Stephen F. Arno and Raymond J. Hoff
Whitebark pine (Pinus albicaulis Engelm.) is a slow-growing, long-lived tree of the high mountains of southwestern Canada and western United States. It is of limited commercial use, but it is valued for watershed protection and esthetics. Its seeds are an important food for grizzly bears and other wildlife of the high mountains. Concern about the species has arisen because in some areas whitebark pine cone crops have diminished as a result of successional replacement and insect and disease epidemics (6,48).
Whitebark Pine is distributed from 37 to 55N latitude and from 128 to 107W longitude (Arno and Hoff 1990). The total global extent of occurrence has been estimated to be 337,067 km2 with an estimated 190,067 km2 in Canada and the remaining 147,000 km2 in the U.S.A. (COSEWIC 2010). The global area of occupancy has not been calculated but would be in excess of 2,000 km2.
Its distribution is split into two broad sections, one following the British Columbia Coast Ranges, the Cascade Range, and the Sierra Nevada. The Rocky Mountain distribution extends along the high ranges in eastern British Columbia and western Alberta, and southward at high elevations to the Wind River and Salt River Ranges in west-central Wyoming. The species occurs as high as 3,050 to 3,660 m in the Sierra Nevada and northwestern Wyoming, 2,590 to 3,200 m in western Wyoming and as low as 900 m in the northern limits of its range in British Columbia.
In the USA, outlying populations of Whitebark Pine are found atop the Sweetgrass Hills in north-central Montana 145 km east of the nearest stands in the Rocky Mountains across the Great Plains grassland, in outlier stands in the Blue and Wallowa Mountains of northeastern Oregon and in small, isolated ranges in northeastern California, south-central Oregon, and northern Nevada (Arno and Hoff 1990).The oldest known whitebark pine tree is found in central Idaho on the Sawtooth National Forest (Perkins and Sweetnam 1996) exhibiting homozygosity for 13 isozyme loci (12 for common alleles and one for a rare allele) (Mahalovich and Hipkins in press).
Global Range: A dominant tree in many upper subalpine forests of western North America; it is limited to subalpine and timberline zones from west-central British Columbia (55N) east to west-central Alberta and south to central Idaho, southwestern Wyoming, and southern California (36N) (Murray, 2005; Ward et al., 2006). Its distribution splits into 2 broad sections, 1 following the Coast and Cascade ranges and the Sierra Nevada, and the other following the northern Rocky Mountains. Scattered populations occur between the 2 sections in Great Basin regions of eastern Washington and Oregon and northern Nevada (Burns and Honkala, 1990; Fryer, 2002). Little (1971) mapped the range of this species, and a digitized representation of that map (USGS 1999) covers approximately 400,000 square km.
Regional Distribution in the Western United States
This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):
BLM PHYSIOGRAPHIC REGIONS :
1 Northern Pacific Border
2 Cascade Mountains
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
Occurrence in North America
Whitebark pine is abundant and vigorous on the dry, inland slope of the Coast and Cascade Ranges. It is absent from some of the wettest areas, such as the mountains of Vancouver Island. In the Olympic Mountains, it is confined to peaks in the northeastern rain shadow zone. Whitebark pine also occurs atop the highest peaks of the Klamath Mountains of northwestern California.
The Rocky Mountain distribution extends along the high ranges in eastern British Columbia and western Alberta, and southward at high elevations to the Wind River and Salt River Ranges in west-central Wyoming.
A small outlying population of whitebark pine is found atop the Sweetgrass Hills in north-central Montana 145 km (90 mi) east of the nearest stands in the Rocky Mountains across the Great Plains grassland (73).
The coastal and Rocky Mountain distributions lie only 100 km (62 mi) apart at their closest proximity (10). Even this narrow gap is not absolute; small groves are found on a few isolated peaks in between in northeastern Washington. In addition to the main distribution, whitebark pine grows in the Blue and Wallowa Mountains of northeastern Oregon and in several isolated ranges rising out of the sagebrush steppe in northeastern California, south-central Oregon, and northern Nevada.
- The native range of whitebark pine.
Whitebark pine is a small to medium-sized native conifer. Tree height typically ranges from 40 to 60 feet (12-18 m) at maturity [30,64,114], reaching 5 feet (1.5 m) in diameter . The largest recorded specimen is in the Sawtooth National Recreation Area of Idaho. It is 69 feet (21 m) tall with a 27.6-foot (8.4-m) circumference and a 47-foot (14-m) crown spread . In pure, upper-subalpine stands, trees seldom exceed 50 (15 m) feet in height. Trees at the species' upper elevational limits grow in low shrub and krummholz forms that are < 3 feet (1 m) tall [47,87,194]. Trees may have a single-stemmed or a clumped, multi-stemmed habit [229,230]. Site differences and Clark's nutcracker seed-caching behavior may affect frequency of clumping (see Regeneration Processes below). A survey of whitebark pine at 10,000 to 10,200 feet (3,000-3,100 m) elevation on the Inyo National Forest, California, showed that multi-stemmed forms were more common: only 5.8% of sample trees were single-stemmed . At 7,700 to 10,500 feet (2,300-3,200 m) on the Breccia Cliffs of Wyoming, 53% of whitebark pine was single-stemmed . Several to all stems in a clump may be genetically distinct individuals .
Bark thickness is thin to moderate, seldom reaching over 0.4 inch (1 cm) . Branches of mature trees are ascending . Needles are in bundles of 5. They may reach 7 inches (18 cm) in length, or as little as 1.5 inches (3.8 cm). Mature female cones are 1.6 to 3 inches (4-8 cm) long . They are located mostly at the tops of the upswept branches and are readily recognizable from the air, probably an adaptation to encourage seed foraging by Clark's nutcrackers. The purple cast of mature cones may further aid Clark's nutcrackers in finding ripe seed. Cone color is also the easiest way for humans to distinguish between whitebark and the morphologically similar limber pine [116,117]. A female whitebark pine cone contains an average of 75 seeds. Whitebark pine's wingless seeds are large and heavy for Pinus species: 7 to 10 mm in length and an average mass of 72 mg (+ 13 mg) per seed [21,89].
Tree stocking in whitebark pine communities can be low , but whitebark pine attains considerable cover on some sites. A stand on the Wenatchee National Forest of Washington supported 143 to 358 whitebark pine/acre with 41-214 feet2/acre basal area . On the Okanogan National Forest of Washington, mean overstory cover in a whitebark pine/pinegrass community was 27% .
Whitebark pines at high elevations often attain extreme age. Stands in the Wind River Range, Wyoming, and Jasper National Park, Alberta, have been aged at > 600 and 700 years, respectively [133,194]. The oldest recorded specimen is on the Sawtooth National Forest of Idaho, over 1,270 years old .
Whitebark pine is extremely wind firm. High-elevation trees on shallow, undeveloped soils frequently endure near-hurricane-force winds .
Catalog Number: US 61140
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Original publication and alleged type specimen examined
Preparation: Pressed specimen
Collector(s): J. S. Newberry
Year Collected: 1854
Locality: Cascade Mountains., Oregon, United States, North America
Elevation (m): 1981 to 1981
- Isotype: Engelmann, G. 1863. Trans. Acad. Sci. St. Louis. 2: 209.
Sierra Nevada Forests
The Limestone salamander is a highly localized endemic of the Sierra Nevada forests foothills conifned to a limited reach of the Merced River. The Sierra Nevada forests are the forested areas of the Sierra Nevada Mountains, which run northwest to southwest and are approximately 650 kilometers long and 80 km wide. The range achieves its greatest height towards the south, with a number of peaks reaching heights of over 4000 meters. Several large river valleys dissect the western slope with dramatic canyons. The eastern escarpment is much steeper than the western slope, in general.
The Sierra Nevada forests ecoregion harbors one of the most diverse temperate conifer forests on Earth displaying an extraordinary range of habitat types and supporting many unusual species. Fifty percent of California's estimated 7000 species of vascular plants occur in the Sierra Nevada, with 400 Sierra endemics and 200 rare species. The southern section has the highest concentration of species and rare and endemic species, but pockets of rare plants occur throughout the range.
Sierra Nevada amphibian endemics are the Yosemite toad, Mount Lyell salamander (Hydromantes platycephalus), the Vulnerable Limestone salamander (Hydromantes brunus), Kern salamander and the Endangered Inyo Mountains salamander (Batrachoseps campi). The non endemic amphibians are: the Endangered Southern mountain yellow-legged frog (Rana muscosa); the Near Threatened Cascades frog (Rana cascadae); Northern red-legged frog (Rana aurora); Pacific chorus frog (Pseudacris regilia); Foothill Yellow-legged frog (Rana boylii); Long-toed salamander (Ambystoma macrodactylum); and the Monterey ensatina (Ensatina eschscholtzii).
A considerable number of mammalian taxa are found in the ecoregion, including the Long-eared chipmunk, Alpine chipmunk, Western heather vole, Walker Pass pocket mouse, and the Yellow-eared pocket-mouse. A diverse vertebrate predator assemblage once occurred in the ecoregion including Grizzly bear (Ursus arctos), Black bear (Ursus americanus), Coyote (Canis latrans), Mountain lion (Puma concolor), Ringtail (Bassariscus astutus), Fisher (Martes pennanti), Pine marten (Martes americana) and Wolverine (Gulo gulo).
There are a small number of reptilian taxa present in the Sierra Nevada forests: sagebrush lizard (Sceloporus graciosus); Northern alligator lizard (Elgaria coerulea); Southern alligator lizard (Elgaria multicarinata); Sharp-tailed snake (Contia tenuis); California mountain kingsnake (Molothrus ater); Common garter snake (Thamnophis sirtalis); Couch's garter snake (Thamnophis couchii); Western gopher snake (Pituophis catenifer); Longnose snake (Rhinocheilus lecontei); and the Common kingsnake (Lampropeltis getula).
A number of bird species are found in the ecoreion including high level predators that include several large owls, hawks and eagles. Other representative avifauna species present are the Blue-headed vireo (Vireo solitarius); Brown-headed cowbird (Molothrus ater); and the Near Threatened Cassin's finch (Carpodacus cassinii).
Habitat and Ecology
Whitebark Pine is a keystone species of the upper and subalpine ecosystems. It is also a foundation species for protecting watersheds as it tolerates harsh, wind-swept sites that other conifers cannot, the shade of its canopy regulates snowmelt runoff and soil erosion, and its roots stabilize rocky and poorly developed soils (Tomback and Kendall 2001). Whitebark Pines may live in excess of 1,000 years. While Whitebark Pine can begin to produce cones at 30-50 years, sizeable cone production usually begins at 60-80 years (COSEWIC 2010). An average generation length of 60 years is used in this assessment.
In upper subalpine sites Whitebark Pine is a major seral species that is often replaced by the shade-tolerant Subalpine Fir (Abies lasiocarpa), Spruce (Picea engelmannii), or Mountain Hemlock (Tsuga mertensiana) (Arno and Weaver 1990). The shade intolerant tree species Lodgepole Pine (Pinus contorta) is also found with Whitebark Pine seral sites. Other minor species sometimes found with Whitebark Pine are Douglas-fir (Pseudotsuga menziesii), lLmber Pine (Pinus flexilis), Alpine Larch (Larix lyalli) (Pfister and others 1977), and Western Wwhite Pine (Pinus monticola). Climax Whitebark Pine sites are found at high elevations, particularly harsh sites in the upper subalpine forests and at treeline on relatively dry, cold slopes, where trees often occur in elfin forests, clusters, groves or tree islands (Arno and Weaver 1990; Steele et al. 1983).
Most Whitebark Pine forests have low diversity in vascular plants (Forcella 1977) with the majority of undergrowth plant cover being composed of Grouse Whortleberry (Vaccinium scoparium), Blue Huckleberry (V. globulare), Black Huckleberry (V. membrenaceum), False Azalea (Menziesia ferruginea), Woodrush (Luzula hitchcockii), and Beargrass (Xerophyllum tenax) (Pfister et al. 1977, Arno and Weaver 1990). Other plants that may be occasional dominants include Idaho fescue (Festuca idahoensis), Parrys rush (Juncus parryi Engelm.), Wheeler Bluegrass (Poa nervosa (Hook.) Vasey), Buffaloberry (Sheperdia spp. Nutt.), Kinnikinnick (Arctostaphylos uva-ursi (L.) Spreng), and Pipsissewa (Chimaphila umbellata (L.) W.Bartram) (Arno and Weaver 1990, Aubry et al. 2008). High elevation climax stands of Whitebark Pine can contain many unique alpine, subalpine, and montane undergrowth species assemblages, some of which are only found in association with Whitebark Pine (Forcella 1977, Tomback and Kendall 2001). Forcella and Weaver (1977) found that Whitebark Pine forests had unexpectedly high biomass but low productivity.
The large, energy-rich wingless seeds of Whitebark Pine (Lanner 1982, Lanner and Gilbert 1994, Tomback 1983) are a food source in the fall and spring diets of 20 wildlife species (Lorenz and others 2008). When there are at least 40 cones produced per Whitebark Pine tree, pine nuts provided 97% of the annual nourishment for Yellowstone National Parks grizzly bears (Robbinset al.2006). Female grizzly bears in the Greater Yellowstone Ecosystem derive 40-50% of their fall nutrition from Whitebark Pine nuts (Felicetti et al. 2003). Female bears that have fattened during the previous fall on good pine nut crops typically produce litters of three cubs compared to twins or singletons after falls of few nuts; the link between increased cub production and great pine nut years occurs because fatter females produce more cubs that are born earlier in the winter den and grow faster because mom produces more milk (Robbins et al.2006).
Comments: Within montane forests and on thin, rocky, cold soils at or near timberline. 1300 - 3700 m (Flora of North America 1993). In moist mountain ranges, whitebark pine is most abundant on warm, dry exposures; but in semiarid ranges, it becomes prevalent on cool exposures and moist sites (Burns and Honkala, 1990). Although its role in the plant community is changing, whitebark pine historically dominated many of the upper subalpine plant communities of the western United States and was a major component of subalpine forests in the northern Rocky Mountains, the northern Cascades, the Blue Mountains, and the Sierra Nevada. It comprises 10 to 15% of total forest cover in the northern Rocky Mountains (Fryer, 2002). It was a minor component of subalpine forests in British Columbia and Alberta, and showed scattered occurrence on the Olympic Peninsula, the southern Cascades and other ranges of southern Oregon and upper northern California, and in northern Nevada (Burns and Honkala, 1990). At high elevations, krummholz whitebark pine communities merge into alpine vegetation. At mid-elevation, whitebark pine communities merge into mixed-conifer forests (Burns and Honkala, 1990). Most whitebark pine stands grow on weakly developed (immature) soils. Many of the sites were covered by extensive mountain glaciers during the Pleistocene and have been released from glacial ice for less than 12,000 years (62); and chemical weathering is retarded by the short, cool, summer season. Throughout its distribution, whitebark pine is often found on soils lacking fine material (Burns and Honkala, 1990).
Climate: Whitebark pine grows in cold, snowy, and generally moist climates. On semiarid ranges it is most common on cold, moist sites, whereas it is most common on warm, dry sites on moist ranges . Whitebark pine is common on ridges and near timberline, where trees are exposed to strong, desiccating winds. Hurricane-force wind velocities (> 73 mi/h (117 km/h)) occur every year on most whitebark pine sites and are especially common on ridgetops. Precipitation in whitebark pine communities ranges from 24 to 63 inches (600-1,600 mm) per year , 2/3rds of which is snow . Frost and snow are possible throughout the growing season, which is about 90 days [17,87,202]. Whitebark pine is more tolerant of wind and ice damage than any other high-elevation conifer except alpine larch. Whitebark pine sites often experience summer drought, especially in southern latitudes of the tree's distribution. Whitebark pine is more drought tolerant than any other high-elevation species [126,173,183].
Topography: Whitebark pine is most common on rocky, well-drained sites [87,126]. Best development occurs on sheltered, north-facing slopes and basins . In the southern Sierra Nevada, whitebark pine is confined to moist north slopes. Topography is rolling to rough with moderate to steep slope [75,126]. Slopes on the Blue Mountains ranged from 5 to 60% . Whitebark pine occurs on all exposures but is most common on south- and west-facing slopes [20,75,105,126,194,230].
