Douglas-fir (Pseudotsuga menziesii)

Douglas fir
Pseudotsuga menziesii

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Douglas fir belongs to the genus Pseudotsuga (False hemlock) and is a member of the pine family (Pinaceae).

Douglas fir (Pseudotsuga menziesii) is a conifer species which, in the UK, has reached heights of over 60m and flowers April to May.

Lifespan: in its native range the oldest known Douglas fir is estimated to be 1400 years old.

 

Characteristics

On the young tree, the bark is grey-green with resin blisters that release a strong fragrance. With age, bark becomes purple-brown with horizontal cracks; when mature it is thick and corky with wide, pale-brown fissures. The bark is non-flammable to protect the tree from fires in its native range. Branches are whorled and ascending. The buds help in identification; they are red-brown, scaly and slender, tapering to a point (up to 7mm); they resemble beech tree buds.

Douglas fir foliage resembles that of silver firs (Abies spp.) Needles are solitary, flat, soft, slightly pointed (1–2.5cm) long; dark green above, below paler with two white bands. The foliage emits a sweet, fruity resinous scent. It hangs in dense, heavy, pendulous masses.

Douglas fir is monoecious: both male and female flowers are found on the same tree. Male flowers are pendulous, oval clusters of yellow stamens growing on the underside of last year’s shoots near the tip. Female flowers are upright tufts or brushes, green to pinkish red, growing at the tips of twigs. The tree is wind pollinated.

Female flowers ripen rapidly into cones which are 5–8cm, oval, slightly elongated and hang downward. Protruding from each scale on the cone is a distinctive three-pointed bract which is unique among conifers. The seeds are oval and fixed to an oval, brown, papery wing.

Douglas fir

 

Douglas fir cones

Douglas fir flowers

Distribution

A native of western North America, from British Columbia to California, this species was introduced to the UK in 1827 by Scottish botanist David Douglas. Its latin name Menziessi comes from another Scottish botanist Archibald Menzies who first discovered the species in 1791.

Widely planted for timber and ornament, it grows best in western parts of the UK with more humid conditions and higher rainfall. Douglas fir currently represents 3% of the total conifer area of the UK.

Human value

The timber has well-marked reddish-brown heartwood which contrasts with its paler creamy sapwood. This produces prominent annual rings which are a feature of cut wood.

Douglas fir is valued as one of the world’s finest coniferous timbers and is a species of great commercial importance. The timber works well and has good strength properties. It is moderately durable but not very permeable to preservatives. Modern uses include structural joinery such as beam work, veneers, furniture, cladding, decking and flooring.

In its native range Douglas fir has been known to reach heights of over 75m and is probably the second tallest species in the world after the Coastal redwood. With a warmer climate predicted for the UK this species could do well in the future.

A native American folk tale tells of how the Douglas fir cone comes to have its curious three-pointed bracts: the bracts are thought to be the tail and back legs of mice which hide inside the cones during a forest fire.

Douglas fir forest
Douglas fir cone

Wildlife value

The longevity of this species makes it able to provide a valuable source of dead wood habitat for cavity nesting birds and bats. The larger birds of prey, such as buzzards, sparrow hawks and hobbies, favour tall conifers for nesting sites and many will make use of Douglas fir trees where they are available.

The seeds of Douglas fir provide food for small mammals and finches. Moths such as the spruce carpet moth and dwarf pug also feed on Douglas fir.

Douglas fir forests in Scotland are known to support the red squirrel and the pine marten as well as numerous invertebrate species. The moist, warm microclimate in Douglas fir stands provides perfect conditions for many fungi and mosses.

Management

Douglas fir is an early pioneer species and moderately shade tolerant when young. It grows rapidly and casts a deep shade once fully grown. It grows well on deep, moist to moderately dry soils, neutral to acid of poor to rich fertility. It grows best in wetter, western parts of the UK.

Douglas fir is cold hardy but suffers from exposure. It can be damaged by late spring frosts and young trees can be prone to toppling so it needs sheltered sites.

Douglas fir is unsuited to calcareous soils and will not grow in competition with heather. It is very intolerant of flooding and water-logging and requires good soil aeration. It is also intolerant of pollution.

Seeds can be collected in September and are best pre-treated to simulate cold conditions and sown in late March or early April when the ground is warmer. When sourcing seed provenances from coastal Washington are thought to offer the best climate tolerance and growth rate for western parts of the UK, while seed from inland Washington is most suitable for the drier parts of eastern Britain. Seed is available from UK registered stands.

Douglas fir can be vulnerable to infection by Phytophthora ramorum when located close to infected plants or trees. It can be susceptible to root rot (Heterobasidion) and the fungal disease Swiss needle cast (Phaeocryptopus gaeumannii).

Douglas fir logs

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Photographs © Forestry Commission.