojave Desert side of the mountains in southern California may also have a stand-replacement fire regime due to the slow build up of fuels in the arid environment [288]. Evidence of a stand-replacement fire regime in a white fir-Jeffrey pine forest type in the Lake Tahoe Basin is presented by Russell and others [264]. Similarly, the subalpine forests are limited by cold and are also slow growing so fires are naturally infrequent and when they do burn it is usually a stand replacing fire in severe weather [5,288].

The following table provides some fire regime intervals for ecosystems in which white fir occurs:

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
silver fir-Douglas-fir Abies amabilis-Pseudotsuga menziesii var. menziesii > 200
California montane chaparral Ceanothus and/or Arctostaphylos spp. 50-100 [59]
curlleaf mountain-mahogany* Cercocarpus ledifolius 13-1000 [28,272]
mountain-mahogany-Gambel oak scrub C. l.-Quercus gambelii < 35 to < 100 
western juniper Juniperus occidentalis 20-70 
Rocky Mountain juniper J. scopulorum < 35 
Engelmann spruce-subalpine fir Picea engelmannii-Abies lasiocarpa 35 to > 200 
blue spruce* P. pungens 35-200 
pinyon-juniper Pinus-Juniperus spp. < 35 [59]
Rocky Mountain lodgepole pine* P. contorta var. latifolia 25-300+ [24,260]
Sierra lodgepole pine* P. c. var. murrayana 35-200 
Colorado pinyon P. edulis 10-49
Jeffrey pine P. jeffreyi 5-30
western white pine* P. monticola 50-200 
Pacific ponderosa pine* P. ponderosa var. ponderosa 1-47 
Rocky Mountain ponderosa pine* P. p. var. scopulorum 2-10
Arizona pine P. p. var. arizonica 2-10 [59]
quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [59,125,213]
mountain grasslands Pseudoroegneria spicata 3-40 (10**) [24]
Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [59]
coastal Douglas-fir* P. m. var. menziesii 40-240 [59,229,259]
California mixed evergreen P. m. var. m.-Lithocarpus densiflorus-Arbutus m. < 35
California oakwoods Quercus spp. < 35 
oak-juniper woodland (Southwest) Quercus-Juniperus spp. < 35 to < 200 
canyon live oak Q. chrysolepis <35 to 200 
California black oak Q. kelloggii 5-30
western redcedar-western hemlock Thuja plicata-Tsuga heterophylla > 200
mountain hemlock* T. mertensiana 35 to > 200 
elm-ash-cottonwood Ulmus-Fraxinus-Populus spp. < 35 to 200 [59]
*fire return interval varies widely; trends in variation are noted in the species summary
**(mean)

POSTFIRE REGENERATION STRATEGY [291]:
Tree without adventitious bud/root crown
Crown residual colonizer (on-site, initial community)
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)


FIRE EFFECTS

SPECIES: Abies concolor

IMMEDIATE FIRE EFFECT ON PLANT:
White fir seedlings, saplings and poles are thin-barked and resin blistered and are highly susceptible to fire damage and kill [178]. 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 [29,168,303]. As trees mature and bark thickens, and some self-pruning of lower branches occurs, they become more resistant to fire [345]. 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 [55]. In larger trees, mortality results from crown scorch, girdled stems from cambial heating, or damage to moderately shallow roots from soil heating [303,328].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
The effects of fire on white fir vary with size and age of tree, stand density, fuel loading and fire conditions.

Prescribed low-intensity summer surface fires in mixed conifer forests of Crater Lake National Park, Oregon, resulted in high mortality of small white firs [303]. Similarly, prescribed, low-intensity fall surface fires in a giant sequoia-mixed conifer forest in Kings Canyon National Park, California, resulted in mortality of 91% of trees less than 6 inches (15 cm) dbh, 39% of trees 6-12 inches (15-30 cm) dbh, and 5% of trees larger than 12 inches dbh [168].

Greater reduction in density is obtained in stands with higher prefire densities. In white fir stands with dense vegetation, consisting of both young stands of pure white fir and open stands of white fir with a shrub understory, fires burned at high intensity and killed most trees in the area studied in the Marble Mountains of California. In lower density forest stands of white fir with old-growth characteristics, fires were of low intensity and burned down rotten logs and standing snags with very little damage to the canopy trees [305]. Prescribed fires resulted in an increase in the density of giant sequoia at the expense of white fir [164,165,169].

Greater mortality of mature trees could be expected in stands with a deep litter layer, since smoldering of the duff for long periods after the fire has passed kills the moderately shallow roots of white fir [4].

PLANT RESPONSE TO FIRE:
Following stand-replacing fires, white fir reestablishes via wind-dispersed seed. Exposed mineral soil seedbeds created by fire favor initial seedling establishment in white fir [159], but seedling survival is better in partial shade [39]. Therefore, seedlings establish soon after fire if a canopy remains [170], but may take several years to establish if the canopy has been removed.