Soils: Soils in whitebark pine communities are classified as cryochrepts . Soils are moderately to poorly developed and well drained. Coarse fragments are well represented [75,126]. Whitebark pine soils are nutrient poor and usually derived from granite or basalt [76,87,126,230], although whitebark pine occasionally grows on sedimentary soils [76,185]. Soil pH is usually strongly acidic, although whitebark pine also occurs on basic soils [65,171,227]. Whitebark pine occurs on serpentine soils in the Blue, Klamath, and Siskiyou mountains [75,184]. Soils textures include coarse sands, sandy loams, and loams [75,230]. Rooting depth is typically shallow; for example, maximum rooting depth at 1 site on the Okanogan National Forest of Oregon was < 12 inches (30 cm) . Krummholz or matted whitebark pine grows mostly on high-elevation sites where glacial scouring has eliminated most of the soil .
Elevation: Whitebark pine occurs from 4,300 to 12,100 feet (1,300-3,700 m) elevation . Ranges by state or province are as follows:
|CA|| 7,000 to 9,500 feet (2,100-2,900 m) in the Cascades |
10,000 to 12,100 feet (3,050-3,700 m) in the Sierra Nevada [17,32,87,172]
|ID||7,300-10,500 feet (2,225-3,200 m) [185,194]|
|OR|| 5,810 -8,500 feet (2,500 m) in the Blue Mts. [48,230] |
5,400 to 9,500 feet (1,620-2,900 m) in the Cascades [17,134,200]
Lowest natural range reported anywhere for whitebark occurs at 3,600 feet (1,110 m) on Mt. Hood
|MT||5,900 to 9,300 feet (1,800-2,830 m) |
|NV||6,400 to 10,00 feet (2,000-3,000 m) |
|WA||5,700 to 8,500 (1,700-2,600 m) in the Cascades and Olympic Mountains [17,126]|
|WY||7,300-10,500 feet (2,225-3,200 m) [17,194]|
|BC|| 5,200 feet (1,600 m) in the Coast Ranges |
5,643 to 7,999 feet (1,720-2,438 m) in the Rocky Mountains [17,86]
|SK||6,500 to 7,500 feet (6,500-7,500 m) |
Key Plant Community Associations
Although its role in the plant community is changing
(see Management Considerations), whitebark pine historically dominated many of the upper subalpine plant
communities of the western United States. Whitebark pine was a major component of subalpine forests in the
Mountains, the northern Cascades, the Blue Mountains, and the Sierra Nevada. It
comprises 10 to 15% of total forest cover in the northern Rocky Mountains. It was a minor component of subalpine forests
in British Columbia and Alberta, and showed scattered occurrence on the Olympic
Peninsula, the southern Cascades and other ranges of southern Oregon and upper
northern California, and in northern Nevada . At high elevations, krummholz whitebark pine
communities merge into alpine vegetation. At
mid-elevation, whitebark pine communities merge into mixed-conifer forests
other conifer species may share dominance with whitebark pine. At mid-elevation, whitebark pine throughout its range
is associated with lodgepole pine (Pinus contorta) [75,87,126,185,230].
Whitebark pine is not commonly perceived as a mid-elevation species, but stand
reconstruction studies show that whitebark pine was an important historical component of mid-elevation forests.
On the Bitterroot National Forest of western Montana, whitebark pine dominated 14% of mid-elevation
(6,500-7,500 feet (1,950-2,250 m)) stands from the 1700s to 1900 [18,77]. Where not
dominant, it was a common component of mid-elevation Rocky Mountain lodgepole pine
(P. c. var. latifolia) forest. By the time of the study
(1991), whitebark pine dominated none of the mid-elevation
study sites. At its lowest elevations throughout its range, whitebark pine overlaps with Douglas-fir
(Pseudotsuga menziesii) . In the coastal states, it associates with mountain hemlock (Tsuga mertensiana), with increasing
codominance of the 2 species to the south .
Subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea
co-occur in northwestern states; subalpine fir is the most frequent codominant
where its range overlaps with that of whitebark pine [54,126,185,230]. In the
Northwest, whitebark pine types between 6,600 and 7,800 feet (2,000-2,400 m) are often found
adjacent to alpine larch (Larix lyallii) communities. The 2 species tend to be
complementary rather than competitive in distribution, with whitebark pine occupying dry south and west
aspects and alpine larch
to more mesic sites [9,16,50,126].
Sadly, whitebark pine communities of the northern Cascades ,
eastern Washington , Idaho, and Montana  are
often characterized as "ghost forests" of whitebark that have been dead for decades, with little regeneration
Washington: Whitebark pine communities in the Cascade Range are often mixed with or
adjacent to mountain big sagebrush (Artemisia tridentata ssp. vaseyana) or mountain grassland communities. On some
sites, whitebark pine patches form "islands" within shrubland or grassland communities:
these mixed communities form highly diverse mosaics. At lower elevations (~ 6,230
feet (1,900 m)),
whitebark pine grades into subalpine fir, or sometimes (at ~ 5,720 feet), coast Douglas-fir
(Pseudotsuga menziesii var. menziesii) communities. Depending on elevation, subalpine fir,
Engelmann spruce, lodgepole shore pine (Pinus contorta var. contorta), and coast
Douglas-fir are common components of whitebark pine communities; subalpine fir
is the most common co-dominant. Shrubs typically show low cover; Oregon boxwood
(Paxistima myrsinites) is the only
constant shrub associate. The herb layer is often diverse.
Whitebark pine forms
fringe forests and woodlands at timberline. It is an important component of alpine
larch communities occurring below ~ 7,330 feet (2,230 m), and persists as krummholz
higher-elevation alpine larch communities .
In Mt. Rainier National Park, krummholz whitebark pine/common juniper (Juniperus
dominate high, rocky ridges above Yakima Park .
In eastern Washington and northern Idaho, whitebark pine is a seral component
of subalpine fir communities and dominates the highest peaks and ridges (> 6,000 ft
(1,800 m)). Understory
cover is typically discontinuous on these high-elevation sites. Engelmann spruce,
Rocky Mountain lodgepole pine, and Rocky Mountain Douglas-fir (Pseudotsuga menziesii
var. glauca) may associate,
especially on mid-elevation sites [54,229].
Grouse whortleberry (Vaccinium scoparium) is the most widespread and constant dominant shrub in
whitebark pine communities throughout the Rocky Mountains . Pinegrass (Calamagrostis
rubescens) is the most common and constant herb; smooth woodrush
(Luzula hitchcockii) and Drummond's
rush (Juncus drummondii) also occur in and sometimes dominate whitebark pine
understories . Oregon boxwood and
common juniper are characteristic shrubs [54,229].
Oregon: In the Blue Mountains of eastern Oregon and Washington, whitebark
pine codominates with subalpine fir between 7,600 and 8,500 feet (2,300-2,550
m). Whitebark pine assumes increasing dominance with elevation; it is the only tree on the highest sites. Rocky Mountain lodgepole
pine, Engelmann spruce, and Rocky Mountain Douglas-fir co-occur. Alpine larch assumes dominance on
cold, moist sites. Elk sedge (Carex geyeri) is usually
dominant on the ground layer; it is the most constant herb across sites [75,230]. In the Cascade Range yellow sedge (C. pensylvanica) and
Wheeler bluegrass (Poa nervosa) are dominant ground layer species .
Idaho: Limber pine, subalpine fir, and/or Rocky Mountain lodgepole pine
co-occur in whitebark pine communities. Elk sedge, Ross' sedge (C. rossii), or cushion plants such as
subalpine fleabane (Erigeron peregrinus) and rosy pussytoes (Antennaria
rosea) dominate the sparse understory
of high-elevation whitebark pine/barrengrounds . On lower-elevation
sites (< 9,000 feet (2,700 m)), grouse whortleberry, common juniper, pink
mountainheath (Phyllodoce empetriformis),
Oregon boxwood, Idaho fescue (Festuca idahoensis), and/or smooth woodrush
are understory dominants [50,194].
Wyoming: Whitebark pine occurs in the Absaroka, Teton, and Wind River ranges.
Best development of whitebark pine habitats occurs on the relatively dry
Wind River Range, where whitebark pine is at the edge of its distribution. Rocky
Mountain lodgepole pine is seral in this type. Rocky Mountain
Douglas-fir, subalpine fir, and Engelmann spruce occur occasionally, but rarely
reproduce well. Grouse whortleberry, heartleaf arnica (Arnica cordifolia), Ross' sedge, and
Wheeler's bluegrass (Poa wheeleri) are common dominant understory components;
common juniper and russet buffaloberry (Shepherdia canadensis) are occasional
California: Pure or nearly pure whitebark pine
communities occur at treeline in the Sierra Nevada and Cascade Range. Western
hemlock typically codominates with whitebark pine in the Cascades and northern Sierra
Nevada but is
increasingly replaced by Sierra Nevada lodgepole pine (P. c.
var. murrayana) from the central Sierra
Nevada southward. In upper montane and subalpine forests (6,000-11,000
(1,830-3,350 m)), whitebark pine is common in mixed stands with Sierra Nevada
lodgepole pine, mountain hemlock, and/or foxtail pine (P. balfouriana)
At lower elevations (7,500 feet in the north and 9,000 feet in the south),
merges with mixed Sierra Nevada lodgepole pine, red fir (Abies magnifica),
and/or Jeffrey pine (P. jeffreyi) forest. Krummholz whitebark pine
into alpine fell-fields at high elevations (9,500-11,100 feet (2,900-3,4900 m), depending on
Klamath Mountain associates in whitebark pine/oceanspray (Holodiscus
communities include mountain hemlock, Shasta red fir (A. m. var. shastensis), western white pine (P. monticola), Jeffrey pine, foxtail pine, and Sierra Nevada lodgepole
Nevada: Limber pine is the primary codominant . Limber pine dominates the lower subalpine zone
(8,000-9,000 feet (2,400-2,700 m)) of the Ruby and Humboldt mountains, while whitebark pine
dominates vegetation in the upper subalpine zone (8,550 to 10,600 feet
(2,610-3,230 m)) . In the Ruby Mountains, whitebark pine forms subalpine communities
Great Basin bristlecone (P. longaeva) and limber pines; it is the only area where
the 3 Strobus species
Due to inaccessibility and previously low interest in managing whitebark pine
types, whitebark pine communities are not well described compared to other subalpine types. There is
agreement in the literature that whitebark pine understories are diverse, and more whitebark pine types exist than have been
Accurate descriptions of whitebark pine communities are further confounded by loss of the
overstory dominant to insects and disease, moving successional pathways onto new
trajectories. The following classifications present preliminary descriptions of whitebark pine
British Columbia 
Habitat: Rangeland Cover Types
This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):
More info for the term: cover
SRM (RANGELAND) COVER TYPES :
409 Tall forb
Habitat: Cover Types
This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):
More info for the term: cover
SAF COVER TYPES :
205 Mountain hemlock
206 Engelmann spruce-subalpine fir
207 Red fir
208 Whitebark pine
209 Bristlecone pine
210 Interior Douglas-fir
211 White fir
215 Western white pine
218 Lodgepole pine
219 Limber pine
224 Western hemlock
226 Coastal true fir-hemlock
227 Western redcedar-western hemlock
229 Pacific Douglas-fir
230 Douglas-fir-western hemlock
247 Jeffrey pine
256 California mixed subalpine
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
KUCHLER  PLANT ASSOCIATIONS:
K002 Cedar-hemlock-Douglas-fir forest
K004 Fir-hemlock forest
K007 Red fir forest
K008 Lodgepole pine-subalpine forest
K012 Douglas-fir forest
K013 Cedar-hemlock-pine forest
K015 Western spruce-fir forest
K022 Great Basin pine forest
This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):
FRES22 Western white pine
FRES24 Hemlock-Sitka spruce
FRES26 Lodgepole pine
Soils and Topography
Despite these general trends, substantial variations occur in local climates, geologic substrates, and degrees of soil development in whitebark pine habitats. Thus, several types of soils have been recognized.
Most soils under whitebark pine stands are classified as Inceptisols (82). Many of these are Typic Cryochrepts, although deposits of volcanic ash may be sufficiently thick in some profiles to warrant recognition as Andic Cryochrepts. Some of the best-developed, ash-layered soils beneath spruce-fir/whitebark pine stands are Typic Cryandepts similar to the zonal Brown Podzolic soils (64). All of these are young soils, showing less leaching, weathering, and horizon development than Spodosols, although they are strongly acidic. Mean pH values of 4.8 to 5.0 were found for the upper mineral soil horizons in three habitat types, probably composed largely of Typic Cryochrepts (66). Data on nutrient availability in these soils have been provided (83).
Throughout its distribution, whitebark pine is often found on soils lacking fine material. Sparse open stands often grow on coarse talus, exposed bedrock, or lava flows having minimal horizon development and only scattered pockets of fine material. These soils would be classified as fragmental and loamy skeletal families within the order Entisols (Cryorthents in granitic substrates) (82). They have been referred to as azonal soils, and more specifically as Lithosols in earlier classifications.
Some dry-site whitebark pine stands in semiarid regions have open, grassy understories, particularly on calcareous rock substrates. The soils have a thick, dark surface horizon and a nearly neutral reaction. The pH is near 6 in Montana (66) and Idaho (71) stands, but in Alberta average values are 7.8 to 8 (9). These soils would evidently be classified as Typic Cryoborolls within the order Mollisols (82). Also, in some of the same areas, soils that have a dark surface but low base saturation are classified as Typic Cryumbrepts.
In all but the driest regions, whitebark pine is most abundant on warm aspects and ridgetops having direct exposure to sun and wind. It is less abundant on sheltered, north-facing slopes and in cirque basins, where subalpine fir, Engelmann spruce (Picea engelmannii), mountain hemlock, or alpine larch (Larix lyallii) become prevalent. Nevertheless, the tallest and best formed whitebark pine trees are. often found in high basins or on gentle north slopes.
Near the northern end of its distribution in the British Columbia coastal mountains, whitebark pine is a minor component of timberline communities at about 1580 m (5,200 ft) elevation (58). In the Olympic Mountains and on the western slope of the Cascades in Washington and northern Oregon, it grows primarily on exposed sites near tree line between 1770 and 2130 m (5,800 and 7,000 ft). (Elevational ranges mentioned are mostly from 7). East of the Cascade crest it becomes abundant within both the subalpine forest and the timberline zone. For instance, it is common between 1620 and 2440 m (5,300 and 8,000 ft) in central Washington's Stuart Range, generally forming krummholz above 2130 m (7,000 ft). The lowest reported natural stand of whitebark pine throughout its range is at 1100 m (3,600 ft) near Government Camp on the southwest slope of Mount Hood in Oregon (28).
Whitebark pine becomes a major component of high-elevation forests in the Cascades of southern Oregon and northern California, growing between 2440 and 2900 m (8,000 and 9,500 ft) on Mount Shasta. In the central and southern Sierra Nevada it is found between 3050 and 3510 m (10,000 and 11,500 ft) but occasionally reaches 3660 m (12,000 ft) as krummholz cushions.
Near the north end of its distribution in the Rockies of Alberta and British Columbia, whitebark pine is generally small, scattered, and confined to dry, exposed sites at timberline, 1980 to 2290 m (6,500 to 7,500 ft). It becomes increasingly abundant southward, especially in Montana and central Idaho. It is a major component of high-elevation forests and the timberline zone between about 1800 and 2500 m (5,900 and 8,200 ft) in northwestern Montana and 2130 and 2830 m (7,000 and 9,300 ft) in west-central Montana. In western Wyoming, it is abundant at 2440 to 3200 m (8,000 to 10,500 ft).
Mean annual precipitation for most stands where whitebark pine is a major component probably is between 600 and 1800 mm (24 and 72 in). The lower part of this precipitation range applies to mountain ranges in semiarid regions where whitebark pine forms nearly pure stands or is accompanied only by lodgepole pine (Pinus contorta var. latifolia). The highest precipitation occurs in inland-maritime ranges and near the Cascade crest where whitebark pine grows primarily with subalpine fir (Abies lasiocarpa) and mountain hemlock (Tsuga mertensiana).
About two-thirds of the precipitation in most stands is snow and sleet, with rain prevailing only from June through September (3). Summer rainfall is often scant in the southern part of whitebark pine's distribution south of about 47° N. latitude. Thus, there is often a droughty period with scant rainfall or remaining snowmelt water for several weeks during mid- to late-summer.
Snowpack usually begins to accumulate in late October. By April, the snowpack reaches maximum depth, ranging from about 60 to 125 cm (24 to 50 in) in stands east of the Continental Divide and in other semiarid areas, to 250 to 300 cm (100 to 120 in) in the relatively moist whitebark pine-subalpine fir stands of the Cascades and inland-maritime mountains. Most stands probably have mean annual snowfalls between 460 and 1270 cm (180 and 500 in). Whitebark pine also grows in stunted or krummholz (shrub-like) form on windswept ridgetops where little snow accumulates.
