Limber pine (Pinus flexilis), also known as white pine or Rocky Mountain white pine, is a long-lived, slow-growing tree of small to medium size. Its wood, light in weight, close-grained, and pale yellow, is used for rough construction, mine timbers, railroad ties, and poles. Its harvest is incidental to that of other, more desirable species.
Regularity: Regularly occurring
Regularity: Regularly occurring
Global Range: Limber pine is a species whose distribution has changed from continuous to patchy since the last glacial period. Approximately 14,000 years ago, limber pine was widespread along the eastern slope of the Colorado Front Range in the central Rocky Mountains (Schoettle 2004). Now it has a widespread but patchy distribution spanning a broad latitudinal and elevational range (1500-3600m). It occurs in the northern and central Rocky Mountains, and the Great Basin regions from British Columbia and Alberta in Canada, south through Oregon, Idaho, Montana, Wyoming, Nevada, Utah, Colorado to New Mexico. Isolated populations occur in the Dakotas, Nebraska, Arizona and California (Johnson, 2001).
Nevada, and into Colorado, Wyoming, and Montana. Isolated populations occur in
the Dakotas [65,69,86,104,106] and Nebraska [30,109].
The U.S. Geological Survey provides a distributional map of limber pine. The Whitebark and Limber Pine Information System
provides distributional information at the stand level.
Regional Distribution in the Western United States
This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):
BLM PHYSIOGRAPHIC REGIONS :
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands
Occurrence in North America
In the northern half of its distribution, limber pine is generally found near lower tree line and on dry sites in the montane forests. Between the 45th and 40th parallels, it grows in both lower and upper elevation forests and anywhere in between on dry, windswept sites. Its position gradually shifts upward in more southerly latitudes, so that in southern portions of its distribution, limber pine is more common from upper montane to alpine tree line, with only minor occurrences in the lower forested zones. Because of this adaptability, limber pine ranges in elevation from about 870 m (2,850 ft) in North Dakota (29) to about 3810 m (12,500 ft) in Colorado (7).
- The native range of limber pine.
exceed 1000 years of age [53,96,127]. Limber pine stands are broadly even-aged , though populations also occur in uneven-aged stands
and on very harsh sites as widely spaced, isolated individuals [96,102,112]. Trees often have an irregular or
multi-stem growth form, and rarely reach over 50 feet (15 m) [11,120,127]. At high elevations they sometimes form krummholz [11,127]. Trunks may reach 6.5 feet (2 m) in diameter . The species is cold and drought tolerant. Trees are ectomycorrhizal, have deep taproots,
and are very windfirm [33,120].
Cones of limber pine are cylindrical, 3 to 6 inches (8-15 cm) long. They release
their seeds if not preyed upon (see Regeneration Processes). The seeds are large
(7-12 mm long) and sometimes have a vestigial wing [21,63,74].
Sierra Nevada Forests
The Limestone salamander is a highly localized endemic of the Sierra Nevada forests foothills conifned to a limited reach of the Merced River. The Sierra Nevada forests are the forested areas of the Sierra Nevada Mountains, which run northwest to southwest and are approximately 650 kilometers long and 80 km wide. The range achieves its greatest height towards the south, with a number of peaks reaching heights of over 4000 meters. Several large river valleys dissect the western slope with dramatic canyons. The eastern escarpment is much steeper than the western slope, in general.
The Sierra Nevada forests ecoregion harbors one of the most diverse temperate conifer forests on Earth displaying an extraordinary range of habitat types and supporting many unusual species. Fifty percent of California's estimated 7000 species of vascular plants occur in the Sierra Nevada, with 400 Sierra endemics and 200 rare species. The southern section has the highest concentration of species and rare and endemic species, but pockets of rare plants occur throughout the range.
Sierra Nevada amphibian endemics are the Yosemite toad, Mount Lyell salamander (Hydromantes platycephalus), the Vulnerable Limestone salamander (Hydromantes brunus), Kern salamander and the Endangered Inyo Mountains salamander (Batrachoseps campi). The non endemic amphibians are: the Endangered Southern mountain yellow-legged frog (Rana muscosa); the Near Threatened Cascades frog (Rana cascadae); Northern red-legged frog (Rana aurora); Pacific chorus frog (Pseudacris regilia); Foothill Yellow-legged frog (Rana boylii); Long-toed salamander (Ambystoma macrodactylum); and the Monterey ensatina (Ensatina eschscholtzii).
A considerable number of mammalian taxa are found in the ecoregion, including the Long-eared chipmunk, Alpine chipmunk, Western heather vole, Walker Pass pocket mouse, and the Yellow-eared pocket-mouse. A diverse vertebrate predator assemblage once occurred in the ecoregion including Grizzly bear (Ursus arctos), Black bear (Ursus americanus), Coyote (Canis latrans), Mountain lion (Puma concolor), Ringtail (Bassariscus astutus), Fisher (Martes pennanti), Pine marten (Martes americana) and Wolverine (Gulo gulo).
There are a small number of reptilian taxa present in the Sierra Nevada forests: sagebrush lizard (Sceloporus graciosus); Northern alligator lizard (Elgaria coerulea); Southern alligator lizard (Elgaria multicarinata); Sharp-tailed snake (Contia tenuis); California mountain kingsnake (Molothrus ater); Common garter snake (Thamnophis sirtalis); Couch's garter snake (Thamnophis couchii); Western gopher snake (Pituophis catenifer); Longnose snake (Rhinocheilus lecontei); and the Common kingsnake (Lampropeltis getula).
A number of bird species are found in the ecoreion including high level predators that include several large owls, hawks and eagles. Other representative avifauna species present are the Blue-headed vireo (Vireo solitarius); Brown-headed cowbird (Molothrus ater); and the Near Threatened Cassin's finch (Carpodacus cassinii).
California Montane Chaparral and Woodlands Habitat
This taxon can be found in the California montane chaparral and woodlands, a near coastal ecoregion in Central and Southern California, USA. This ecoregion is disjunctive, with a major element in Southern California and another along the Monterey County coast. The ecoregion encompasses most of the Transverse Range that includes the San Bernardino Mountains; San Gabriel Mountains; portions of the Santa Ynez and San Rafael Mountains; Topatopa Mountains; San Jacinto Mountains; the Tehachapi, Greenhorn, Piute, and Kiavah Mountains that extend roughly northeast-southwest from the southern Sierra Nevada; and the Santa Lucia Range that parallels the coast southward from Monterey Bay to Morro Bay.
The California montane chaparral and woodland ecoregion consists of a complex mosaic of coastal sage scrub, lower chaparral dominated by chamise, upper chaparral dominated by manzanita, desert chaparral, Piñon-juniper woodland, oak woodlands, closed-cone pine forests, yellow pine forests, sugar pine-white fir forests, lodgepole pine forests, and alpine habitats. The prevalence of drought-adapted scrub species in the flora of this ecoregion helps distinguish it from similar communities in the Sierras and other portions of northern California. Many of the shared Sierra Nevadan species typically are adapted to drier habitats in that ecoregion, Jeffrey Pine (Pinus jeffreyi) being a good example.
Oak species are an important component of many chaparral and forest communities throughout the ecoregion. Canyon Live Oak, Interior Live Oak, Tanbark Oak (not a true Quercus species), Engelmann Oak, Golden-cup Oak, and Scrub Oak are some examples. Mixed-conifer forests are found between 1371 to 2896 meters elevation with various combinations and dominance of incense cedar, sugar pine, and white fir, Jeffrey Pine, Ponderosa Pine, and mountain juniper. Subalpine forests consist of groves of Limber Pine (Pinus flexilis), Lodgepole Pine, and Jeffrey Pine. Very old individual trees are commonly observed in these relict subalpine forests. Within this zone are subalpine wet meadows, talus slope herbaceous communities, krumholz woodlands, and a few small aspen groves.
In addition to these general vegetation patterns, this ecoregion is noted for a variety of ecologic islands, communities with specialized conditions that are widely scattered and isolated and typically harbor endemic and relict species. Examples include two localities of Knobcone Pine (Pinus attenuata) on serpentine soils, scattered vernal pools with a number of endemic and relict species, and isolated populations of one of North America’s most diverse cypress floras, including the rare Gowen Cypress (Cupressus goveniana goveniana) restricted to two sites on acidic soils in the northern Santa Lucia Range, Monterey Cypress (Cupressus macrocarpa) found only at two coastal localities near Monterey Bay, and Sargent Cypress (Callitropsis sargentii LR/LC) restricted to serpentine outcrops. Monterey Pine (Pinus radiata) is also restricted to three coastal sites near Monterey Bay.
