Western White Pine

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Western White Pine

Cones and foliage of Western White Pine

Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Pinaceae
Genus:	Pinus
Subgenus:	Strobus
Species:	P. monticola

Binomial name

Pinus monticola
Douglas ex D. Don

Western White Pine (Pinus monticola; family Pinaceae) is a species of pine that occurs in the mountains of the western United States and Canada, specifically the Sierra Nevada, the Cascade Range, the Coast Range, and the northern Rocky Mountains. The tree extends down to sea level in many areas, particularly in Oregon and Washington. It is the state tree of Idaho.

Mature trees growing in a mixed stand, some showing dieback due to Blister Rust

Western White Pine is a large tree, regularly growing to 30-50 m and exceptionally up to 70 m tall. It is a member of the white pine group, Pinus subgenus Strobus, and like all members of that group, the leaves ('needles') are in fascicles (bundles) of five, with a deciduous sheath. The needles are finely serrated, and 5-13 cm long. The cones are long and slender, 12-32 cm long and 3-4 cm broad (closed), opening to 5-8 cm broad; the scales are thin and flexible. The seeds are small, 4-7 mm long, and have a long slender wing 15-22 mm long.

It is related to Eastern White Pine (Pinus strobus), differing from it in having larger cones, slightly longer-lasting leaves (2-3 years, rather than 1.5-2 years) with more prominent stomatal bands, and a somewhat denser and narrower habit. The branches are borne in regular whorls, produced at the rate of one a year; this is pronounced in narrow, stand-grown trees, while open specimens may have a more rounded form with wide-reaching limbs. It is widely grown as an ornamental tree, but has been heavily logged throughout much of its range in the past.

Western white pine growing in Portland, Oregon

It has been seriously affected by the White Pine Blister Rust (Cronartium ribicola), a fungus that was accidentally introduced from Europe in 1909. The United States Forest Service estimates that 90% of the Western White Pines have been killed by the blister rust west of the Cascades. Large stands have been succeeded by other pines or non-pine species. The rust has also killed much of the Whitebark Pine outside of California.

Resistance to the blister rust is genetic, and due to Western White Pine's genetic variability some individuals are relatively unaffected by the rust. The US Forest Service has a program for locating and breeding rust-resistant Western White Pine and Sugar Pine (see external link below). Seedlings of these trees have been introduced into the wild.