Pinus albicaulis

Whitebark pine occurs in subalpine and timberline zones from west-central British Columbia (55o N) east to west-central Alberta and south to central Idaho, southwestern Wyoming, and southern California (36o N). 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 [17,21,128]. The Flora of North America provides a distributional map of whitebark pine. The Whitebark and Limber Pine Information System provides distributional information at the stand level.

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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 [29]:

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

CAIDMTNVORWAWY
ABBC

Whitebark pine grows in the highest elevation forest and at timberline.  Its distribution is essentially split into two broad sections, one  following the British Columbia Coast Ranges, the Cascade Range, and the  Sierra Nevada, and the other covering the Rocky Mountains from Wyoming to  Alberta.

    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.

Pinus albicaulis Engelm.:
China (Asia)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Whitebark Pine is limited in distribution to the high mountains of western North America, where it has been present for the past 8,000 years. It occurs along high-elevation ridges, and is therefore not contiguous. Whitebark Pine forests extend longitudinally between 107° and 128° West and latitudinally between 37° and 55° North (Arno and Hoff 1990, McCaughey and Schmidt 1990). In Canada, it grows along the coastal range in British Columbia and in the Rocky Mountains in Alberta. In the USA the range extends from the Canadian border of the Cascade Mountains through Washington and Oregon to southern California and is at high altitudes throughout the Rocky Mountains of Montana, Idaho and Wyoming.

Many Whitebark Pine stands are geographically isolated by large intervening valleys between them (Arno and Hoff 1990). Whitebark Pine is typically found just below the alpine timberline and extends downward in elevation into associations with several other conifers. The upper elevation limits of Whitebark Pine decrease with increasing latitude. It occurs as high as 3,050–3,660 m in the Sierra Nevada and 2,590–3,200 m in western Wyoming; and as low as 900 m in the northern limits of its range in British Colombia (Arno and Hoff 1990).

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.

Pinaceae -- Pine Family

    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).

Trees to 21m; trunk to 1.5m diam., straight to twisted and contorted; crown conic, becoming rounded to irregularly spreading. Bark pale gray, from distance appearing whitish to light gray and smooth, in age separating into thin plates. Branches spreading to ascending, often persistent to trunk base; twigs stout, pale red-brown, with light brown, often glandular puberulence, somewhat roughened by elevated scars, aging gray to pale gray-brown. Buds ovoid, light red-brown, 0.8--1cm; scale margins entire. Leaves 5 per fascicle, mostly ascending and upcurved, persisting 5--8 years, 3--7cm ´ 1--1.5(--2)mm, mostly connivent, deep yellow-green, abaxial surface less so, adaxial surface conspicuously whitened by stomates, margins rounded, minutely serrulate distally, apex conic-acute; sheath 0.8--1.2cm, shed early. Pollen cones cylindro-ovoid, ca. 10--15mm, scarlet. Seed cones remaining on tree (unless dislodged by animals), not opening naturally but through animal agency, spreading, symmetric, broadly ovoid to depressed-ovoid or nearly globose, 4--8cm, dull gray- to black-purple, sessile to short-stalked; scales thin-based and easily broken off; apophyses much thickened, strongly cross-keeled, tip upcurved, brown; umbo terminal, short, incurved, broadly triangular, tip acute. Seeds obovoid; body 7--11mm, chestnut brown, wingless. 2 n =24.

More info for the terms: basal area, cover, frequency, shrub, tree

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 [64].  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 [6]. 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 [47]. 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 [115]. Several to all stems in a clump may be genetically distinct individuals [127].

Bark thickness is thin to moderate, seldom reaching over 0.4 inch (1 cm) [21]. Branches of mature trees are ascending [89]. 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 [64]. 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 [110], 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 [126]. On the Okanogan National Forest of Washington, mean overstory cover in a whitebark pine/pinegrass community was 27% [230].

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 [169].

Whitebark pine is extremely wind firm. High-elevation trees on shallow, undeveloped  soils frequently endure near-hurricane-force winds [32].