The ecoregion is also home to a few endemic or near-endemic mammalian vertebrates, such as the White-eared Pocket Mouse (Perognathus alticolus EN), a mammal known only to two disjunct mountain ranges in southern California: San Bernardino Mountains in San Bernardino County (ssp. alticolus), and the Tehachapi Mountains, in Kern, Ventura, and Los Angeles counties. The near-endemic fossorial Agile Kangaroo Rat (Dipodomys agilis) is found in the southern disjunctive unit of the ecoregion, and is known only to the Los Angeles Basin and foothills of San Gabriel and San Bernardino mountains in Ventura, Los Angeles, and Riverside counties north to Santa Barbara County and through the southern Sierra Nevada, including Mount Pinos, Tehachapi and San Gabriel mountains, and northern San Fernando Valley. Non-endemic mammals found in the ecoregion include Botta's Pocket Gopher (Thomomys bottae) and Trowbridge's Shrew (Sorex trowbridgii). Some larger vertebrate predators can be found in the ecoregion, including Puma (Puma concolor), Bobcat (Lynx rufus), Coyote (Canis latrans), and Ringtails (Bassariscus astutus).
The ecoregion boasts five endemic and near-endemic amphibians, largely Plethodontid salamanders. Some specific salamander taxa found here are the endemic Tehachapi Slender Salamander (Batrachoseps stebbinsi VU), known from isolated sites in the Caliente Creek drainage, Piute Mountains, and Kern County, California along with scattered populations in the Tehachapi Mountains to Fort Tejon, Kern County; the near-endemic Blackbelly Slender Salamander (Batrachoseps nigriventris); the Monterey Ensatina (Ensatina eschscholtzii); the Channel Islands Slender Salamander (Batrachoseps pacificus), endemic to a narrow range restricted solely on Anacapa, Santa Cruz, Santa Rosa, and San Miguel islands; and the Arboreal Salamander (Aneides lugubris), found only in California and Baja California. A newt found here is the Coast Range Newt (Taricha torosa). Anuran taxa in the ecoregion include the Foothill Yellow-legged Frog (Rana boylii NT); the Southern Mountain Yellow-legged Frog (Rana muscosa EN), a California endemic occurring in several disjunctive populations; and the Northern Red-legged Frog (Rana aurora).
The California montane chaparral and woodlands ecoregions contains a number of reptiles such as the Coast Horned Lizard (Phrynosoma coronatum), who ranges from Northern California to Baja California. Also found here is the Sagebrush Lizard (Sceloporus graciosus); the Western Fence Lizard (Sceloporus occidentalis); the Southern Alligator Lizard (Elgaria multicarinata); and the Side-blotched Lizard (Uta stansburiana). The Two-striped Garter Snake (Thamnophis hammondii) is a restricted range reptile found near-coastally from Monterey County, California southward to Baja California.
The California Condor once inhabited much of the ecoregion, with the western Transverse Range acting today as a refuge for some of the last wild populations, after considerable conservation efforts, especially in the Los Padres National Forest. The Heermann's Gull (Larus heermanni NT) is found in coastal areas of the ecoregion.
Comments: Limber pine dominates on dry rocky sites at many elevations (1500-3600m) within its range. It can occur scattered throughout forested regions on more mesic sites, especially in low density, open areas. At higher elevations, Pinus flexilis can define the boundary of the treeline; occurring in high montane forests, often at the timberline (Schoettle 2004, Flora of North America 1993). In these areas (i.e., Utah and the West) it is often very long-lived and slow growing, occurring on dry, harsh sites. In the northern half of its distribution, limber pine is generally found near lower tree line and on dry sites in the montane forests, but between the 45th and 40th parallels, it grows in both lower and upper elevation forests and anywhere in between on dry, windswept sites. Its position gradually shifts upward in more southerly latitudes, so that in southern portions of its distribution, limber pine is more common from upper montane to alpine tree line, with only minor occurrences in the lower forested zones (Burns and Honkala, 1990). In some areas, limber pine grows in greater numbers on certain soils, but the relationships vary geographically; but in general, the substrates are Entisols (Burns and Honkala, 1990). It grows on a variety of topographies, from gently rolling terrain to cliffs and is most often found on rocky ridges and steep rocky slopes and can survive in extremely windswept areas at both the lower and upper tree line (Burns and Honkala, 1990).
Climatic data for actual limber pine habitat are quite scarce, but the general distribution of limber pine in Alberta, Montana, central Idaho, and east of the Continental Divide in Wyoming and Colorado, is in forested areas having a continental climate (Baker, 1944). This climate is typified by a relatively small amount of precipitation, with the wettest months during the growing season, very low humidity, and wide annual and diurnal temperature ranges. Winter conditions may be very cold, but relatively dry, and often include rapid fluctuations in temperature associated with chinook winds. Notable exceptions to this distribution are the small populations in eastern Oregon and adjacent Idaho, which lie within the Pacific maritime influence (Baker, 1944). In the remainder of its distribution, it grows in climates that tend to have either more evenly distributed yearly precipitation or a winter peak in precipitation along with summer convectional storms (strongly influenced by Pacific maritime weather patterns). Only at its southern limits in the mountains of eastern and southern California does the pine encounter a strong pattern of proportionately high winter precipitation (Baker, 1944). The amount of precipitation, however, is relatively smaller than that of the Pacific Northwest.
Limber pine grows across a wider range of elevations that any other tree species in the central Rocky Mountains , inhabiting some of the driest sites capable of supporting trees [11,85,102,111]. In many high-elevation sites it occupies or forms the upper treeline [30,69,83,94,122], but in
northern parts of its range it is found at low elevations along plains grassland
edges [22,94,96]. It typically occurs on steep, rocky, well-drained, windswept, and nutrient-poor sites on exposed ridges and summits [1,10,11,32,42]. Limber pine is often reported growing on calcareous soil [11,19,85]. It is also reported on soils derived from many other types of parent material [12,17,23,42,68,101].
Ground cover and litter accumulation in limber pine stands are often sparse, accumulating only under individual trees [11,127]. Severe sheet erosion of fine particles often occurs from summer convection storms over sparsely vegetated sites. Snowpack accumulations on limber pine sites may be light as a result of high insolation and winter winds .
Site preference often separates limber pine and whitebark pine, which is ecologically similar in many respects . Limber pine has a wider geographical distribution and altitudinal range than whitebark pine. Relative to whitebark pine, limber pine occurs on warm, dry sites at
low and middle elevations. Where their ranges overlap, the 2 species sometimes grow
together on droughty soils. Occasionally, limber pine grows at higher elevations than whitebark pine. South of the range of whitebark pine in California, Colorado, Nevada, and southern Wyoming, the more drought-resistant limber pine replaces whitebark pine and may form the alpine treeline [74,112,121].
Elevations reported in the literature for limber pine are as follows:
7,500 to 11,000 feet (2,290-3,350 m) in California 
5,000 to 12,500 feet (1,500-3,800 m) in Colorado [27,42,49]
4,000 to 6,000 feet (1,200-1,800 m) in Montana [85,91]
6,500 to 11,500 feet (2,000-3,500 m) in Nevada 
5,000 to 7,000 feet (1,500-2,100 m) in Oregon 
6,000 to 11,600 feet (1,830-3,540 m) in Utah 
Key Plant Community Associations
Plant community associates of limber pine are described below by state.
California: In the Sierran subalpine, limber pine grows in association with Sierra lodgepole pine (Pinus contorta var. murrayana), bush chinquapin (Chrysolepis sempervirens), greenleaf manzanita (Arctostaphylos patula), curlleaf mountain-mahogany (Cercocarpus ledifolius), and whitethorn ceanothus (Ceanothus cordulatus) . In montane areas of southern California, limber pine is reported with white fir (Abies concolor), Jeffrey pine (P. jeffreyi), singleleaf pinyon (P. monophylla), Sierra lodgepole pine, whitebark pine (P. albicaulis), foxtail pine (P. balfouriana), Great Basin bristlecone pine (P. longaeva), western juniper (Juniperus occidentalis),
curlleaf mountain-mahogany, and big sagebrush (Artemisia tridentata) [68,108].
Colorado: Tree associates include interior ponderosa pine (P. ponderosa var. scopulorum), Rocky Mountain lodgepole pine (P. c. var. latifolia), subalpine fir (A. lasiocarpa), Engelmann spruce (Picea engelmannii), Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca), white fir, whitebark pine, Rocky Mountain bristlecone pine (P. aristata), and quaking aspen (Populus tremuloides). Associated understory species include bearberry (Arctostaphylos uva-ursi), common juniper (J. communis), big sagebrush, purple pinegrass (Calamagrostis purpurascens), spike fescue (Leucopoa kingii), and Thurber fescue (Festuca thurberi) [27,38,42,49,87,100].
