Pinaceae -- Pine family

    Robert Steele

    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.

Limber pine occurs from Alberta and British Columbia south to California, Arizona, and New Mexico. It is scattered widely across the Great Basin in Utah,
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.

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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 [14]:

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

AZ	CA	CO	ID	MT	NE	NV
NM	ND	OR	SD	UT	WY
AB	BC

Limber pine grows from Alberta and southeastern British Columbia to New  Mexico, Arizona, and eastern California. Notable outliers of this general  distribution are found in the western portions of North Dakota, South  Dakota, and Nebraska, and in eastern Oregon and southwestern California.

    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.

Pinus flexilis E. James:
United States (North America)
Mexico (Mesoamerica)
China (Asia)

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.

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).

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Trees to 26m; trunk to 2m diam., straight to contorted; crown conic, becoming rounded. Bark gray, nearly smooth, cross-checked in age into scaly plates and ridges. Branches spreading to ascending, often persistent to trunk base; twigs pale red-brown, puberulous (rarely glabrous), slightly resinous, aging gray, smooth. Buds ovoid, light red-brown, 0.9--1cm, resinous; lower scales ciliolate along margins. Leaves 5 per fascicle, spreading to upcurved and ascending, persisting 5--6 years, 3--7cm ´ 1--1.5mm, pliant, dark green, abaxial surface with less conspicuous stomatal bands than adaxial surfaces, adaxial surfaces with strong, pale stomatal bands, margins finely serrulate, apex conic-acute to acuminate; sheath 1--1.5(--2)cm, shed early. Pollen cones broadly ellipsoid-cylindric, ca. 15mm, pale red or yellow. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, spreading, symmetric, lance-ovoid before opening, cylindro-ovoid when open, 7--15cm, straw-colored, resinous, sessile to short-stalked, apophyses much thickened, strongly cross-keeled, umbo terminal, depressed. Seeds irregularly obovoid; body 10--15mm, brown, sometimes mottled darker, wingless or nearly so. 2 n =24.

Limber pine is a slow growing, long-lived species, sometimes taking several hundred years to reach maturity [26,75]. Mature trees may
exceed 1000 years of age [53,96,127]. Limber pine stands are broadly even-aged [89], 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 [41]. 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].

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 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 not blue-green, Leaves white-striped, Needle-like leaves triangular, Needle-like leaves somewhat rounded, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaf habit drooping, 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, Seed cones bearing a scarlike umbo, Umbo with missing or very weak prickle, Bracts of seed cone included, Seeds brown, Seeds wingless.

Apinus flexilis (E.James) Rydberg

More info for the terms: cover, litter, tree

Limber pine grows across a wider range of elevations that any other tree species in the central Rocky Mountains [94], 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 [127].

Site preference often separates limber pine and whitebark pine, which is ecologically similar in many respects [112]. 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 [80]

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 [114]

5,000 to 7,000 feet (1,500-2,100 m) in Oregon [19]

6,000 to 11,600 feet (1,830-3,540 m) in Utah [123]

More info for the terms: association, shrub, shrubs, tree

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) [81]. 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 [17].

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) [7]. It co-occurs with southwestern white pine (P. strobiformis) in the Sangre de Cristo Mountains [116].

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) [19].

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 [50].

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:

Arizona [67,79]

California [51,92]

Colorado [8,20,25,42,49,57]

Idaho [102,103]

Montana [85,91]

North Dakota [32]

New Mexico [20,25,67,79]

Utah [41,73,127]

Wyoming [1,102,124]

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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 [99]:

109 Ponderosa pine shrubland

209 Montane shrubland

210 Bitterbrush

402 Mountain big sagebrush

412 Juniper-pinyon woodland

413 Gambel oak

415 Curlleaf mountain-mahogany

504 Juniper-pinyon pine woodland

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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):

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SAF COVER TYPES [28]:



206 Engelmann spruce-subalpine fir

208 Whitebark pine

209 Bristlecone pine

210 Interior Douglas-fir

217 Aspen

218 Lodgepole pine

219 Limber pine

220 Rocky Mountain juniper

237 Interior ponderosa pine

239 Pinyon-juniper

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 [60] 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

K033 Chaparral

K037 Mountain-mahogany-oak scrub

K038 Great Basin sagebrush

K046 Desert: vegetation largely lacking

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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 [31]:

FRES20 Douglas-fir

FRES21 Ponderosa pine

FRES23 Fir-spruce

FRES26 Lodgepole pine

FRES29 Sagebrush

FRES34 Chaparral-mountain shrub

FRES35 Pinyon-juniper

In some areas, limber pine grows in greater numbers on certain soils,  but the relationships vary geographically. In general, the substrates are  Entisols. In Montana, limber pine grows mainly on calcareous substrates  (26). Similarly, in eastern Idaho and western Wyoming, it grows mainly on  soils derived from limestone or sandstone and is notably absent on  adjacent granitic substrates (34), yet the population in South Dakota  grows on soils derived from granitic rock (38). In central Idaho, limber  pine is found largely on soils derived from sedimentary rocks; it is  notably absent on granitic substrates, but grows in cracks of recent lava  at Craters of the Moon National Monument (33). In eastern Oregon, a  recently discovered population is on soils derived from serpentine (17).  In Utah, it grows on soils developed from limestone, as on the Wasatch  Plateau (9), and on soils derived from quartzites, shales and limestones  of the Uinta Range (26). In southern Utah, it is most common on soils  derived from sandstone and limestone (44). In northeastern Nevada, it also  grows on various calcareous substrates (25), but in California, on  substrates derived from granitic, obsidian, and pumice materials (30).

    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.

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 (2,3). 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 (3).

    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.

High montane forests, often at timberline; (1000--)1500--3600m; Alta., B.C.; Ariz., Calif., Colo., Idaho, Mont., Nebr., Nev., N.Mex., N.Dak., Oreg., S.Dak., Utah, Wyo.

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.

Foodplant / parasite
erumpent aecium of Cronartium ribicola parasitises stem of Pinus flexilis
Remarks: season: 3-6
Other: major host/prey

As well as being dominant in the forest cover type Limber Pine (Society  of American Foresters Type 219), limber pine is a minor component of the  following (32); Engelmann Spruce-Subalpine Fir (Type 206), Whitebark Pine  (Type 208), Bristlecone Pine (Type 209), Interior Douglas-Fir (Type 210),  Aspen (Type 217), Lodgepole Pine (Type 218), and Interior Ponderosa Pine  (Type 237).

    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).

Fire can easily kill young limber pines because  of their thin bark. Fuel loads on most limber pine sites are too light,  however, to generate severe fire damage, and most of the large trees  normally survive. Porcupines feed on limber pine, especially in the winter  months (11). Several insects attack the pine in various ways. In Montana,  the budworm (Choristoneura lambertiana ponderosana) feeds on the  new needles of limber pine (37). A cone moth (Dioryctria spp.)  is presumed to have damaged limber pine seed in North Dakota (29). In  northern Idaho, the woolly aphid (Pineus coloradensis) attacked  limber pine seedlings growing in test plots, but the pine showed  considerable resistance to this insect (16). Mountain pine beetle (Dendroctonus  ponderosae) also occasionally attacks limber pine (1).

    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).

More info for the terms: fuel, fuel moisture

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) [55]. Further general site descriptions appear in Keown 1982 [56]. 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
stands [55].

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.

More info for the term: tree

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 [98]. Postfire regeneration of limber pine
is a consequence of seed dispersal and caching by Clark's nutcrackers [53,66].

Limber pine is often killed by fire because of its relatively thin bark. Keeley and Zedler [53] argue that the lack of evolution of thick, fire-resistant bark in this species is a result of very long and unpredictable fire return intervals in the unproductive sites where it occurs. The degree of stem scorch usually determines the extent of fire injury to trees. Young trees are usually killed by any fire that scorches their stems. Mature trees with thicker bark can survive [29]. The vulnerability of this species to fire is reduced by the open stand structure, sparse fuels, and sparse undergrowth of limber pine communities [85,101].

More info for the terms: association, fuel, series

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 [53] 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 [15]
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
pinyon-juniper	Pinus-Juniperus spp.
whitebark pine*	Pinus albicaulis	50-200 [15]
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 [15]
quaking aspen (west of the Great Plains)	Populus tremuloides	7-120 [15,34,77]
mountain grasslands	Pseudoroegneria spicata	3-40 (10)** [3]
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

**mean

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More info for the terms: climax, succession, xeric

According to Tomback and Linhart [112] 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 [89] 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."

More info for the terms: fitness, mutualism, phenology, tree

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 [66]. 

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 [123]. Tomback and Linhart
[112] 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 [123].

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 [97].

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More info for the term: phanerophyte

RAUNKIAER [88] LIFE FORM:

Phanerophyte

More info for the term: tree

Tree

POSTFIRE REGENERATION STRATEGY [105]:

Initial offsite colonizer (off-site, initial community)

Secondary colonizer (on-site or off-site seed sources)

Fischer and Clayton [29] suggest that limber pine growing in open stands can be
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
classes.

Limber pine is relatively intolerant of  shade and therefore seral to most of its associated trees, the exceptions  being quaking aspen, Rocky Mountain juniper, and possibly ponderosa pine.  It is also considered seral to bristlecone pine and Douglas-fir but will  codominate with these species on severe dry sites (23). As a result, on  most forest sites, limber pine normally acts as a pioneer species  following fire or tree removal. Except on the most severe sites, where   trees remain widely spaced, limber pine shows little evidence of  maintaining its population in the presence of other conifers. It is most  accurately classed as a species intolerant of shade.