Strong winds, thunder storms, and severe blizzards are common to whitebark pine habitats. Wind gusts of hurricane velocity in the tree crowns (more than 117 km/h or 73 mi/h) occur each year on most sites, but most frequently on ridgetops.
Habitat & Distribution
Associated Forest Cover
In the dry ranges of the Rockies south of latitude 47° N. and in south-central Oregon, whitebark pine is found within the highest elevations of the cover type Lodgepole Pine (Type 218). In the Rockies, whitebark pine adjoins Interior Douglas-Fir (Type 210) and Limber Pine (Type 219). In the East Humboldt, Ruby, Jarbidge, and Bull Run Ranges of northeastern Nevada, whitebark's principal associate is limber pine (23).
In the timberline zone, conditions for tree development are so severe that any species that can become well established is considered a part of the climax community. In Montana and northern Idaho, the whitebark pine stands in the timberline zone (above forest line or where subalpine fir becomes stunted) make up the Pinus albicaulis-Abies lasiocarpa habitat types (24,66). Whitebark pine is also a climax species in other habitat types, mostly on dry sites, in Montana, central Idaho, and western Wyoming (71,72,83). Pinus albicaulis/Vaccinium scoparium is probably the most widespread and abundant habitat type that includes pure whitebark pine stands in the Rocky Mountains. Various aspects of the ecology of this habitat type in Montana and Wyoming have been described (26,27,83).
In the subalpine forest of the Northern Rockies whitebark pine is a principal long-lived seral component of the Abies lasiocarpa/Luzula hitchcockii and Abies lasiocarpa-Pinus albicaulis/Vaccinium scoparium habitat types (66). Prior to the early 1900's, whitebark pine was apparently more abundant in the subalpine forest as a result of natural fires, which favored its survival and regeneration over competing fir and spruce (6,46,63). In the southern Canadian Rockies and the inland mountains of southern British Columbia, whitebark pine is also primarily a seral associate in the highest elevations of the subalpine fir-spruce forest (1,9,65).
Principal undergrowth species in Rocky Mountain and northern Cascade stands include grouse whortleberry (Vaccinium scoparium), mountain arnica (Arnica latifolia), red mountain heath (Phyllodoce empetriformis), rustyleaf menziesia (Menziesia ferruginea), smooth woodrush (Luzula hitchcockii), beargrass (Xerophyllum tenax), elk sedge (Carex geyeri), Parry rush (Juncus parryi), Ross sedge (Carex rossii), and Idaho fescue (Festuca idahoensis). In south-central Oregon the primary undergrowth species are long-stolon sedge (Carex pensylvanica) and Wheeler bluegrass (Poa nervosa) (41). Undergrowth is sparse in Sierra Nevada stands.
Diseases and Parasites
Less damaging insect infestations are caused by aphids (Essigella gillettei) that feed on needles, mealybugs (Puto cupressi and P. pricei) that feed on trunks and branches, and the lodgepole needletier (Argyrotaenia tabulana), a potentially destructive defoliator. At least one species of Ips, the Monterey pine Ips (Ips mexicanus), infests the bole, and Pityogenes carinulatus and P. fossifrons also infest the bole (31). Two species of Pityophthorus (P. aquilonius and P. collinus) have been collected from whitebark pine (18). The ponderosa pine cone beetle (Conophthorus ponderosae) infests cones of whitebark pine (86).
The principal disease is the introduced white pine blister rust (caused by Cronartium ribicola) (38). Blister rust is particularly destructive where the ranges of whitebark pine and blister rust coincide with good conditions for infection. This occurs where adequate moisture permits infection of local Ribes spp.(currant and gooseberry bushes, the rust's alternate hosts) in early summer and prevents drying of the infected Ribes leaves throughout the summer. Where there is a source of inoculum from lowland forests, the spores that infect pine can be carried by wind to the trees, but cool, moist conditions are needed for infection (14). Blister rust damage is severe and prevents tree development in some timberline areas of the northern Cascades, northern Idaho, and northwestern Montana where whitebark pine is the major pioneer species (48). (Resistance is discussed under "genetics".)
Several other diseases infect whitebark pine, generally with minor consequences (34,35,69). These diseases are stem infections that produce cankers (some similar to blister rust), such as Atropellis pinicola, A. piniphila, Lachnellula pini (Dasyscypha pini), and Gremmeniella abietina; a wood rot organism Phellinus pini; several root and butt rots caused by Heterobasidion annosum, Phaeolus schweinitzii, and Poria subacida; and several needle cast fungi including Lophodermium nitens, L. pinastri, Bifusella linearis, and B. saccata. When foliage is covered by snow for long periods, a snow mold, Neopeckia coulteri, appears (34,35,69).
The dwarf mistletoes (Arceuthobium spp.) cause severe local mortality. The most widespread species is the limber pine dwarf mistletoe (A. cyanocarpum), which causes extensive damage to whitebark pine on Mount Shasta and some nearby areas of northern California (56). In the northern Rockies, the lodgepole pine dwarf mistletoe (A. americanum) occasionally occurs on whitebark pine where this tree grows in infested lodgepole pine stands. In the Oregon Cascades, the hemlock dwarf mistletoe (A. tsugense) is damaging to whitebark pine (33,56).
In addition to these parasitic organisms, several harmless saprophytes grow on whitebark pine: Lachnellula pini (Dasyscypha agassizii) on dead bark and cankers of blister rust, D. arida, Tympanis pinastri, and Phoma harknessii on twigs (34). Cenococcum graniforme has been identified as an ectotrophic mycorrhizal fungus of whitebark pine (80).
Wildfire is an important vegetation recycling force in whitebark pine stands, although long intervals (50 to 300 years or more depending on the site) usually occur between fires in a given grove (4). Lightning has been the major cause of fires in most stands; however, increased recreational use of forests results in accidental fires. Many of the fires have spread upslope into whitebark pine after developing in lower forests. Tiny spot fires are most common because fuels are generally sparse and conditions moist and cool. Nevertheless, occasional warm and dry periods accompanied by strong winds allow fires to spread. Spreading fires often remain on the surface and kill few large trees, but, under extreme conditions, severe wind-driven fires burn large stands (4). Wildfire (enhanced by fuels created by epidemics of Dendroctonus ponderosae in lodgepole and whitebark pine), followed by seed dissemination by Clark's nutcrackers, may be the principal means by which whitebark pine becomes established in the more productive sites near its lower elevational limits. Conversely, after a severe fire on dry, wind-exposed sites, regeneration of whitebark pine (often the pioneer species) may require several decades (6,77).
Wind breakage of the crowns or holes occurs when unusually heavy loads of wet snow or ice have accumulated on the foliage. This damage is prevalent in large, old trees having extensive heart rot. Snow avalanches also are an important damaging agent in some whitebark pine stands.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
Comments: Although historical sources include Utah in the distribution, more recent workers have not found it to occur there (Flora of North America, 1993). It is absent from some of the wettest areas, such as the mountains of Vancouver Island; and in the Olympic Mountains, it is confined to peaks in the northeastern rain shadow zone and also occurs atop the highest peaks of the Klamath Mountains of northwestern California (Burns and Honkala, 1990). The Rocky Mountain distribution extends along the high ranges in eastern British Columbia and western Alberta, and southward at high elevations to the Wind River and Salt River Ranges in west-central Wyoming (Burns and Honkala, 1990). A small outlying population of whitebark pine is found atop the Sweetgrass Hills in north-central Montana 145 km (90 mi) east of the nearest stands in the Rocky Mountains across the Great Plains grassland (Thompson and Kuijt, 1976). The coastal and Rocky Mountain distributions lie only 100 km (62 mi) apart at their closest proximity (Bailey, 1975) and even this narrow gap is not absolute; small groves are found on a few isolated peaks in between in northeastern Washington. In addition to the main distribution, it grows in the Blue and Wallowa Mountains of northeastern Oregon and in several isolated ranges rising out of the sagebrush steppe in northeastern California, south-central Oregon, and northern Nevada (Burns and Honkala, 1990). Communities are found in four of Oregon's ecoregions: Blue Mountains, Klamath Mountains, Eastern Cascade Slopes and Foothills, and Cascades (Murray, 2005).
Fire Management Considerations
Effects of fire exclusion: Kendall and Keane  state "whitebark pine will continue to decline if fire is not allowed to periodically set back the successional clock." Secondary succession, accelerated by white pine blister rust and bark beetle outbreaks, results in rapid replacement of whitebark pine by shade-tolerant, fire-sensitive species such as subalpine fir and mountain hemlock. Without burning, genetically valuable seed produced by blister-rust resistant whitebark pine is wasted: no new openings are created where Clark's nutcracker can cache seed and seedlings can establish . Based upon fire records from the U.S. Forest Service's Northern Region, Arno  estimated that less than one-half of 1% of the seral whitebark pine type had burned in 1970-1985. At that rate, he calculated a theoretical fire-return interval of 3,000+ years. Arno and other fire researchers caution that in reality, wildfire inevitably returns to fire-prone ecosystems . Fuel build-ups resulting from long-term fire exclusion dictate that when fire does return, it burns more acreage at greater severity than was historical. Estimated loss of whitebark pine from the 1988 Yellowstone fires was 30% of cone-producing stands in the north of the Park, and 12% in the east. Total reduction of whitebark pine cover was estimated at 54% .
Wilderness: Across its range, the proportion of whitebark pine habitat that falls within Wilderness boundaries is greater than that of nearly any other tree species . Whitebark pine in Wilderness Areas is not immune to decline: Kendall and Arno  estimated that as of 1990, 90% of whitebark pine in Glacier National Park, much of it in wilderness boundaries, had died from white pine blister rust. Fire management of whitebark pine is particularly problematic in small Wilderness Areas, where management-ignited fires are seldom an option [101,163]. Yet conservation of whitebark pine may be impossible without reintroduction of fire to Wilderness Areas . Since firelines in Wilderness areas are costly, damaging, difficult to construct in remote areas, and often in violation of the Wilderness Act, wilderness fires for resource benefit present the best management option . As of this writing (2002), studies are underway to determine fire histories and explore management options in small, isolated Wilderness Areas . Renkin and Despain  summarized a 17-year trend (1972-1988) of fire occurrence under the prescribed natural fire program in Yellowstone National Park. They found that the high moisture levels in whitebark pine ecosystems did not favor crown fires in most years (1988 being an exception), and fire occurrence was less than expected (based on amount of unburned area available) in whitebark pine communities. In mixed-conifer forests where whitebark pine was a component of the vegetation, fire occurrence was greater than expected in subalpine fir-Engelmann spruce and old-growth lodgepole pine with a subalpine fir-Engelmann spruce understory, and less than expected in seral lodgepole pine. Keane  states "the most important management action for conserving and maintaining vital whitebark pine ecosystems is to allow fires to burn in wilderness areas and play a more natural role in the ecosystem."
Restoring whitebark pine with fire: Long-term outlook for whitebark pine is not without hope, but restoring whitebark pine ecosystems cannot be accomplished without returning fire to subalpine landscapes. Keane and Arno  state "maintenance of native FIRE REGIMES is the single most important management action to ensure conservation of whitebark pine." Whitebark pine will continue to decline in the short term, but natural selection will probably increase genetic blister-rust resistance in whitebark pine populations [108,198]. It is also likely that future disturbances, particularly large fires and mountain pine beetle attacks, will kill many of these genetically valuable trees. Despite the dangers of landscape-level fire to whitebark pine populations, returning fire to the landscape is best way to restore whitebark pine. Kendall and Keane  state "It is important to note that fire exclusion has a far greater negative than positive consequence for whitebark pine. In the absence of fire, atypical amounts of fuel accumulate that foster more fires that are lethal to mature whitebark pine trees." Reintroduction of stand-replacing fire fosters whitebark pine regeneration by providing open sites suitable for Clark's nutcracker caching and seedling establishment. It also reduces impacts of mountain pine beetle infestations by creating mosaics of mutiaged stands that are less conducive to beetle epidemics . It is encouraging that 40% of the progeny of healthy trees in stands otherwise heavily infested with blister rust show some genetic resistance to blister rust . Without intervention, it is likely that the small proportion of whitebark pine resistant to white pine blister rust will be killed in stand-replacement fires before they can reproduce .
Management-ignited fires can be used for fire hazard reduction and whitebark pine restoration treatments . Fire researchers emphasize that it is less important to reconstruct historic stand structures than to reintroduce fire to whitebark pine ecosystems. It is crucial to create open sites that are favorable for Clark's nutcracker caching and growth of natural and artificial regeneration. Six Demonstration Areas have been established in the Selway-Bitterroot Wilderness Complex of Idaho and Montana as part of the Restoring Whitebark Pine Ecosystems Project. Ongoing restoration treatments include prescribed fire and silvicultural cuttings. Since the research is ongoing, conclusions and recommendations are based on limited data, and further suggestions will be forthcoming as the project continues .
Large, stand-replacement fires are not recommended in areas where whitebark pine is in severe decline (for example, northern Idaho and northwestern Montana). Small-scale prescribed burning is recommended; otherwise, natural whitebark pine regeneration will be extremely slow . Prescribed burning is best conducted in fall, after an early frost (<25oF (-4oC)) kills herbaceous plants and shrub foliage. Such foliage quickly cures and can propagate fire. In other seasons whitebark pine ecosystems are usually too wet to burn, or in extreme fire years, downslope vegetation is so dry that spotting may ignite fire in lower elevations. Aids for conducting stand inventories, prioritizing whitebark pine habitat for prescribed fire, designing and implementing treatments, and posttreatment monitoring and available . Follow-up thinning treatments, especially of subalpine fir, are usually needed to encourage whitebark pine growth . Augmenting natural regeneration with blister-rust resistant seed sources is recommended in areas where whitebark pine seed sources are absent or greatly reduced [84,210].
Unfortunately, restoration treatments may increase bark beetle predation on whitebark pine. On the Beaver Ridge Demonstration Area in northern Idaho, Six  found that Pityogenes fossifrons beetles were the most serious posttreatment pest species: they preferred young, apparently healthy whitebark pine in Clark's nutcracker openings, but also attacked a few fire-damaged mature trees. Ips spp. colonized slash heavily and attacked a few fire-damaged mature trees, but mostly left healthy trees alone. Mountain pine beetle numbers, which are rising in the study area, rose on the treatment sites but did not significantly respond to treatments. To reduce Pityogenes fossifrons infestation, Six  recommended spraying high-value whitebark pine in Clark's nutcracker openings with carbaryl for 2 posttreatment years (refer to Fire Case Studies).Fuels: Information on tree biomass is useful in determining fuel loads and predicting potential fire behavior. Moeur  provides a model for estimating crown widths and foliage weights of whitebark pine and other northern Rocky Mountain conifers. Regression equations [35,36] and tables  are available for estimating whole-tree weight and weights of boles, branches, branchwood with foliage, and live and dead crowns of whitebark pine and other western conifers. Van Wagtendonk and others [220,221,222] provide models for calculating weight, depth, heat content, and other fuel properties of whitebark pine and other Sierra Nevada conifers.
Plant Response to Fire
Seedling establishment: Whitebark pine establishes from seed on open mineral soil seedbeds created by mixed-severity and stand-replacement fires. Clark's nutcrackers prefer open sites with mineral soil for caching, and readily cache seed on large openings created by stand-replacement fire and in smaller openings created by mixed-severity fire. Most seed is cached in the 1st good conecrop year following fire, but Clark's nutcrackers may continue to build up the seed bank for decades as long as the site remains open and whitebark pine seed is available. Cone-bearing trees close to burns are usually the parent trees, but some Clark's nutcrackers collect and transport seed from distant trees . Because whitebark pine shows delayed germination and subalpine climates are often unfavorable for germination and growth, good establishment may not occur in the 1st few years after caching. Given a good seed bank, good seedling establishment usually occurs within the 1st decade after fire. Following a wildfire in the Bob Marshall Wilderness of western Montana, whitebark pine showed no establishment at postfire years 1 or 2, but seedling density was 264/acre at postfire year 3 . In Yosemite National Park, a 2-hectare, mixed-severity August wildfire killed the majority of krummholz whitebark pine; a few trees survived or were missed. At postfire year 4, a total of 54 whitebark pine seedlings was counted on burn transects. Only 3 whitebark pine seedlings were found on transects in the adjacent, unburned control. Seedling heights ranged from 0.4 to 5 inches (Âµ=1.5 + 1.0 in.) (1-13 cm (Âµ=3.9 + 2.6 cm)). Most seedlings were near objects such as rocks, logs, and bases of burned trees. Such objects help Clark's nutcrackers remember where cached seed was stored, but when the seed is not retrieved, such placement may aid whitebark pine establishment by shading germinants. Tomback  noted that postfire whitebark pine establishment was still underway at the Sierra Nevada study site. At postfire year 4, she observed Clark's nutcrackers collecting seed from lower-elevation, erect-form whitebark pine and caching it on the burn.