Idaho: In Craters of the Moon National Monument, limber pine is commonly associated with antelope bitterbrush (Purshia tridentata), rubber rabbitbrush (Chrysothamnus nauseosus), and mountain big sagebrush (A. t. var. vaseyana). Associated grasses include Sandberg bluegrass (Poa secunda), bottlebrush squirreltail (Elymus elymoides), and Indian ricegrass (Achnatherum hymenoides) [12,23]. In the mountains of east-central Idaho, limber pine grows in association with Douglas-fir, subalpine fir, and whitebark pine .
Montana: Associated tree and shrub species include Rocky Mountain Douglas-fir,
Rocky Mountain lodgepole pine, Engelmann spruce, whitebark pine, subalpine fir, quaking aspen, common juniper, creeping juniper (J. horizontalis), and Rocky Mountain juniper (J. scopulorum). Associated shrubs include snowberry (Symphoricarpos spp.), Wood's rose (Rosa woodsii), and russet buffaloberry (Shepherdia canadensis). Associated grasses include Idaho fescue (Festuca idahoensis), rough rescue (F. altaica), and bluebunch wheatgrass (Pseudoroegneria spicata) [5,55,83,85,91,107].
New Mexico: In the Sandia Mountains limber pine occurs with Rocky Mountain Douglas-fir, white fir,
quaking aspen, Engelmann spruce, and corkbark fir (A. l. var. arizonica) . It co-occurs with southwestern white pine (P. strobiformis) in the Sangre de Cristo Mountains .
Nevada and Utah: Limber pine commonly occurs in association with Rocky Mountain bristlecone, interior
ponderosa (P. ponderosa var. scopulorum), Rocky Mountain lodgepole, whitebark, Jeffrey, and singleleaf pinyon pines. It also occurs with Engelmann spruce, white fir, subalpine fir, quaking aspen, common juniper, and Utah juniper (J. osteosperma). Associated shrubs include Rocky mountain maple (Acer glabrum), Gambel oak (Quercus gambelii), and multiple species of sagebrush, mountain-mahogany, ceanothus, currant (Ribes spp.), manzanita (Arctostaphylos spp.), and snowberry [9,37,82,114].
Oregon: In the Wallowa Mountains of eastern Oregon limber pine commonly occurs with Douglas-fir and Rocky Mountain juniper. Herbaceous associates include western yarrow (Achillea millefolium), sagebrush fleabane (Erigeron austiniae), and silverleaf phacelia (Phacelia hastata) .
South Dakota: A population of limber pine in the Black Hills is associated with
interior ponderosa pine and white spruce (Picea glauca). Understory species include bearberry and common juniper .
Wyoming: Associated species reported for northwestern Wyoming include Rocky
Mountain lodgepole pine, Engelmann spruce, whitebark pine, Rocky Mountain Douglas-fir, subalpine fir, Rocky Mountain juniper, and common juniper [13,24,70].
Published classifications that include limber pine as an indicator or
dominant species are presented below:
North Dakota 
New Mexico [20,25,67,79]
Habitat: Rangeland Cover Types
This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):
More info for the term: cover
SRM (RANGELAND) COVER TYPES :
109 Ponderosa pine shrubland
209 Montane shrubland
402 Mountain big sagebrush
412 Juniper-pinyon woodland
413 Gambel oak
415 Curlleaf mountain-mahogany
504 Juniper-pinyon pine woodland
Habitat: Cover Types
This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):
More info for the term: cover
SAF COVER TYPES :
206 Engelmann spruce-subalpine fir
208 Whitebark pine
209 Bristlecone pine
210 Interior Douglas-fir
218 Lodgepole pine
219 Limber pine
220 Rocky Mountain juniper
237 Interior ponderosa pine
256 California mixed subalpine
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
KUCHLER  PLANT ASSOCIATIONS:
K008 Lodgepole pine-subalpine forest
K011 Western ponderosa forest
K012 Douglas-fir forest
K015 Western spruce-fir forest
K017 Black Hills pine forest
K018 Pine-Douglas-fir forest
K019 Arizona pine forest
K020 Spruce-fir-Douglas-fir forest
K021 Southwestern spruce-fir forest
K022 Great Basin pine forest
K023 Juniper-pinyon woodland
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K046 Desert: vegetation largely lacking
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):
FRES21 Ponderosa pine
FRES26 Lodgepole pine
FRES34 Chaparral-mountain shrub
Soils and Topography
Limber pine grows on a variety of topographies, from gently rolling terrain to cliffs. It is most often found on rocky ridges and steep rocky slopes and can survive in extremely windswept areas at both lower and upper tree line.
In the remainder of its distribution, limber pine grows in climates that tend to have either more evenly distributed yearly precipitation or a winter peak in precipitation along with summer convectional storms. Throughout its broad range, limber pine is mostly absent in areas strongly influenced by Pacific maritime weather patterns. Only at its southern limits in the mountains of eastern and southern California (10) does the pine encounter a strong pattern of proportionately high winter precipitation (3). The amount of precipitation, however, is relatively smaller than that of the Pacific Northwest.
Habitat & Distribution
erumpent aecium of Cronartium ribicola parasitises stem of Pinus flexilis
Remarks: season: 3-6
Other: major host/prey
Associated Forest Cover
In Canada, Montana, and central Idaho, limber pine forms pure stands at lower tree line or mixes with Douglas-fir (Pseudotsuga menziesii), and to a lesser extent, ponderosa pine (Pinus ponderosa) and Rocky Mountain juniper (Juniperus scopulorum). It also appears as a minor component in stands of lodgepole pine (Pinus contorta), Engelmann spruce (Picea engelmannii), and occasionally subalpine fir (Abies lasiocarpa). On some sites in Idaho and Montana, it is associated with whitebark pine (Pinus albicaulis). In Canada, it is sometimes found with white spruce (Picea glauca).
Southward into Wyoming, southern Idaho, and northern portions of Colorado, Utah, and Nevada, limber pine may dominate windswept slopes and ridges at upper or lower tree line or appear in stands of white fir (Abies concolor), lodgepole pine, and Douglas-fir. In this region, limber pine appears most often with Engelmann spruce, subalpine fir, and quaking aspen (Populus tremuloides), least often with ponderosa pine. In Wyoming, limber pine occasionally coexists with whitebark pine, particularly in the Wind River Range. The two species also coexist on a few sites in northeastern Nevada (5,25), but usually where their ranges overlap they occupy different soils.
Farther south in the remainder of its range, limber pine forms open stands near upper tree line, both separately and with Great Basin bristlecone pine (Pinus longaeva) (44) but less often with Rocky Mountain bristlecone pine (Pinus aristata) (6,18). It is also associated with whitebark pine on the east side of the Sierra Nevada (4). Occasionally, it mixes as a minor seral species with subalpine fir and white fir (23). Where limber pine would normally mix as a seral species with other conifers, as it does farther north, the closely related southwestern white pine (Pinus strobiformis) appears in these situations, but this species does not extend onto the dry windy sites where limber pine is climax (23).
Diseases and Parasites
Limber pine is susceptible to several major diseases. Spongy root and butt rot (Armillaria mellea) and the red-brown butt rot (Phaeolus schweinitzii) attack limber pine over much of its range. The crumbly brown cubical rot (Fomitopsis pinicola) and red ring rot (Phellinus pini) commonly cause heart rot in mature and damaged trees (15,27). Limber pine is susceptible to white pine blister rust (Cronartium ribicola) and can suffer considerable mortality when susceptible species of the rust's alternate host (Ribes) are nearby. The limber pine dwarf mistletoe (Arceuthobium cyanocarpum) is a common parasite of this tree. Occasionally, lodgepole pine dwarf mistletoe (A. americanum) attacks limber pine, and the Douglas-fir dwarf mistletoe (A. douglasii) and southwestern dwarf mistletoe (A. vaginatum subsp. cryptopodium) occur as rare parasites (12). Several foliage diseases also attack this tree, the most damaging being brown-felt snow mold (Neopeckia coulteri) (15).
Broad-scale Impacts of Plant Response to Fire
In 1976 spring prescribed burning was conducted in open-canopy limber pine stands in the Little Belt Mountains of central Montana at about 5,500 feet (1,675 m) . Further general site descriptions appear in Keown 1982 . Air temperatures ranged from 55 to 65 degrees Fahrenheit (13-18
oC). Relative humidity was 20% to 40%, and winds were calm to 25
miles per hour (40 km/h). Fuel moisture was 7%. The management objective was to improve understory browse and forage.