Tree, Evergreen, Monoecious, Habit erect, Trees without or rarely having knees, Primary plant stem smooth, Tree with bark smooth, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds not resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins finely serrulate (use magnification or slide your finger along the leaf), Leaf apex acute, Leaves < 5 cm long, Leaves > 5 cm long, Leaves < 10 cm long, Leaves yellow-green above, Leaves yellow-green below, Leaves not blue-green, Leaves white-striped, Needle-like leaves somewhat rounded, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaves per fascicle mostly 5, Needle-like leaf sheath early deciduous, Twigs pubescent, Twigs viscid, Twigs not viscid, Twigs without peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones < 5 cm long, Woody seed cones > 5 cm long, Seed cones bearing a scarlike umbo, Umbo with missing or very weak prickle, Umbo with obvious prickle, Bracts of seed cone included, Seeds brown, Seeds wingless, Seed wings narrower than body.

Apinus albicaulis (Engelmann) Rydberg

More info for the terms: natural, serpentine soils

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 [139]. 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 [226], 2/3rds of which is snow [17]. 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 [139]. 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% [87]. 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 [76]. 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) [230]. Krummholz or matted whitebark pine grows mostly on high-elevation sites where glacial scouring has eliminated most of the soil [182].

Elevation: Whitebark pine occurs from 4,300 to 12,100 feet (1,300-3,700 m) elevation [64]. Ranges by state or province are as follows:

Location Elevation 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) [17] NV 6,400 to 10,00 feet (2,000-3,000 m) [52] 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) [17]

More info for the terms: codominant, cover, mesic, shrub, shrubs, tree

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
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. 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 [17]. At high elevations, krummholz whitebark pine
communities merge into alpine vegetation. At
mid-elevation, whitebark pine communities merge into mixed-conifer forests
[17,30].

Several
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) [194]. In the coastal states, it associates with mountain hemlock (Tsuga mertensiana), with increasing
codominance of the 2 species to the south [87].
Subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea
engelmannii)
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
restricted
to more mesic sites [9,16,50,126].
Sadly, whitebark pine communities of the northern Cascades [126],
eastern Washington [229], Idaho, and Montana [171] are
often characterized as "ghost forests" of whitebark that have been dead for decades, with little regeneration
[130].
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
in
higher-elevation alpine larch communities [126].
In Mt. Rainier National Park, krummholz whitebark pine/common juniper (Juniperus
communis) forests
dominate high, rocky ridges above Yakima Park [69].
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 [17]. 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 [229]. 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 [17].
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 [185]. 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
dominants [194].
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)
[87,136,182].
At lower elevations (7,500 feet in the north and 9,000 feet in the south),
whitebark pine
merges with mixed Sierra Nevada lodgepole pine, red fir (Abies magnifica),
and/or Jeffrey pine (P. jeffreyi) forest. Krummholz whitebark pine
merges
into alpine fell-fields at high elevations (9,500-11,100 feet (2,900-3,4900 m), depending on
latitude) [17,32,87,202]. 

In the Warner Mountains, whitebark pine co-occurs with Sierra Nevada
lodgepole pine, Washoe pine (P. washoensis), white
fir (A. concolor), and Jeffrey pine [136,179].

Klamath Mountain associates in whitebark pine/oceanspray (Holodiscus
discolor)
communities include mountain hemlock, Shasta red fir (A. m. var. shastensis), western white pine (P. monticola), Jeffrey pine, foxtail pine, and Sierra Nevada lodgepole
pine [156,184].
Nevada: Limber pine is the primary codominant [17]. 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)) [125]. In the Ruby Mountains, whitebark pine forms subalpine communities
with 

Great Basin bristlecone (P. longaeva) and limber pines; it is the only area where
the 3 Strobus species
overlap [117,125].
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
classified [50,54,194,195].
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
plant communities.
California [87,110,136,179,182,184,202]

Idaho [50,54,65,161,185,194,195]

Nevada [125,132]

Montana [65,168,171]