Fire may encourage growth in white fir by eliminating competition. Evidence from a fire-scarred white fir stump in Oregon shows that after being scarred as a sapling-sized tree, it had growth release [3]. However, trees damaged or weakened by fire are also more susceptible to attack by insects and disease. Fire scars may allow a point of entry for a variety of disease and decay organisms [178,337], and fire-weakened trees that are attacked by insects can be killed within a few years [303].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
The response of white fir to fire is inconsistent and may vary with fire frequency and severity, associated vegetation in the postfire community, location of seed trees, postfire insect and disease effects, and postfire browsing by animals. Mean annual post-fire mortality of 17.8% in white fir was related primarily to fire-caused crown scorch and possibly fine root mortality in Sequoia National Park [233]. White fir is considered more fire resistant than its associated species at high elevations, but less resistant than associated species at low elevations [178,219]. Tree associates Douglas-fir and ponderosa pine are favored by more frequent fires [345]. If the time between fires is long enough, white fir seedlings can germinate and establish under brush cover and thus establish crown dominance over time [65,178,211].

In the mixed conifer zone of the Sierra Nevada, white fir seedling are often abundant under montane chaparral shrubs that form brushfields after high severity crown fires. Conard and Radosevich [65] found white fir reproducing abundantly on shrub-dominated sites, with a combined seedling and sapling density ranging from 445 to 4,453 per acre (1100-11,000/ha) where crown fires had occurred 38 to 62 years earlier. Densities of both snowbrush ceanothus and manzanita were higher on burned than on unburned and on logged than on unlogged plots [329]. Fire severity can be an important determinant of shrub response in white fir stands. Preharvest burning in a 70-year-old white fir stand in northeastern California resulted in 410,000 snowbrush ceanothus seedlings/ha in moderate-consumption burns, and 94% seed mortality in more severe burns - killing seeds to a depth of 10 cm in the soil [330,331].

Minnich [218] studied conifer reproduction on burned areas in mixed conifer forests in the San Gabriel and San Bernardino mountains of southern California. He found that seeds originating from outside the burned area were responsible for abundant white fir production on burns older than 10 years, but that reproduction was scant on burns less than 5 years old. Similarly, no white fir seedlings established within 5 years of a crown fire in the Sierra Nevada, even though several mature trees survived the fire and thus provided a seed source [65]. Another Sierra Nevada study found negligible white fir reproduction 17 years following a stand-replacing fire, even though a seed source was readily available [51]. Less than 1 year following underburning in a giant sequoia grove, white fir seedling establishment in June was abundant, with 39% survival in October [6].

Most mortality in white fir after the 1st year postfire in mixed conifer in southern Oregon was associated with bark beetles [303].

Near the Plumas National Forest, prescribed fire in a mixed-conifer-California black oak forest with a white fir component successfully reduced fuel load. When a wildfire burned through the site previously burned under prescription, fire severity and fire suppression costs were less compared to adjacent land where fire had been excluded [221]. For further information on this study, see the Research Paper by Moghaddas [221].

Fall prescribed fire on the Tharp Creek Watershed of Sequoia National Park produced 16.4% and 17.8% mean annual mortality for all size classes of white fir on 2 white fir-mixed conifer sites that were monitored for 5 years after fire. Mortality was concentrated in the subcanopy. Probability of mortality increased with percentage of crown killed and decreased with DBH. Basal area changes were also monitored before and after the fire. Compared to the unburned control, mean percent change in white fir basal area decreased an average of 0.10% on 1 site and increased 0.61% on the other. From 1989 to 1994 (includes 1 year of prefire data), percent change in white fir basal area was reduced an average of 4.97% and 6.03% on the 2 burned sites compared to the control site [233]. For more information, see a summary of the study in Fire Case Studies.

For further information on white fir's response to fire, see these Research Project Summaries:

FIRE MANAGEMENT CONSIDERATIONS:
The possible uses of fire in white fir communities include the maintenance of more desirable seral species by thinning small white fir, fuel reduction, seedbed preparation, sanitation against insects and diseases, improvement of visual resources in national parks, creating openings for wildlife habitat, and the establishment of semi-natural processes (including nutrient cycling [226,338]) [74,154,157,301,309,350].

Thinning: Prescribed burning in areas where white fir is not desired may be useful to control its abundance and promote the growth of more desirable seral species. Burning in some areas may create conditions favorable for suckering of aspen or Rocky Mountain maple [295]. Replacing conifer cover with aspen, shrub, or herbaceous vegetation can improve water yield [55]. Prescribed fire has been used to effectively eliminate fire-intolerant species such as white fir and Douglas-fir and to favor more fire-tolerant species such as ponderosa pine [27,98,115,227] and giant sequoia [163,168]. A dramatic decline in white fir basal area was observed following prescribed burning in the Sierra Nevada [233]. This may be useful in areas experiencing high levels of mortality due to stress from competition for water and resources in overcrowded stands and subsequent vulnerability to insects and disease [268]. Stephenson and Calcarone [288] developed a model to predict areas of montane conifer forest with overcrowded stand conditions. Areas predicted to be experiencing high stand densification meet all of the following criteria: vegetation type is a conifer forest, elevation is below 7,500 feet (2300 m), mean annual precipitation is greater than 25.6 inches (650 mm), canopy cover is greater than 60%, and slope is less that 60%. Fuel loads may be too hazardous to secure desired mortality of white fir while maintaining relatively low mortality of mature trees. Spring burning in old-growth ponderosa pine at Crater Lake National Park resulted in 30% mortality of ponderosa pine greater than 9 inches (22 cm) in diameter [298]. When fire prescriptions cannot ensure that young white fir will not ignite the crown of overstory trees, cutting all trees under a specified size before burning reduces this fire hazard [27]. In three different studies, white fir less than 9 inches (23 cm) dbh [170], 6 inches (15cm) dbh [223], and 11 feet tall [48] were felled before burning. This method can help to reduce fire damage from future wildfires, as well [5]. Cutting without subsequent burning is less effective [27]. A method of prescribed burning that decreases the probability of damage to mature white fir is given by Weatherspoon and others [332]. However, prescribed burning is not recommended as a thinning tool where true fir is the desired crop tree. In underburned white fir stands in southern Oregon, 36% of the residual white fir trees had sufficient scorch to cause partial cambial death that was associated with stained and decayed wood even 2 years after the burn [98].