Postfire growth: Few studies have been conducted on postfire growth rates of whitebark pine. Sund  found that on the Sleeping Child Burn described below, whitebark pine seedling heights at postfire year 26 ranged from 0.4 to 94 inches (1-238 cm), with seedling height highly correlated (p < 0.001) with seedling age. Seedling height was greatest on ridges (Âµ=10.3 in. (36.2 cm)), followed by south and north slopes (Âµ=12.0 and 11.9 in. (30.6 and 29.7 cm)), and was least on roadside plots (Âµ=7.6 in. (19.2 cm)).
Effects of fire size and other disturbance agents: Large stand-replacement fires can favor whitebark pine over wind-dispersed conifers if cone-bearing whitebark pine are nearby. For example, in 1961 the lightning-ignited Sleeping Child Fire burned over 27,900 acres (11,300 ha) on the Bitterroot National Forest, Montana. Blister rust infection in the area was light, so whitebark pine seed sources were not limited. Clark's nutcrackers primarily collected whitebark pine seed from trees in the adjacent unburned forest; however, some birds traveled 5 miles (8 km) or more to collect seed. Conifer re-establishment was assessed at postfire year 26 (1987). Whitebark pine and Rocky Mountain lodgepole pine dominated study plots, with whitebark pine showing dominance on north slopes and lodgepole pine showing dominance on south slopes and ridgetops. Lodgepole pine was absent from many upper subalpine plots. Although the oldest conifers in the burn were 25 years of age, the oldest whitebark pine were 21 years old, demonstrating both whitebark pine's tendency to delay postfire establishment and its ability to compete with other conifers despite the delay. Typical of species with wind-dispersed seed on large burns, subalpine fir showed good establishment at the burn's perimeter, and poor establishment in the burn's interior .
The combination of mountain pine beetle attacks and blister rust infection followed by large, stand-replacing fire is harmful because whitebark pine seed sources are severely reduced. The Sundance Fire in northern Idaho provides an example. A history of bark beetle infestation and high incidence of blister rust in the area had already reduced whitebark pine seed sources prior to the wildfire. A survey conducted at postfire year 25 revealed a 27% blister rust infection rate in mature whitebark pine adjacent to the burn. Most whitebark pine in unburned plots were snags with mountain pine beetle galleries. On unburned plots, mean density of live whitebark pine > 0.4 inch (1 cm) in diameter was 0.008 tree site (single tree or cluster)/m2. In contrast, seed source density for the Sleeping Child Burn was 0.064 tree site/m2,and the Sleeping Child Burn had more whitebark pine regeneration.Comparison of whitebark pine regeneration on the 2 burns is given below. Data are mean densities (1 standard deviation, range) .
|Burn area||Burn year||Study year||Density (tree site/m2)|
|Sundance||1967||1992||0.0077 (0.0131, 0-0.0800)|
|Sleeping Child||1961||1987||0.0700 (0.1041, 0-0.5120)|
Tomback and others  state that whitebark pine seed production near the Sundance Burn was so low that Clark's nutcrackers were not caching many seeds. Without active management including artificial regeneration, the long-term outlook for whitebark pine in the area does not look good. Twenty-nine percent of the seedlings on the Sundance Burn show symptoms of blister rust; actual rate of seedling infection is probably higher.
Fire scorching may increase whitebark pine's susceptibility to mountain pine beetle attack [62,72]. A 1990s investigation of 2nd-order fire effects following the 1988 wildfires in Yellowstone National Park revealed the following trends in whitebark pine mortality at postfire year 7 :
|green (survived fire)||36.1|
|postfire insect kill (mostly mt. pine & pine engraver beetles)||2.8|
Broad-scale Impacts of Fire
Modeling: Several fire effects, fuel, and fire behavior models applicable to whitebark pine ecosystems are available at fire.org. McKenzie and others  provide a model for predicting coarse-scale fire effects in whitebark pine and other potential natural vegetation types of the Columbia River Basin. Keane  summarizes several ecosystem processes and landscape fire succession models that apply to whitebark pine and mixed-conifer subalpine ecosystems. FIRESUM is specific to whitebark pine and models the interactive effects of fire, mountain pine beetles, and white pine blister rust on whitebark pine growth, basal area, and regeneration .
Immediate Effect of Fire
Mature whitebark pine survive low-severity surface fire. Moderate-severity surface fire kills the majority of mature trees. Severe surface and crown fires kill even the largest whitebark pine [24,100,159]. For example, the 1975 Waterfalls Canyon Wildfire in Grand Teton National Park, Wyoming, was classified as moderate severity (< 60% mortality of mature trees) in the subalpine fir-Engelmann spruce zone. Among the 4 overstory species, direct fire lowest in whitebark pine .
|Percent fire kill of mature whitebark pine compared to mature overstory associates |
|Rocky Mountain lodgepole pine||36|
POSTFIRE REGENERATION STRATEGY :
Tree without adventitious bud/root crown
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)
Fire adaptations: Two strategies allow whitebark pine to survive in fire-prone ecosystems: survival of large and refugia trees, and postfire seedling establishment facilitated by Clark's nutcrackers. Mature trees usually survive low-, and sometimes moderate-severity surface fires. Bark thickness is moderate: thinner than ponderosa pine but thicker than lodgepole pine. Pole- and smaller-sized whitebark pine usually do not survive surface fires , but patchy fires resulting from fuel-limited whitebark pine habitats reduces whitebark pine mortality . In western Montana, Arno  frequently found whitebark pine with multiple fires scars dating from 1600 to 1900, demonstrating ability to survive low- and moderate-severity surface fires [126,229].
Whitebark pine seedlings establish on open sites created by mixed-severity and stand-replacement fires [115,214,223]. Late-successional species dominate when fire-return intervals are long, but fires were historically likely to return before whitebark pine was successionally replaced . Although whitebark pine recruitment is depressed in many areas, whitebark pine seedlings were historically highly competitive with other conifer species in the postfire environment. For example, 25 years after an 1892 stand-replacement wildfire on Mt. Adams in Washington, whitebark pine seedling establishment was equal to that of western hemlock (9% of total recruitment) and better than that of lodgepole pine and Engelmann spruce. Hofmann  noted that whitebark pine seedlings were fairly evenly distributed over the 80-acre (32 ha) burn, even though parent seed trees were at least a mile away.
FIRE REGIMES: Whitebark pine ecosystems have a mixed-severity fire regime of widely ranging fire intensities and frequencies [2,17,25,157]. Mixed-severity fires create complex landscapes of dead whitebark pine stands intermingled with live stands of different ages [18,38,97]. Whitebark pine stands also experience nonlethal surface fires and infrequent stand-replacement fires [2,10,97,159]. Under whitebark pine's highly variable fire regime, fire-return intervals range from 30 to 350+ years [17,25,157]. In a review paper, Agee  lists mean fire-return intervals of 29 to 300 years in whitebark pine habitats, with moderate-severity fire-return interval means of 25 to 75 years and stand-replacement fire-return interval means of 140+ years.
Whitebark pine wood is highly flammable even when green, and the dry, windswept upper slopes where whitebark pine grows are predisposed to lightning strikes. Whitebark pine and mixed-conifer communities with a whitebark component experience fire frequently; however, fire is usually unable to spread widely due to discontinuous canopies and sparse understory fuels [34,38,194]. Fire severity is low where surface fuels are sparse, and the resulting underburn kills mostly small trees and fire-susceptible overstory species, leaving live, mature whitebark pine. Understory species such as pinegrass and grouse whortleberry provide fine fuels that spread surface fires , which crown and consume conifers in dense patches. On 3 sites on the Bitterroot National Forest, Montana, Arno  reported minimum/maximum fire-return intervals of 2/68 (Âµ=33), 4/78 (Âµ=30), and 8/50 (Âµ=41) years. Brown and others  found fires in the subalpine mixed-conifer zone of the Selway-Bitterroot Wilderness of Montana and Idaho were mostly mixed severity, with patchy, fine-grained patterns. Return intervals ranged from 25 to 60 years. Fires were still patchy and of mixed severity in pure whitebark pine stands at high elevations, but fire-return interval lengthened to a 115-year mean.
Infrequent stand-replacement fires are an important component of whitebark pine's fire ecology [11,97]. Occasional stand-replacement fire maintains whitebark pine as an early to mid-seral species in subalpine fir communities in Washington's Cascade Range  and elsewhere. Arno  found that in the Bitterroot Mountains, subalpine communities on moist, north-facing slopes were most likely to experience long return-interval, stand-replacement fires. He stated, "stand-replacement fire is essential to maintain whitebark on moist slopes because of the rapid rate of succession" .
Small, patchy fires are also important to whitebark pine regeneration, especially where whitebark pine is seral. Large and small fires create regeneration opportunities, recycle nutrients and biomass, and maintain whitebark pine on the landscape . Fires historically started in summer and fall and burned over many weeks . Extent of stand-replacement burns varies; ranges from 2.5 to 120 acres (1-50 ha) are typical [166,211]. Small-acreage fires were, and are, more common. For example, a 12-year study (1979-1990) in the Selway-Bitterroot Wilderness Area showed that 84% of wildland fires for resource benefit (prescribed natural fires) burned less than 4 hectares. A single year (1988) accounted for 39% of the area burned . Large fires typically occurred in drought years, burned through lower-elevation plant communities as well the subalpine, and lasted from weeks to months .
Fire regime examples: Fire histories of Yellowstone National Park show the mean fire-return interval in underburned whitebark pine stands ranged widely, from 66 to 204 years. Underburns were often patchy and restricted to 1 or several stands. Whitebark pine and mixed-conifer communities from 6,000 to 11,000 feet (2,000-3,300 m) experienced stand-replacement fire every 350 years or more. Slow fuel accretion and moist fuels restricted fire spread, and large fires occurred only in extreme fire weather years such as 1988 [25,181].
In the Sierra Nevada fuel loadings were historically light between 7,500 to 10,000 feet (2,300-3,050 m), and fires were usually of low severity. Large, stand-replacing fires occurred rarely but played an important successional role: fires created openings in which whitebark pine and the nonserotinous Sierra Nevada lodgepole pine established. In the absence of fire, red fir is successionally replacing the 2 pines at elevations below 10,000 feet. Fire records for Yosemite National Park from 1931 to 1978 show that most subalpine fires occurred in the lower, red fir zone (representing 10% of total Park area but 37% of total Park fires), where whitebark pine is seral. Although fires were not as common in the mid-subalpine lodgepole pine-mountain hemlock zone - where mature, cone-bearing whitebark pine is most prevalent - the fires burned over larger areas (14% of total fires, equaling 19,677 acres). The upper subalpine zone (> 10,000 feet) - where whitebark occurs in pure to nearly pure stands - represents 14% of total Park area and experienced no fires between 1931 and 1978. Fires were rare in the upper subalpine, but were "intense" when they did occur, especially in krummholz whitebark pine .
On the Cascade Range, fire regime of westside whitebark pine forests is typically stand replacement. Forests with a lodgepole pine component burn more frequently and severely; stands without lodgepole pine burn less frequently and have greater potential for creeping ground fire . On the east side, whitebark pine forests appear to have the shortest fire-return interval of high-elevation forests . Stand-replacement fires are rare on the east side .
Fire exclusion: Fire exclusion has favored shade-tolerant, late-successional species throughout whitebark pine's range [100,157,191]. Because fire-return intervals are often long where whitebark pine is climax, fire exclusion has affected high-elevation whitebark pine less than whitebark pine at mid-elevations, where whitebark pine was historically a highly productive seral species . At the landscape level, however, fire exclusion in the upper subalpine has shifted succession away from whitebark pine to later-successional species . Murray and others  suggest that livestock grazing in the 19th century reduced fire frequency even before fire suppression was practiced. Small, isolated mountain ranges may be most affected by anthropogenically altered FIRE REGIMES. Subalpine portions of the West Bighole Range, an isolated spur of the Bitterroot Range on the Montana-Idaho border, have experienced reduced fire frequencies and an 87% decrease in area burned since European-American settlement. From 1754 to 1873, actual fire rotation was 184 years; modeling predicts a fire rotation of 1,364 years based upon fire frequencies from 1874 to 1993.
The following table provides fire regime intervals for plant communities and ecosystems where whitebark pine is dominant or common. See the FEIS summary for the species dominants for further information on FIRE REGIMES listed below.
|Community or Ecosystem||Dominant Species||Fire-Return Interval Range (years)|
|silver fir-Douglas-fir||Abies amabilis-Pseudotsuga menziesii var. menziesii||>200|
|grand fir||Abies grandis||35-200 |
|mountain big sagebrush||Artemisia tridentata var. vaseyana||15-40 [15,41,154]|
|Wyoming big sagebrush||Artemisia tridentata var. wyomingensis||10-70 (40**) [224,235]|
|western larch||Larix occidentalis||25-100 |
|whitebark pine||Pinus albicaulis||50-300+ |
|Rocky Mountain lodgepole pine*||Pinus contorta var. latifolia||25-300+ [11,13,181]|
|Sierra lodgepole pine*||Pinus contorta var. murrayana||35-200|
|Jeffrey pine||Pinus jeffreyi||5-30|
|western white pine*||Pinus monticola||50-200|
|Pacific ponderosa pine*||Pinus ponderosa var. ponderosa||1-47 |
|interior ponderosa pine*||Pinus ponderosa var. scopulorum||2-30 [13,22,123]|
|quaking aspen (west of the Great Plains)||Populus tremuloides||7-120 [13,74,153]|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 |
|coastal Douglas-fir*||Pseudotsuga menziesii var. menziesii||40-240 [13,160,180]|
|western redcedar-western hemlock||Thuja plicata-Tsuga heterophylla||> 200|
|mountain hemlock*||Tsuga mertensiana||35 to > 200 |
More info for the terms: climax, cover, stand-replacement fire, tree
Arno  characterizes whitebark pine as a generally minor seral species in lower subalpine communities, a major seral species in the upper subalpine, a co-climax species in lower timberline, and a climax species in upper timberline. Whitebark pine tolerates open, sunny to moderately shady sites [122,171,183]. It is typically the 1st tree species found on sites where fire or another deforestation event has occurred [93,126]. In Canada and the northwestern United States, many subalpine whitebark pine communities are seral, and subject to successional replacement by shade-tolerant conifers . After whitebark pine cover is established, shade-tolerant species often establish in the shelter of established whitebark pines [43,126,183,229]. Callaway  found that in the Bitterroot Mountains of western Montana, whitebark pine facilitated establishment and growth of later-successional subalpine fir on high-elevation sites. Seedling and sapling subalpine fir were highly aggregated around mature whitebark pine on upper subalpine sites (> 8,580 ft (2,600 m)), but not at relatively low-elevation subalpine sites (7,260 ft (2,200 m)). On upper subalpine sites, mature subalpine fir adjacent to living or dead mature whitebark pine showed more rapid growth rates compared to mature subalpine fir growing in the open. Whitebark pine is most productive on sites where it is seral . On landscapes across the West, whitebark pine is increasingly becoming displaced by later-successional species. Murray and others  estimated that since 1753, 50% of 6 subalpine watersheds on the Idaho-Montana border have shifted to late-successional subalpine fir. Only 3% of the subalpine landscape has shifted to seral whitebark pine.
Whitebark pine in the Cascade Range occupies a seral role in subalpine parklands and forests [2,69,126]. Early to mid-seral conditions in these associations are mostly maintained by occasional stand-replacement fire. In the absence of fire, subalpine fir usually forms closed stands of mature trees . In high-elevation whitebark pine communities, stands are typically open even in "near-climax" conditions [4,67]. Subalpine fir is sometimes present in the understory, suggesting eventual replacement in even these high-elevation types. However, successional patterns in high-elevation ecosystems are largely undocumented and difficult to predict . On Mount Rainier, whitebark pine and subalpine fir are invading subalpine meadows simultaneously .
In Crater Lake National Park, Oregon, whitebark pine is the dominant tree on Wizard Island. Sierra Nevada lodgepole pine is invading the island and appears to be replacing whitebark pine in importance .