Oregon [48,67,75,93,134,230]

Washington [4,54,56,67,75,126,229,230]

Wyoming [65,143,194]

Alberta [136,188]

British Columbia [1]

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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 [189]:

409 Tall forb

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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 [60]:

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

217 Aspen

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

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

KUCHLER [112] 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

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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):

ECOSYSTEMS [71]:

FRES20 Douglas-fir

FRES22 Western white pine

FRES23 Fir-spruce

FRES24 Hemlock-Sitka spruce

FRES26 Lodgepole pine

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). Chemical weathering is retarded by the short, cool, summer  season. Also, nitrogen-fixing and other microbiotic activity that might  enrich the soil is apparently restricted by low soil temperature and high  acidity on many sites.

    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).

Whitebark pine grows in a cold, windy, snowy, and generally moist  climatic zone. In moist mountain ranges, whitebark pine is most abundant  on warm, dry exposures. Conversely, in semiarid ranges, it becomes  prevalent on cool exposures and moist sites. Weather data from several  whitebark pine sites in the Inland Northwest suggest the climatic  interpretations that follow (3,83). Summers are short and cool with mean  July temperatures ranging from 13° to 15° C (55° to 59°  F) in the whitebark pine forest and from 10° to 12° C (50°  to 54° F) in the adjacent timberline zone. A cool growing season, as  defined by mean temperatures higher than 5.5° C (42° F) (11),  lasts about 90 to 110 days in the whitebark pine forest, but light frosts  and snowfalls sometimes occur even in mid-summer. The hottest summer days  reach temperatures of 26° to 30° C (79° to 86° F).  January mean temperatures range from about -9° C (15° F) in  Montana to about -5° C (23° F) in the Cascades and Sierra  Nevada. Long-term record low temperatures in Montana and Wyoming stands  are probably -40° to -50° C (-40° to -58° F).

    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.

Thin, rocky, cold soils at or near timberline, montane forests; 1300--3700m; Alta., B.C.; Calif., Idaho, Mont., Nev., Oreg., Wash., Wyo.

Habitat and Ecology

Systems

• Terrestrial

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).

Whitebark pine is most frequently found growing with other high mountain  conifers, although pure whitebark pine stands are common in dry mountain  ranges. The forest cover type Whitebark Pine (Society of American  Foresters Type 208) (70) is used to designate pure stands or mixed stands  in which the species comprises a plurality. Whitebark pine is also a minor  component of Engelmann Spruce-Subalpine Fir (Type 206) in the Rockies,  eastern Cascades, and the Blue Mountains; Mountain Hemlock (Type 205) in  much of the Cascades and British Columbia coastal mountains; and  California Mixed Subalpine (Type 256) in the California Cascades, Sierra  Nevada, and Klamath Mountains. In these open, upper subalpine forests,  whitebark pine is associated with mountain hemlock, California and Shasta  red fir (Abies magnifica vars. magnifica and shastensis),  Sierra lodgepole pine (Pinus contorta var. murrayana),  western white pine (P. monticola), and locally, foxtail (P.  balfouriana) and limber (P. flexilis) pines.

    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.

Mountain pine beetle (Dendroctonus  ponderosae) is by far the most damaging insect in mature stands of  whitebark pine (13). Much of the mature whitebark pine in the northern  Rockies was killed by this insect between 1909 and 1940 (3,19,31).  Epidemics evidently spread upward into the whitebark pine forest after  becoming established in the lodgepole pine forests below. In the 1970's,  an epidemic developing in lodgepole pine in the Flathead National Forest  of Montana killed most of the whitebark pine in some areas. This insect  usually kills only the larger whitebark pine trees because such trees have  an inner bark layer thick enough for the larvae to inhabit. Small trees  are also killed in areas of intense infestation.

    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.

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).

More info for the terms: cover, fire exclusion, fire management, fire occurrence, fire-return interval, fire-sensitive species, fuel, natural, prescribed fire, prescribed natural fire, resistance, restoration, selection, severity, shrub, stand-replacing fire, succession, tree, wildfire

Effects of fire exclusion: Kendall and Keane [108] 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 [97]. Based upon fire records from the U.S. Forest Service's Northern Region, Arno [12] 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 [38]. 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% [111].