Limber pine mortality at postfire year 1 was 20% in grassy stands and as high as 80% in shrubby
The Research Project Summary Response of vegetation to prescribed burning in a Jeffrey pine-California
black oak woodland and a deergrass meadow at Cuyamaca State Park, California, provides information on prescribed
fire and postfire responses of many plant community species including limber pine.
Plant Response to Fire
Regeneration of limber pine end Engelmann spruce was assessed in a high-altitude area disturbed by fire in 1905. The south-facing sites were on Niwot Ridge in Colorado's Roosevelt National Forest. The uppermost elevation of the burn reached slightly below the tree limit at about 11,000 feet (3,355 m). Although limber pine regeneration at the uppermost elevation is less than at lower elevations, limber pine colonization at all elevations began shortly after the fire. The author found no evidence that
treeline changed following the fire . Postfire regeneration of limber pine
is a consequence of seed dispersal and caching by Clark's nutcrackers [53,66].
Immediate Effect of Fire
The thin bark of young limber pine trees does not protect them from even
low-severity fires. Because the bark at the base of older trees is often 2 inches (5 cm) thick, these trees can withstand stem scorch from low-severity
fires. Terminal buds are somewhat protected from the heat associated
with crown scorch by the tight clusters of needles around them [1,29,53,85,127].
Wildfires are less frequent in limber pine communities than in other conifer habitats because of limited productivity and fuel accumulation associated with poor soil development, short growing seasons, and late snowmelt [29,53,78,85,96,117,127].
Keeley and Zedler  categorized 38 pines within a series of 5 fire predictability regimes. They include limber pine among those pines growing in areas with very low site (and therefore fuel) productivity and unpredictable fire return intervals of up to 1000 years. Where enough biomass accumulates to carry fires, limber pine may be cached by Clark's nutcrackers and establish in burned sites previously dominated by other conifers [53,66].
Where limber pine grows in association with other trees, the FIRE REGIMES of those species are relevant. FIRE REGIMES for some associated communities or ecosystems are listed here:
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|sagebrush steppe||Artemisia tridentata/Pseudoroegneria spicata||20-70 |
|mountain big sagebrush||Artemisia tridentata var. vaseyana||20-60 [5,16]|
|Wyoming big sagebrush||Artemisia tridentata var. wyomingensis||10-70 (40**) [119,126]|
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1000 [6,95]|
|mountain-mahogany-Gambel oak scrub||Cercocarpus ledifolius-Quercus gambelii|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||Juniperus scopulorum|
|Engelmann spruce-subalpine fir||Picea engelmannii-Abies lasiocarpa||35 to > 200|
|whitebark pine*||Pinus albicaulis||50-200 |
|Rocky Mountain lodgepole pine*||Pinus contorta var. latifolia||25-300+ [3,90]|
|Sierra lodgepole pine*||Pinus contorta var. murrayana||35-200|
|Jeffrey pine||Pinus jeffreyi||5-30|
|Rocky Mountain ponderosa pine*||Pinus ponderosa var. scopulorum||2-10|
|Arizona pine||Pinus ponderosa var. arizonica||2-10 |
|quaking aspen (west of the Great Plains)||Populus tremuloides||7-120 [15,34,77]|
|mountain grasslands||Pseudoroegneria spicata||3-40 (10)** |
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100|
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||15]|
*fire-return interval varies widely; trends in variation are noted in the species summary
More info for the terms: climax, succession, xeric
According to Tomback and Linhart  limber pine (and whitebark pine) "are pioneering species that are either seral or topoedaphic climax species under different environmental conditions. In fact, seed dispersal by Clark's nutcrackers to outlying sites, treeline, and other harsh environments essentially increases the ecological niche breadth (in the Hutchinsonian sense) of these species. Clark's nutcrackers can maintain climax communities, colonize previously unforested sites, or initiate succession."
The later stages of succession in xeric subalpine forests vary due to differences in sites and seed availability. In the Colorado subalpine, Rebertus and others  studied conifer population age structure and succession on 3 burns greater than 100 years old. The sequence of conifer colonization appeared to be consistent: 1st limber pine, then Engelmann spruce, and later subalpine fir, with a delay between the 1st limber pine and
later subalpine fir of as long as 140 years. The authors suggested that the early advantage of limber pine was due to avian seed dispersal and exceptional drought tolerance in seedlings. Spatial analysis
suggested that limber pine facilitated the establishment of the other 2 species by providing shade or wind protection. On the xeric to slightly xeric sites, limber pine formed broadly even-aged, non-regenerating populations that were gradually replaced by the spruce and fir. On the most extreme sites, limber pine formed all-aged, self-maintaining populations with no evidence of replacement by the other species. The authors note that in lower elevation stands along the Front Range, limber pine is successional to Douglas-fir. In the even lower Pawnee National Grasslands of Colorado, limber pine forms all-aged, self-replacing populations. "Hence, many successional pathways could be operating at different sites or stages in stand development."
Limber pine reproduces entirely from seed; it does not layer lower branches in the soil [22,122].
Seeds are not effectively dispersed by wind. Small mammals and birds, especially Clark's nutcrackers and pinyon jays, disperse limber pine seeds
[63,64,66,110,125]. The minimum seed-bearing age of limber pine ranges from 20 to 40 years.
There are 2 to 4 years between large seed crops [58,59,101]. Seeds from krummholz trees have
low germination potential .
Clark's nutcrackers have co-adapted an important mutualism with limber pine
and are the primary harvester and disperser of its seeds. Limber pine regeneration
on burns is largely from germinants of Clark's nutcrackers seed caches [63,64,66,110,125].
The birds begin harvesting seeds in late August, while the cones are still green and slightly closed. They remove the cones by pecking them loose,
fly them to perches, and peck between the scales to remove the seeds. As cones begin to open on the trees in September, Clark's nutcrackers remove exposed seeds.
An individual bird can store as many as 125 seeds in its sublingual pouch, then
flies to a cache area and deposits numerous caches from its pouchful of seeds. In a burned-over area in northern Utah,
Clark's nutcrackers cached an estimated 12,140 seeds per acre (30,000/ha) in 1 year [62,101,112].
Mating system: Limber pine seed dispersal by corvids leads to a genetic population structure different from that of wind-dispersed conifers with respect to patterns of gene flow and genetic relationships among neighboring trees. The seed caching
by birds influences the distribution, population age structure, and spacing of limber pine. Clusters of seedlings germinating from a single cache may generate
multi-stemmed growth forms that contain 2 or more distinct genotypes. A consequence of this growth form is
a tendency toward clumped stand structure. Because seeds within an individual
cache were often collected from a single parent tree, trees within clumps may be
more closely related compared to trees from neighboring clumps [64,110,113],
although multi-stemmed growth is most often a result of apical meristem damage
that results in several leaders on an individual tree . Tomback and Linhart
 found that on 361 limber pine sites in Colorado, 30% showed clumping.
Several genetic studies have shown that from 0 to 82% of individuals
within limber pine clumps are closely related [101,117,123]. On the Pawnee
National Grassland, clump members were related, on average, as nearly half-sibs.
Genetic consequences of this kinship include possible inbreeding. On the plus
side, closely related trees within clumps often form roots grafts, which may
increase survivorship and fitness of the entire clump .
Pollen phenology also influences gene flow. In Colorado, most sites that differ in elevation by more than 1,300 feet (400 m) in elevation do not have overlapping pollination periods, restricting
pollination between populations that are widely separated by elevation; however,
pollen transfer between intermediate populations and a high level of gene flow via
bird-dispersed seeds appear to maintain interpopulation gene flow .
Growth Form (according to Raunkiær Life-form classification)
Initial offsite colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)
Fire Management Considerations
maintained by periodic fires that reduce the undergrowth. Where limber
pine and Douglas-fir codominate, fire can be a thinning agent that slightly
favors limber pine over Douglas-fir in the younger age
Reaction to Competition
Life History and Behavior
More info for the term: phenology
Limber pine cones ripen from August to
September, and seeds are dispersed from September to October
[26,44,58,59]. Cones open in the fall. Observed dates for phenological events
of mature in limber pine east of the Continental Divide in Montana and Yellowstone National Park,
Wyoming, are given here :
Shoots start: April 30 to June 6
Buds burst: April 30 to June 26
Pollen starts: June 20 to July 14
Pollen ends: July 4 to July 22
Shoots end: June 22 to August 5
Winter buds formed: June 11 to August 16
Cones full size: August 15 to August 16
Cones open (seed dispersal): August 23 to August 30
Also see Regeneration Processes regarding pollen phenology.