Breeding system: Most genetic diversity is harbored within populations; between-population diversity is low in whitebark pine. Gene flow is facilitated by wind dispersal of pollen and bird dispersal of seed [39,40,57]. Probably due to long-range movement of Clark's nutcrackers dispersing whitebark pine seeds over time, genetic diversity of whitebark pine is low compared to other North American pine species [39,40].
On a fine scale, genetic structure of whitebark pine consists of clusters of close relatives. As a consequence of Clark's nutcracker's habit of planting seeds from a parent tree in the same cache, individuals within clusters often cross- or self-pollinate. This results in inbreeding. Trees within clumps are usually related as half-siblings, full siblings, or selfed. Neighboring clumps (probably planted by a different bird and/or collected from a different parent tree) are not closely related to each other [61,127,208,213].
Seed production: Cone production requires 2 years, as is typical for pines (Pinus spp.). Cones are 1st produced at 20 to 30 years of age on good sites. Trees do not reach full cone production until 60 to 100 years of age on most sites [125,146]. Peak cone production extends for another 250 years, then gradually declines. Some 1,000-year-old trees still reproduce . Cone production is characterized by frequent years of small cone crops and less frequent years of moderate to heavy crops . In the Greater Yellowstone area, moderate or large whitebark pine conecrop years occurred 2 or 3 times a decade (1980-1990) . Best reproduction occurs when day/night July temperatures are above 68/39 degrees Fahrenheit (20o/4o C), and there is no summer water stress .
Factors limiting reproduction: A number of agents reduce natural regeneration in whitebark pine. White pine blister rust, fire exclusion, bark beetles, animals, and fungal diseases reduce ability of mature trees to reproduce. White pine blister rust is the greatest threat to whitebark pine regeneration . In blister rust-infected trees, branch die-off 1st occurs on the ends of large, cone-producing branches. Although tree mortality may not occur for decades, infected trees rapidly loose ability to produce seed . By reducing the gene pool, genetic consequence of white pine blister rust is inbreeding depression (expression of maladaptive or lethal genes) [84,232]. However, other factors also contribute to poor regeneration and decline (see Other Management Considerations). Using historical stand reconstruction studies on the Bitterroot National Forest, Arno and others  determined that whitebark pine dominated 14% of the landscape in 1900. By the end of that century, combined effects of fire exclusion and white pine blister rust had reduced whitebark pine to the point that whitebark pine longer dominated any of the study sites. Remaining stands with cone-bearing whitebark pine were one-half their former size. Mountain pine beetle epidemics can depress whitebark pine regeneration for decades by killing mature, cone-bearing trees . On the Sundance Burn in northern Idaho, scant whitebark pine regeneration has been attributed to mountain pine beetle attacks prior to large-scale wildfire coupled with blister rust damage to whitebark pines on the burn's periphery .
Animal seed predation on whitebark pine seed is high. Except following good conecrop years, whitebark pine seedling establishment is probably incidental due to high rates of seed predation [214,229]. Even Clark's nutcracker harvesting of whitebark pine seed, often presented as a classic example of animal-plant mutualism , may be detrimental on some sites. Although individual Clark's nutcrackers only remove seeds that they plant themselves , researchers fear that in areas of high blister rust infection, whitebark pine seed will become so rare that Clark's nutcrackers will consume most of the seed they cache, leaving few seed reserves for regeneration . Clark's nutcrackers were the most efficient harvesters of whitebark pine seed on the Bridger-Teton National Forest of Wyoming, showing a 97% forage success rate (measured as time spent harvesting/seeds collected). Other important predators that harvested directly from whitebark pine cones included pine grosbeaks (92% success rate), ravens (79%), red squirrels (60%), and chipmunks (35%) . Similarly, vertebrates harvested 100% of mature whitebark pine seeds on the slopes of Bachelor Butte in the Cascade Range of Oregon. Most successful seed collectors were Clark's nutcrackers, Douglas' squirrels, least chipmunks, and golden-mantled ground squirrels, respectively . Mammalian and bird seed predation reduced the amount of soil-cached seed significantly (p<0.01) on the Gallatin National Forest of Montana. Northern pocket gophers were the most important seed predator .
Little is known of insect cone predators and their possible effects on whitebark pine regeneration. Further studies are needed in this area. Anderton and Jenkins  have documented whitebark pine seed predation by seed bugs (Leptoglossus occidentalis) and larch cone flies (Strobilomyia macalpinei) on the Bitterroot National Forest, Montana. Insect damage ranged from 0.4 to 7.1% of total seed crop in their study. A study across California, Oregon, Washington, Idaho, and Montana found that seed bugs were the most serious insect pest (27% of total whitebark pine seedcrop destroyed), with fir coneworms (Dioryctria abietivorella) damaging up to 13% of whitebark pine seeds .
Seed dispersal: Because cones are indehiscent, seed caching by Clark's nutcrackers is the only important means of dispersal . Clark's nutcrackers break through the cone scales with their beaks to remove the seeds, then bury the seeds in shallow caches for use as future food [203,204]. Whitebark pine seedbeds are, therefore, almost entirely the choice of Clark's nutcrackers . In good conecrop years, the birds cache many more seeds than they recover for food . Hutchins and Lanner  estimated that 1 Clark's nutcracker caches 98,000 seeds in a good conecrop year. Many unretrieved seeds germinate and produce new trees [89,116,120]. The birds prefer burns and other open, disturbed areas as cache sites, although they also select closed, shady sites that are unfavorable for whitebark pine regeneration [203,204]. Norment and Conner  found that Clark's nutcrackers are most abundant on small (0.1- to 2-ha), disturbed patches or nonforested patches. Approximately 40% of caches on plots in the Sierra Nevada were on sites favorable for whitebark pine regeneration .
Germination: Germination and the 1st few weeks of seedling life may be the most critical stages of whitebark pine's life history. Seedlings do not emerge until (a) embryonic development has occurred and (b) the seedbed is moist . Clark's nutcrackers often cache whitebark pine seeds before they are fully ripe and developed . Embryonic development continues after planting and requires stratification and weathering of the seedcoat before germination occurs . Germinants typically emerge 2 or more years after caching, when embryos are mature and seedbeds are moist long enough for seeds to fully imbibe (> 4 days under laboratory conditions) [124,208]. Some germination occurs in fresh seed the 1st growing season after caching. Germination of 1st-year, mature seed collected on the Bridge-Teton National Forest, Wyoming, ranged from 6.7 to 56.7% . Above-average precipitation may favor emergence. On the Gallatin National Forest, seeds that were hand planted in 1988, a dry year, showed reduced 1st-year emergence compared to seeds planted in 1989, a moist year. Emergence is best on burned or other mineral soils compared to soils with litter . Light-severity burns do not prepare as good a seedbed as more severe burns [147,225]. Because they are relatively free from competition, seedlings on burns have the best chance of growing into mature trees .
Seed banking: Whitebark pine appears to be the only North American pine (Pinaceae) with a seed bank. Due to seed caching by Clark's nutcrackers and delayed seed germination, whitebark pine may show good seedling establishment even if the previous year's cone crop was poor. Studies conducted after the 1988 fires on the Gallatin National Forest and Yellowstone National Park found that germination rates of natural regeneration were greatest 2 years after good cone crops. Some seeds germinated the spring after Clark's nutcracker planting, while others germinated in the 3rd (and last) year of the study. Synchronous germination occurred in both seedling clusters and single germinants. As of 1995, mean survivorship of seedling clusters > 1 year of age was 25%. The role of precipitation was unclear, but favorable precipitation was positively correlated (r=0.935) with good seedling establishment on the Yellowstone site . Clark's nutcrackers have been observed caching seed as far as 13 miles (22 km) from parent trees . They sometimes relocate cached seed to new sites , so actual dispersal distances may be greater. Longer travel distances may translate to fewer seedlings, however. Seedling density on the Sleeping Child Burn of western Montana decreased significantly (p > 0.05) as distance from seed source increased .
Seedling establishment and growth: Due to delayed germination and Clark's nutcracker caching habits, good seedling establishment requires many years. Clark's nutcrackers continue to cache seeds on burns and other disturbed sites as long as sites remain open and soils are bare. Burns where fire was exceptionally hot may not show good establishment for several postfire decades . For example, the Sleeping Child and Saddle Mountain burns of western Montana 1st showed whitebark pine establishment 5 and 7 years after fire, respectively, with best establishment occurring 2 or more years after favorable summer rains promoted cone production .
Whitebark pine seedlings are generally considered hardy after their 1st few weeks of life [17,208]. Seedlings rapidly grow deep roots and thick, drought-resistant stems , enabling whitebark pine seedlings to better survive drought compared to their more sun-intolerant conifer associates. Even so, droughty, coarse-textured soils may reduce whitebark pine establishment. Light shade improves seedling survivorship; however, McCaughey  found that heavy shade increased drought-related seedling mortality on the Gallatin National Forest. He suggested that in dry years, increased cover might intercept critical precipitation. Shrub nurse plants may increase whitebark pine seedling survivorship, but herbaceous species with abundant fibrous roots appear to inhibit establishment. Based upon relative species abundance, whitebark pine seedlings on the Sleeping Child and Saddle Mountain burns were most frequently associated with grouse whortleberry, and seldom associated with smooth woodrush and beargrass (Xerophyllum tenax) [199,214].
Whitebark pine survivorship is generally considered best on burns ; however, given open conditions and mineral soil, seedlings may show good survivorship on a variety of sites. In Yellowstone National Park, whitebark pine seedlings showed best establishment on moist, moderately to severely burned sites compared to moist, unburned sites and dry burned/unburned sites. On the Gallatin National Forest, however, seedling establishment was similar on burned and unburned sites with similar moisture regimes .
Most seedlings gain rapid root growth, acquiring top-growth more slowly. First-year germinants on the Gallatin National Forest showed root lengths ranging from 2 to 7.1 inches (5-18 cm) . In Yosemite National Park, mean top-growth rate of seedlings at 10,000 feet (3,050 m) elevation was 0.9 inch (2.3 cm)/year, while seedlings at 10,810 (3,295 m) gained an average 0.7 inch (1.7 cm) per year .
A number of agents may damage or kill seedlings. Heat damage to unshaded stem tissue is the common cause of death. Browsing animals also kill seedlings. Northern pocket gophers cause highest mortality on whitebark pine seedlings on the Gallatin National Forest, although browsing elk, chipmunks, and birds - including Clark's nutcrackers - also consume seedlings . Tomback  found that 2 years after emergence, survivorship of natural whitebark pine regeneration on 2 Sierra Nevada sites averaged 41 and 65% of 1st-year cohorts.
Most growth occurs in mid-summer . Growth on cold sites may be very slow , taking as long as 17 years to produce a 5-inch-long (12-cm) branch . Tree-ring data from the central and southern Sierra Nevada show that best growth occurs following warm, wet winters, and slowest growth occurs after cool, dry winters .
Asexual regeneration: Whitebark pine reproduces by layering where long-lasting snowloads bend lower branches and thin, flexible stems onto soil. Layering is most common in krummholz whitebark pine [17,146]. Krummholz whitebark pine rarely sets seed and when it does, the seed often shows poor germination. Krummholz patches usually originate from lower-elevation seed transported into the upper subalpine by Clark's nutcrackers. Once krummholz is established, layering is its primary method of patch expansion . Except in the upper subalpine, layering is not an important method of whitebark pine regeneration .
Growth Form (according to Raunkiær Life-form classification)
More info for the term: phanerophyte
RAUNKIAER  LIFE FORM:
Reaction to Competition
On a broad range of dry, wind-exposed sites, whitebark pine is a climax or near-climax species that persists indefinitely in association with subalpine fir and other tolerant species because it is hardier, more drought tolerant, more durable, and longer-lived. Even on these severe sites, however, a successional trend may be observable on a small scale: whitebark pine pioneers on an open site and is later surrounded and locally replaced by tolerant fir and hemlock (29). In dry areas of Wyoming's Wind River and in south-central Oregon, whitebark pine forms a co-climax with lodgepole pine in dense subalpine forest stands (41,72).
Observations of whitebark pine natural regeneration suggest that this species could be perpetuated on dry sites under a variety of even-aged or uneven-aged silvicultural systems. To establish whitebark pine on moist sites, some stand opening and light, localized site preparation are probably necessary. Wind-throw and wind breakage are a danger to residual trees, especially spruce and fir, in partial cuttings. Watershed values (and often esthetic values) are high on whitebark pine sites, however, and use of heavy equipment could be damaging. Whitebark pine can be regenerated by outplanting seedlings, or sowing seeds in mineral soil or at the soil-litter interface (60).
Life History and Behavior
More info for the term: formation
Male and new female cones are initiated from mid-July to mid-September, just prior to winter bud formation. They resume growth in April or May. Pollen disperses from male cones and 1st-year female cones open for pollination from May to mid-August, varying with latitude, elevation, and temperature [57,86,144,146]. Second-year female cones enlarge during June and July. Seeds of 2nd-year female cones ripen in mid-August to mid-September [144,146]. Germinants emerge after June snowmelt through early September . Seeds hand-planted on the Gallatin National Forest in fall began emerging in late June and stopped emerging by late July . Phenology for whitebark pine on Bachelor Butte, in the Cascades Range of central Oregon, follows. Data were collected at 7,710 to 8,300 feet (2,350-2,530 m) elevation .
|bud break||late May -mid-June|
|branch, needle, & cone elongation||July|
|male cone drop||17 Aug., after 1st snow|
|seed ripening||late Aug.|
Mean timing for whitebark pine phenological and animal interactions on the Bridger-Teton National Forest :
|Event||Date||Total seedcrop harvested|
|red squirrels begin foraging||mid-July||4%|
|Clark's nutcrackers begin foraging||early August||5%|
|1st germinable seed||early August||10%|
|Clark's nutcrackers begin caching||mid-August||18%|
|cones mature||early Sept.||35%|
|chipmunks begin harvesting||late Sept.||65%|
|Clarks nutcrackers recache seed from 1 site to another||mid-October||90%|
Whitebark pine has large, wingless, nutrient-rich seeds that remain in the indehiscent cone after maturity. It is not adapted for wind dissemination and is almost entirely dependent on Clark's nutcracker (Nucifraga columbiana) for successful dispersal and reproduction (Flora of North America, 1993; Lanner, 1982; Burns and Honkala, 1990; Murray, 2005). Nutcrackers feed almost exclusively on whitebark pine seeds when they are available and store the seeds for year-round use. With a full pouch of seeds, nutcrackers fly to a suitable site and cache clusters of up to 15 seeds 2-3 cm below the soil surface. The birds have been observed traveling anywhere from several hundred meters to over 10 km to cache seeds (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). Various mammals (red squirrel, black bear, grizzly bear, chipmunk, golden-mantled ground squirrel, deer mice) also transport and cache seeds (Hutchins and Lanner, 1982; Tomback, 1978), but not nearly to the extent of the Clark's nutcracker. Trees do not reach full cone production until 60 to 100 years of age on most sites (Lewis, 1971; McCaughey and Tomback, 2001). Peak cone production extends for another 250 years, then gradually declines.
Whitebark pine is easily grafted on rootstock of either whitebark pine or western white pine. The grafts grow much faster when the stock plant is western white pine (44).
Seed Production and Dissemination
The large, heavy, wingless seeds are borne in dense, fleshy, egg-shaped cones usually 5 to 8 cm (2 to 3 in) long. The cone is dark purple, turning brown as it cures in late summer. It is unusual among cones of North American pines in remaining essentially closed (indehiscent) after ripening rather than spreading its scales to release seeds (75). Most of the cones are harvested by animals. Some fall to the ground where they disintegrate rapidly by decay and depredations by mammals and birds. A small percentage remain on the tree into winter. A few cones, complete with weathered scales but without seeds, remain on the branches for several years after ripening.
Clark's nutcrackers and red squirrels attack most of the ripening cone crop in the tree tops during August and September. As a result, it is common to find no evidence of cones in a whitebark pine stand except when a careful search is made for cone scales on the ground (10).
Clark's nutcrackers have an essential role in planting whitebark pine seeds (42,49,51,74,76,77). Nutcrackers can carry as many as 150 whitebark pine seeds in their sublingual (throat) pouch and they cache groups of one to several seeds in the soil at a depth of 2 to 3 cm (1 in), suitable for germination. Nutcrackers cached an estimated 33,600 limber pine seeds per hectare (13,600/acre) in one open, burned area during one summer; a similar pattern of seed caching would be expected for whitebark pine. Whitebark pine seeds sustain these birds and their young much of the year, but a large proportion of the seed caches go unrecovered.