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 [187]. Whitebark pine in Wilderness Areas is not immune to decline: Kendall and Arno [107] 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 [109]. 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 [97]. As of this writing (2002), studies are underway to determine fire histories and explore management options in small, isolated Wilderness Areas [163]. Renkin and Despain [178] 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 [97] 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 [100] 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 [108] 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 [78]. 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 [84]. 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 [108].

Management-ignited fires can be used for fire hazard reduction and whitebark pine restoration treatments [37]. 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 [100].

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 [210]. 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 [100]. Follow-up thinning treatments, especially of subalpine fir, are usually needed to encourage whitebark pine growth [210]. 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 [190] 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 [190] 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 [155] 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 [193] 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.

More info for the terms: density, mixed-severity fire, stand-replacement fire, stand-replacing fire, tree, wildfire

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 [206]. 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 [20]. 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 (µ=1.5 + 1.0 in.) (1-13 cm (µ=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 [205] 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 [199] 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 (µ=10.3 in. (36.2 cm)), followed by south and north slopes (µ=12.0 and 11.9 in. (30.6 and 29.7 cm)), and was least on roadside plots (µ=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 [205].

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) [210].

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 [210] 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 [175]:

Tree condition Percent green (survived fire) 36.1 fire killed 59.7 postfire insect kill (mostly mt. pine & pine engraver beetles) 2.8 unknown mortality 1.4

More info for the terms: basal area, fuel, natural, succession

Modeling: Several fire effects, fuel, and fire behavior models applicable to whitebark pine ecosystems are available at fire.org. McKenzie and others [151] provide a model for predicting coarse-scale fire effects in whitebark pine and other potential natural vegetation types of the Columbia River Basin. Keane [98] 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 [101].

More info for the terms: severity, surface fire, wildfire

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 [24].

Percent fire kill of mature whitebark pine compared to mature overstory associates [24] whitebark pine 35 Rocky Mountain lodgepole pine 36 Engelmann spruce 47 subalpine fir 59

More info for the terms: adventitious, initial off-site colonizer, secondary colonizer, tree

POSTFIRE REGENERATION STRATEGY [196]:
Tree without adventitious bud/root crown
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)

More info for the terms: climax, fire exclusion, fire frequency, fire regime, fire severity, fire suppression, fire-return interval, frequency, fuel, ground fire, mean fire-return interval, mixed-severity fire, mixed-severity fire regime, natural, severity, stand-replacement fire, succession, underburn, wildfire

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 [100], but patchy fires resulting from fuel-limited whitebark pine habitats reduces whitebark pine mortality [2]. In western Montana, Arno [11] 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 [159]. 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 [85]  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 [2] 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 [164], which crown and consume conifers in dense patches. On 3 sites on the Bitterroot National Forest, Montana, Arno [10] reported minimum/maximum fire-return intervals of  2/68 (µ=33), 4/78 (µ=30), and 8/50 (µ=41) years. Brown and others [38] 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 [126] and elsewhere. Arno [11] 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" [12]. 

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 [158]. Fires historically started in summer and fall and burned over many weeks [97]. 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 [38]. Large fires typically occurred in drought years, burned through lower-elevation plant communities as well the subalpine, and lasted from weeks to months [158].

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 [34].

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 [126]. On the east side, whitebark pine forests appear to have the shortest fire-return interval of high-elevation forests [2]. Stand-replacement fires are rare on the east side [126].

