Scientific name: Thuja plicata Donn ex D. Don in Lambert 1824

Synonyms: Libocedrus craigiana H.Low ex Gordon, Libocedrus gigantea H.Low ex Gordon, Thuja asplenifolia Carrière, Thuja californica K.Koch, Thuja douglasii Nutt. ex Parl., Thuja flabellata Beissn., Thuja gigantea Nutt., Thuja lobbiana Gordon, Thuja lobbii Gordon, Thuja lycopodioides Beissn., Thuja menziesii Douglas ex Endl., Thuja plicatilis Beissn., Thuja wareana Lodd. ex Loudon

Common names: Western red-cedar, Canoe cedar, Giant arbor-vitae, Giant cedar, Pacific red-cedar, Shinglewood

Description

Tree to 75 m tall under favorable conditions but not more than 50 m in most of its range and occasionally stunted on extreme sites, with trunk to 5(-7) m in diameter. Bark furrowed, fibrous, reddish brown or grayish brown. Crown rigidly conical in youth, becoming irregular with numerous short branches rising from the trunk, the tips hanging in long festoons with age. Scale leaves mostly 1-3 mm long, dark green on the upper side of the sprays, with whitish green stomatal markings beneath. Facial leaves not evidently glandular. Leaves of main branchlets to 6 mm, with long tips pressed against the twigs. Pollen cones 1-3 mm long, with four to nine pairs of pollen scales, reddish brown. Seed cones 10-18 mm long, with five or six pairs of scales of which the middle two or three are fertile, each scale with a distinct spiny point below the tip. Seeds one or two per scale, 4-7.5 mm long, including the slightly longer wings, each wing about as wide as the body. The species name refers to the folding of the lateral scale leaves around the base of the facial ones.

Western North America from southern Alaska to northern California and in the Rocky Mountains from central Alberta and British Columbia to central Idaho. Mixed coastal and montane conifer forests, usually on soils that remain moist throughout the growing season; 0-1,500(-2,000) m.

Conservation Status

Red List Category & Criteria: Least Concern

Despite extensive logging, the extensive range and abundance of Thuja plicata makes it ineligible for any threatened category and it is therefore assessed as Least Concern.

The two more or less disjunct areas in which this species occurs: Pacific coastal mountains and Rocky Mountains, experience a different climate and therefore sustain different forest types. The mostly much wetter (winter rainfall, up to 6,600 mm p.a.) and milder coastal ranges support the tallest conifer forests in the world, with Sequoia sempervirens in the southern part exceeding 110 m and with Abies grandis to 80 m, Abies procera 85 m, Picea sitchensis 87 m, Pinus lambertiana 75 m, Pseudotsuga menziesii 100 m, and Tsuga heterophylla to 80 m tall. Many of these trees also exceed any of their congeners elsewhere in overall size (Van Pelt 2001). Thuja plicata, with max. 75 m, is one of the longest-lived in these forests, with veteran trees often in excess of 1,000 years. Other conifers in these coastal forests are Chamaecyparis lawsoniana (extreme southern part of range), Xanthocyparis nootkatensis, Calocedrus decurrens, Abies amabilis, Pinus monticola, Tsuga mertensiana, and Taxus brevifolia in the understorey. Common angiosperm trees are Acer macrophyllum, Alnus rubra along rivers, and Populus trichocarpa; in the shrub layer are especially abundant Vaccinium spp., Rubus spectabilis and Ribes bracteosum. Deep layers of mosses and liverworts cover the forest floor and lower sections of tree trunks as well as fallen logs, on which latter most conifers find the only substrate to germinate. In the interior Abies grandis, Abies lasiocarpa, Larix occidentalis, Picea engelmannii, Picea glauca, Pinus contorta, Pinus ponderosa, Pseudotsuga menziesii var. glauca, and Taxus brevifolia are the most commonly associated conifers. Here annual precipitation does not exceed 1,200 mm and winters are much colder than along the coast.

This species is common especially in the coastal sections of its extensive range and somewhat less so in the interior parts. (Selective) logging of mature trees and 'old growth' forest in which this species is a codominant continues in many areas where the forest is not on protected land. In situations where secondary forest growth is managed to favour other species (e.g. Pseudotsuga menziesii), this would lead to a decrease of occupancy of Thuja plicata. Plantation forestry focusing on this species should eventually reduce the level of exploitation of natural stands, in particular in 'old growth' forest with its high ecological value. At present this species is not considered to be in danger of extinction.

The wood of this species provided the main building material for the Amerindian tribes along the Pacific coast, who developed a technique to split large planks from the lower boles of big trees without destroying the trees themselves. Nowadays, its main use is for making shingles used in roofing residential buildings; as in most Cupressaceae, the wood is decay-resistant and easy to work. For large construction purposes it is less suitable as it tends to split, but it can be used for a variety of smaller utilities from garden sheds, glass houses, and furniture to tools. Western Red-cedar has been used in forestry plantations in some countries in NW Europe on a rather limited scale; it requires high rainfall and performs best in the wetter parts of the British Isles. Thuja plicata has been widely planted as an ornamental tree in parks and large gardens. It is also suitable for hedges as it grows back quickly from clipping. Fewer cultivars are known from this species than from Thuja occidentalis, but it is nevertheless of substantial importance in the horticultural trade.

This species is present in many protected areas, including some famous National Parks in both Canada and the USA.

References

Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland