Plant 170

Calocedrus decurrens (Torr.) Florin (Cupressaceae)



In 1869, the Scottish-American advocate for the preservation of wilderness, John Muir, was passionate in his description of incense cedars in their native range: 'the cinnamon-colored boles of the old trees are without limbs as they make striking pillars in the woods where the sun chances to shine on them - a worthy companion to the kingly sugar and yellow pines'.

Calocedrus decurrens had been discovered by the North American soldier and politician John Frémont in California in 1846. It was introduced to Britain seven years later by the Scottish botanist and plant collector John Jeffrey for the Oregon Association of Edinburgh. The Association, formed in 1849 by a group of Scottish horticulturalists, was interested in continuing David Douglas's botanical exploration of Western North America.

Incense cedar is a characteristic tree of the dry conifer forests found across the mountains of California and Oregon. Like several other conifer species, its wood is fragrant, resistant to decay and weathering. Consequently, it is popular for outdoor uses including shingles and fence posts. Eventually replaced by tropical hardwoods, incense cedar itself superseded eastern red cedar (Juniperus virginiana) as the North American domestic source of pencil wood.

In the wild, incense cedar attains heights of more than 45 metres, with trunk diameters of more the two metres; both single- and multi-stemmed individuals are found. The bark is a rich reddish-brown, thick and fibrous with long, deeply furrowed, interlacing ridges. Female cones, which are held erect on the branches, are up to two centimetres long. Across its range, incense cedar tolerates hot, dry sites with poor soils, growing in conditions more typical of Cupressus or Juniperus. However, the largest specimens of incense cedar are found on sunny, well-watered sites, such as riparian areas in canyons or near subalpine lakeshores.

In the United Kingdom, however, all specimens consistently display a stiff columnar or narrowly pyramidal habit. The uniformly-green foliage of incense cedar is easily distinguished from that of other conifers; it is set vertically rather than horizontally, which allows both sides of each leaf equal exposure to light. Several young, wild-collected specimens of incense cedar grow at Harcourt Arboretum; with historic specimens, that form part of the Arboreum's historic landscape continuing to thrive. The specimen situated on the edge of Education Glade is probably one of the original introductions to Britain from California. In 1983 it was 31 metres tall, its trunk was 3.7 metres in circumference.

Further reading

Farjon A 2005. A monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew


Ben Jones