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Douglas-fir
Pseudotsuga glauca forest.jpg
Rocky Mountain Douglas-fir forest in Pike National Forest, Colorado (United States).
Conservation status
Scientific classification
Genus:
Pseudotsuga
Species:
menziesii
Pseudotsuga menziesii levila.png
     Green: Coast Douglas-fir (Pseudotsuga menziesii var. menziesii)

     Blue: Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca)

Synonyms
  • Abies menziesii Mirb.
  • Abies mucronata Raf.
  • Abies taxifolia Poir.
  • Pinus douglasii Sabine ex D. Don
  • Pinus taxifolia Lamb.
  • Pseudotsuga douglasii (Sabine ex D. Don) Carrière
  • Pseudotsuga mucronata (Raf.) Sudw.
  • Pseudotsuga taxifolia Britton
  • Pseudotsuga taxifolia var. viridis ined.

The Douglas fir (Pseudotsuga menziesii) is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three varieties: coast Douglas-fir (P. menziesii var. menziesii), Rocky Mountain Douglas-fir (P. menziesii var. glauca) and Mexican Douglas fir (P. menziesii var. lindleyana).

Despite its common names, it is not a true fir (genus Abies), spruce (genus Picea), or pine (genus Pinus). It is also not a hemlock; the genus name of "Pseudotsuga" means "false hemlock."

The massive mega-genome of Douglas fir was sequenced in 2017 by the large PineRefSeq consortium, revealing a specialized photosynthetic apparatus in the light-harvesting complex genes.

Naming

The common name honors David Douglas, a Scottish botanist and collector who first reported the extraordinary nature and potential of the species. The common name is misleading since it is not a true fir, i.e., not a member of the genus Abies. For this reason the name is often written as Douglas-fir (a name also used for the genus Pseudotsuga as a whole).

The specific epithet menziesii is after Archibald Menzies, a Scottish physician and rival naturalist to David Douglas. Menzies first documented the tree on Vancouver Island in 1791. Colloquially, the species is also known simply as Doug fir or Douglas pine (although the latter common name may also refer to Pinus douglasiana). Other names for this tree have included Oregon pine, British Columbian pine, Puget Sound pine, Douglas spruce, false hemlock, red fir, or red pine (although again red pine may refer to a different tree species—Pinus resinosa and red fir may refer to Abies magnifica).

One Coast Salish name for the tree, used in the Halkomelem language, is lá:yelhp. In the Lushootseed language, the tree is called čəbidac.

Description

Douglas-firs are medium-size to extremely large evergreen trees, 20–100 metres (70–330 ft) tall (although only coast Douglas-firs reach such great heights) and up to 8 ft (2.4 m) in diameter. The leaves are flat, soft, linear, 2–4 centimetres (341 12 in) long, generally resembling those of the firs, occurring singly rather than in fascicles; they completely encircle the branches, which can be useful in recognizing the species. As the trees grow taller in denser forest, they lose their lower branches, such that the foliage may start as high as 110 ft (34 m) off the ground. Douglas-firs in environments with more light may have branches much closer to the ground.

Douglas fir cone
Douglas-fir female cone

The female cones are pendulous, with persistent scales, unlike those of true firs. They are distinctive in having a long tridentine (three-pointed) bract that protrudes prominently above each scale (it resembles the back half of a mouse, with two feet and a tail).

Distribution

Pseudotsuga menziesii var. menziesii, the coast Douglas-fir, grows in the coastal regions from west-central British Columbia southward to central California. In Oregon and Washington, its range is continuous from the eastern edge of the Cascades west to the Pacific Coast Ranges and Pacific Ocean. In California, it is found in the Klamath and California Coast Ranges as far south as the Santa Lucia Range, with a small stand as far south as the Purisima Hills in Santa Barbara County. One of the last remaining old growth stands of conifers is in the Mattole Watershed, and is under threat of logging. In the Sierra Nevada, it ranges as far south as the Yosemite region. It occurs from near sea level along the coast to 1,800 m (5,900 ft) above sea level in the mountains of California.

Another variety exists further inland, Pseudotsuga menziesii var. glauca, the Rocky Mountain Douglas-fir or interior Douglas-fir. Interior Douglas-fir intergrades with coast Douglas-fir in the Cascades of northern Washington and southern British Columbia, and from there ranges northward to central British Columbia and southeastward to the Mexican border, becoming increasingly disjunct as latitude decreases and altitude increases. Mexican Douglas-fir (P. lindleyana), which ranges as far south as Oaxaca, is often considered a variety of P. menziesii.

