|Coast Douglas firs in Marysville, Washington|
Pseudotsuga menziesii is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is known as Douglas fir,  Douglas-fir,  Oregon pine,  and Columbian pine.  There are two varieties: coast Douglas-fir (P. menziesii var. menziesii), and Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca). 
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 the latter may refer to a different tree species— Pinus resinosa). 
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).  The leaves are flat, soft, linear, 2–4 centimetres (3⁄4–1 1⁄2 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 high off the ground. Douglas-firs in environments with more light may have branches much closer to the ground.
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).
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.   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.
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.
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.
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.
The species is extensively used in forestry as a plantation tree for softwood timber. The timber is used for joinery, veneer, flooring and construction due to its strength, hardness and durability.  It is also naturalised throughout Europe,  Argentina and Chile (called Pino Oregón), and in New Zealand sometimes to the extent of becoming an invasive species (termed a wilding conifer) subject to control measures.
The species has ornamental value in large parks and gardens. 
Douglas fir pine leaves can be used to make pine-needle tea.
Many different Native American groups used the bark, resin, and pine needles to make herbal treatments for various diseases. 
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This was the preferred species for Hawaiian war canoes. The Hawaiians, of course, did not log the trees; they had to rely on driftwood.
- "Douglas-Fir". National Christmas Tree Association.
- Emily K. Brock, Money Trees: The Douglas-Fir and American Forestry, 1900–1944. Corvallis, OR: Oregon State University Press, 2015.
- Uchytil, Ronald J. (1991). "Pseudotsuga menziesii var. menziesii". Fire Effects Information System (FEIS). US Department of Agriculture (USDA), Forest Service (USFS), Rocky Mountain Research Station, Fire Sciences Laboratory – via https://www.feis-crs.org/feis/.
- Conifers.org: Pseudotsuga menziesii
- Arboretum de Villardebelle – cone photos
- Humboldt State University — Photo Tour: Douglas-fir, Pseudotsuga menziesii — Institute for Redwood Ecology
- Pseudotsuga menziesii - information, genetic conservation units and related resources. European Forest Genetic Resources Programme (EUFORGEN)