Type of substrate undoubtedly influences the  rooting habit of limber pine. On many of the very rocky sites where it  grows, the root system must follow the pattern of rock fracturing. As a  result, most limber pine are quite wind firm. In nurseries, where there  are better soil conditions, it develops a more uniform root system and can  be transplanted by the ball and burlap method if previously root pruned  (7). Roots of limber pine are also known to associate with a mycorrhizal  fungus (Gomphidius smithii) (40).

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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 [93]:

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.

No information is currently available.

Germination is epigeal (41). Like seed  size, rate of seedling development depends on the geographic source. In  one study (36), 2-year-old nursery grown seedlings from Alberta averaged  4.3 cm (1.7 in), while those from New Mexico had reached 7.4 cm (2.9 in).  Fall-sown seed, properly fertilized, produced a pencil-sized 2-0 seedling  suitable for field planting (14). In the wild, many seedlings develop in  clusters from Clark's nutcracker seed caches (20). The seedlings withstand  this competition well and often retain the clumped habit into maturity.

Large seed crops are produced  every 2 to 4 years and seed numbers generally range from 7,050 to  15,000/kg (3,200 to 6,800/lb) and average 10,800/kg (4,900/lb) (38). Seed  size varies geographically, with a tendency for increasingly larger seeds  in more southerly latitudes (14,36). Although some trees produce seed  having an ineffective vestigial wing (21), most limber pine seeds are  wingless.

    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.

Limber pine is monoecious-male and  female strobili are borne separately on the same tree. As with most pines,  male strobili predominate in the lower crown and female strobili most  often develop at the apical end of main branches in the upper crown. Male  strobili emerge from buds in the spring and are arranged in small clusters  of indistinct spirals. They may be green or yellow to reddish purple but  turn brown when mature and about to shed their pollen. Pollen is shed   during June and July. Female strobili emerge from buds shortly after the  male strobili and are green or red to purple. Cone scales flex and they  remain receptive to pollen for only a relatively short time during June  and July. After pollination, scales close and the strobili begin to  develop slowly.

    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).

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).

The slow growth rate and poor form normally  attributed to limber pine discourages commercial interest in its use for  timber and there is little information regarding its growth and yield.  There apparently has been no attempt, however, to plant this species on  forest sites superior to those chosen by birds and rodents that cache the  seed. Where occasional limber pines grow in more densely forested stands  with other tree species, sapling and pole size trees are often straight  and single stemmed. One study (29) suggests, however, that limber pine  growth rates may be greater on exposed windy knolls than on warmer south  slopes and more moist north slopes.

Population Differences    Genetic variation exists within limber pine in a general north-south  pattern, but the range of variability for any one trait is small. Some  isolated populations in Wyoming, Nebraska, and Colorado appear to be more  similar to those from more southern latitudes than to populations at the  same latitude (36).

    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).

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


No available public DNA sequences.

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 9
Specimens with Barcodes: 11
Species With Barcodes: 1

Canada

Rounded National Status Rank: N3 - Vulnerable

United States

Rounded National Status Rank: N4 - Apparently Secure

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).

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.

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).

More info for the term: resistance

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 [25]. Forage
productivity can be increased by periodic surface fires [29].

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) [45].

Limber pine is susceptible to numerous other fungal diseases [101]. 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.

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).

Needs: Conservation of genetic diversity for future breeding stock is needed.

More info for the terms: reclamation, restoration

Because of its slow growth, limber pine has been used only to a limited extent in land reclamation projects [120]. 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 [104].

Grossnickle and Reid [33] 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 [59].

More info for the term: cover

The degree to which limber pine provides cover for wildlife species is as follows [26]:
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

The wood of limber pine has little commercial value. Its potential for
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 [102].

Limber pine is used in the nursery trade
for landscaping [35,36,40].

The large, wingless seeds of limber pine have high energy content.
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 [85].
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].

Limber pine browse is rated fair in energy value and poor in protein value [26].
The seeds are highly nutritious, providing amino acids, lipids, and averaging
7,178 calories per gram [64].

Although limber pine browse is unpalatable to large mammals, it
provides some food for birds and small mammals. The palatability of limber pine for livestock and wildlife has been rated as follows
[26]:
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

Limber pine is seldom sought for timber, but small quantities are  occasionally harvested along with more desirable species. The wood has  been used for rough construction, mine timbers, railroad ties, and poles  (2).

    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 , much branched with a strongly tapering trunk, is little utilized because of its form and relative inaccessibility. It reportedly forms intermediates with P . strobiformis where the two overlap. The fresh-cut wood has the odor of turpentine.

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.