Fuel reduction: Heavy fuel loadings and well-developed understories of shade tolerant conifers like white fir set the stage for stand-replacing crown fires [5,350]. By leaving the largest trees and treating fuels, fire tolerant forest conditions can be created, so that fire severity can be reduced. These treatments are sensible where low-severity fire regimes are now supporting high severity fires due to fuel build ups, but not in areas with stand-replacement fire regimes, where weather is the driving factor in fire severity [5]. Prescribed, low-intensity fires will kill large numbers of small white fir and reduce fuel loading, helping to reduce this threat [4,159,164,171,287,303]. Not all forest floor fuel is consumed in an initial prescribed burn [266], and much of the initial volume reduction may be replaced by material killed but not consumed in the initial fire [4,55,86,164,168,303]. The fuel ladder is generally broken by the 1st fire, so that a 2nd fire is generally easier to control, 5-10 years after the 1st [4,171]. Fire effects monitoring in Sequoia and Kings Canyon national parks reveal an average initial reduction in fuel load by 71% (93% duff and 56% woody), 1 year after prescribed burning, an increase in total fuel load from the 1-year postfire to the 5-year postfire inventory and a total fuel load exceeding prefire levels after 10 years, with woody fuels nearly double their prefire levels and duff at 28% prefire levels [163,164]. Tree density was reduced from 498 prefire to 295 post; white fir was 60% pre and 56% 1 year post; 10 years post was at 51% and giant sequoia had increased from 7% to 23% [163,255]. Between 80 and 90% of shrubs on a site will be top-killed by fire. Those capable of sprouting will do so based on season of burn and degree of duff consumption or fire severity. Sprouting shrubs are most susceptible to fire kill under dry conditions in late spring and early fall when fuel consumption is highest [4,159,160]. Summer and fall burning more effectively reduce white fir and giant sequoia fuels than does spring burning [7,167]. Fire used for fuel reduction must be handled carefully to avoid escape and stand damage [350]. Fuel accumulations are site specific but can be estimated using prediction equations based on stand basal area, tree height or diameter or with depth of forest floor and stand overstory age. Info on production and estimation of fuels and fuel characteristics are available for Sierra Nevada mixed conifer [313,314,315], giant sequoia [266,335], ponderosa pine and mixed conifer in the Southwest [265], and for mixed conifer in Arizona [122]. Fire behavior models may be used to predict how silvicultural and fuels treatments will affect fire behavior [287]. In areas with high fuel loadings, dense multistoried stands, and smoke restrictions, it may be necessary to use silvicultural tools that include prescribed fire [123,222,246].

Preharvest underburning/site preparation: Underburning before timber harvesting with the shelterwood method in mixed conifer forests can be used to aid natural regeneration, and reduce shrub seed reserves in the soil [55]. Prescriptions developed in the Blue Mountains of northeastern Oregon recommend felling all understory trees less than 6 inches (15 cm) in diameter before burning. The combination of cutting and burning removes all advanced regeneration, thus sanitizing the site of heart rot which is present in many 5- to 6-inch diameter (12.5 -15 cm) white fir (these trees are white fir x grand fir hybrids). Following harvest, seedling establishment of all conifers was abundant [223]. In some locations preharvest underburning is not recommended because it stimulates dormant shrub seeds to germinate [329]. In the Siskiyou Mountains, soil erosion can be a problem following fires that remove duff layers on granitic soils [30]. Severe fires can eliminate dwarf mistletoe by destroying infected stands [69]. In the Blue Mountains of Oregon, prescribed burning was initiated to sanitize the sites of heart rot and stagnated understory, prepare the site, and encourage natural regeneration [222,246].

Fire can enhance range and wildlife habitats by rejuvenating forage and browse species [55,222,237,246]. Use of prescribed fire for fuel management in California spotted owl habitat is suggested to reduce the threat of stand replacement fires [274,333]. Prescriptions may include leaving snags and larger size fuels for wildlife habitat [222,246]. Additionally, moisture stored in these logs may expedite forest recovery by providing important refuges for roots and associated mycorrhizal fungi of pioneering vegetation [23].

Restoring fire to its natural role in Sierra Nevada forests by prescribed burning at lower and middle elevation types and by allowing lightning fires to burn in higher elevation forests is suggested [169]. Returning fire and natural process to areas that evolved with mixed fire regimes requires a deliberate approach based on descriptions of the mosaic of aggregations that constituted the presettlement forest communities, a determination of the kinds of vegetation changes that it is feasible to make, and the degree of success to be expected from different vegetation management techniques, keeping in mind that that the initial restoration program will determine the character of the vegetation mosaic for centuries to come [52]. Structural maintenance objectives may be biologically infeasible, thereby restricting management to the pursuit of process maintenance objectives [53]. This is complicated by the need to return the forest community to prefire exclusion structure before reintroducing fire to the ecosystem. Managers need region specific fire regime data to develop process-based management schemes [302], and/or determine reference conditions for key ecosystem functional and structural components that may be used in an ecosystem management context [115]. Characteristics for mixed conifer forest reference stands at Sequoia are given by Riegel and others [257]. Tools available to fire managers for prescribed burning planning include PREFEX, a small expert system for managing fire effect information [99], and the Fire Monitoring Handbook [255]. Smoke production and air quality must be considered [58]. Water quality was not adversely affected by prescribed burning in a ponderosa pine-mixed conifer watershed in east-central Arizona [121].