The effects of whitebark pine seed planting by Clark's nutcrackers are readily observable. Despite its heavy wingless seed, this species often regenerates promptly on burned or clearcut areas where a seed source is absent (46,59,76,77,78). Moreover, whitebark pine seedlings in open areas frequently arise together in tight clumps of two to five. The species has become established atop a young geologic formation-Wizard Island in Crater Lake, Oregon, (43)- where seed dispersal by birds would have been necessary. Lone whitebark pine trees grow along alpine ridges, often several miles from the nearest possible seed source (7). Numerous clumped whitebark pine seedlings and saplings can be found far from a seed source in lower elevation forests (for example with ponderosa pine), where whitebark pine does not develop beyond sapling stage. Clark's nutcrackers migrate down to these stands in autumn, bringing whitebark pine seeds with them (7,74).
Various mammals also transport and cache whitebark pine seeds (42,74). Red squirrels harvest large quantities of whitebark pine cones and store them in rotten logs and on the ground. Black and grizzly bears raid many of these cone caches, scattering many seeds. Chipmunks, golden-mantled ground squirrels, and deer mice eat loose seeds and also cache seeds that may ultimately germinate. Red squirrels also cache whitebark pine seeds; from 3 to 176 seeds per cache have been found (47).
A few seeds probably fall onto favorable seedbeds near the parent trees. Rarely, seeds may be carried by snow avalanches into lower elevations. Because of periodic disturbances and cold air drainage in avalanche chutes, whitebark pine saplings often occupy these sites at low elevations. Presumably, most of these trees arise from nutcracker caches.
The poor germination rate (8 to 14 percent) of whitebark pine seed under field conditions is apparently related to the development and condition of the embryo and to seed coat factors (60). Seeds from three Canadian sources germinated poorly, despite a variety of seed coat scarification techniques with and without cold stratification (68). The best results were obtained when a small cut was made in the heavy seed coat and the seed was placed adjacent to germination paper to facilitate water uptake. The seed coat is evidently a major cause of delayed regeneration or seed dormancy. Another factor explaining the low germination was the low proportion of seeds with fully developed embryos. In another test, using seed collected from Idaho, 61 percent of the seed germinated after clipping of the seed coat (67). Stratification for 60 days plus clipping resulted in 91 percent germination. Cold stratification for at least 150 days followed by cracking of the seed coat has been fairly successful, resulting in 34 percent germination (37).
Flowering and fruiting
The female or seed cones ripen by early September of the second year (81). Although there are no good exterior signs of cone and seed ripeness, the cone scales open slightly-but not enough to release the seeds-and can be pulled apart after September 1.
Growth and Yield
In Montana, the best sites for whitebark pine timber growth are generally in the Abies lasiocarpa/Luzula hitchcockii habitat type, Menziesia ferruginea phase (66). Although whitebark pines of good form and moderately large size [dominant trees 50 to 75 cm (20 to 30 in) in d.b.h. and 21 to 30 m (70 to 100 ft) tall at 250 to 300 years of age] sometimes develop on these sites, associated Engelmann spruce grows larger and is the primary object of management. In some commercial forest sites between 1520 and 1830 m (5,000 and 6,000 ft) in southwestern Alberta, whitebark pine grows larger than associated lodgepole pine and spruce (25). In south-central Oregon, annual yields of merchantable timber in a lodgepole pine-whitebark pine type were estimated to be about 2.0 m³/ha (29 ft³/acre) (41).
On the best sites, where whitebark pine is a component of the spruce-subalpine fir forest, it produces timber of good quality with only a moderate amount of defect. The resulting lumber has properties similar to those of western white pine (45) but is graded lower largely because of its slightly darker appearance (85).
At higher elevations where the species is abundant, it forms a short tree with large branches and is unsuitable for timber production. Detailed information on productivity in some of the pure, high-elevation whitebark pine stands- Pinus albicaulis/Vaccinium scoparium habitat type suggests that annual yields of merchantable timber are low, about 0.7 to 1.4 m³/ha (10 to 20 ft³/acre) (27,83,66).
On favorable sites near the forest line, this species develops into a large, single-trunk tree commonly 11 to 20 in (35 to 65 ft) tall and has a life span of 500 years or more. The oldest individuals on some cold, dry sites probably attain 1,000 years. The ancient trees often have a broad crown composed of large ascending branch-trunks. The largest recorded whitebark pine, growing in central Idaho's Sawtooth Range, is 267 cm (8 ft 9 in) in d.b.h. and 21 m (69 ft) tall (2). Upwards through the timberline zone, whitebark pine becomes progressively shorter and assumes multi-stemmed growth forms, evidently arising from the germination of nutcracker seed caches (30,52). Because seeds in these caches often come from the same tree, the individual trees that make up a single multi-stemmed tree are often siblings. As a result, tree "clumps" may be composed of individuals more closely related to one another than to adjacent clumps.
At its upper limits, whitebark pine is reduced to shrublike growth forms (20). Such krummholz stands are often extensive on wind-exposed slopes and ridgetops. Primary causes of krummholz are thought to be inadequate growing season warmth, which prevents adequate growth, maturation, and hardening (cuticle development) of new shoots (79). As a result, shoots are easily killed by frost or by heating and desiccation on warm sunny days in early spring when the soil and woody stems are frozen and thus little water is available to replace transpiration losses. Mechanical damage from ice particles in the wind is also a factor limiting krummholz growth to microsites where snowpack accumulates and provides protection from sun and wind.
Evolution and Systematics
Trunks of trees withstand wind and snow via spiral growth.
"Modern pipes, such as those used for natural gas and oil, often have spiral reinforcements, which are also found in the structure of diatoms, in the trachea of insects, and in conveyor vessels of plants. This method of increasing the mechanical resistance by means of fiber spirals, which are easier compressed and stretched without breaking, is also applied in the spiral growth of tree trunks. For inexplicable reasons, many trees start growing spirally under strong pressure from wind and snow, as is often encountered in the mountains or in subarctic regions. Under such circumstances the wood fibers may deviate up to 30° from the vertical direction of growth. Since this spiral growth offers the plant better protection against mechanical destruction, it may well be regarded as a kind of defensive reaction." (Tributsch 1984:28-29)
"Through spiral grain, conduits for sap lead from each root to all branches. This uniform distribution of sap is indicated by the paths of vessels and tracheids, and has been proven experimentally by means of dyed sap injected into the base of stems or taken up by roots. Trees receiving water only from roots at one side of the root collar nevertheless stay green and continue growing. Spiral grain in bark distributes food from each branch to other flanks of the stem and to most roots. Experimental interruptions of the sap and food conduits caused the cambial zone to reorient new conduit cells in new directions, bypassing the interruption. In particular, spiral grooves cut into the stem surface caused spiral grain. The new cells reorient through division and growth. Although spiral grain is largely under genetic control, trees appear to have a spiral grain especially where needed for distribution of water when root spheres are dry at one side. Compared with straight-grained trees, spiral-grained stems and branches bend and twist more when exposed to strong wind, in this way offering less wind resistance and being less likely to break. Through the bending and twisting, snow slides down from branches rather than breaking them, but the main function of spiral grain is the uniform distribution of supplies from each root to all branches, and from each branch to many roots." (Kubler 1991:125)
Learn more about this functional adaptation.
- Kubler H. 1991. Function of spiral grain in trees. Trees-Structure and Function. 5(3): 125-135.
- Tributsch, H. 1984. How life learned to live. Cambridge, MA: The MIT Press. 218 p.
Molecular Biology and Genetics
Resistance to white pine blister rust is the most notable phenotypic variation observed in whitebark pine. The species was extremely susceptible to blister rust both in the field and nursery in artificial inoculation tests and has been rated by many people as the most susceptible of all the world's white pines (15). In stands where mortality has been as high as 90 percent, however, many individuals have survived and some are free of rust symptoms. Genetic testing, using artificial inoculation methods to expose seedlings from uninfected wild parents, has demonstrated resistance to be genetic (38). Four main defense mechanisms were observed: absence of infections of needles or stem, shedding of infected needles before the fungus could reach the stem, a chemical interaction between the fungus and short-shoot tissue that killed the fungus, and chemical reactions in the stem that killed host cells, with subsequent walling off of the fungus.
A small trial plantation of first-generation wind-pollinated seedlings from resistant whitebark pine parents was established at Marks Butte near Clarkia, Idaho, in 1979 (37). A survey in 1989 revealed 10 surviving seedlings of 200 planted. The survivors were about 1 foot tall. Much of the mortality was due to vegetative competition, especially by beargrass. Survival of planted resistant seedlings would provide a first step toward returning whitebark pine as an important component of the subalpine plant communities, where the adverse impact of birds and rodents on the rust-induced mortality is high and where remaining seed supply is great.
Many attempts have been made to cross whitebark pine with the other four white pine species in its subsection Cembrae and with most species in subsection Strobi. Almost all have ended in failure or inconclusive results (16). Only the cross with limber pine, from subsection Strobi, offers slight hope (22). No putative hybrids of whitebark pine have been identified in natural stands.
Barcode data: Pinus albicaulis
Statistics of barcoding coverage: Pinus albicaulis
Public Records: 7
Specimens with Barcodes: 7
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
Whitebark Pine (Pinus albicaulis) is experiencing serious decline due to White Pine Blister Rust (WPBR) and Mountain Pine Beetle (MPB). In areas where WPBR and MPB are both present the decline in population numbers and population resilience is such that population sustainability in the long-term is predicted to decrease. Work is being conducted to identify seed trees that exhibit some degree of resistance to WPBR. This work is being complicated where populations are also under attack from MPB. Additional research needs to be initiated into the affects of WPBR and MPB on the mutualism between corvids and Whitebark Pine in regard to seed dispersal. Initial research indicates that when seed-producing trees decline in number, a point is reached where Clarks Nutcracker does not visit the site. Without the caching of seed by Clarks Nutcracker recruitment of seedlings will not occur and local population extirpation is expected. Although concrete figures cannot be given for the entire range of the species, a decline rate of 50% as a minimum figure, incorporating both past decline (past 100 years) and suspected future decline (next 80 years), is reasonable and therefore qualifies the species for Endangered under criterion A4.
- 2008Vulnerable (VU)
- 1998Vulnerable (VU)
National NatureServe Conservation Status
Rounded National Status Rank: N2 - Imperiled
Rounded National Status Rank: N3 - Vulnerable
NatureServe Conservation Status
Rounded Global Status Rank: G3 - Vulnerable
Reasons: A common tree where it occurs, it is limited to only upper subalpine forests of many western North American mountain ranges. It is, however, severly threatened in the majority of its range by introduced white pine blister rust (Cronartium ribicola), outbreaks of mountain pine beetle (Dendroctonus ponderosae), succession resulting from decades of fire suppression, climate change resulting in decreases in suitable habitat, and various synergies between these factors. Although a few areas such as the southern Sierra Nevada in California and the interior Great Basin ranges, as well as scattered stands in the rest of the range, still appear to contain large numbers of relatively healthy trees, it is expected that the blister rust will eventually become abundant in the vast majority of the range, causing significant tree mortality. Tree mortality rates exceeding 50% have already been documented in numerous parts of the range. A small percentage (1-5%) of trees appear naturally resistant to the blister rust, and restoration strategies hope to propagate these genotypes for use in restoration, although even rust-resistant trees will remain threatened by other factors. In addition, it has relatively low genetic variation and exists as a fragmentary species, making it more vulnerable than its range might indicate. This is a keystone species of high-elevation western ecosystems whose decline is expected to have cascading effects on ecosystem function and biodiversity.
Environmental Specificity: Narrow. Specialist or community with key requirements common.
Comments: Whitebark pine survivorship is generally considered best on burns (Fryer, 2002), however, given open conditions and mineral soil, seedlings may show good survivorship on a variety of sites. Two strategies allow whitebark pine to survive in fire-prone ecosystems: survival of large and refugia trees, and postfire seedling establishment facilitated by Clark's nutcrackers. Mature whitebark pine survive low-severity surface fire. Moderate-severity surface fire kills the majority of mature trees. Severe surface and crown fires kill even the largest whitebark pine (Keane and Arno, 1993; Fryer, 2002). Plant life at timberline is challenged by poorly developed soils, heavy snowfall, a short growing season, ice storms, and ferocious winds; and several physical traits permit whitebark pine to endure a harsh environment - flexible branchlets shed snow, stout stems, and well anchored root systems (Murray, 2005). Although well-adapted to surviving at timberline, whitebark pine is not a strong competitor with other trees because of its relative shade intolerance and slow growth (Murray, 2005).
Over 90 percent of Wwhitebark Pine forests occur on public lands in the U.S. and Canada.
In the U.S.A. Whitebark Pine occurs on 5,085,904 acres (20.06% of the total) on 12 National Forests in northern Idaho and Montana: 2,773,620 of those acres (54.5%) are within wilderness or inventoried roadless areas and another 40,661 acres are designated or proposed research natural areas (Shelly et al. 2010). Another 427,000 acres of Whitebark Pine occur in three National Parks in Montana and northwestern Wyoming (from NPS websites). Acreages for other areas not available.
In Canada the total population is estimated to be around 200 million trees (COSEWIC 2010).
Global Short Term Trend: Decline of 50 to >90%
Comments: Whitebark pine is declining at an unprecedented rate. In the Sundance Burn (Selkirk Range) or northern Idaho, Tomback et al. (1995) observed 29% of regeneration trees following a prescribed burn were infected once again with blister rust. Keane et al. (1994) noted 22% of landscape in Bob Marshall Wilderness Complex (Montana) with high mortality, and 39% with moderate mortality, due to blister rust. Keane et al. (1996) and others estimated a 45% decline in whitebark pine cover types in the Columbia River Basin and the Bob Marshall Wilderness Complex of Montana. Ironically, whitebark pine decline is greatest on seral sites, where its productivity was historically best. The area occupied by seral whitebark pine has plummeted 98% (Keane et al., 1996; Fryer, 2002). Agents causing major whitebark pine mortality include white pine blister rust, successional replacement, bark beetles, fire, root diseases, and weather. Generation time is long; trees generally start producing cones when 25-30 years old, start producing sizable cone crops when 60-80 years old, and can live to be over 500 years old (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). In Oregon, Murray (2005) anticipates 95-99% mortality of trees infected with blister rust. In Oregon's Crater Lake National Park, blister rust infects up to 20% of whitebark pine and Murray and Rasmussen (2000) predict 46% decline by 2050. During the past several years, mountain pine beetle outbreaks have erupted leading to noticeable loss of whitebark pine in the southern Cascades (Murray, 2005). Thus trends should be considered over a 100 year time frame. Introduced white pine blister rust, increases in mountain pine beetle, fire suppression, climate change, and their synergistic effects are causing significant ongoing declines in this species; see Threats for details.
Global Long Term Trend: Decline of 50-90%
Comments: See Threats for details
The initial reduction in Whitebark Pine is attributed to the exotic pathogen, White Pine Blister Rust (Cronartium ribicola) introduced in Whitebark Pine cover types ca. 1925 (McDonald and Hoff 2001). Mean blister rust mortality is 35% (range of 8-58%) and mean infection of 66% (range of 17-89%) in stands sampled throughout the northwestern United States and southwestern Canada (Kendall and Keane 2001). Whitebark Pine does possess documented rust resistance. Artificial inoculation trials of the open-pollinated, phenotypically rust resistant trees in the Northern Rockies indicate rust resistance ranges from 30% (Hoff and others 1980) to 47.4% (Mahalovichet al.2006). In the Cascade Range, the percent of canker-free seedlings in 26.3% (Sniezkoet al.2007).The more recent mortality can be attributed to wildfire and a native pest, Mountain Pine Beetle (Dendroctonus ponderosae Hopkins). The likelihood of continuing mortality due to these disturbance agents is very much linked to the future cyclic pattern of warm weather and drought at higher elevations where whitebark pine is abundant (Logan and Powell 2001). There have been three outbreaks of mountain pine beetle during this time. The first one in the 1920s-30s killed significant areas of Whitebark Pine and left many Ghost Forests. The second outbreak was in the 1970s-80s. The third one began in 2001 and has been killing significant areas of Whitebark Pine over the last few years (Shellyet al.2010).
Approximately 60 years of fire suppression have resulted in seral replacement of Whitebark Pine to Subalpine Fir (Abies lasiocarpa (Hook) Nutt.), Engelmann Spruce (Picea engelmannii Parry ex Engelm.), Mountain Hemlock (Tsuga mertensiana (Bong.) Carrire) (Keane and Arno 1993), and Lodgepole Pine (Pinus contorta Douglas ex Louden).Due to Whitebark Pines range in the upper subalpine and alpine forests, it is presumed the impacts of warming temperatures will result in a decline in suitable habitat, increase mountain pine beetle activity, an increase in the number, intensity, and extent of wildfires (Aubryet al.2008). A Random Forests multiple regression tree was used to generate a bioclimate model for Whitebark Pine based on the Hadley and Canadian General Circulation Model (1% increase GGa/yr) to estimate the climate of each pixel; by 2090, Warwellet al.(2007) predict Whitebark Pine is projected to diminish to an area equivalent to less than 3% of its current distribution. Koteen (1999) predicts climate change will probably affect the Whitebark Pine distribution, especially forests at the lowest elevational range.
