Pinus flexilis - James
Limber Pine
Other English Common Names: Rocky Mountain white pine
Other Common Names: limber pine
Taxonomic Status: Accepted
Related ITIS Name(s): Pinus flexilis James (TSN 183343)
French Common Names: pin flexible
Unique Identifier: ELEMENT_GLOBAL.2.140758
Element Code: PGPIN040F0
Informal Taxonomy: Plants, Vascular - Conifers and relatives
 
Kingdom Phylum Class Order Family Genus
Plantae Coniferophyta Pinopsida Pinales Pinaceae Pinus
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Pinus flexilis
Taxonomic 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.
Conservation Status
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NatureServe Status

Global Status: G4
Global Status Last Reviewed: 01Nov2011
Global Status Last Changed: 13Apr2009
Rounded Global Status: 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).
Nation: United States
National Status: N4
Nation: Canada
National Status: N2N3 (05Feb2016)

U.S. & Canada State/Province Status
United States Arizona (SNR), California (SNR), Colorado (SNR), Idaho (SNR), Montana (S5), Nebraska (S1), Nevada (SNR), New Mexico (SNR), North Dakota (S1), Oregon (S4), South Dakota (S1), Utah (SNR), Wyoming (S4)
Canada Alberta (S2), British Columbia (S2)

Other Statuses

Committee on the Status of Endangered Wildlife in Canada (COSEWIC): Endangered (28Nov2014)
Comments on COSEWIC: Designated Endangered in November 2014. Considered a medium priority candidate for re-assessment in 2011.

This tree species is imminently and severely threatened throughout its Canadian range by White Pine Blister Rust (an introduced pathogen), Mountain Pine Beetle, and climate change. Surveys at a number of sites in 2009 document an average of 43% and 35% of infected or dead trees, respectively. Repeated survey information leads to an estimated decline in the Canadian population of about 1% per year. At that rate, close to 2/3 of mature individuals are expected to be lost over the next 100 years, and local subpopulations could become extirpated.

NatureServe Global Conservation Status Factors

Range Extent Comments: 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).

Number of Occurrences:  
Number of Occurrences Comments: 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; and occurs in native to higher elevations in Utah and the interior West (Burns and Honkala, 1990).
(Burns and Honkala, 1990).

Overall Threat Impact: High
Overall Threat Impact 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).

Short-term Trend: Decline of 10-30%
Short-term Trend 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).

Long-term Trend: Decline of 30-50%
Long-term Trend 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.

Intrinsic Vulnerability Comments: Limber pines are long lived (some individuals over 2000 years) but have a slow growth rate reaching sexual maturity between 50-200 years (Johnson 2001, Schoettle 2004, Alberta Sustainable Resource Development and Alberta Conservation Association 2007). Large cone crops can be produced on optimum low density open sites with wide-ranging seed dispersal across the landscape depending upon corvid species such as the Clark's nutcracker (Nucifraga columbiana) and pinyon jays (Gymnorhinus cyanocephalus) (Johnson 2001, Schoettle 2004). The mutalistic relationship between limber pine and the nutcracker is highly evolved and important for the survival and well-being of both species (Alberta Sustainable Resource Development and Alberta Conservation Association 2007). Rodents also disperse seeds over shorter distances (Tomback et al. 2005). Roots of limber pine are known to be associated with a mycorrhizal fungus (Gomphidius smithii) (Alberta Sustainable Resource Development and Alberta Conservation Association 2007).

Environmental Specificity: Moderate. Generalist or community with some key requirements scarce.
Environmental Specificity 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).

Other NatureServe Conservation Status Information

Distribution
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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).

U.S. States and Canadian Provinces
Color legend for Distribution Map

U.S. & Canada State/Province Distribution
United States AZ, CA, CO, ID, MT, ND, NE, NM, NV, OR, SD, UT, WY
Canada AB, BC

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
ND Billings (38007)*, Slope (38087)
NE Kimball (31105)
SD Custer (46033), Pennington (46103)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
10 Middle Little Missouri (10110203)+, Middle Cheyenne-Spring (10120109)+, Upper Lodgepole (10190015)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
Ecology & Life History
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Basic Description: Pinus flexilis is a cold and drought tolerant, shade intolerant, slow-growing, long-lived (up to 2000 years) native tree of western North America. It often has irregular or multi-stem growth form on harsh exposed sites, may even form krummholz at higher elevations and rarely reaches over 15m in height. Deep taproots reach for water inaccessible to other species. Tree roots are also associated with the mycorrhizal fungus (Gomphidius smithii). As a pioneer species, it regenerates well after fire or canopy-opening disturbances. In forested areas, it may act as a nurse tree facilitating establishment of later successional species. The species is often used to define ecosystem boundaries, such as treeline. Limber pine has a mutualistic relationship with Clark's nutcracker (Nucifraga columbiana) for seed dispersal across the landscape.
Reproduction Comments: 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).