FIRE CASE STUDIES

SPECIES: Abies concolor

FIRE CASE STUDY CITATION:
Zouhar, Kris, compiler. 2001. Effects of a prescribed burn at Tharp's Creek, Sequoia National Park, on white fir. In: Abies concolor. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ ].

REFERENCE:
Mutch, Linda S.; Parsons, David J. 1998. Mixed conifer forest mortality and establishment before and after prescribed fire in Sequoia National Park, California. Forest Science. 44(3): 341-355. [233].

Download a PDF of this study.

SEASON/SEVERITY CLASSIFICATION:
fall/mixed

STUDY LOCATION:
The Tharp's Creek (burned) and Log Creek (unburned) watersheds are located in the Giant Forest area of Sequoia National Park, California. Two reference stands (upper and lower) are located in each watershed.

PREFIRE VEGETATIVE COMMUNITY:
White fir dominates in all stands, with an inverse J-shaped size distribution. Sugar pine is most common in Lower Tharp's and upper Log stands. Red fir (Abies magnifica) is present in significant numbers only in the Lower Log stand. Giant sequoia (Sequoiadendron giganteum), incense-cedar (Calocedrus decurrens), Jeffrey pine (Pinus jeffreyi) and California black oak (Quercus kelloggii) are only minor components of these stands. Shrub cover ranges form 2% to 20% in the four stands and is comprised mainly of greenleaf manzanita (Arctostaphylos patula), mountain whitethorn (Ceanothus cordulatus), bush chinquapin (Chrysolepsis sempervirens), and gooseberry (Ribes spp.). Litter and duff are the predominant ground cover, with scattered herbaceous vegetation.

TARGET SPECIES PHENOLOGICAL STATE:
The phenological state of white fir on the site at the time of burning is not given, however, judging from the timing of the fire, it is likely that white fir seeds had been dispersed and the trees were dormant.

SITE DESCRIPTION:
The study sites comprise the headwater drainages of Tharp's Creek and Log Creek. Soils of both watersheds are predominantly pachic xerumbrepts, derived from granodiorite. Slopes are moderate to steep. The aspect of Tharp's watershed ranges from south to south-east, and Log watershed aspect is primarily west to south-west and north-west. Elevations are 6875 to 7150 feet (2097-2180 m) in the Tharp's watershed and 7080 to 7775 feet (2158-2371 m) in the Log watershed. Mean annual precipitation in the area is 50 inches (1255 mm), with about half falling as snow. Mean January and July temperatures are 32 degrees Fahrenheit (0°C) and 64 degrees Fahrenheit (18°C), respectively.

FIRE DESCRIPTION:
The Tharp's prescribed burn was a 35 acre (14 ha) fire ignited October 23-26, 1990. Ignition occurred primarily in early evening and into the night when relative humidity was 30-40%. Average fuel moistures for litter ad duff were 28%, for 100 hr fuels 14%, and for 1000 hr fuels 64%. Air temperatures during ignition ranged from 50 to 60 degrees Fahrenheit (10-16 °C) and winds were calm. Fire behavior ranged from a backing fire with flame lengths of 0.2 to 0.5 feet (0.05-0.15 m) and rates of spread up to 0.3 feet (0.1 m)/minute, to a strip headfire with flame lengths of 2 to 8 feet (0.6-2.4 m). Areas with heavy fuel concentrations and standing snags burned with the greatest severity. Total preburn fuel load was 94 tons/acre (210 Mg/ha) and total reduction was 85%, with the highest reduction in litter/duff (97%) and 1-hr fuels.

FIRE EFFECTS ON TARGET SPECIES:
The prescribed burn in the Tharp's Creek watershed resulted in a dramatic rise in mortality rates for 5 years following the fire when compared both with the prefire mortality rates and with the unburned Log Creek watershed. Average annual mortality for all trees greater than 4.6 feet (1.4 m) tall in the Lower and Upper Tharp's Creek plots during the 5 year preburn period was 0.8% and 0.6%, respectively. Annual mortality rates in the 1st postburn year increased to 35.2% and 49.4%, and declined to 2.6% and 5.0% by the fifth postfire year. While these rates are well above prefire mortality rates, the 2.6% is within the range of annual mortality rates recorded for the Log Creek watershed for the same period. The greatest reduction in white fir numbers was in the intermediate and subcanopy classes.

