distributed North American tree. In 1867 a French horticulturist named Carrière proposed putting these geographically dispersed but somewhat similar trees into a new genus, Pseudotsuga. By the latter 1800s most taxonomists accepted the new genus name, despite vigorous opposition from a few. One called it “a barbarous combination of the Greek word pseudo = false with the Japanese word tsuga = hemlock.” Another wrote, “One would expect that Pseudotsuga would resemble Tsuga most of all conifers, but Douglas-fir does resemble this genus least of all.” The choice of Pseudotsuga (“false hemlock”) as the new genus name was indeed puzzling, but the buds, needles, and number of chromosomes of this unusual tree kept it from being placed within existing genera such as pine (Pinus), spruce (Picea), or fir (Abies).
Despite acceptance of the genus name Pseudotsuga, attempts to find a suitable species name for this tree remained elusive. Finally, in 1950, Portuguese botanist J. A. F. Franco proposed the currently accepted scientific name for western North America’s common Douglas-fir: Pseudotsuga menziesii (Mirb.) Franco, honoring Archibald Menzies. (The last name, Franco, identifies the person credited with authorship of the scientific name.) It may seem odd that a taxonomist from Portugal would break the impasse in naming an iconic American tree, but his successful effort is less of a fluke than it might seem. Franco was a distinguished European botanist, credited with authoring the name of 193 plant species over his illustrious fifty-six-year career. The newly proposed name avoided duplication of previously used names and was consistent with the international taxonomic framework for naming coniferous trees. Finally, Douglas-fir had acquired officially recognized common and scientific names. For centuries earlier, Salish peoples along the Northwest coast used the terms láyelhp and čebidac, among others, as names to identify these trees.
Douglas-fir’s genetic diversity, which exceeds that of its associates and nearly all other trees worldwide, accounts for some of its outstanding attributes and sets it apart as a singular species. It has thirteen pairs of chromosomes (called diploids) compared to only twelve pairs (or fewer) in virtually all other conifer species in the Northern Hemisphere, including the other species in the genus Pseudotsuga. The physical expression of wide genetic diversity plays out in the tree’s uncanny ability to grow on vastly different sites—varying from six-hundred-year-old dwarfs (inland variety) occupying lava flows in the American Southwest to towering 300-foot-tall giants (coastal variety) anchored in the deep, wellwatered soils of the Pacific Northwest.
Though the coastal and inland varieties of Douglas-fir merge in southern British Columbia, in the western United States an area of semi-arid grassland and sagebrush east of the Cascades separates the two varieties. The coastal variety occupies the coastal mountains and lowlands south past San Francisco to the vicinity of Monterey, the Cascades and Sierra Nevada south to the moist canyons of Yosemite National Park, and the Lake Tahoe area of extreme western Nevada. Curiously, only the coastal variety inhabits California, while the inland form grows in all the western states except California.
Inland Douglas-fir is abundant in central and southern British Columbia but becomes much less common in the harsh, continental climate of Alberta—where it is confined to lower slopes of the Rocky Mountains and grows only as far north as Jasper National Park. In the United States, inland Douglas-fir is abundant in the mountains of eastern Washington, central and eastern Oregon, Idaho, Montana, and southward throughout the Rocky Mountain chain. It also occurs in the high-desert mountain ranges of Arizona, New Mexico, and extreme eastern Nevada, and in increasingly scattered groves all the way to the tropical mountains of southern Mexico, covering a north–south distance of more than 2500 miles—an exceptionally broad range for any American tree. Variation of the inland variety in isolated mountainous areas of Mexico spurred a proposal in 1949 to add four new species to the genus Pseudotsuga. However, genetic work indicates that Douglas-fir migrated southward in Mexico during the Pleistocene Ice Age; isolated populations moved along north–south mountain corridors and occasionally reconnected, but apparently left too little time for any to differentiate into additional species. While the proposal for adding new species was rejected, there is some consensus among taxonomists that the Mexican populations have enough in common, and are sufficiently different from the other two varieties of Douglas-fir, that they deserve recognition as a third variety.
Both coastal and inland varieties of Douglas-fir form tall trees in low and mid-elevation forests within their ranges. For example, coastal Douglas-firs grow from sea level to 3500 feet in northwestern Washington and the inland variety from 7000 to 9000 feet in southern Colorado, New Mexico, and Arizona. Inland Douglas-firs extend upward as shorter trees on south- and west-facing slopes and exposed ridges into the subalpine zone. Sometimes they morph into sheared, shrubby trees in wind-funneling passes along the crest of the Rocky Mountains, and occasionally Douglas-fir takes on the dense, low shrubby form called krummholz above the limit of even stunted, erect trees on high mountain peaks.
Because it adapts to a wide variety of habitats and appears in many forms, no simple description encompasses Douglas-fir. Young trees are the West’s most familiar wild Christmas trees. As they continue to grow, young Douglas-firs produce a broad cone-shaped canopy of upward-projecting limbs with abundant branchlets. When they mature, the trees develop an irregular canopy made up of spreading limbs with drooping branchlets that contrast with the more symmetrical branching habit of their true fir (genus Abies) associates, such as grand fir (A. grandis), white fir (A. concolor), red fir (A. magnifica), and subalpine fir (A. lasiocarpa).
Douglas-fir’s needlelike leaves are about an inch long and attached to all sides of the twigs or branchlets, and unlike those of spruce, they are not stiff or prickly to touch. The cones are very distinctive because of the three-pronged, pitchfork-shaped bracts that project from between the scales.
The cones are green at first but turn tan as they mature and grow up to 2.5 to 4 inches long in the coastal variety and somewhat shorter in the inland variety. They are often abundant, and found hanging among the branchlets or lying on the ground. Sometimes squirrels clip off the dense green cones, the size and shape of a small dill pickle, and then gather them up and cache them in a rotten log or underground burrow in order to have a seed supply as winter food. The brownish mature cones dry out on the tree, their scales flex open, and the papery-winged seeds are dispersed by the wind, sometimes several hundred feet. A sticky pitch may be present on both green and mature cones.
When cones aren’t available for identification, not even old cones on the ground, the tree’s buds are another distinctive feature. They are a rich chestnut-brown color, oval and sharp-pointed, and covered with overlapping papery scales. After the buds burst open in late spring, new light green twigs start to emerge. The bud scales bend backward during this period but remain attached to the previous year’s woody twigs. In contrast, buds of true firs and many other conifers are less conspicuous, blunt, light colored, and covered with wax.
The bark of young Douglas-fir trees is smooth, gray, and spotted with pea-size blisters filled with sticky resin. With age the bark becomes rough, and after a century or longer develops into a dark gray-brown corky substance with deep vertical furrows and no resin blisters. Cutting into the bark of a maturing Douglas-fir with a knife exposes wavy bands of contrasting dark brown and light tan. Mature Douglas-firs, such as one-hundred-year-old “second-growth” that sprang up after historical logging, often have a vertical strip of dried pitch on their bark. The bark is also commonly covered with lichens, some a dull dark color, while others may be bright yellow or a beautiful pastel blue-green. Near the base of big old trees, particularly the coastal variety, bark often thickens to at least 6 inches and protects the tree’s sap-filled growing tissue from lethal heating by fire, which occurs at about 145° Fahrenheit.
One striking attribute of Douglas-fir is exceptional height. Oldgrowth coastal Douglas-firs in sheltered valleys commonly reach 250 feet tall and attain diameters of 5 to 8 feet. Occasionally these monarchs tower 300 feet or slightly higher, putting them among a handful of the tallest tree species in the world, surpassed only by the California coastal redwoods (Sequoia
