Calocedrus decurrens

The incense cedar, known scientifically as Calocedrus decurrens, is a large coniferous tree. It is native to western North America and belongs to the Cupressaceae family. This tree is a vital part of its ecosystem because it provides food and shelter for many species. It is also highly valued by humans for its unique wood and aromatic properties. In its natural habitat, it can reach massive sizes and live for more than 500 years.

The physical structure of the incense cedar is quite distinct. It typically grows into a large tree with a broad, conic crown. This means the branches spread out in a shape similar to a cone. The bark starts out smooth and orange-brown when the tree is young. As the tree ages, the bark becomes grayish and begins to peel off in long strips. This process is called exfoliating. On very old trees, the lower trunk becomes deeply fissured, or split into grooves.

The foliage of the incense cedar consists of small, scale-like leaves. These leaves are arranged in flattened sprays. They grow in opposite decussate pairs, which means each pair is at a right angle to the one below it. This arrangement creates the appearance of whorls, or circular patterns, of four leaves. The leaves are bright green on both sides. If you crush the foliage, it releases a scent that smells similar to shoe polish. The seed cones are long and transition from pale green to yellow as they mature. They take about eight months to reach maturity after pollination.

This tree has developed remarkable ways to survive harsh environments. It possesses thick basal bark, which helps it resist drought and fire. While a very hot, stand-replacing crown fire can kill the tree, it can spread rapidly after lower-intensity burns. This ability gives it a competitive advantage over species like the bigcone Douglas-fir. The incense cedar is also shade tolerant, though not as much as grand or white fir. It often grows slowly to ensure it can outlast its competition for resources.

Many different organisms interact with the incense cedar in the wild. For example, the wood wasp, Syntexis libocedrii, uses the tree as a host. This wasp lays its eggs in smoldering wood immediately after a forest fire. The tree also hosts a parasitic plant called incense-cedar mistletoe, which hangs from its branches. Other organisms, like the fungus Tyromyces amarus, enter the tree through fire scars. While the tree can suffer from Gymnosporangium rust disease, this condition is rarely fatal. During the winter, many bird species use the tree as a foraging substrate to find food.

Human history is closely tied to the use of this tree. Native Americans in California used the plant for many traditional purposes. They used it for medicine, basket making, hunting bows, and building materials. One Northern California tribe even used branchlets to filter sand from water when leaching toxins from acorn meal. The wood itself is soft, light, and resistant to rot. Because it sharpens easily without splintering, it was once the primary material used to make wooden pencils. Today, the wood is used for house siding, interior paneling, and moth-resistant chests.

In modern times, the incense cedar is often grown as an ornamental tree in gardens and parks. It is used in habitat restoration projects and xeriscapic gardens, which are designed to save water. Interestingly, the tree's shape changes depending on where it is planted. In its native California, it has a broad shape. However, in cooler climates like Great Britain or Northern Europe, it can develop a very narrow, columnar crown. Scientists are still looking for the exact reason why these cooler temperatures cause such a change in its growth pattern.