Habitat 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.

Economic Attributes
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Economically Important Genus: Y
Management Summary Not yet assessed
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Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 13Apr2009
NatureServe Conservation Status Factors Author: M. Anions
Element Ecology & Life History Edition Date: 22Nov2010
Element Ecology & Life History Author(s): Cordeiro, J.

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
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  • Alberta Sustainable Resource Development and Alberta Conservation Association. 2007. Status of limber pine (Pinus flexilis) in Alberta. Alberta Sustainable Resource Development. Wildlife Status Rpt 62. Edmonton, AB. 17pp.

  • Alberta Sustainable Resource Development and Alberta Conservation Association. 2007. Status of the limber pine (Pinus flexilis) in Alberta. Alberta Sustainable Resource Development, Wildlife Status Report No. 62. Edmonton, Alberta. 17 pp.

  • Alberta Sustainable Resource Development. 2009. Gene conservation plan for native trees in Alberta. Technical Publication T-1141: 108 pp.

  • Andersen, M.D. and B. Heidel. 2011. HUC-based species range maps. Prepared by Wyoming Natural Diversity Database for use in the pilot WISDOM application operational from inception to yet-to-be-determined date of update of tool.

  • Baker, F.S. 1944. Mountain climates of the western United States. Ecological Monographs 14:223-254.

  • Breshears, D.D., N.S. Cobb, P.M. Rich, K.P. Price, C.D. Allen, R.G. Balice, W.H. Romme, J.H. Kastens, M.L. Floyd, J. Belnap, J.J. Anderson, O.B. Myers, and C.W. Meyer 2005. Regional vegetation die-off in response to global-change-type drought. Proc. Natl. Acad. Sci. U.S.A. 102:15144-15148.

  • Burns, K.S., A.W. Schoettle, W.R. Jacobi, and M.F. Mahalovich. 2008. Options for the management of white pine blister rust in the Rocky Mountain Region. USDA Forest Service General Technical Report RMRS-GTR-206: 26 pp.

  • Burns, R. M., and B. H. Honkala, eds. 1990. Silvics of North America, vol. 1: Conifers. U.S. Department of Agriculture, Agriculture Handbook 654, Washington, DC. 675 pp.

  • Coop, J.D. and A.W. Schoettle. 2009. Regeneration of Rocky Mountain bristlecone pine (Pinus aristata) and limber pine (Pinus flexilis) three decades after stand-replacing fires. Forest Ecology and Management. 257: 893-903

  • Cripps, C.L. and, R.K. Antibus. 2011. Native ectomycorrhizal fungi of limber and whitebark pine: necessity for forest sustainability? pp. 37-44 in R.E. Keane, D.F. Tomback, M.P. Murray, and C.M. Smith (eds.). The future of high-elevation, five-needle white pines in western North America. USDA Forest Service, Proceedings RMRS-P-63.

  • Daly, C. and D. Shankman. 1985. Seedling establishment by conifers above tree limit on Niwot Ridge, Front Range, Colorado, U.S.A. Arctic and Alpine Research 17(4):389-400.

  • Douglas, G.W., G.D. Straley, and D. Meidinger, eds. 1998b. Illustrated Flora of British Columbia, Vol. 1, Gymnosperms and Dicotyledons (Aceraceae through Asteraceae). B.C. Minist. Environ., Lands and Parks, Wildl. Branch, and B.C. Minist. For. Res. Program. 436pp.

  • Evert, E. F. 2010. Vascular Plants of the Greater Yellowstone Area: Annotated Catalog and Atlas. Park Ridge, IL.

  • Flora of North America Editorial Committee. 1993a. Flora of North America north of Mexico. Vol. 2. Pteridophytes and gymnosperms. Oxford Univ. Press, New York. xvi + 475 pp.

  • Hamann, A., and T. Wang. 2006. Potential effects of climate change on ecosystem and tree species distribution in British Columbia. Ecology 87 (11) Pp 27732786.

  • Hoff, R., R.T. Bingham and G.I. McDonald. 1980. Relative blister rust resistance of white pines. Eur. J. For. Pathol. 10: 307-316.

  • Johnson, K.A. 2001. Pinus flexilis. In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available online: (accessed 4 February 2009).

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Kartesz, J.T. 1996. Species distribution data at state and province level for vascular plant taxa of the United States, Canada, and Greenland (accepted records), from unpublished data files at the North Carolina Botanical Garden, December, 1996.

  • Krajina, V. J., K. Klinka and J. Worral. 1982. Distribution and ecological characteristics of trees and shrubs of British Columbia. UBC Faculty of Forestry. 131 pp.

  • Krochmal, A. and C. Krochmal. 1982. Uncultivated nuts of the United States. Agriculture Information Bulletin 450, U.S. Department of Agriculture, Forest Service: Washington, D.C.. 89 pp.