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 [100]. At the landscape level, however, fire exclusion in the upper subalpine has shifted succession away from whitebark pine to later-successional species [3]. Murray and others [164] 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 [13] 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 [13] whitebark pine Pinus albicaulis 50-300+ [2] 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 [13] 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 [13] 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 [13] *fire-return interval varies widely; trends in variation are noted in the species summary
**mean

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More info for the terms: climax, cover, stand-replacement fire, tree

Arno [14] 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 [212]. After whitebark pine cover is established, shade-tolerant species often establish in the shelter of established whitebark pines [43,126,183,229]. Callaway [43] 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 [108]. On landscapes across the West, whitebark pine is increasingly becoming displaced by later-successional species. Murray and others [165] 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 [126]. 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 [4]. On Mount Rainier, whitebark pine and subalpine fir are invading subalpine meadows simultaneously [68].

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 [93].

More info for the terms: competition, cover, density, fire exclusion, fresh, indehiscent, layering, litter, mutualism, natural, shrub, tree, wildfire

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 [207]. Cone production is characterized by frequent years of small cone crops and less frequent years of moderate to heavy crops [104]. In the Greater Yellowstone area, moderate or large whitebark pine conecrop years occurred 2 or 3 times a decade (1980-1990) [159]. Best reproduction occurs when day/night July temperatures are above 68/39 degrees Fahrenheit (20o/4o C), and there is no summer water stress [226].

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 [28]. 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 [17]. 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 [18] 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 [23]. 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 [210].

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 [204], may be detrimental on some sites. Although individual Clark's nutcrackers only remove seeds that they plant themselves [147], 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 [215]. 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%) [89]. 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 [134]. 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 [147]. 

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 [8] 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 [104].

Seed dispersal: Because cones are indehiscent, seed caching by Clark's nutcrackers is the only important means of dispersal [89]. 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 [144]. In good conecrop years, the birds cache many more seeds than they recover for food [204]. Hutchins and Lanner [89] 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 [166] 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 [204].

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 [212]. Clark's nutcrackers often cache whitebark pine seeds before they are fully ripe and developed [117]. Embryonic development continues after planting and requires stratification and weathering of the seedcoat before germination occurs [124]. 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% [89]. 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 [147]. 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 [145].

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 [208]. Clark's nutcrackers have been observed caching seed as far as 13 miles (22 km) from parent trees [223]. They sometimes relocate cached seed to new sites [89], 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 [199].

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 [11]. 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 [214]. 

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 [40], 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 [147] 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 [147]; 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 [208].

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) [146]. 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 [204].

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 [146]. Tomback [204] 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 [87]. Growth on cold sites may be very slow [229], taking as long as 17 years to produce a 5-inch-long (12-cm) branch [197]. 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 [70].

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 [205]. Except in the upper subalpine, layering is not an important method of whitebark pine regeneration [17].

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RAUNKIAER [176] LIFE FORM:
Phanerophyte

More info for the term: tree

Tree

Although whitebark pine has been  tentatively rated very intolerant of competition or shade (12), recent  observers (8,25,60,66,71) believe that it is intermediate or intolerant,  about equivalent to western white pine or interior Douglas-fir. Whitebark  pine is less tolerant than subalpine fir, spruce, and mountain hemlock;  however, it is more tolerant than lodgepole pine and alpine larch. In  moist, wind-sheltered sites where spruce, fir, or hemlock are capable of  forming a closed stand, whitebark pine can become a long-lived seral  dominant in the aftermath of fires, snow avalanches, or blowdowns.

    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).

On most sites, whitebark pine develops a deep and  spreading root system. It is well anchored into the rocky substrate and is  seldom uprooted despite its large, exposed crown and the violent winds to  which it is subjected. Lanner (50), however, observed shallow rooting that  allowed windthrow in whitebark pines growing on moraines in Wyoming. These  trees had pancake like root systems only 40 cm (16 in) deep. Shallow  rooting probably occurs also where the species inhabits high-elevation  bogs.

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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 [146]. Seeds hand-planted on the Gallatin National Forest in fall began emerging in late June and stopped emerging by late July [147]. 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 [134].

