Western redcedar (Thuja plicata): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table.

At a glance

Item	What the source records
Scientific name	Thuja plicata Donn ex D. Don, cypress family (Silvics)
Other names	Pacific redcedar, giant-cedar, arborvitae, canoe-cedar and shinglewood (Silvics); giant arborvitae and shinglewood (Wood Handbook)
Native status, USDA PLANTS	Native in Alaska, in Canada and in the lower 48 states
Age and size, Silvics	Often reaches 800 to 1,000 years. One large Washington tree is 592 cm (233 in) across, 54.3 m (178 ft) tall, with a crown 16.5 m (54 ft) wide
Green weight of the wood, NRS-38	27 lb per cubic foot, without bark

Native range

The Silvics of North America handbook (Agriculture Handbook 654, Volume 1, 1990) calls western redcedar the only Thuja species native to western North America. It grows along the Pacific coast from Humboldt County, California, to Sumner Strait in southeastern Alaska, on its northern and western shores. In California the handbook says it is common only in the lower Mad River drainage and in the wet area south of Ferndale. North of the California-Oregon border the coastal range includes the western slopes of the Cascades north of Crater Lake and, on the east side, the slopes north of roughly latitude 44 degrees 30 minutes north. The interior range runs from the western slope of the Continental Divide in British Columbia across the Selkirk Mountains to western Montana and northern Idaho, with the southern limit in Ravalli County, Montana. The handbook says optimal growth is near the latitudinal center of the range, on Washington's Olympic Peninsula, and that the coastal and interior ranges are essentially isolated from each other.

It puts extant redcedar volume at 824 million cubic meters (29 billion cubic feet) in British Columbia and 228 million cubic meters (8 billion cubic feet) in the United States. Elevation reaches from sea level to 910 m (3,000 ft) in southeastern Alaska and to 2,290 m (7,500 ft) at the rim of Crater Lake in Oregon. The tree tolerates a wide range of soils, is abundant in many forested swamps and, the handbook notes, grows in England on loams, clays, sands and chalk downland. It is a major component of two forest cover types, Western Redcedar and Western Redcedar-Western Hemlock.

Cones, seed and layering

Silvics says open-grown trees begin to produce strobili at 10 years and usually every other year after. The species is monoecious, with reddish male strobili on lower branches and green female strobili nearer the treetops. Pollination comes in March and April in southern coastal stands and May and June in coastal Alaska and the interior. Each mature strobilus usually yields only 3 to 6 seeds, but heavy seed crops are common, and major seedfall comes in October and November. The handbook records annual seed crops of 247,000 to 2,470,000 seeds per hectare in coastal forests and 54,000 to 274,000 in the interior. It says mineral soil that has been disturbed seems a major requirement for regeneration from seed and that rotten wood in contact with soil is the preferred seedbed in old redcedar groves. It also describes three kinds of natural vegetative reproduction: layering, rooting of fallen branches and branch development on fallen trees, which it says are more abundant than seedlings in mature Idaho stands.

Shade, roots and growth

The handbook says western redcedar is outranked for shade tolerance only by Pacific silver fir, western hemlock and Pacific yew, and that it is usually considered a climax or near-climax species though present in all stages of succession. Roots are extensive: in a mixed northern Idaho stand redcedar made up 17 percent of the basal area but 82 percent of the root length. Taproots are poorly defined or absent, fine roots form a dense network, and root grafting is common. Silvics says suppressed redcedars 200 years old but only 7.6 cm (3 in) in diameter and 7.6 m (25 ft) tall are not unusual, and it ties that survival possibly to the ability to produce new root growth in full shade and to root grafting.

Wood

The Wood Handbook (FPL-GTR-282, 2021) says the heartwood is reddish or pinkish brown to dull brown, the sapwood is nearly white and often not more than 3 cm (1 in) wide, and the wood is generally straight grained with a uniform but rather coarse texture and very low shrinkage. It calls the wood lightweight, moderately soft, low in strength as a beam or post and low in shock resistance, with heartwood very resistant to decay. It lists shingles, lumber, poles, posts and piles as principal uses and says Washington leads in lumber production, followed by Oregon, Idaho and Montana. Silvics calls shingles and shakes the most important special use, and also names utility poles, fence posts, pilings, pulp, clothes closets and chests, caskets, crates, boxes and beehives, with perfumes, insecticides and soaps made from leaf oil.

Wood Handbook figure	Green	At 12% moisture content
Specific gravity (Table 5-3b)	0.31	0.32
Modulus of rupture, lbf per square inch (Table 5-3b)	5,200	7,500
Side hardness, lbf (Table 5-3b)	260	350

The green weight is in the NRS-38 table, the same figure used in the log weight calculator.

Damaging agents the handbook names

Silvics says western redcedar resists most damaging agents better than the trees it grows with, but because it lives longer, damaged trees are common.

Wind and fire. Redcedars are as windfirm as Douglas-fir on dry sites but often windthrown in wet environments, including the moist sites where growth is highest. Along the coast the species is more severely damaged by fire than any of its associates.
Insects. The handbook says the tree suffers little insect damage. It names a gall midge that sometimes seriously damages seeds, a weevil that occasionally damages newly planted seedlings in British Columbia, a bark beetle that kills larger trees on poor sites in southeastern Alaska, and the western cedar borer, which causes degrade and cull in sawtimber.
Fungi. More than 200 fungi are found on western redcedar, though it is less susceptible than most associates. The handbook says living western redcedars in British Columbia carry a larger accumulated volume of decay than any other major conifer there, and hollow old trees are common in the interior. It names root and butt rots and trunk rots as the most important fungal attacks in North America, and a leaf blight, Didymascella thujina, as the major seedling disease.
Browsing and pollution. Deer, elk or rodents often browse seedlings and saplings severely, which the handbook says may be the most important stand-establishment problem. Salt spray damages redcedar more than Sitka spruce.

For who takes reports of regulated pests, see reporting a pest in the United States, and pests and diseases by country sets out which ones agencies regulate.