Populations and mortality of white fir trees >4.6 feet (1.4 m) tall in the Lower Tharp's stand:

Live trees/ha Mean annual % mortality
Canopy class 1985 1990 1995 1986-1990 1991-1995
Dominant 8 8 5 0.0 7.0
Codominant 87 83 61 1.2 5.5
Intermediate 125 121 57 0.7 13.7
Subcanopy 155 149 17 0.7 30.7
All classes 375 361 140 0.8 16.4

Populations and mortality of white fir trees >4.6 feet (1.4 m) tall in the Upper Tharp's stand:

Live trees/ha Mean annual % mortality
Canopy class 1985 1990 1995 1986-1990 1991-1995
Dominant 34 34 20 0.0 9.8
Codominant 76 75 49 0.3 8.1
Intermediate 108 105 31 0.6 19.5
Subcanopy 120 114 8 1.0 28.0
All classes 338 328 108 0.6 17.8

Primary factors associated with mortality in both watersheds during the prefire period and on the Log Creek watershed in general, were dwarf mistletoe, fir canker, fir engravers and stem/root failure that caused crushing by another tree. The postfire mortality in the Tharp's Creek watershed was most directly related to fire-caused crown scorch. There is no indication of a relationship between pre-existing disease or insect conditions and fire-induced mortality, since similar percentages of trees that survived the fire had dwarf mistletoe, and fire engravers associated with them. Fine root mortality may have also played a role in the death of trees several years after the fire, since the 97% reduction of litter and duff indicates a particularly severe fire that would have likely caused substantial fine root mortality. During the prefire period, the Lower Tharp's stand had a slight decline in total basal area due primarily to the death of numerous codominant and intermediate white fir trees, while the Upper Tharp's stand had an increase in basal area during this period. Both stands had a large decline in basal area after the burning due primarily to fire-related mortality. The most important change in size structure in the Log Creek watershed was in the smallest size classes. In the Tharp's Creek stands, there was a dramatic change in the size structure during the postfire period with a decline in mean number of trees/ha in most sized classes, including 75% of the trees < 50 cm dbh killed, and 25% of trees larger than 50 cm dbh killed. The different tree species present died in proportion to their frequency in the watershed. A large number of seedlings had established after the burn on Tharp's Creek and had more rapid height growth relative to seedlings in the Log watershed.

FIRE MANAGEMENT IMPLICATIONS:
Suppression and higher incidence of insects and disease in higher density stands are cited as primary reasons for mortality in unburned stands. In this study, a drought during the 1987-1992 time period is thought to have contributed to the stress that led to mortality in the larger size classes in the Log Creek watershed. In white fir, the probability of mortality increased with percentage of crown scorch, and decreased with dbh. This type of information can help improve the ability of mangers to predict tree morality from prescribed burning and to plan burning conditions to meet specific mortality objectives. Differences in mortality between the Upper Tharp's stand and the Lower Tharp's stand are thought to be due to differences in fire severity between the two stands, with the more severe fire causing higher rates of initial mortality in the larger size classes. The large reductions in tee densities and basal areas in the Tharp's watershed will provide more opportunities for successful establishment of less shade-tolerant species and will help reduce fuel inputs, presumably reducing the hazard of uncontrollable wildfire in the future. However, future burns will likely be necessary to maintain reduced tree densities and low fuel accumulation rates. Mortality is expected to continue to decline over the next several years until they reach near pre-burn levels. It is also expected that the large number of seedlings that established after the burn will result in substantial amounts of ingrowth within the next 10 years.


MANAGEMENT CONSIDERATIONS

SPECIES: Abies concolor

WOOD PRODUCTS VALUE:
Historically white fir was considered undesirable for timber. Now that the availability of premium timber species has declined, white fir is being recognized as a highly productive and valuable tree species and is widely used in the wood products industry [109,148,178]. White fir is a general, all-purpose, construction-grade wood used extensively for solid construction framing and plywood, and to a lesser extent, for pulpwood [148,278]. It is also used for poles and pilings because of its straight grain and low taper, but requires large amounts of preservatives because the heartwood decays rapidly. It is poorly suited for firewood because of its low specific gravity and heat production (80% as much heat by volume as Douglas-fir produces), but it is used for firewood anyway [278].

IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Stands dominated by white fir seldom produce enough forage for domestic livestock grazing except on harvested or open forest sites, or where grasses and sedges dominate the understory [81]. These forests do, however, provide abundant browse and cover for large and small wildlife species [83,295]. Deer, elk, and bear often use white fir habitats as either summer or winter range [2,189]. Mule and black-tailed deer generally eat small amounts of white fir during the spring, fall, and winter, and sometimes larger amounts during the summer [152,177,189]. Mule deer are especially fond of succulent, new white fir growth in the spring [114,178,185]. Spring browsing of white fir by deer can be particularly heavy when small white firs are the only green food available; all of the current or previous year's growth may be consumed [119]. Porcupines enjoy the bark of white fir, and may destroy saplings in their enthusiasm [138,185,201]. Rodents feed on the cambial tissue of white fir in preference to that of Douglas-fir. During the winter, mice feed on the leaders of small white firs near snow level. In the spring, they feed on seedlings, sometimes destroying a large proportion of the current year's seedlings [138,201]. Pocket gophers also feed on white fir seedlings in the winter and spring [157,178]. White fir needles are an important part of the diet of blue grouse [127,197]. White fir seeds are eaten by several species of small mammals and birds including grouse [183,323], chipmunks and mice [324], flying squirrels [346], chickadees, crossbills, and Clark's nutcracker [127,197]. In the southern Cascades and Sierra Nevada, the Douglas squirrel cuts and caches white fir cones during late summer and fall, before the cones are fully mature [106,114,185]. Hollow logs and snags of white fir can be important to various birds and animals for foraging in the interior wood [240].

