Pinus monticola

Western white pine

Pinaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Pinaceae (pines). Genus - Pinus L. Species - Pinus monticola Douglas ex D. Don

Ecology: Western white pine is classified as shade intolerant to very intolerant. It is usually seral to fir (Abies spp.), spruce (Picea spp.), or hemlock (Tsuga spp.). Western white pine is restricted to climates characterized by dry summers and a predominance of winter precipitation. The most extensive and best stands of western white pine are found in the river bottoms and less steep lower slopes of the Priest, Coeur d'Alene, St. Joe, and Clearwater River basins.

Identification

Trees to 70m; trunk to 2.5m diam., straight; crown narrowly conic, becoming broad and flattened. Bark gray, distinctly platy, plates scaly. Branches nearly whorled, spreading-ascending; twigs slender, pale red-brown, rusty puberulent and slightly glandular (rarely glabrous), aging purple-brown or gray, smooth. Buds ellipsoid or cylindric, rust-colored, 0.4--0.5cm, slightly resinous. Leaves 5 per fascicle, spreading to ascending, persisting 3--4 years, 4--10cm 0.7--1mm, straight, slightly twisted, pliant, blue-green, abaxial surface without evident stomatal lines, adaxial surfaces with evident stomatal lines, margins finely serrulate, apex broadly to narrowly acute; sheath 1--1.5cm, shed early. Pollen cones ellipsoid, 10--15mm, yellow. Seed cones maturing in 2 years, shedding seeds and falling soon thereafter, clustered, pendent, symmetric, lance-cylindric to ellipsoid-cylindric before opening, broadly lanceoloid to ellipsoid-cylindric when open, 10--25cm, creamy brown to yellowish, without purple or gray tints, resinous, stalks to 2cm; umbo terminal, depressed. Seeds compressed, broadly obovoid-deltoid; body 5--7mm, red-brown; wing 2--2.5cm.

Threats

In the WFDP: It is likely that western white pine is susceptible to suppression in this energy-limited system. The primary agents of mortality for western white pine in the WFDP are: mountain pine beetle (Dendroctonus ponderosae) and white pine blister rust (Cronartium ribicola).

Fire effects: Mature western white pine, with its moderately thick bark (3 cm), moderately flammable foliage, height, and evanescent [self-pruned away] lower limbs, is rated moderate in fire resistance. However, dense stands, lichen growth, and resinous bark can decrease western white pine's resistance to fire. Fire of any intensity will damage the cambium layer of young trees, usually resulting in death of the tree. In a mature western white pine stand, a cool fire will kill scattered trees, while only scarring others. However, the fire scars provide a vector for butt rots to enter the tree. Moderate to severe fire in a mature western white pine stand results in cambium damage and crowning, which usually results in the death of the tree. The large amount of humus in western white pine forests renders the trees susceptible to death from heating of the roots. After a stand-replacing fire, western white pine will seed in from adjacent areas. After a cool to moderate fire that leaves a mosaic of mineral soil and duff, western white pine will reoccupy the site from seed stored in the seed bank.

Pests and pathogens: The most serious damaging agent of western white pine is white pine blister rust (Cronartium ribicola). This rust was introduced into this country at the turn of the century from infected seedlings that had been imported from nurseries in France. White pine blister rust has a life cycle requiring alternate hosts for its completion: five-needled pines and currants (Ribes spp.). The rust produces spores on currants that infect white pines. These spores can be dispersed by wind up to 17 km. The spores germinate on the needles, and use the stomatal openings as a vector to the bole of the tree. This usually results in the death of the host tree. The most damaging root disease of western white pine is Armillaria spp., which causes fading foliage, growth reduction, dead and rotten roots, and black rhizomorphs, resulting in weakened or dead trees. Western white pine is susceptible to mountain pine beetle (Dendroctonus ponderosae) and emarginate ips (Ips emarginatus), and is the principal host for the ips beetle (Ips montanus).

Reproduction

Flowering and Fruiting - Western white pine is monoecious. Three complete growing seasons are required for seed to mature. The greenish-yellow to bright pink ovulate strobili are borne on stalks at tips of the upper branches. The erect conelets are from 1.5 cm to 4.0 cm long at time of pollen dissemination, and they grow to 2.5 cm to 5.0 cm long by the end of the first growing season. Oval staminate strobili are about 10 cm long, borne in clusters of 15 to 25 on branches of the middle crown.

Seed Production and Dissemination -Western white pines can begin cone production as early as age 7 and become more prolific with age. Cones of western white pine become ripe during August and September of the second year after the strobilus buds are initiated. Color of ripe cones ranges from yellowish or beige-brown through reddish brown and dark brown. Western white pine cones are about 20 cm to 25 cm long.

Seedling Development - Western white pine seed requires 30 to 120 days of cold, moist conditions before germination commences. Early root and shoot growth of western white pine seedlings usually is not rapid. During the first growing season, a high percentage of seedlings die, principally because of diseases, but insects, rodents, and birds cause serious seedling losses.

Vegetative Reproduction -Western white pine does not naturally reproduce by sprouting or layering.

Species Distribution

Citation

USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA. $131.95, hardcover; 1600 pages. ISBN-13: 978-0520253124.

Burke Museum of Natural History and Culture
Burke Museum. 2016 [Online]. University of Washington.
Photo credit: Clayton J. Antieau 2007

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97.
Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.