Thuja plicata

Western redcedar


The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Cupressaceae (cypress). Genus - Thuja L. Species -Thuja plicata Donn ex D. Don

Ecology: Western redcedar is very shade tolerant. It is one of the most shade tolerant species growing in cedar-hemlock ecosystems of the northern Rocky Mountains. It is usually considered a climax or near climax species, but it can be found in all stages of forest succession. It invades disturbed areas as widely distributed seeds but regenerates vegetatively in undisturbed areas, tolerating competition in both. Moisture and soil conditions strongly influence the successional status of western redcedar.


Trees to 50(--75) m, sometimes stunted in harsh environments; trunk to 2(--5) m diam., often buttressed at base; crown conical. Bark reddish brown or grayish brown, 10--25 mm thick, fibrous, fissured. Branches arching, branchlets pendent. Leaves of branchlets (1--)3--6 mm (sprays sometimes bearing only very small leaves), apex acute, with white markings on abaxial surface when fresh, glossy green on adaxial surface of branchlets. Pollen cones 1--3 mm, reddish. Seed cones ellipsoid, 10--14 mm, brown; fertile scales 2--3 pairs, each with evident, nearly terminal, deltate projection. Seeds 8--14 per cone, 4--7.5 mm (including wings), reddish brown.


In the WFDP: Pathogens affecting western redcedar in the WFDP include: laminated root rot (Phellinus weirii) and Armillaria root rot (aka Honey fungus; Armillaria spp.).

Fire effects: Western redcedar fire resistance is low to moderate. Its thin bark, shallow root system, low dense branching habit, and highly flammable foliage make it susceptible to fire damage. Western redcedar is commonly killed by fire. Because of their large size, however, old western redcedar trees can often survive if they are not completely girdled by fire. Shallow roots under the duff layer are often scorched when the duff layer burns and even surface fires may kill western redcedar. Fire injury to roots can lead to fungal infection, chronic stress, and growth losses. The most common causes of fire mortality are root charring and crown scorching.


Flowering and Fruiting - The species is monoecious; male and female strobili are produced on different branches of the same tree, at different heights-the reddish male strobili on lower branches and the green female strobili nearer the treetops and farther from the trunk. When grown in the open, western redcedars begin to produce strobili at 10 years of age and usually every other year thereafter.

Seed Production and Dissemination - Each mature strobilus usually produces only 3 to 6 seeds, but the strobili are often numerous and heavy seed crops are common. Seeds are small; they fall faster and do not fly as far as the seeds of western hemlock, Sitka spruce, and Douglas-fir, but dissemination is adequate within 100 m of a seed source. The seeds usually germinate well without stratification, and they retain their initial viability for at least 7 years when stored dry.

Seedling Development - Most seeds escape rodent and bird predation, but seedling mortality is high during the germination period. Western redcedar seedlings are less tolerant of high soil temperature and of frost than are the seedlings of Engelmann spruce, grand fir, and Douglas-fir. The exposed upper foliage of young redcedars often sunburns severely.

Vegetative Reproduction - Three types of natural vegetative reproduction occur: layering, rooting of fallen branches, and branch development on fallen trees. The resulting "veglings" are more abundant than seedlings in mature Idaho stands. Saplings that have been knocked down in the western Cascades often regenerate when their branches root.

Species Distribution


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.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

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.