  • Lanner, R.M. 1985. Effectiveness of the seed wing of Pinus flexilis in wind dispersal. The Great Basin Naturalist 45(2):318-320

  • Lanner, R.M. 1996. Made for Each Other: A Symbiosis of Birds and Pines. Oxford University Press: New York. 160 pp.

  • Lanner, R.M. and S.B. Vander Wall. 1980. Dispersal of limber pine seed by Clark's nutcracker. Journal of Forestry 78(10):637-639.

  • Little, E.L., Jr. 1979. Checklist of United States trees (native and naturalized). Agriculture Handbook No. 541. U.S. Forest Service, Washington, D.C. 375 pp.

  • Millar, C.I., R.D. Westfall, and D. L. Delany. 2007. Response of high-elevation limber pine (Pinus flexilis) to multi-year droughts and 20th century warming; Sierra Nevada, California, USA. Can. J. For. Res. 37:2508-2520.

  • Schoettle, A.W. 2004. Ecological roles of five-needle pines in Colorado: potential consequences of their loss. Pages 124-135 in: R.A. Sniezko, S. Samman, S.E. Schlarbaum, and B.E. Howard (eds.). Breeding and Genetic Resources of Five-needle Pines: Growth, Adaptability and Pest Resistance. USDA Forest Service Proceedings RMRS-P-32. Rocky Mountain Forest and Range Experimental Station, Fort Collins, CO.

  • Schoettle, A.W., R.A. Sniezko, A. Kegley, and K.S. Burns. 2011. Preliminary overview of the first extensive rust resistance screening tests of Pinus flexilis and Pinus aristata. pp. 265-269 in R.E. Keane, D.F. Tomback, M.P. Murray, and C.M. Smith (eds.). The future of high-elevation, five-needle white pines in western North America. USDA Forest Service, Proceedings RMRS-P-63.

  • Schuster, W.S., D.L. Alles, and J.B. Mitton. 1989. Gene flow in limber pine: Evidence from pollination phenology and genetic differentiation along an elevational transect. American Journal of Botany 76(9):1395-1403.

  • Smith, C.M., D. Langor, C. Myrholm, J. Weber, C. Gillies, and J. Stuart-Smith. 2011. Limber Pine health in the Canadian Rockies. pp. 63-65, in R.E. Keane, D.F. Tomback, M.P. Murray, and C.M. Smith (eds.). The future of high-elevation, five-needle white pines in western North America. USDA Forest Service, Proceedings RMRS-P-63.

  • Smith, C.M., D. Langor, C. Myrholm, J. Weber, C. Gillies, and J. Stuart-Smith. 2013. Changes in blister rust infection and mortality in limber pine over time. Canadian Journal of Forest Research: (accepted for publication).

  • Smith, S.E., and D.J. Read. 1997. Mycorrhizal symbiosis. Academic Press, San Diego, CA, USA.

  • Tomback, D.F. 2001a. Blister rust in white pine ecosystems: The imminent decline of western montane biodiversity. Phytopathology 91:S155

  • Tomback, D.F. 2001b. Clark's nutcracker: agent of regeneration. Pages 88-104 in D.F. Tomback, S.F. Arno, and R.E. Keane (eds.) Whitebark Pine Communities: Ecology and Restoration. Island Press: Washington, DC.

  • Tomback, D.F. and Y.B. Linhart. 1990. The evolution of bird-dispersed pines. Evolutionary Ecology 4:185-219.

  • Tomback, D.F., A.W. Schoettle, K.E. Chevalier and C.A. Jones. 2005. Life on the edge for limber pine: seed dispersal within a peripheral population. EcoScience 12(4):519-529

  • Weisberg, P.J. and W.L. Baker. 1995. Spatial variation in tree regeneration in the forest-tundra ecotone, Rocky Mountain National Park, Colorado. Canadian Journal of Forest Research 25(8):1326-1339.

  • Welsh, S.L., N.D. Atwood, L.C. Higgins, and S. Goodrich, eds. 1987. A Utah Flora. Great Basin Naturalist Memoir 9, Brigham Young University, Provo, Utah. 894 pp.

  • Woodmansee, R.G. 1977. Clusters of limber pine trees: a hypothesis of plant-animal coaction. Southwest Naturalist 21(4):511-517.

  • van Mantgem, P.J., N.L. Stephenson, J.C. Byrne, L.D. Daniels, J.F. Franklin, P.Z. Fule, M.E. Harmon, A.J. Larson, J.M. Smith, A.H. Taylor and T.T. Veblen. 2009. Widespread increase in tree mortality rates in the western United States. Science 323:521-524.

  • van Wagtendonk, J.W., J.M. Benedict, and W.M. Sydoriak. 1998. Fuel bed characteristics of Sierra Nevada conifers. Western Journal of Applied Forestry 13(3):73-84.

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