Degree of Threat: Very high - high
Comments: Introduced white pine blister rust, increases in mountain pine beetle, fire suppression (kills the trees, or leaves weakened survivors vulnerable to attack by native mountain pine beetles which tend to kill mature trees that are the best cone producers), development (a variety of road-building and development projects such as at Timberline Lodge, Crater Lake's Rim Drive, and several ski areas), climate change and associated successional replacement, and their synergistic effects threaten this species' survival, with the blister rust believed to be the most compelling threat throughout the range (Fryer, 2002; Murray, 2005; Murray and Rasmussen, 2000; Ward et al., 2006).
WHITE PINE BLISTER RUST: White pine blister rust, a fungal disease caused by the pathogen Cronartium ribicola, was inadvertently introduced to Vancouver, British Columbia in 1910. In most parts of whitebark pine's range today, the majority of surveyed stands are declining in condition as a result of blister rust infection. For example, blister rust infection was found in 96% (164 of 170) of surveyed stands in Washington and Oregon (Ward et al. 2006), 83% in Bob Marshall Wilderness Complex in Montana (Keane et al., 1994), "the vast majority" of stands in Alberta, and "all of the regions sampled" during the most recent British Columbia survey (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). Throughout the species' range there are few stands that show no infection (Alberta Sustainable Resource Development and Alberta Conservation Association 2007).
In general, moist, humid conditions are believed to promote the spread of white pine blister rust and dry conditions to slow it; therefore increased global warming trends should favor the spread of the disease (see below). Stands that combine high elevation, dry conditions, and a fire regime of non-lethal underburns at long intervals are believed to be some of the healthiest remaining, avoiding the worst impacts of both blister rust and fire suppression; such stands occur mostly in the southern parts of the range in the Rocky Mountains (less than 10% of range) (Keane 1999). Nevertheless, environmental conditions at the extremes of whitebark pine's distribution - including cool temperatures, shorter growing seasons, and greater aridity - that were initially thought to provide some refuge from blister rust infection (e.g. USFWS 1994) are now known to only slow its spread. The epidemic is still spreading into and increasing within environments previously considered inhospitable, and the vast majority of the natural range is now believed to harbor the pathogen (Wars et al. 2006, Alberta Sustainable Resource Development and Alberta Conservation Association 2007).
The percentage of individual trees infected appears to vary widely throughout the range, with some areas having very high infection (> 90% per Alberta Sustainable Resource Development and Alberta Conservation Association 2007) and a few areas believed to have low impacts as yet. The highest infection levels (50-100%) are believed to occur in the northwestern U. S. and southwestern Canada in the northern Rockies and Cascades (Tomback 2002, Whitebark Pine Ecosystem Foundation 2006); Tomback (2002) also notes high infection in the intermountain ranges. Ward et al. (2006) state that "there is a high degree of localized variation in the prevalence of blister rust infection...hot spots of higher damage can occur...even in areas of moderate infection." In Oregon and Washington, the average percentage of infected living trees per stand (for stands that had infected treees) ranged from 11% to 95% (Ward et al. 2006). At two locations east of the Continental Divide in the northern Rocky Mountains, Montana, 35% of sampled trees were infected (Resler and Tomback 2008). At four biogeographically variable sites in the Greater Yellowstone Ecosystem, 85% sampled trees were infected (Tinker and Bockino 2007). In Alberta, approximately 60% of sampled trees were infected in the northern region, 16% were infected in the central region, and 73% were infected in the southern region (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). In British Columbia, in 483 stands distributed over the major mountain ranges, forest district levels of infection ranged from 18% to 53% (average 34%) (Zeglen 2002 cited in Alberta Sustainable Resource Development and Alberta Conservation Association 2007). In contrast, in California, whitebark pine is not believed to be in serious decline in the Sierra or Warner Moutains; T. Keeler-Wolf (pers. comm. 2008) states that "despite the white pine blister rust problem and others [elsewhere in the range], there is still tons of [whitebark pine] in the Sierra and although some has died from disease it is still the most abundant subalpine conifer." A 2002 survey in Sequoia and Kings Canyon National Parks in the southern Sierra Nevada documented cankers on few to no trees (Duriscoe and Duriscoe 2002 cited in Whitebark Pine Ecosystem Foundation 2006). The interior Great Basin ranges also appear to be minimally impacted by blister rust at this time (Whitebark Pine Ecosystem Foundation 2006).
Within each stand, the percentage of dead trees (mortality) from blister rust alone, and from all causes combined, tends to be significantly less than the percentage of infected living trees. Nevertheless, some areas have already experienced substantial (>50%) mortality (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). Furthermore, most mature trees infected with blister rust suffer loss of reproductive potential well before mortality occurs; thus many infected trees are no longer contributing to the maintenance of the population even though they remain alive (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). In Oregon and Washington, the average mortality per stand from all causes ranged from 2% to 41% (Ward et al. 2006). In a study that measured 17 permanent plots in western Montana at two intervals separated by 20 years, there was an average mortality rate of 42% over the 20 year period (Keane and Arno 1993 cited in Alberta Sustainable Resource Development and Alberta Conservation Association 2007). At four biogeographically variable sites in the Greater Yellowstone Ecosystem, 52% of the whitebark pine sampled were dead from multiple causes (Tinker and Bockino 2007). In southern Alberta, the average mortality in a recent survey was 61%; at eight permanent plots in this region, the mortality rate increased from 26% to 61% between 1996 and 2003. However, mortality is lower in central and northern Alberta (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). In British Columbia, in 483 stands distributed over the major mountain ranges, the range of mortality caused by blister rust was estimatd to be between 4% and 22% (average 10%) and the range of mortality from all causes was estimatd to be between 6% and 31% (average 19%) (Zeglen 2002 cited in Alberta Sustainable Resource Development and Alberta Conservation Association 2007).
Although projections of the future should technically not be considered in evaluating short term trend, it is worth mentioning that several studies have found these to be grim. In Mt. Rainier National Park, Washington, without any management intervention, 150-175 year simulations predict a 65-94% chance of whitebark pine extinction in the Park (Cottone 2001 cited in Ward et al. 2006, Ettl and Cottone 2004 cited in Alberta Sustainable Resource Development and Alberta Conservation Association 2007). In Crater Lake National Park, an overall decline of 0.4 percent per year for mature trees is predicted, which would lead to a 20 percent reduction in the Park within 50 years (Murray and Rasmussen 2000, 2003 cited in Ward et al. 2006). Murray (2005) predicts 95-99% mortality in Oregon populations due to blister rust.
However, there is some hope for the persistence and recovery of this species since naturally resistant trees have been found at many locations. Natural resistence to white pine blister rust infection is believed to exist in approximately 1-5% of the total whitebark pine population (Keane 1999), although resistant trees are still susceptible to other causes of mortality such as mountain pine beetle attack. Some researchers familiar with the species do expect it to persist, although noting that the structure of stands and the landscape pattern of their distribution may be different than the historical condition.
MOUNTAIN PINE BEETLE (Dendroctonus ponderosae): Mountain pine beetle is native to western North America and appears to have periods of higher and lower population density over time. For example, between 1909 and 1940 and again from the 1970s to the 1980s, outbreaks of mountain pine beetle killed whitebark pine throughout the U.S. Rocky Mountains (Whitebark Pine Ecosystem Foundation 2006). Drought and warmer temperatures in recent years have allowed unprecedented increases in beetle abundance and distribution. The first decade of the 20th century has seen further outbreaks within much of the U.S. range as well as attacks in British Columbia and Alberta of unprecedented scope and severity.
Studies in various parts of whitebark pine's range suggest the severity of impacts. 2006 aerial surveys indicated large-scale outbreaks of beetles in whitebark pine in northern Idaho, west-central and southwestern Montana, and the Greater Yellowstone Ecosystem (Gibson 2006 cited in Whitebark Pine Ecosystem Foundation 2006). In the Greater Yellowstone Ecosystem, the current mountain pine beetle outbreak is unprecedented in scope and severity: more than 700,000 whitebark pines were killed by beetles in 2004 (Whitebark Pine Ecosystem Foundation 2006), and at four biogeographically variable sample sites, 70% of whitebark pine were attacked by the beetle (Tinker and Bockino 2007). Observations in 2005 suggested that mountain pine beetle occurrence in whitebark pine is increasing in Oregon and Washington locations as well, such as Okanogan and Wenatchee National Forests and Crater Lake National Park (Ward et al. 2006). While whitebark pine losses due to mountain pine beetle in British Columbia and Alberta were relatively minor prior to the 1980s, warming climates have led to an expansion of beetle outbreaks into higher elevation forest containing whitebark pine (Campbell and Antos 2000, Campbell and Carroll 2007 cited in BC CDC 2008). In the 1980s outbreak, the beetle is believed to have affected a large decrease (30-40%) in mature whitebark pine canopy cover in southern Alberta. In British Columbia, 2007 aerial surveys indicated widespread beetle infestations and tree death, with about 7% of BC forests containing whitebark pine infested (Campbell and Carroll 2007 cited in BC CDC 2008) and impacts expanding into Alberta. This epidemic is projected to continue over the next few years (BC CDC 2008).
As for white pine blister rust, a small percentage of whitebark pine trees (3-5%) appear able to resist mountain pine beetle attack (BC CDC 2008).
FIRE SUPPRESSION AND SUCCESSIONAL REPLACEMENT: Prior to about 1930, the replacement of whitebark pine by later successional species such as spruce and fir was usually interrupted by naturally occurring fires. However, decades of fire suppression have allowed spruce and fir to become dominant in many forests that were historically dominated by whitebark pine. This threat appears to be particularly significant in the northern Rocky Mountains of the United States and the intermountain region (Whitebark Pine Ecosystem Foundation 2006), and in moister areas at lower elevations (Ward et al. 2006). Whitebark pine survives low severity fires better than its competitors because it has thicker bark, thinner crowns, and deeper roots. It is also well-adapted to recolonizing burned areas, as its seed disperser, Clark's nutcracker, appears to prefer open sites for seed caching (Keane 1999). Prescribed burn to control blister rust often results in reinfected trees returning in greater numbers that regenerate more slowly than non-infected trees (Tomback et al., 1995).
CLIMATE CHANGE: Major reductions in habitat suitable for this subalpine species are expected as the climate warms (BC CDC 2008). Modeling mostly predicts a decline in whitebark pine due to global increases in temperature and more frequent summer droughts (Mattson et al., 2001; McCaughey and Tomback, 2001). Climate modeling for Yellowstone National Park predicts that independent of other agents of decline such as blister rust, whitebark pine is the most at-risk conifer in the Park due to drying conditions in high-elevation habitats (Bartlein et al., 1997). However, impact of climate change on whitebark pine is inconclusive: Keane et al. (1996) and others predict expansion of whitebark pine in Glacier National Park due to more frequent fire return intervals resulting from global warming. Increased global temperature makes the species more vulnerable to fungus such as blister rust (Murray, 2005).
SYNERGIES: Numerous studies have found that whitebark pine trees stressed by blister rust are more susceptible to attack by mountain pine beetle. Mortality from the combination of blister rust and mountain pine beetle has apparently exceeded 50% in areas including Glacier National Park, northwestern Montana, north-central Idaho, and northern Washington, and mortality is increasing rapidly in the Cascades and Sierra Nevada Range (Whitebark Pine Ecosystem Foundation 2006). Furthermore, the significant threat from both white pine blister rust and mountain pine beetle threatens the success of restoration strategies based on cultivating tree resistant to either threat alone (Whitebark Pine Ecosystem Foundation 2006). In addition, the tendency of both of these agents to kill mature, reproductive trees accelerates successional replacement processes resulting from fire suppression; and fire suppression itself is believed to have an inhibitory effect on whitebark pine's recovery from major beetle outbreaks (Keane 1999). Finally, climate change interacts significantly with the mountain pine beetle threat, as warmer temperatures increase he proportion of whitebark pine's range vulnerable to beetle attack (BC CDC 2008). Warmer temperatures also appear to permit the beetle to complete its life cycle more quickly (i.e. in one year) and to make summer dispersal flights more dependably (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). Logging has also been noted as a threat in British Columbia; while it is not a significant threat on its own, since it occurs in healthy stands it reduces the number of intact stands as yet minimally affected by other threats, which may be important for future survival (E. Campbell, pers. comm. 2007 cited in BC CDC 2008).
Identification, harnessing and deploying (tree planting) rust resistant Whitebark Pine in the Whitebark Pine genetics program (Mahalovich and Dickerson 2004, Mahalovichet al.2006, McCaugheyet al.2009).
Ex situ gene conservation including seed and pollen in cold storage, clone banks, and seed orchards; in situ gene conservation including phenotypically, blister rust resistant Whitebark Pine and long-term genetic tests (Mahalovich 2000, Mahalovich and Dickerson 2004).
Prescribed fire is used for site preparation for artificial regeneration of rust-resistant seedlings, to enhance natural regeneration, and for release to favour Whitebark Pine (Keane and Parson 2010).Tree protection against Mountain Beetle include verbenone (anti-aggregate pheromone) (Kegley and Gibson 2004) and carbaryl applications (Gibson and Bennett 1985).
Biological Research Needs: Research is ongoing to combat white pine blister rust through the identification, propagation, and planting of resistant trees. Research is also being conducted on the appropriate prescribed burning and silvicultural treatments to restore successionally advanced whitebark pine communities (Keane 1999, Tomback 2002).
Relevance to Humans and Ecosystems
Other uses and values
Whitebark pine is a keystone species in upper subalpine communities . Tomback and others  and the authors below have identified several critical roles whitebark pine plays in subalpine ecosystem function. Some items listed below are explained in other sections of this summary.
- is a pioneer species after fire or other disturbances (see Fire Ecology or Adaptations)
- facilitates succession (see Successional Status)
- serves as a source of community diversity by providing structural complexity, forms ecotone edges with alpine and wet meadow communities 
- provides critical wildlife habitat and food (see Importance to Livestock and Wildlife)
- promotes plant and animal diversity 
- protects watersheds by reducing soil erosion and slowing snow runoff
Wood Products: Mainly due to the species' inaccessibility, whitebark pine wood is not considered commercially valuable. Large-diameter whitebark pine in mixed stands were harvested in the past. Whitebark pine is classified as a soft-wood pine, and its wood has bending, compression, and shearing properties similar to eastern (P. strobus) and western white pine. Wood density is slightly higher than most white pines, and is similar to Douglas-fir [55,96].
Grazing: A short growing season, drought, and commonly shallow, rocky soils make whitebark pine habitats slow to recover from grazing [126,229]. Whitebark pine/grouse whortleberry habitats seem more tolerant of grazing than whitebark/bunchgrass types . "Moderate overgrazing" on whitebark pine sites may increase lupines (Lupinus spp.), luina (Luina nardosima), and other unpalatable herbs at the expense of bunchgrasses. "Severe overgrazing" can create large, highly erosive patches of bare soil . Willard  provides guidelines for assessing range condition in whitebark pine ecosystems, including plant species indicators and soil condition indicators.
Moderate grazing on subalpine mixed conifer-meadow ecotones may encourage invasion of whitebark pine and other conifers into meadows. Conifer invasion into meadows on the Wind River Mountains of Wyoming began about 1890, concurrent with cattle grazing. Tree invasion ceased in 1963, concurrent with cessation of cattle grazing. Dunwiddie  suggests that moderate cattle grazing favors whitebark pine and other conifers by reducing competition with meadow vegetation.
Other values: As a long-lived species, whitebark pine tree-ring chronologies are a valuable source of long-term climate information. Perkins and Swetnam  have correlated patterns of tree growth and climate for more than 1,000 years from whitebark pine stands in the Sawtooth Mountains of Idaho.
Whitebark pine is planted worldwide as an ornamental .
Whitebark pine seeds are a traditional Native American food . The easternmost population of whitebark pine, isolated in the Sweetwater Mountains of Montana, may have originally been planted by Native Americans as a food source .