There are about 33 species of mammals commonly present in the white fir forest type in California, and of these 7 are generally associated with mature forests [178]. Hollowed-out trunks of old white fir trees, dead or alive, are denning sites for mammals ranging form weasels to porcupines to black bears [186]. In one study, abundance of white fir had a strong positive association with California mountain beaver habitat use [42]. About 123 species of birds are found in the white fir type of California and southern Oregon, about 50 of which are associated primarily with mature forests, and many of which use mature white fir trees and snags for foraging, roosting, nesting and/or breeding [155,178,212,228,318]. These include bald eagles [78,293], northern spotted owls [107,182,304], California spotted owls [44,61,128,319,320], flammulated owls [321], brown creepers and red-breasted nuthatches [1]. In Oregon, mature white fir forests provide nesting and feeding habitat for important bird species, such as the goshawk, pileated woodpecker, white-headed woodpecker, and, when near lakes or streams, osprey and bald eagle [149]. Reptiles in white fir forests are represented by 17 species, mostly at lower elevations, 8 of which are associated with mature forests [178].

In the southwest, desert bighorn sheep and white-tailed deer occasionally browse white fir [183,277]. 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 [190,295]. 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 [12,101,295]. 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 [101,295]. White fir forests in the Southwest provide habitat for Mexican spotted owls in Arizona, New Mexico [116,194], and Utah [342]; goshawks in Arizona [70,196,256]. Thick-billed parrots, reintroduced in the mountains of southeastern Arizona, occur in mixed-conifer forests with white fir [280]. 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 [251].

PALATABILITY:
Because they contain resins, terpenes, and other substances that make the foliage irritating to the digestive tract, most conifers are not particularly palatable to grazing animals. White fir may be slightly palatable to goats [267]. Immature foliage is enjoyed by mule and black-tailed deer [119,189]. White fir seeds are palatable to numerous species of small rodents, although seeds of Douglas-fir, ponderosa pine, and sugar pine are preferred [106,250].

NUTRITIONAL VALUE:
White fir browse is low in protein [92].

COVER VALUE:
White fir's evergreen foliage provides good hiding cover year-round and is usually continuous from the ground upward on trees less than 8 to 10 inches (20-25 cm) dbh [148]. White fir stands of this nature provide excellent hiding cover for large wildlife species such as deer, elk, and black bear [141,187]. If enough shrubs are present in the understory to provide adequate hiding cover, mature white fir forests are used by deer during fawning and by elk during calving [149,174].

In mixed conifer forests of the Sierra Nevada, cavity-nesting birds prefer white fir snags over the snags of associated trees. Cavity nesters using white fir snags include the American kestrel, mountain chickadee, brown creeper, mountain bluebird, house wren, tree swallow, northern flicker, and several nuthatch, sapsucker and woodpecker species [252]. Other forest songbirds nest within white fir foliage. Hollowed trunks of older trees are used by several species of mammals such as black bears, for hibernation; American martens, for dens and rest sites; and bushy-tailed woodrats, flying squirrels and other small mammals for cover [185,240]. Most bear dens in Yosemite National Park are found in the hollowed trunks of white fir [202].

VALUE FOR REHABILITATION OF DISTURBED SITES:
White fir can be planted on disturbed sites within forest vegetation types where it naturally occurs. It is a good soil stabilizer and may be particularly useful on roadcuts [249]. Fir seedlings exhibit very slow initial growth, and are therefore usually outplanted as 2- to 3-year-old seedlings or 3- to 4-year-old transplants [108]. Transplanting nursery stock is more successful than direct seeding [249]. White fir can be propagated from stem cuttings, which root easily when treated with a rooting medium [88]. Because this wide-ranging tree exhibits a large degree of genetic variation, seed or planting stock for rehabilitation projects is best provided by a local source [214,249]. Methods for collecting, processing, testing, storing, and planting white fir seeds have been discussed in detail [90,108].

OTHER USES AND VALUES:
White fir is a valuable ornamental tree. It is often used for ornamental plantings in rural and urban landscapes in northern US cities, because it is attractive and frost-hardy [185,202]. White fir is not, however, very tolerant of air pollution and therefore seems best suited for suburbs or rural areas [175]. White fir eventually attains great size and is best grown in parks or other open public areas. White fir is used extensively in the Christmas tree industry [148,178]. Native Americans used the needles for tea [149].

OTHER MANAGEMENT CONSIDERATIONS:
Ecosystem management: Changes in white fir ecosystems are evident and well documented and are attributed to many human activities and their interactions on the landscape (for example, see [72,209,234]). Some management objectives call for some form of "ecological restoration", or the "restoration of natural conditions", or the reversal of recent, human-caused ecological degradation, based on reference conditions. These reference conditions can occur over a range of temporal and spatial scales, and are determined by detailed study of historical and ecological data, including fire history, of a particular site or ecosystem [115,123,161,227,290]. Once these historical reference conditions are estimated, they may be used to delineate management objectives based on conditions that are within a range of historical variability for a particular site, and the tools necessary to achieve them [123].