Limber pine reproduces entirely from seed; it does not layer lower branches in the soil (Daly and Shankman, 1985; Weisberg and Baker, 1995; Tomback, 1991). Seeds are not effectively dispersed by wind as small mammals and birds, especially Clark's nutcrackers and pinyon jays, disperse limber pine seeds (Lanner, 1985; 1996; Lanner and Vander Wall, 1980; Tomback, 2001; Woodmansee, 1977). The minimum seed-bearing age of limber pine ranges from 20 to 40 years. There are 2 to 4 years between large seed crops (Krochman and Krochman, 1982; Burns and Honkala, 1990). Seeds from krummholz trees have low germination potential (Lanner and Wall, 1980). Clark's nutcrackers have evolved an important mutualism and are the primary harvester and disperser of its seeds.
Limber pine regeneration on burns is largely from germinants of Clark's nutcrackers seed caches (Lanner, 1985; 1996; Lanner and Wall, 1980; Tomback, 2001; Woodmansee, 1977). The birds begin harvesting seeds in late August, while the cones are still green and slightly closed. They remove the cones by pecking them loose, fly them to perches, and peck between the scales to remove the seeds. As cones begin to open on the trees in September, Clark's nutcrackers remove exposed seeds. An individual bird can store as many as 125 seeds in its sublingual pouch, then flies to a cache area and deposits numerous caches from its pouchful of seeds. In a burned-over area in northern Utah, Clark's nutcrackers cached an estimated 12,140 seeds per acre (30,000/ha) in 1 year (Burns and Honkala, 1990; Tomback and Linhart, 1990).
Mating system: Limber pine seed dispersal by corvids leads to a genetic population structure different from that of wind-dispersed conifers with respect to patterns of gene flow and genetic relationships among neighboring trees. The seed caching by birds influences the distribution, population age structure, and spacing of limber pine. Clusters of seedlings germinating from a single cache may generate multi-stemmed growth forms that contain 2 or more distinct genotypes. A consequence of this growth form is a tendency toward clumped stand structure. Because seeds within an individual cache were often collected from a single parent tree, trees within clumps may be more closely related compared to trees from neighboring clumps (Lanner, 1996; Tomback, 2001), although multi-stemmed growth is most often a result of apical meristem damage that results in several leaders on an individual tree (Welsh et al., 1987). Tomback and Linhart (1990) found that on 361 limber pine sites in Colorado, 30% showed clumping. Several genetic studies have shown that from 0 to 82% of individuals within limber pine clumps are closely related (Burns and Honkala, 1990; van Wagtendonk et al., 1998; Welsh et al., 1987). On the Pawnee National Grassland, clump members were related, on average, as nearly half-sibs. Genetic consequences of this kinship include possible inbreeding. On the plus side, closely related trees within clumps often form roots grafts, which may increase survivorship and fitness of the entire clump (Welsh et al., 1987).
Pollen phenology also influences gene flow. In Colorado, most sites that differ in elevation by more than 1,300 feet (400 m) in elevation do not have overlapping pollination periods, restricting pollination between populations that are widely separated by elevation; however, pollen transfer between intermediate populations and a high level of gene flow via bird-dispersed seeds appear to maintain interpopulation gene flow (Schuster et al., 1989).
Seed Production and Dissemination
The seeds are disseminated largely by rodents and birds. Of the birds, Clark's nutcracker is most important; it can transport pine seed for at least 23 km (14 mi) from seed source to communal caching areas (42). It can carry up to 125 limber pine seeds per trip in a sublingual pouch and buries in the ground one to five seeds per cache at a depth of 2 to 3 cm (0.8 to 1.2 in). Estimates indicate that Clark's nutcrackers cached in 1 year about 30,000 seeds per hectare (12,140/acre), most of which were limber pine (22). The birds' preferred cache sites were windswept ridges and southerly aspects where snow does not accumulate and the ground is exposed early in the spring. The locations of most limber pine stands probably reflect the site preferences of dispersal agents rather than those of the pine, since its only other apparent means of dissemination is gravity.
Flowering and Fruiting
Fertilization takes place in the spring or early summer, about 13 months after pollination. Cones and seeds mature rapidly following fertilization. As they mature, cones change color from green to lustrous yellow. They are light brown when mature in August and September. Seed dispersal takes place during September and October (41).
Growth and Yield
Molecular Biology and Genetics
Races Three possible races of limber pine have been suggested, distinguished by height growth of the seedlings: (1) a northern race ranging from Alberta to north central Colorado and northern Utah and including the only sample from California; (2) a southeastern race that includes populations from the Wyoming-Nebraska border, east central Colorado, and north central New Mexico; and (3) a southwestern race in southern Utah and western Colorado (Nevada populations were not sampled) (43). Further study, however, found no geographically associated patterns or trends when a much wider variety of characteristics was analyzed from the same seed sources (36).
Hybrids Although zones of intergradation between limber pine and southwestern white pine are found in north central Arizona and north central New Mexico (36), no true hybrid populations of limber pine have been recorded. Limber pine has been crossed artificially with western white pine (Pinus monticola), southwestern white pine (P. strobiformis), Mexican white pine (P. ayacahuite), Himalayan pine (P. griffithii), eastern white pine (P. strobus), and possibly whitebark pine (P. albicaulis) (35).
Barcode data: Pinus flexilis
Statistics of barcoding coverage: Pinus flexilis
Public Records: 9
Specimens with Barcodes: 11
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
Pinus flexilis var. flexilisThere is no question that Limber Pine is experiencing declines due to White Pine Blister Rust (WPBR) and Mountain Pine Beetle (MPB). In areas where WPBR and MPB are both present the decline in population numbers and population resiliency is such that population sustainability over the long-term is predicted to decrease. Work is being conducted to identify seed trees that exhibit some degree of resistance to WPBR. This work is being complicated where populations are also under attack from MPB. Research needs to be initiated into the affects of WPBR and MPB on the mutualism between corvids and Limber Pine in regard to seed dispersal. However, there have been no wide-scale extirpations of Limber Pine populations and the range of the species has not contracted since the last assessment. Therefore, Limber Pine is still evaluated to be of Least Concern. It is recommended that this variety and species be re-evaluated by the Conifer Specialist Group periodically.
Pinus flexilis var.reflexa This is a rare variety limited to five known locations and assessed as Near Threatened (almost qualifies as threatened under criterion B2ab(iii,v)).
National NatureServe Conservation Status
Rounded National Status Rank: N3 - Vulnerable
Rounded National Status Rank: N4 - Apparently Secure
NatureServe Conservation Status
Rounded Global Status Rank: G4 - Apparently Secure
Reasons: A multifactor combination of climate stress, dwarf mistletoe, white pine blister rust, and bark beetles have created complex stress situations in limber pine forests which has caused high mortality in populations in many areas (Schoettle 2004, Millar et al. 2007). A major drought event from 1985 to 1995 caused a widespread 'mortality wave', whereas a subsequent 1999-2004 drought event didn't affect as many populations, with healthy regeneration currently occurring in some areas (Miller et al. 2007). However there is still high potential for an extensive rapid drought-induced die-off at a subcontinental scale (Breshears et al 2005, Coop & Schoettle 2009), particularly when trees have the physiological cost of defending against pathogens which can divert resources from other plant functions or make it more sensitive to environmental stresses (Schoettle 2004). Changing fire regimes combined with the poor competitiveness with other species and poor regeneration due to blister rust also cause concern for altering distribution and survival, however limber pine is a generalist and pioneer species, as well is cold and drought tolerant, making it capable of growing in a wide variety of environmental and physiological circumstances (Schoettle 2004).
Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Comments: Pinus flexilis is considered a generalist species with a physiological plasticity with respect to temperature and with the ability to tolerate a wide variety of environmental conditions over a broad latitudinal and elevation range. Its long roots enables its survival on xeric sites where other conifers cannot live. On mesic sites following canopy-opening disturbance, limber pine can act as a nurse tree for other species, however is shade intolerant and a poor competitor with other species (Schoettle 2004).