Value for rehabilitation of disturbed sites
Restoration: Increasing mortality from successional replacement, white pine blister rust, bark beetles, and other agents foretell that whitebark pine will not remain an important component of subalpine communities without long-term, active management intervention [12,100]. Whitebark pine researchers recommend the following:
1. Assess the local extent, successional status, and vigor of whitebark pine. If it appears that cone crops will dwindle in the future ,
2. inventory stands to document tree age, stand structure, cone-production potential, and projected time frame of successional replacement [12,18,19].
3. Apply and evaluate management-ignited and wildland for resource benefit fires designed to kill late-successional trees and favor whitebark pine (see Fire Management Considerations).
4. Conduct seed trials with blister rust-resistant stock in areas where natural whitebark pine seed sources have disappeared .
Artificial regeneration: Whitebark pine can be grown in the nursery from seed , and there is considerable interest in outplanting nursery-grown, blister-rust resistant stock to replace dead and dying mature whitebark pine . Transplanted whitebark pine has shown fair survivorship rates; further studies are needed to determine which habitat/aspect/elevational combinations are best for artificial regeneration. Whitebark pine appears to tolerate broad, possibly regional seed transfer. Transfer guidelines are available [135,218]. Planting seed may be a good restoration option, as natural dormancy of whitebark pine seed may help ensure germination under conditions favorable for establishment (see Regeneration Processes). On the Gallatin National Forest, seedlings established from hand-planted seed showed mean 1st-year survivorship rates of 73% in a drought year (1988) and 90% in a wet year (1989) . Kendall  recommends developing a cold-stored genetic seed bank for whitebark pine, emphasizing that collections from small, isolated populations should be a priority. Authorities from the U.S. Forest Service Nursery in Coeur d'Alene, Idaho,  provide guidelines for collecting whitebark pine seed in the field, growing whitebark pine in the greenhouse, and transporting seedlings to planting sites.
Genetic considerations: Hoff and others [83,84] provide advice on managing whitebark pine in the field to promote genetic resistance for blister rust. Experts on whitebark pine genetics have raised the possibility of establishing "seed orchards" similar to those successfully used for western white pine, an important timber species that has also been decimated by blister rust. Seed orchard trees are started from seed collected from parent trees showing blister-rust resistance. The seedlings are planted on favorable sites (sometimes even in greenhouses). Given ideal growth conditions, age of reproduction of parent trees can be greatly reduced. (Some whitebark on moist sites on the Kootenai National Forest have produced female cones at 10 years of age (pers. observ.); trees in greenhouses may set seed as early as 7 years). Natural and artificial cross-breeding of symptomless whitebark parents will enhance genetic selection for blister-rust resistance and provide opportunities for restocking blister rust-decimated landscapes with orchard progeny, many of which will inherit mechanisms for blister-rust resistance .
Yanchuk [233,234] provides guidelines for prioritizing conifer species for genetic conservation programs in British Columbia. Selection is based on species protection status, conservation breeding programs already in place, and relative capacity for regeneration. As of this writing (2002), whitebark pine was rated the species in greatest need of genetic conservation management.
Due to its clumping habit, whitebark pine has an unusual genetic population structure (see Breeding system). Planting whitebark pine without regard for its natural habit of growing in clumped family groups may have long-term consequences on natural selection processes operating on whitebark pine .
Importance to Livestock and Wildlife
Whitebark pine is a valuable source of food and cover for wildlife [147,212]. Bears, rodents, and birds consume the seeds [66,90,92,143,203]. The trunks provide nesting sites for cavity nesters including northern flickers and mountain bluebirds [107,148]. Blue grouse use the branches for roosting and escape cover [107,137].
Bears: Whitebark pine ecosystems provide critical habitat for grizzly and black bears. Agee and others  found that grizzly bear sightings in North Cascades National Park, Washington, were more frequent than statistically expected in whitebark pine/alpine larch habitats. Whitebark pine seeds are a high-quality bear food [141,143,152]. Red and Douglas' squirrels provide an important ecological link between whitebark pine and bears by making the seeds more readily available. Grizzly and black bears rarely harvest whitebark pine cones from trees; they raid squirrel middens laden with whitebark pine seeds [105,143,204]. Bear consumption of whitebark pine seed peaks just before hibernation in late October and early November. Bears feeding on whitebark pine seeds tend to feed on nothing else, and a good supply of seeds increases bear fecundity. In Yellowstone National Park, female grizzly bears were less likely to abort, and more likely to have larger litters (3 cubs compared to 1-2 cubs) in good conecrop years. Most importantly, grizzly bear death rate was nearly double when bear consumption of whitebark pine seeds was low . Grizzly bears and humans have fewer troublesome encounters when whitebark pine seeds crops are large. In Yellowstone National Park, grizzly bear summer and fall movement is related to availability of whitebark pine seed. In good crop years, grizzly bear tend to congregate in remote whitebark pine communities. When seed is limited, they tend to forage in more populated, lower-elevation sites. Yearling cubs and females with cubs-of-the-year are most likely to be displaced to lower elevations in poor conecrop years [33,141,142].
Large ungulates: Whitebark pine is a minor browse species for big game, but whitebark pine understories often provide valuable forage. Rocky Mountain mule deer consume trace amounts of whitebark pine . Productivity in whitebark pine understories is highly variable. Stands with grassy understories are usually most productive. Herbage production on the Wenatchee National Forest averaged 204 lbs/acre in whitebark pine/pinegrass communities and 115 lbs/acre in whitebark pine/green fescue communities. In contrast, a whitebark pine/grouse whortleberry/smooth woodrush community site showed herbage production of 22 lbs/acre [126,229].
Birds: Many bird species use whitebark pine ecosystems. Tomback and Kendall  provide a list of year-round and neotropical species that nest in or otherwise use whitebark pine ecosystems.
Whitebark pine provides ecologically critical linkage between Clark's nutcracker and lower-elevation, Clark's nutcracker-dependant pines (i.e., limber pine and pinyon pines (Cembroides)). When the seed crop of 1 pine species is insufficient, Clark's nutcrackers migrate up- or downslope to harvest species with more bountiful seed crops. Loss of whitebark pine, their preferred species, reduces Clark's nutcracker populations, and may have negative consequences for other pine species with seeds dispersed by Clark's nutcrackers .
Palatability/nutritional value: Whitebark pine seeds are highly nutritious. They are especially high in lipids. Content of seed collected from the Gallatin National Forest was 52% fat, 21% carbohydrate, 21% protein, 3% ash, and 3% water. Major minerals present were copper, zinc, iron, manganese, magnesium, and calcium . Energy content of fresh, mature whitebark pine seed collected on the Bridger-Teton National Forest ranged from 5,526 to 7,308 calories/g (Âµ=6,800 calories/g) [89,115]. Tomback  reported similar energy values (Âµ=7,716 calories/g) for whitebark pine seed from the Sierra Nevada.
Cover value: Wildlife and livestock use whitebark pine/shrub communities for shade and bedding cover . In Silverbow County, Montana, elk primarily used whitebark pine with a subalpine fir component as fall cover. Female mule deer used whitebark pine communities 15% of their time in summer and 3% in fall. Male mule deer used whitebark pine communities 4% of their time in summer; insufficient data precluded estimates of their fall usage . Whitebark pine ridgetops are prime calving habitat for woodland caribou. Additional fire-created openings in whitebark pine ecosystems might be an asset to caribou reproduction .
Blue grouse feed and roost in whitebark pine crowns during much of the year. This tree provides both hiding and thermal cover in sites where few if any other trees grow. The large, hollow trunks of old trees and snags provide homesites for cavity-nesting birds. The seeds of whitebark pine were occasionally used as a secondary food source by Native Americans (17,54).
Whitebark pine helps to stabilize snow, soil, and rocks on steep terrain and has potential for use in land-reclamation projects at high elevation (68). It provides shelter and fuel for hikers and campers and is an important component of the picturesque setting that lures hundreds of thousands of visitors into the high mountains (21).
Pinus albicaulis, with many common names including whitebark pine, white pine, pitch pine, scrub pine, and creeping pine, occurs in the mountains of the Western United States and Canada, specifically the subalpine areas of the Sierra Nevada, the Cascade Range, the Pacific Coast Ranges, and the Rocky Mountains from Wyoming through the Continental Ranges. It shares the common name creeping pine with several other "creeping pine" plants.
The whitebark pine is typically the highest-elevation pine tree of these mountains, marking the tree line. Thus, it is often found as krummholz, trees dwarfed by exposure and growing close to the ground. In more favourable conditions, trees may grow to 20 meters (66 ft) in height, although some can reach up to 27 meters (89 ft).
Whitebark pine (Pinus albicaulis) is a member of the white pine group, Pinus subgenus Strobus, section Strobus and like all members of that group, the leaves ('needles') are in fascicles (bundles) of five, with a deciduous sheath. This distinguishes whitebark pine and relatives from the lodgepole pine (Pinus contorta), with two needles per fascicle, and Ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi), which both have three per fascicle; these three all also have a persistent sheath at the base of each fascicle.
Distinguishing whitebark pine (Pinus albicaulis), from the related limber pine (Pinus flexilis), also a "white pine", is much more difficult, and needs seed or pollen cones. In Pinus albicaulis, the cones are 4–7 centimeters (1.6–2.8 in) long, dark purple when immature, and do not open on drying, but the scales easily break when they are removed by Clark's Nutcracker (see below) to harvest the seeds; rarely are there intact old cones under them. Its pollen cones are scarlet.
In Pinus flexilis, the cones are 6–12 centimeters (2.4–4.7 in) long, green when immature, and open to release the seeds; the scales are not fragile. Usually there are intact old cones under them. Their pollen cones are yellow.
Whitebark pine (Pinus albicaulis) can also be hard to distinguish from western white pine (Pinus monticola) in the absence of cones. However, whitebark pine needles are entire (smooth when rubbed gently in either direction), whereas western white pine needles are finely serrated (feeling rough when rubbed gently from tip to base). Whitebark pine needles are also usually shorter, 4–7 centimeters (1.6–2.8 in) long, overlapping in size with the larger 5–10 centimeters (2.0–3.9 in) needles of the western white pine.
Source of food
The whitebark pine is an important source of food for many granivorous birds and small mammals, including most importantly the Clark's Nutcracker, the major seed disperser of the pine. Clark's Nutcrackers each cache about 30,000 to 100,000 each year in small, widely scattered caches usually under 2 to 3 cm (0.79 to 1.18 in) of soil or gravelly substrate. Nutcrackers retrieve these seed caches during times of food scarcity and to feed their young. Cache sites selected by nutcrackers are often favorable for germination of seeds and survival of seedlings. Those caches not retrieved by time snow melts contribute to forest regeneration. Consequently, whitebark pine often grows in clumps of several trees, originating from a single cache of 2–15 or more seeds. Douglas Squirrels cut down and store whitebark pine cones in their middens. Grizzly Bears and American Black Bears often raid squirrel middens for whitebark pine seeds, an important pre-hibernation food. Squirrels, Northern Flickers, and Mountain Bluebirds often nest in whitebark pines, and elk and Blue Grouse use whitebark pine communities as summer habitat.
A study in the mid-2000s showed that whitebark pine had declined by 41 percent in the Western Cascades due to two threats: white pine blister rust and mountain pine beetles. Whitebark deaths in North Cascades National Park doubled from 2006 to 2011.
White pine blister rust
Many stands of Pinus albicaulis nearly range-wide are infected with white pine blister rust (Cronartium ribicola), a fungal disease that was introduced from Europe. In the northern Rocky Mountains of the U.S., whitebark pine mortality in some areas exceeds 90 percent, where the disease infests 143,000 acres (580 km2). Cronartium ribicola occurs in whitebark pine to the northern limits of the species in the coastal ranges of British Columbia and the Canadian Rocky Mountains. The blister rust has also devastated the commercially-valuable western white pine in these areas, and made serious inroads in limber pine (Pinus flexilis) populations as well. Nearly 80 percent of whitebark pines in Mount Rainier National Park are infected with blister rust.
There is currently no way to stop the spread and effects of blister rust. However, a small number of trees (fewer than 5%) in most populations harbor genetic resistance to blister rust. There have been some restoration efforts by the U.S. Forest Service, Bureau of Land Management, and National Park Service in the northern Rocky Mountains. Restoration efforts involve harvesting cones from potentially and known resistant whitebark pines, growing seedlings, and outplanting seedlings in suitable sites.
In California, where the blister rust is far less severe, whitebark pine are still fairly common in the High Sierras.
Mountain pine beetle
There are widespread outbreaks of mountain pine beetle in the western U.S. and Canada. Since 2000, the climate at high elevations has been warm enough for the beetles to reproduce within whitebark pine, often completing their life cycle within one year and enabling their populations to grow exponentially. Entire forest vistas, like that at Avalanche Ridge near Yellowstone National Park’s east gate, are expanses of dead gray whitebarks. This warming has been attributed by some researchers to global warming.
In 2007, the U.S. Fish and Wildlife Service estimated that beetles had killed whitebark pines across 500,000 acres (200,000 ha) in the West, while in 2009, beetles were estimated to have killed trees on 800,000 acres (320,000 ha), the most since record-keeping began. The pine beetle upsurge has killed nearly 750,000 whitebark pines in the Greater Yellowstone Ecosystem alone.[when?]
Fire suppression has led to slow population declines over the last century by altering the health and composition dynamics of stands without the fire ecology balancing their habitat and suppressing insect-disease threats. In the absence of low-level wildfire cycles, whitebark pines in these stands are replaced by more shade-tolerant, fire-intolerant species such as subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii). In addition, senescent and blister rust infected pine trees are not destroyed by natural periodic ground fires, further diminishing the whitebark pine forest's vitality and survival.
On July 18, 2011, the U.S. Fish and Wildlife Service reported that the whitebark pine needed protection and that, without it, the tree would soon be extinct. However, the agency announced it would neither be able to list the tree as endangered nor protect the organism, as it lacked both the necessary staff and funding to do so. In June 2012, the Canadian federal government declared whitebark pine endangered in accordance with the Species at Risk Act. As such, it is the first federal endangered tree in Western Canada.
In response to the on-going decline of the tree throughout its range, the Whitebark Pine Ecosystem Foundation was formed. Their mission is to raise awareness and promote conservation by sponsoring restoration projects, publishing a newsletter called "Nutcracker Notes", and hosting an annual science and management workshop for anyone interested in whitebark pine. This U.S. group collaborates closely with the Whitebark Pine Ecosystem Foundation of Canada.
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- Petit, Charles (January 30, 2007). "In the Rockies, Pines Die and Bears Feel It". New York Times.
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- Lorenz, T. J.; Aubry, C.; Shoal, R. (2008). A review of the literature on seed fate in whitebark pine and the life history traits of Clark's nutcracker and pine squirrels (PDF). Portland, OR: U.S. Dept. of Agriculture, Forest Service, Pacific Northwest Research Station. OCLC 222226528.
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- Whitebark Pine Ecosystem Foundation
- Whitebark Pine Ecosystem Foundation of Canada
- Chase, J. Smeaton (1911). Cone-bearing Trees of the California Mountains. Chicago: A. C. McClurg & Co. p. 99. LCCN 11004975. OCLC 3477527.
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- Lanner, R. M. (1996). Made for each other: a symbiosis of birds and pines. OUP. ISBN 0-19-508903-0.
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- Murray, M.P. (2005). "Our Threatened Timberlines: The Plight of Whitebark Pine Ecosystems" (PDF). Kalmiopsis 12: 25–29.
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|Wikimedia Commons has media related to:|
- Pinus albicaulis from USDA Plants Profile
- Pinus albicaulis from Jepson Manual Treatment
- Pinus albicaulis from Gymnosperm Database
- Pinus albicaulis from Flora of North America
- Pinus albicaulis – U.C. Photos Gallery
- "Whitebark Pine". United States Geological Survey. Archived from the original on 2007-07-14.
- Whitebark Pine Communities from the United States Geological Survey
- Official website of the Whitebark Foundation
- High Elevation White Pine – Pinus albicaulis from the USDA Forest Service's Rocky Mountain Research Station
The fresh-cut wood of Pinus albicaulis is sweet-scented. Seeds are dispersed mainly by Clark's nutcracker [ Nucifraga columbiana (Wilson), family Corvidae].
Names and Taxonomy
(Pinaceae) [53,64,79,95,114]. Whitebark pine is the only
stone pine (subgenus Strobus, section Strobus, subsection Cembrae)
native to North America [53,118].
Whitebark and limber pine (P. flexilis) have been crossed in the
laboratory, and putative hybrids between the 2 species have been identified on
the Rocky Mountain Front of Montana. Such entities are rare and
apparently infertile [51,59].
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