For example, decades of research in giant sequoia groves of the Sierra Nevada (e.g., [46,47,167,262,286,292,294,296]) make it one of the better understood ecosystems, and reference conditions are available for these forests [286,290]. Still, there are limitations here that may also be faced by scientists and land managers in other forest ecosystems [290]. Researchers have found it easier to determine past fire regimes than to determine past grove structures. Surface fires had 2 to 3-year mean fire return intervals at Sequoia National Park for more than 1300 years before the era of fire suppression [172,296]. Most giant sequoia groves are now overwhelmingly dominated by white fir which couldn't have survived in such numbers under such a fire regime [289]. This increased density of white fir in giant sequoia groves may have implications for changes in the natural fire regime from surface fires to crown fires. It may also have implications for damage by insects and diseases, such as annosus root rot, that may also affect giant sequoia [248]. Using silvicultural techniques to restore prehistoric structure alone may not restore healthy ecosystem function, but it is possible that restoration of fire may restore the former structure of sequoia groves [289,290]. For example, giant sequoia seedlings numbered between 7,514 and 40,130 per acre (18,560 and 99,120 per ha) after prescribed burning at Redwood Mountain [170]. Conversely, where group selection harvest with different slash treatments was applied in giant sequoia stands in an attempt to simulate the structural complexity of the prehistoric, patchy, high intensity fire regime that once existed there, regeneration in the small openings was dominated by white fir instead of giant sequoia. Giant sequoia seedling density ranged from 0 to 57seedlings/acre (0-141.5 seedlings/ha). Important ecosystem processes, such as increased seed dispersal in giant sequoia following patchy, high intensity fire and large scale nutrient cycling, are not duplicated by harvest alone [285]. It may be necessary to use a combination of treatments.

In areas shifting from fire-climax ponderosa pine to fire-intolerant white fir, the ecologically appropriate treatment may be to thin white fir stems from below and follow with prescribed fire, monitoring the effects of the treatment and fine-tuning as needed. It is important that such activities avoid the following: 1) excessive opening of overstory canopies; 2) road building and damage to soils; 3) thinning in mid- to high elevation and moist forests where dense understories and long fire intervals are more characteristic; and 4) large-scale conversion of closed-canopy forests to open-canopy, even-aged stands since this would adversely affect many wildlife species such as the northern spotted owl and lynx who depend on closed canopy and dense forests, respectively [79]. Leaving some mid and late successional stands would allow for a diversity of stand ages, structures, characteristics on the landscape. Definitions and characteristics of different stages of forests in which white fir is a component are available [281,282].

Wildlife: Managing white fir forests for wildlife habitat involves complex interactions of several plant and wildlife species, and consideration of stages of forest development that are important to the species of interest. Relationships of habitat for Rocky Mountain elk and Rocky Mountain mule deer to timber management and stand characteristics in white fir forests in Oregon have been explored [49,76]. White fir habitat is not used heavily by Columbian black-tailed deer who seem to prefer the mixed conifer, montane hardwood and annual grassland habitats on the west slope of California's coast range, suggesting that the exclusion of fire and subsequent changes in these forests may have adversely affected habitat for these deer [192]. Bird species diversity was found to be higher in the early postfire and mature forest successional stages in the Sierra Nevada, and lowest in the brush-dominated phase of succession [51]. Hollow logs and snags can be important to various birds and animals for nesting, foraging, denning and roosting sites [240]. Therefore, leaving snags and logs might be an important consideration in a management prescription. Leaving "high-cut stumps" was evaluated as a possible method for simulating snags for wildlife habitat [228]. White fir forests are home to several sensitive, threatened and endangered species. 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 and are vulnerable to some forest management practices [251]. Management recommendations for wildlife habitat are given for wildlife in general [60], nongame birds [276], the northern goshawk and its prey species in the southwest [70,256], for the California spotted owl [50,210,319,320], Mexican spotted owl [95,312], and bald eagle [78,80]. Forest practices that emphasize the retention of mature trees and coarse woody debris also promote the abundance and diversity of truffles, which are integral an functionally important members of forest ecosystems [23].

Timber harvest and regeneration treatments: White fir can be regenerated naturally or artificially. Advanced regeneration of white fir greater than 4.5 ft (1.4 m) at the time of release tended to grow taller than projected growth of planted seedlings of Douglas-fir on similar sites in southwest Oregon [173]. Most white fir stands have been managed for timber production using even-aged management techniques [178,180,181]. Even-aged management by seed tree method is described by Aune [32] with guidelines for selecting appropriate individuals to leave as seed trees in white fir. Clearcutting and shelterwood cutting have been successful at promoting regeneration of white fir, as long as the maximum downwind width of openings does not exceed 1.5 to 2 times the height of trees left as seed sources [178]. Shelterwood methods generally result in the best regeneration of white fir [201,261], although heavy overstory removal in some areas may favor Douglas fir, ponderosa pine, or hardwoods over white fir. With less overstory removal, such as by light shelterwood cutting or selection cutting, regeneration of shade-tolerant white fir will be favored. Any kind of partial cutting where white fir is present will favor white fir and increase its importance in the stand [178]. Partial harvesting of an old-growth interior ponderosa pine stand in northeastern California resulted in increased growth rate of white fir. However, mortality exceeded recruitment into the largest size classes presumably due to competition with the tremendous number of smaller stems stressing the older trees. The dramatic increase in the smaller diameter classes is most likely a response to partial cutting without burning [87]. Group selection and patch clearcutting resulted in good regeneration in an Arizona mixed conifer forest [94]. The group selection method is discussed by Laacke [179] with reference to white fir. Response of white fir to different timber harvest treatments are given by Vora [327], and show an increase in white fir numbers with no treatment as well as with heavy overstory removal in northeastern California after 40 years. These unexpected results impress the variability of ecosystem response and suggest site specific management plans.