Pinus flexilis var. flexilis
Populations of Limber Pine occurring in the Great Plains in the states of Colorado, North Dakota, South Dakota, Montana and Nebraska are disjunct and therefore have no gene flow outside their individual population occurrences. These populations are stable except for the population in South Dakota that has been infected by White Pine Blister Rust (WPBR) (Cronartium ribicola). However, these populations are at risk from climate change or some other stochastic event. North Dakota, South Dakota and Nebraska rank their populations as state imperiled (S1) under the conservation ranking system of NatureServe.From 1985 -1995 a significant drought in California led to high mortality of high-elevation conifers especially Limber Pine. As White Pine Blister Rust moves southward in the Rocky Mountains scientists predict the decline of high-elevation white pines including Limber Pine. In the southern and central Rocky Mountains populations of Limber Pine and other conifers have and are continuing to die from a massive infestation by mountain pine beetles (MPB) (Dendroctonus ponderosae). Additionally, dwarf mistletoe (DM) (Arceuthobium cyanocarpum) has been noted as causing increased mortality of Limber Pine in some states in the Rocky Mountains and a fungus (Ophiostoma sp.) carried by mountain pine beetles is infecting many populations of Limber Pine. In Montana, red band needle blight (RBNB) (Dothistroma septospora) has and is causing significant mortality. WPBR, MPB, DM, RBNB and climate change are leading to more isolated populations, adversely affecting gene flow and ultimately genetic diversity. Cumulatively these factors are causing individual Limber Pines and small populations to undergo increased physiological stress which allows for other biotic and abiotic factors that in isolation would not lead to increased mortality to do so. Where WPBR, MPB, and DM are present we are observing isolated cases of population extirpations and an overall decline in Limber Pine populations.
Pinus flexilis var. reflexa
This taxon is much more scattered than var. flexilis which occurs to the north of it, and is restricted to the highest altitudes of the mountains in northern Mexico and the southwest of the USA. Populations are accordingly disjunct and often small
Global Short Term Trend: Decline of 10-30%
Comments: Limber pine populations are still declining largely due to the white pine blister rust. Alberta populations are largely infected by white pine blister rust with the average mortality of more than 27% between 2004-2005 (Alberta Sustainable Resource Development and Alberta Conservation Association 2007).
Global Long Term Trend: Decline of 30-50%
Comments: Schoettle (2004) notes that the white pine blister rust has infected limber pines since 1945 in the northern Rocky Mountains, in southern Wyoming since 1970s and noted in Colorado in 1998. Miller et al. (2007) reports a significant drought-induced mortality from 1985-1995 in California however no additional widespread mortality in California from a subsequent 1999-2004 drought event which did affect millions of hectares elsewhere in the western United States. Coop & Schoettle (2009) forecast the decline of important high elevation pines of the southern Rockies due to the recent spread of white pine blister rust into this region. Van Mantgem et al. (2009) notes that noncastastrophic mortality rates have increased rapidly in recent decades with doubling periods ranging from 17 to 29 years among western regions for tree mortality in unmanaged old forests.
Pinus flexilis var. flexilis
Limber Pine is highly susceptible to infection and death from the disease white pine blister rust caused by the non-native pathogen Cronartium ribicola. Limber Pine populations in the northern US Rocky Mountains have been infected by WPBR for over 50 years and mortality is high in many sites. The disease has continued to spread south and now infects Limber Pine in MT, ID, WY, CO, SD, NM and CA with heavily infected stands in each of these states. New locations of infected stands are being found yearly. In 2003, Limber Pine in the drainages of the Great Sand Dunes National Park and Preserve were found to be heavily infected with WPBR; this infection centre is over 200 km from the nearest known source of inocula and long distance transport of WPBR spores from California is suspected as the initial source. The disease was confirmed on Limber Pine in Rocky Mountain National Park in 2010 but infection is still light. Risk analyses suggest that 50% of the 5-needle pine stands in Colorado have average climate conditions that will support the spread of the disease; the remaining habitats are likely to intermittently have years of suitable conditions for the disease. It is unlikely that extensive Limber Pine forests will escape WPBR infection over time.
Limber Pine has not evolved in the presence of C. ribicola; as a result it only has very low frequencies of resistance to the disease. WPBR kills Limber Pine trees of all ages and young trees are especially susceptible. Even before the disease kills the larger trees it kills the cone bearing branches and severely restricts seed production. WPBR threatens the sustainability of Limber pine populations by compromising the regeneration cycle with high mortality of all aged trees, reduced seed production of the mature trees and high susceptibility of young seedlings and saplings. These impacts are being seen in many Limber Pine forests now and are expected to expand to other landscapes as the disease continues to spread. Until natural selection results in an increase in durable WPBR resistance, ecosystems impacts will continue.
Initial modeling suggests that the slow regeneration time, delayed maturation (>50 years for a tree to become reproductive and over 100 years before producing large cone crops), and low initial frequency of heritable resistance in Limber pine will lead to high mortality in native populations for centuries to come. While this mortality is selection against susceptible individuals, it is likely to reduce populations to below a sustainable threshold. Limber Pine is largely dependent on corvid species to disperse its seeds and studies suggest that once populations are impacted to the point that seed production is very low, the mutualism with the corvids may fail, as the birds do not visit such stands. Extirpation of populations is likely to occur which will lead to further genetic isolation of remaining populations.
The recent epidemic of Mountain Pine Beetle (MPB) is further threatening the sustainability of Limber Pine populations. Limber Pine is an excellent host for MPB and larger beetle broods are often produced on Limber Pine compared to other pine hosts. MPB generally only attack larger trees (those above 10 cm d.b.h.) and do not attack the smaller advanced regeneration trees. However, MPB further reduces the seed production of the population and in the presence of WPBR the rust will continue to kill the susceptible seedlings that are able to get established. While MPB epidemics are not unprecedented in Limber Pine forests, the current epidemic is more extensive than in the past and the presence of WPBR severely compromises the recovery capacity of the populations after the MPB epidemic passes.
In areas of high WPBR incidence, MPB is killing the remaining live reproductive trees which are often those that possess some genetic resistance to the disease. This is setting back the natural selection for resistance in Limber Pine that has already occurred. In those populations that have more recently been invaded by C. ribicola, MPB is killing the seedtrees from which seeds must be collected to test for resistance, slowing the identification of resistance trees and estimates of resistance in populations. MPB in all locations is affecting the availability of seed for collections for restoration plantings.
The extirpation of populations in the high mountain and tree line habitats will likely transition those lands from forests to non-forested landscapes. Limber Pine is often the only tree species that can tolerate those harsh habitats and therefore there will be no replacement tree species to occupy the site. Loss of the trees will also affect snow accumulation and snow melt on the wind-exposed high elevation sites.
Pinus flexilis var reflexa
WPB does not seem to have reached these isolated southern populations.
Degree of Threat: High
Comments: White pine blister rust (Cronartium ribicola) causes high mortality but also results in low recruitment, extinction and isolation, and exerts strong selective pressure at the seedling-sapling stage with high rates of seedling mortality. The physiological cost of plant defences to blister rust can divert resources from other plant functions or make the tree more sensitive to environmental stresses, herbivory, pests, such as the mountain pine beetle (Dendroctonus ponderosae) or other pathogens. As populations become more isolated, gene flow is interrupted affected genetic diversity (Schoettle 2004). Limber pine appears to have less resistance to blister rust than other North American white pines with greenhouse infection levels as high as 98 to 100% and seedling mortality of 75% (Johnson 2001).
Periods of climate stress combining high temperature and sustained low precipitation which has caused past forest dieback events will most likely reoccur in western North America. Forest stands at higher density combined with this climate stress most likely promoted bark beetle epidemics (Millar et al. 2007).
Damage by porcupines has been noted in North Dakota and consumption of seeds by mammals, particularly red squirrels, is noted in Alberta as detrimental and an important constraint. Dwarf mistletoe (Arceuthobium cyanocarpum), a parasitic vascular plant, has caused high mortality of limber pine in some states in the Rocky Mountains, and the blue stain fungus (Ophiostoma sp.) carried by pine beetles is infecting many populations (Millar et al. 2007). Red band needle blight (Dothistroma septospora) has caused significant mortality in Montana (Alberta Sustainable Resource Development and Alberta Conservation Association 2007).
Fire can easily kill young limber pines because of their thin bark, but fuel loads on most limber pine sites are too light, however, to generate severe fire damage, and most of the large trees normally survive (Burns and Honkala, 1990).