Event Date bud break late May -mid-June branch, needle, & cone elongation July pollination 8-11 Aug. 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 [89]:

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%

Unlike associated subalpine fir,  Engelmann spruce, and mountain hemlock, whitebark pine spreads only to a  minor extent through layering-rooting of lower branches that are pressed  against moist ground. At the upper elevational limit of tree growth,  whitebark pine forms islands of shrub-like growth (flagged krummholz and  cushion krummholz, similar in general appearance to the layered krummholz  of fir and spruce described by Marr (55). A recent inspection of whitebark  pine krummholz in the Montana Bitterroot Range confirmed that layering  occurs (5). Investigation revealed that much of the spread of an  individual krummholz plant results from branches extending horizontally  from a central point, but also that in some plants these long branches  become pressed into the surface soil and have developed large roots, which  clearly constitutes layering.

    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).

Germination is epigeal (81). The newly  germinated seedlings of whitebark pine are large compared with other  mountain conifers. Cotyledons number 7 to 9 (36), and while still in the  cotyledon stage, the seedlings are 8 to 10 cm (3 to 4 in) tall, with a 13  to 18 cm (5 to 7 in) taproot (25).

Large seed crops are produced  at irregular intervals, with smaller crops and crop failures in between.  Cone crops may be produced more frequently in the southern parts of  whitebark pine's distribution (10). In a Sierra Nevada study area,  whitebark pine cone crops were moderate to heavy in each of four years,  1973 to 1976 (74). A study of 29 whitebark pine stands in the northern  Rockies found that cone production averaged about 14,000 per hectare  (6,000 per acre) over an 8-year period (84). Seeds number from 4,850 to  9,900/kg (2,200 to 4,500/lb) (60,81).

    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).

Whitebark pine is monoecious. The female  strobili and cones develop near the tip of upper crown branches while the  male or pollen strobili develop throughout the crown on the current year's  growth (10,60). Whitebark pine flowers are receptive and pollen is shed  during the first half of July, but at some mid-elevation sites the species  probably flowers in June. The ripe pollen strobili are a distinct carmine,  which distinguishes them from the yellow pollen strobili of limber pine.  The importance of various factors limiting pollination and fertilization  is unknown. The isolation of some individual trees and small populations  planted by birds, such as Clark's nutcracker, may prevent pollination.  Also, animal planting of genetically similar seeds in a given area might  increase the level of inbreeding, which might reduce regeneration success.

    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.

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 a slow-growing, long-lived  tree. It can attain small to moderately large size after 250 or more years  depending on site conditions. Growth and yield information on this species  is scarce because it is of little interest for commercial timber  production. Occasionally, old growth whitebark pine makes up a modest  proportion of the timber harvested on moist, high-elevation sites.

    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.

Most of the wide phenotypic growth form variation in whitebark pine is  apparently the result of differences in site and climate. Krummholz  whitebark pines have apparently arisen from nutcracker caches of seeds  from erect trees (77), implying that the prostrate form is environmentally  induced. Conversely, Clausen (20) hypothesized that the alpine (krummholz)  and subalpine (tree) forms have a genetic basis. Determination of this  will have to await genetic tests. Enzyme studies suggest that  high-elevation forms of Engelmann spruce and subalpine fir do have a  genetic basis (32), but another study showed that a prostrate form of the  European stone pine (Pinus cembra), closely related to whitebark,  can spontaneously produce an erect tree stem (40).

    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.

The following is a representative barcode sequence, the centroid of all available sequences for this species.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 7
Specimens with Barcodes: 7
Species With Barcodes: 1

The World Conservation Union's Species Survival Commission (IUCB-SSC) lists whitebark pine as vulnerable (populations decreasing) [91].

Candidate [219]

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 1998
  Vulnerable
  (Oldfield et al. 1998)

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).

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N3 - Vulnerable

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

Population

Population Trend

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).

There's trouble ahead for the whitebark pine, a mountain tree that's integral to wildlife and water resources in the western United States and Canada...

Major Threats

Conservation Actions

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).

Whitebark pine's greatest values are for wildlife habitat, watershed  protection, and esthetics. Seeds are an important, highly nutritious food  source for many seed eating birds and small mammals, as well as for black  bears and grizzly bears (47,57,61).

    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).