Fossils (wood, pollen) of Pseudotsuga are recorded from the Miocene and Pliocene of Europe (Siebengebirge, Gleiwitz, Austria).

Ecology

Douglas-fir prefers acidic or neutral soils. However, it exhibits considerable morphological plasticity, and on drier sites P. menziesii var. menziesii will generate deeper taproots. Pseudotsuga menziesii var. glauca exhibits even greater plasticity, occurring in stands of interior temperate rainforest in British Columbia, as well as at the edge of semi-arid sagebrush steppe throughout much of its range, where it generates even deeper taproots than coast Douglas-fir is capable.

Pseudotsuga menziesii 01221
A snag provides nest cavities for birds

Mature or "old-growth" Douglas-fir forest is the primary habitat of the red tree vole (Arborimus longicaudus) and the spotted owl (Strix occidentalis). Home range requirements for breeding pairs of spotted owls are at least 400 ha (4 square kilometres, 990 acres) of old growth. Red tree voles may also be found in immature forests if Douglas-fir is a significant component. The red vole nests almost exclusively in the foliage of the trees, typically 2–50 metres (5–165 ft) above the ground, and its diet consists chiefly of Douglas-fir needles. A parasitic plant sometimes utilizing P. menziesii is Douglas-fir dwarf mistletoe (Arceuthobium douglasii).

The leaves are also used by the woolly conifer aphid Adelges cooleyi; this 0.5 mm long sap-sucking insect is conspicuous on the undersides of the leaves by the small white "fluff spots" of protective wax that it produces. It is often present in large numbers, and can cause the foliage to turn yellowish from the damage it causes. Exceptionally, trees may be partially defoliated by it, but the damage is rarely this severe. Among Lepidoptera, apart from some that feed on Pseudotsuga in general (see there) the gelechiid moths Chionodes abella and C. periculella as well as the cone scale-eating tortrix moth Cydia illutana have been recorded specifically on P. menziesii.

Pseudotsuga menziesii 7971
Mature individual in the Wenatchee Mountains

The coast Douglas-fir variety is the dominant tree west of the Cascade Mountains in the Pacific Northwest, occurring in nearly all forest types, competes well on most parent materials, aspects, and slopes. Adapted to a moist, mild climate, it grows larger and faster than Rocky Mountain Douglas-fir. Associated trees include western hemlock, Sitka spruce, sugar pine, western white pine, ponderosa pine, grand fir, coast redwood, western redcedar, California incense-cedar, Lawson's cypress, tanoak, bigleaf maple and several others. Pure stands are also common, particularly north of the Umpqua River in Oregon.

Poriol is a flavanone, a type of flavonoid, produced by P. menziesii in reaction to infection by Poria weirii.

Uses

The species is extensively used in forestry management as a plantation tree for softwood timber.

The timber is used for timber frame construction/joinery, veneer, flooring and construction due to its strength, hardness and durability. It is also naturalised throughout Europe, Argentina and Chile (called Pino Oregón). In New Zealand it is considered to be an invasive species, called a wilding conifer, and subject to control measures.

Douglas fir is an abundant West coast species that sees wide use in heavy timber structures. This species is strong, available in a number of specifications including kiln dried and grade stamped, and can be supplied in very long lengths to 60 feet. West coast mills are sophisticated in their processing of timbers making lead times predictable and availability reliable. Paints adhere well to Douglas fir. Stains perform well on Douglas fir timbers with the mild caution that the natural color of this species varies and care must be taken to insure uniformity of color. Pitch pockets that may ooze resin can be present in timbers that have not been kiln dried. Because of the timber sizes available, stamped timber grading, and relatively short lead times, Douglas fir sees wide use in both public and residential projects.

The species has ornamental value in large parks and gardens.

The buds have been used to flavor eau de vie, a clear, colorless fruit brandy.

Native Hawaiians built waʻa kaulua (double-hulled canoes) from coast Douglas-fir logs that had drifted ashore.

Douglas-fir has been commonly used as a Christmas tree since the 1920s, and the trees are typically grown on plantations.

Douglas-fir pine leaves can be used to make pine-needle tea. They possess a tangy citrus flavor and may serve in some recipes as a wild substitute for rosemary.

Many different Native American groups used the bark, resin, and pine needles to make herbal treatments for various diseases.

As of 2012, the only wooden ships still currently in use by the United States Navy are Avenger-class minesweepers, made of Douglas-fir.

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