The decline in population numbers during the naturalization process of Cronartium ribicola is unavoidable yet management can facilitate the recovery from that dip in population numbers. Increasing the frequency of genetic resistance in the populations is the foundation for recovery. This can be achieved through combinations of (1) supporting the regeneration cycle by protecting seed trees and stimulating natural regeneration in populations that have some resistance to increase population numbers and promote selection for resistance and/or (2) identifying resistant seed trees, collecting seeds and planting seedlings from those trees. In areas that are heavily impacted already by WPBR, the seed source is likely to be compromised to the point that out planting resistant seedlings is the only option. In areas that have not been impacted as heavily (more southern populations), proactive silvicultural treatments to stimulate regeneration by removing competing vegetation or site preparation can be viable options in addition to planting resistant seedlings. A proactive strategy has been developed for Limber pine and management guides for Limber Pine have been developed for the USFS Rocky Mountain (R2) and Southwestern (R3) Regions and BLM lands in Wyoming. Rocky Mountain National Park is currently developing a management plan to sustain and conserve Limber pine. To fully implement these plans more work is need to develop appropriate silvicultural prescriptions and identify resistant seed sources.
Low frequencies of genetic resistances to WPBR exist in Limber Pine, however, the geographic distribution of these resistance mechanisms is still not known. Substantial rust screening efforts for Limber pine began in 2006. Only populations and ‘families’ from the Southern Rocky Mountains have been screened for resistance and some seed trees with heritable resistance have been identified (even in populations not yet challenged by the rust) and are now being protected from MPB attack with chemical spraying or anti-aggregate pheromone treatment. More resistant seed trees are needed to build seed sources for out planting with sufficient genetic diversity. Initial studies reveal geographic variation in resistance in the southern Rockies and suggest it varies along environmental gradients. The first tests for several ‘families’ from California and Montana have now begun. Rust screenings of seed trees from range-wide populations are needed as well as research on the mechanisms of resistance to assess their durability and interactions with climatic factors. Tests for the association of resistance traits with other adaptive traits could affect plant performance in a changing climate and needs further work. Seed transfer guidelines have been developed for Limber pine in the Interior West but are based on inadequate data. Range-wide gene ecology studies are needed to avoid planting errors that will lead to maladaption and failure now and in the future for this long-lived species. This research has begun but needs to be accelerated.
Limber Pine seeds for gene conservation, rust resistance and research have been collected from some populations the Southern Rockies yet still more are needed in this portion as well as the rest of the range. Restoration seed collections are needed range-wide. Because current technologies to screen for rust resistance require progeny testing, only seed-producing trees can be tested for rust resistance. Therefore seeds should be collected from seed trees and populations before MPB kills the mature trees; if not, identifying rust resistant trees from these populations will be delayed for 30-50 years while the advanced regeneration that escapes MPB attack becomes seed producing.
Biological Research Needs: Research is needed on: frequency and factors determining cone production; repercussions and proportion of seeds consumed on site versus dispersed and cached; clustered distribution dynamics from seed caching; cone production per tree by growth form and site type; genetic basis for morphological variation or lack thereof; long distance dispersal of white pine blister rust spores; resistance mechanisms to the blister rust; rust resistant genotypes; role of mycorrhizal fungus on tree growth and survival; development of seed storage protocols and seed transfer rules; establishment of other species with nurse tree role of limber pine (Schoettle 2004, Alberta Sustainable Resource Development and Alberta Conservation Association 2007).
Management of limber pine forests associated with Douglas-fir typically
favors the growth of the economically important Douglas-fir. Of
primary management importance in these areas is watershed protection and
enhancement. The slow rate of vegetation recovery in areas where limber pine occurs requires dispersed,
low-impact recreation to maintain the aesthetic appeal of these forests . Forage
productivity can be increased by periodic surface fires .
Limber pine trees are infected and killed by white pine blister rust (Cronartium ribicola) throughout
the tree's range. Ribes species are obligate alternate hosts of the rust [46,47,48,76,116]. Limber pine appears to have less resistance to blister rust than other North American white
pines (Strobi), with greenhouse infection levels as high as 98
to 100% [45,113]. In a 3-year greenhouse study of relative seedling
susceptibility to blister rust, limber pine mortality was 75% (n=348). In comparison, mortality in whitebark pine was 33%
(n=207) and 86% in southwestern white pine (n=323) .
Limber pine is susceptible to numerous other fungal diseases . It can be heavily infected or killed by limber pine dwarf-mistletoe (Arceuthobium cyanocarpum)
[12,39,71,72], and is susceptible to infestation by mountain pine beetles, cone beetles, coneworms, and budworms [54,61,101].
The Whitebark and Limber Pine Information System provides a database for storing and analyzing data on site characteristics,
stand structure, regeneration, and mortality and infection rates from white pine blister rust and
other damaging agents.
Relevance to Humans and Ecosystems
Value for rehabilitation of disturbed sites
Because of its slow growth, limber pine has been used only to a limited extent in land reclamation projects . Vegetation
recovery is slow on the exposed, hot, dry, rocky sites where it is found, and
soil erosion can prevent complete restoration. However, limber pine's drought tolerance and ability to survive at high elevations indicate that it has potential for use in revegetation projects .
Grossnickle and Reid  tested the feasibility of including limber pine seedlings in the reclamation of a high-elevation mining site in Colorado. The site was a molybdenum tailing pond buried in deep mine waste rock. One-year-old containerized
limber pine, lodgepole pine, and Engelmann spruce seedlings were inoculated with 3 species of ectomycorrhizal fungi prior to outplanting. Because of greenhouse colonization of seedling roots by a 4th
"wild" strain of ectomycorrhizal fungus, no uncolonized seedlings were outplanted. Some of the seedlings were also treated in the field with fertilizer or sewage sludge combined with wood chips. All seedlings were protected from wind and sun with cedar shingles.
During the 4th growing season, significant (p = 0.05) differences in seedling height among the fungal treatments were detected. The addition of the sewage sludge/wood chip slurry improved seedling height
of all 3 species in 1 of the fungal treatments. At the end of the 4th growing season, overall survival of limber pine, lodgepole pine, and Engelmann spruce seedlings was
60%, 52% and 62%, respectively. The authors noted that in all instances, seedling mortality appeared to be caused by unfavorable soil and climatic conditions and not by pathogen, insect, or animal damage.
Limber pine cones may yield 1,100 to 1,300 cleaned seeds per pound, and stored seed has been shown viable for at least 5 years. Freshly collected seeds may germinate without pretreatment, but cold, moist stratification
of up to 90 days improves germination .
The degree to which limber pine provides cover for wildlife species is as follows :
CO MT ND UT WY
Pronghorn ---- ---- Poor Poor Fair
Elk ---- ---- ---- Good ----
Mule deer ---- ---- ---- Good ----
White-tailed deer ---- ---- Good ---- Good
Small mammals Good ---- ---- Good Good
Small nongame birds Good ---- Good Good Good
Upland game birds ---- Good ---- Good Good
Waterfowl ---- ---- ---- ---- Poor
Wood Products Value
timber and fuelwood production is low, because the trees are slow growing with
irregular form [1,2,20,42,49,85,96,101]. Limber pine has been used locally for
mine props and railroad ties .
Other uses and values
Importance to Livestock and Wildlife
Pine "nuts" provide critical food for rodents and birds, which cache the
seeds for later use. Other small mammals and birds benefit from these caches. Bears also feed from caches
[62,66]. Sites with limber pine provide key winter range for deer and elk .
Bighorn sheep use open stands on ridges. Difficult access and low grass production result in low forage
value of limber pine stands for livestock [1,42].
The seeds are highly nutritious, providing amino acids, lipids, and averaging
7,178 calories per gram .
provides some food for birds and small mammals. The palatability of limber pine for livestock and wildlife has been rated as follows
CO MT ND UT WY
Cattle Poor Poor Poor Poor Poor
Domestic sheep Poor Poor Poor Poor Poor
Horses Poor Poor Poor Poor Poor
Pronghorn ---- ---- Poor Poor Poor
Elk Poor Poor ---- Poor Fair
Mule deer Poor Poor Poor Poor Fair
White-tailed deer ---- ---- Poor ---- Fair
Small mammals ---- ---- ---- Good Good
Small nongame birds ---- ---- Poor Good Good
Upland game birds ---- ---- ---- Good Good
Waterfowl ---- ---- ---- ---- Poor
Although of marginal value for lumber, limber pine has other resource values. Its ability to grow on harsh sites often provides the only tree cover for wildlife. The large seeds are a nutritious food source for birds, rodents, and bears and were used as food by Native Americans and early pioneers (20,21,29). In areas where timber is scarce, limber pine may be an important source of fuelwood. Increasing demands for fuelwood could deplete the accessible dead trees and eventually conflict with wildlife needs for shelter and nesting cavities.
Limber pine's abilities to withstand severe wind and dry site conditions are desirable shelterbelt traits, but its slow growth rate may discourage its selection for that purpose. Young trees, however, can withstand considerable bending, a necessary trait for reforestation of snow avalanche paths, and much of the pine's natural habitat lies within avalanche areas. Some limber pine habitats are also valuable watersheds, and as a pioneer species, the pine is a logical choice for initial site protection and for increasing snowpack (39). The pine's characteristic branching pattern also adds to the esthetic appeal of the landscape, especially along ridge lines.
This tree's ability to endure very dry environments has allowed it to attain considerable age in some areas. One tree in southern California was found to be well over 1,000 years old (13); another in central Idaho was 1,650 years old (31). This feature makes limber pine a useful species in dendrochronologic studies.
Limber pine has potential as a Christmas tree, but its qualities are surpassed by southwestern white pine (14,43). Seedlings from several seed sources have grown too slowly for economical Christmas tree operations but have ornamental value as dwarfed trees and even bonsai (14). Some bonsai nurserymen also collect dwarfed limber pine from severe windy sites. As an ornamental, this species deserves more attention than current use would indicate. The ornamental trade has selected at least seven cultivated varieties: 'Columnaris'- a fastigiate form; 'Glauca' and 'Firmament'- both with exceptionally bluish-green foliage; 'Glenmore'- with longer, more silvery foliage; 'Nana'- a dwarf bushy form; 'Pendula'- with pendulous branches; and 'Tiny Temple'- a low growing form (7,19).
Pinus flexilis, the limber pine, is a species of pine tree-the family Pinaceae that occurs in the mountains of the Western United States, Mexico, and Canada. It is also called Rocky Mountain white pine.
A limber pine in Eagle Cap Wilderness, Oregon has been documented as over 2000 years old, and another one was confirmed at 1140 years old. Another candidate for the oldest limber pine was identified in 2006 near the Alta Ski Area in Utah; called "Twister", the tree was confirmed to be at least 1700 years old and thought to be even older.
P. flexilis is found in the subalpine areas of the Rocky Mountains from southwest Alberta Canada south through Colorado and New Mexico into the northern states of Mexico; from mountains in the eastern Pacific Northwest states through the Great Basin states of Nevada and Utah. It is also found in California: in the Eastern Sierra Nevadas; the eastern California White Mountains; and the Southern California San Bernardino Mountains and San Gabriel Mountains of the Transverse Ranges. Continuing south the species is found in the San Jacinto Mountains, Santa Rosa Mountains, and Hot Springs Mountain of the Peninsular Ranges; and a small disjunct population in the Black Hills in South Dakota.
P. flexilis is typically a high-elevation pine, often marking the tree line either on its own, or with whitebark pine (Pinus albicaulis), either of the bristlecone pines, or lodgepole pine (Pinus contorta). In favourable conditions, it makes a tree to 20-meter (66 ft), rarely 25-meter (82 ft) tall. However, on exposed treeline sites, mature trees are much smaller, reaching heights of only 5-meter (16 ft) - 10-meter (33 ft). In steeply-sloping, rocky and windswept terrain in the Rocky Mountains of southern Alberta, limber pine is even more stunted, occurring in old stands where mature trees are consistently less than 3m in height.
P. flexilis is a member of the white pine group, Pinus subgenus Strobus, and like all members of that group, the leaves ('needles') are in fascicles (bundles) of five, with a deciduous sheath. This distinguishes it from the lodgepole pine, with two needles per fascicle, and the bristlecone pines, which share five needles per fascicle but have a semi-persistent sheath.
Distinguishing limber pine from the related whitebark pine (P. albicaulis), also a white pine, is very much more difficult, and can only easily be done by the cones. In limber pine, the cones are 6-centimeter (2.4 in) - 12-centimeter (4.7 in) long where the species overlap, green when immature, and open to release the seeds; the scales are not fragile. In whitebark pine, the cones are 4-centimeter (1.6 in) - 7-centimeter (2.8 in) long, dark purple when immature, and do not open on drying, but are fragile and are pulled apart by birds (see below) to release the seeds. A useful clue is that whitebark pines almost never have intact old cones lying under them, whereas limber pines usually do. 
In the absence of cones, limber pine can also be hard to tell from Western white pine (P. monticola) where they occur together in the northern Rockies and the Sierra Nevada east slope. The most useful clue here is that limber pine needles are entire (smooth when rubbed gently in both directions), whereas Western white pine needles are finely serrated (feeling rough when rubbed gently from tip to base). Limber pine needles are also usually shorter, 4-centimeter (1.6 in) - 7-centimeter (2.8 in) long, to Western white pine's 5-centimeter (2.0 in) - 10-centimeter (3.9 in) (though note the overlap).
Limber pine is susceptible to white pine blister rust, caused by Cronartium ribicola, a fungus that was introduced accidentally from Europe. Limber pine mortality is high in many areas throughout its range, except Arizona, where it has not yet been found. However, there is little hope of controlling the blister rust in existing trees. Research is under way, locating and breeding from the occasional naturally resistant limber pines, and by studying the resistance mechanisms of the European and Asian white pines (e.g. Swiss pine, Macedonian pine), which are strongly resistant to the disease.
The popular cultivar P. flexilis 'Vanderwolf's Pyramid' is widely available as an ornamental tree for gardens. 'Vanderwolf's Pyramid' derives from P. reflexa, though it is usually listed in nursery catalogs under P. flexilis.
The Southwestern white pine is popular as a windbreak tree or an ornamental tree due to its drought tolerance. It is also grown as a Christmas tree, liked for the soft needles but with stiffer branches than an Eastern white pine.
P. flexilis, is an important source of food for several species, including red squirrels and Clark's nutcrackers. American black bears may raid squirrel caches for limber pine nuts. Squirrels, Northern flickers, and mountain bluebirds often nest in the trees.
- Conifer Specialist Group (1998). Pinus flexilis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
- "Old Tree". Oregon Field Guide. 2010. Retrieved 2010-02-21.
- Richard, Terry (September 24, 2012). "Ancient limber pine, likely Oregon's oldest living tree, draws twin brothers to Wallowas quest (photo essay, video)". The Oregonian. Retrieved 2015-02-18.
- "Stay Flexible, Grow Old". BYU Magazine. Spring 2007. Retrieved 2015-02-18.
- Moore, Gerry; Kershner, Bruce; Tufts, Craig; Mathews, Daniel et al. (2008). National Wildlife Federation Field Guide to Trees of North America. New York: Sterling. p. 81. ISBN 1-4027-3875-7.
- "Pinus flexilis". Flora of North America. efloras.org.
- Letts, M.G.; Nakonechny, K.N.; Van Gaalen, K.E.; Smith, C.M. (2009). "Physiological acclimation of Pinus flexilis to drought stress on contrasting slope aspects in Waterton Lakes National Park, Alberta, Canada". Canadian Journal of Forest Research 39 (3): 629–641. doi:10.1139/X08-206.
- "Pinus subgenus Strobus". Michael P. Frank's Cone Collection. Arboretum de Villardebelle.
- Roady, Laura. "Whitebark Pine". Montana Outdoors. Montana Fish, Wildlife & Parks. Retrieved 15 March 2015.
- Chase, J. Smeaton (1911). Cone-bearing Trees of the California Mountains. Chicago: A. C. McClurg & Co. p. 99. LCCN 11004975. OCLC 3477527. LCC QK495.C75 C4, with illustrations by Carl Eytel - Kurut, Gary F. (2009), "Carl Eytel: Southern California Desert Artist", California State Library Foundation, Bulletin No. 95, pp. 17-20 retrieved Nov. 13, 2011
|Wikimedia Commons has media related to Pinus flexilis.|
- USDA Plants Profile: Pinus flexilis (Limber pine).
- Gymnosperm Database: Pinus flexilis
- Flora of North America: profile and map - Pinus flexilis
- Pinus flexilis —Jepson Manual Treatment — Calif. distribution: High Sierra Nevada, Transverse Ranges, Peninsular Ranges, east of Sierra Nevada, Mojave Desert mountains.
- Pinus flexilis cone photos
- High Elevation White Pine Educational Website: Pinus flexilis
- Old Tree Documentary produced by Oregon Field Guide
Names and Taxonomy
Comments: Limber pine is a member of the pine family, Pinaceae within the section Strobus, subsection Strobi; similar to stone pines (subsection Cembrae) with large wingless or nearly wingless seeds that depend on corvid species (such as the Clark's nutcracker, Nucifraga columbiana) for seed dispersal across the landscape, however in contrast to stone pines, limber pine cones open when dry.
subgenus Strobus, subsection Strobi of Pinus
Rocky Mountain white pine