Calocedrus decurrens, with the common names incense cedar and California incense cedar (syn. Libocedrus decurrens Torr.), is a species of conifer native to western North America, with the bulk of the range in the United States, from central western Oregon through most of California and the extreme west of Nevada, and also a short distance into northwest Mexico in northern Baja California. It grows at altitudes of 50–2900 m. It is the most widely known species in the genus, and is often simply called 'incense cedar' without the regional qualifier.
Calocedrus decurren is a large tree, typically reaching heights of 40–60 metres (130–200 ft) and a trunk diameter of up to 3 metres (9.8 ft). The largest known tree is 69 metres (226 ft) tall with 4.5 metres (15 ft) diameter trunk.) It has a broad conic crown of spreading branches. The bark is orange-brown weathering grayish, smooth at first, becoming fissured and exfoliating in long strips on the lower trunk on old trees.
The foliage is produced in flattened sprays with scale-like leaves 2–15 mm long; they are arranged in opposite decussate pairs, with the successive pairs closely then distantly spaced, so forming apparent whorls of four; the facial pairs are flat, with the lateral pairs folded over their bases. The leaves are bright green on both sides of the shoots with only inconspicuous stomata. The foliage, when crushed, gives off an aroma somewhat akin to shoe-polish.
The seed cones are 20–35 mm long, pale green to yellow, with four (rarely six) scales arranged in opposite decussate pairs; the outer pair of scales each bears two winged seeds, the inner pair(s) usually being sterile and fused together in a flat plate. The cones turn orange to yellow-brown when mature about 8 months after pollination. The pollen cones are 6–8 mm long.
This tree is the preferred host of a wood wasp, Syntexis libocedrii a living fossil species which lays its eggs in the smoldering wood immediately after a forest fire. The tree is also host to Incense-cedar mistletoe (Phoradendron libocedri), a parasitic plant which can often be found hanging from its branches.
The incense cedar is one of the most fire and drought tolerant plants in California. Although the tree is killed by hot, stand-replacing crown fire, it spreads rapidly after lower intensity burns. This has given the incense cedar a competitive advantage over other species such as the Bigcone Douglas-fir in recent years.
The wood is the primary material for wooden pencils, because it is soft and tends to sharpen easily without forming splinters.
Calocedrus decurrens is cultivated by plant nurseries as ornamental tree, for planting in gardens and parks.. It is used in traditional, drought tolerant, native plant, and wildlife gardens; and used in designed natural landscaping and habitat restoration projects in California. It is valued for its columnar form and evergreen foliage textures.
The tree is also grown in gardens and parks in cool summer climates, including the Pacific Northwest in the Northwestern United States and British Columbia, eastern Great Britain and continental Northern Europe. In these areas it can develop an especially narrow columnar crown, an unexplained consequence of the cooler climatic conditions that is rare in trees within its warm summer natural range in the California Floristic Province. Other cultivated species from the Cupressaceae family can have similar crown forms. This plant has gained the Royal Horticultural Society's Award of Garden Merit.
Incense cedar tree in McMinnville, Oregon
Incense cedar trunks in Lassen Volcanic National Park, California.
- Flora of North America: Calocedrus decurrens
- U.S. Forest Service Silvics Manual: Libocedrus decurrens
- Farjon, A. (2005). Monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew. ISBN 1-84246-068-4
- Gymnosperm Database: Calocedrus decurrens
- Jepson Manual Treatment: Phoradendron libocedri (Incense-cedar mistletoe)
- Franklin, Janet; Spears-Lebrun, Linnea A.; Deutschman, Douglas H.; Marsden, Kim. 2006. Impact of a high-intensity fire on mixed evergreen and mixed conifer forests in the Peninsular Ranges of southern California, USA. Forest Ecology and Management. 235(1-3): 18-29. 
- University of Michigan—Dearborn: Native American Ethnobotany of Calocedrus decurrens
- Chesnut, Victor King (1902). Plants used by the Indians of Mendocino County, California. Government Printing Office. p. 404. Retrieved 24 August 2012.
- Mitchell, A. F. (1996). Alan Mitchell's Trees of Britain. Collins ISBN 0-00-219972-6
- RHS Plant Selector Calocedrus decurrens AGM / RHS Gardening
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