Tree Profiles: Douglas-fir (Pseudotsuga menziesii), Part 1
This is the first of a two part series on Douglas-fir. The following examines the tree’s habitat, developmental traits, longevity, height, bark, needles, and cones.
Douglas-fir (Pseudotsuga menziesii) , also referred to as Douglas fir, Doug-fir, Douglas tree, Douglas pine, Douglas spruce, Oregon pine, Pino Oregon, red fir, and yellow fir, is an evergreen conifer species. Throughout its history, the tree has been designated a pine, spruce, hemlock, and true fir. In 1867, Douglas-fir was assigned its own genus, Pseudotsuga, which translates to false hemlock.
Douglas-fir was first documented in 1791 by Archibald Menzies, a Scottish physician and naturalist, who discovered it on Vancouver Island. The latin name menziesii is a reference to Menzies. The tree species became popular in 1826 when it was introduced to cultivation by Scottish botanist and explorer David Douglas. It is now considered one of the world’s most important trees.
Distribution & Habitat
Douglas-fir is native to North America and eastern Asia. In North America, the range of Douglas-fir extends from central British Columbia to the Pacific Coast Ranges, east to the Rocky Mountains, and south into Central Mexico. The coast Douglas-fir variety is the dominant tree from British Columbia to central California. Its range continues to the Pacific Coast Ranges, and the Pacific Ocean. In California, coast Douglas-fir may be found from the Klamath and California Coast Ranges to the Santa Lucia Range. Outliers have been reported in the Purishima Hills in Santa Barbara County. Across the Sierra Nevada, Coast Douglas-fir is common in the Yosimete region.
Further east, coast Douglas-fir is displaced by another variety: Rocky Mountain Douglas-fir. The two varieties intermingle from British Columbia to northern Washington, and southeast to Mexico. A third variety, Mexican Douglas-fir, has been reported down to Oaxaca. Douglas-fir has been naturalized throughout Europe, New Zealand, Argentina, and Chile. Throughout its range, Douglas-fir is associated with numerous trees, including bigleaf maple, California incense-cedar, coast redwood, grand fir, Lawson’s cypress, ponderosa pine, Sitka spruce, sugar pine, tan oak, western hemlock, western red cedar, and western white pine.
Douglas-fir grows at a medium rate, increasing in size by 13 to 24 inches each year. It thrives most when exposed to full sun or partial shade. It requires a minimum of four hours of direct sunlight each day for optimal growth. The tree has a pyramidal shape. Its branches are typically spreading to drooping. Douglas-fir can take root under a variety of climatic conditions. On drier sites, Douglas-fir will generate deep taproots. The coast Douglas-fir variety prefers moist, mild climates. It develops at a faster rate than Rocky Mountain Douglas-fir. The Rocky Mountain variety is hardier than its coastal counterpart, but it takes longer to mature, and has a shorter lifespan. On both varieties, the wood is straight-grained and moderately hard. The sapwood is typically colored white to pale yellow, while the heartwood has an orange-red coloration. When infected by Poria weirii, Douglas-fir manufactures a flavanone called Poriol.
Douglas-fir has one of the longest life spans of any tree species. Healthy, mature trees can live up to a thousand years old.
Douglas-fir is a medium to large evergreen tree. The coastal variety can reach heights of 70 to 330 feet, with a spread of 12 to 20 feet. The Rocky Mountain variety is smaller, seldom exceeding 130 feet in height.
When young, Douglas-fir has a smooth bark surface. As the tree matures, its bark thickens, and turns dark brown. Ridges form on the bark surface, causing it to develop a rougher texture.
Douglas-fir forms needles, which are soft and spiral. The needles resemble those of fir trees. They grow in a simple formation, and are notable for their durability. Individual needles may typically grow 2 to 4 cm long. The coloration of the needles is determined by the variety. Coast Douglas-fir generally produces dark yellow-green needles. Occasionally, coast Douglas-fir may have dark green to blue-green needles. Rocky Mountain Douglas-fir usually has dark green to blue-green needles, though outliers featuring yellow-green needles have been reported. When crushed, the needles exude a sweet fragrance.
Douglas-fir is a monoecious tree. Both male and female strobili, or cones, form on individual trees. The cones hang downward from the tree’s branches. Cone production begins when trees are between 12 and 15 years old. Young cones are small, and oval-shaped. As the cones mature, they become more pendulous, and laden with scales. Distinctive three-point bracts protrude from above each scale. The cones range in color from reddish-brown to gray. By the time they have fully developed, the cones may reach 3 to 4 inches in diameter. In late summer, the cones open to release seeds. Instead of dissipating, the cones will cling to the trees until late fall or early winter.
Photo courtesy of RVwithTito CC-by-2.0