Uneven-aged management, such as the single-tree selection method [132], may produce stands that most closely resemble reference conditions. However, uneven-aged management of white fir, requiring repeated selective harvests (multiple entry), has not been recommended in the past because it promotes several pest problems, such as decay fungi and insects, which take advantage of wounded trees and freshly cut stumps, especially in the Pacific Northwest [9,118,148,238]. Thinning operations also favor these pests because 20 to 50% of the residual trees may be wounded [9,148]. Suggestions for reducing injuries during stand management activities are given by Aho and others [10]. Immediate removal of stumps may be effective in preventing the spread of disease fungi, but it is highly disturbing to the soil and may cause excessive erosion and loss of site productivity [97]. Chemically treating freshly cut fir stumps may be an alternative [289].

Competition and Animal damage: Establishment of white fir may be difficult where graminoid cover is dense [295]. Dense brush does not prevent regeneration of white fir, but it may slow down establishment, with white fir taking 30 to 50 years to overtop shrubs [180]. Managers have sometimes used cattle to control brush and aid in regeneration following clearcutting in the mixed conifer forests of the Sierra Nevada [21]. However, free-ranging cattle favor riparian areas in these forests, so their usefulness in this endeavor may be related to the proximity of the site to a riparian area [166]. Furthermore, white fir seedling establishment may be difficult where damage from livestock trampling is possible [157,178]. Protective plastic tubing can be used to protect seedlings threatened by gophers and other rodents. Browsing of seedlings by deer and elk can reduce height growth for years, but seldom kills plants. Browsing does not seriously affect growth of trees over 4 feet (1.2 m) tall [180]. Methods of mechanical and chemical control of shrub competition are available [67,180].

Pests and diseases: Heavy to severe mortality of white fir was reported throughout Idaho and Utah in the late 1980's most likely attributed to insects and diseases [199]. Filip and Schmitt [98] provide a review of root diseases, stem decays, and dwarf mistletoes of true firs, and the effects of management techniques, especially silvicultural techniques such as commercial and precommercial thinning on these diseases. It has been argued that if we leave late-successional reserves or "overmature" stands for critical habitat in the short-term that we are increasing "the risks of insect outbreaks, tree-killing pathogens, and catastrophic wildfires" [62,86]. Others suggest that insect and disease outbreaks are part of the evolutionary scene and helped to create mosaics of contrasting successional stages on the landscape [247].

Dwarf mistletoes: The trunks of California white fir are often malformed or broken off where dwarf-mistletoe infections have created stem cankers that cause weak spots and reduce the strength of the lumber produced [178,185,200]. Two species, white fir mistletoe (Phoradendron bolleanum ssp. pauciflorum), and white fir dwarf mistletoe (Arceuthobium abietinum f. sp. concoloris) are responsible, and can be a serious problem in some areas [137,178]. White fir dwarf mistletoe occurs on white fir throughout most of its range in California, Nevada, Arizona, and southern Oregon [137]. White fir may be infected by Douglas-fir dwarf mistletoe in Utah and New Mexico [56,137]. Infected trees may suffer significant growth losses and become more prone to infection by other diseases such as Cytospora abietis, a fungus that causes "flagging" and kills branches and further reduces growth [137]. Infected trees are also more susceptible to attacks by bark beetles and heart rots. Dwarf mistletoe and fir canker were the most important pathogens, followed by fir engraver, associated with death in white fir in Sequoia National Park over a 5 year period [233]. A detailed discussion of the dwarf mistletoes as ecological components of forest canopies is provided by Mathiasen [200].

Decay fungi: White fir can be severely damaged or is highly susceptible to a number of decay fungi including annosus root disease (Heterobasidion annuosum), Armillaria root disease (Armillaria spp.), laminated root diseases, yellow cap fungus (Pholiota limonella), Indian paint fungus (Echindontuim tinctorium), and white pocket rot (Phellinus pini) [97,239,273]. Decay fungi may enter the tree through wounds (e.g. annosus) associated with mechanical injuries, fire, insects and/or frost cracks; or may be dormant in the tree and activated by wounding (e.g. Indian paint fungus) [8,11,96,238]. Stem decay losses in white fir can be large, with over 20% attributable to annosus root disease in eastern Oregon [10,11]. Annosus root disease may be the most damaging pathogen to true firs east of the Cascades in the Pacific Northwest [118]. Although it does not usually kill white fir directly, annosus produces moisture stress and loss of vigor and can predispose the tree to attack by bark beetles. Filip [96] presents an equation for estimating the volume of timber loss due to stem decay in white and other true fir stands. Symptoms and diagnosis of annosus root disease are given by Schmitt [271].

Insects: The fir engraver beetle is the most damaging white fir pest, causing major losses throughout the range of white fir [344]. Maintenance of stand health and vigor is the only known control. Of the many insects that feed on white fir foliage, a few can cause serious damage. The Douglas-fir tussock moth is a serious defoliator [178,341,343], as are the western spruce budworm [195,247], the New Mexico fir looper, and the white fir needle miner [178]. White fir seedlings and saplings lack chemical defenses against, and tend to be killed by budworm feeding, while healthy mature trees usually survive [247]. Susceptibility to budworm may be reduced by thinning young white fir [247,295]. Extensive spraying with chemical insecticides has been shown to be futile [247]. Further discussion of western spruce budworm population dynamics and ecology is available [326,344]. Insects that may cause damage to white fir cones and seeds include seven genera, the most abundant and damaging of which are seed maggots and the fir cone looper [178]. Cutworms may cause significant seedling mortality [119,178].

White fir is sensitive to oxidant damage from air pollution [157,216,263], but less sensitive than some associated species [40].


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