Douglas-fir: By any other name

The tree we know today as Douglas-fir (Pseudotsuga menziesii) baffled botanists for decades. People have known it as yellow spruce, red spruce, red fir, Douglas spruce, and Oregon pine. It’s not unusual for a plant to have many common names, but this one has tried on many botanical names as well. Botanists first called it Pinus taxifolia, the pine with yew-like leaves. Later, they tried squeezing it in with spruces, then firs. In 1867, 75 years after it was made known to western science, they finally gave up and created a new genus (Pseudotsuga) to house Douglas-fir and its oriental cousins. Pseudotsuga, meaning false hemlock, reflects its similarity to true hemlocks, or Tsuga, which, to compound the confusion, is the Japanese word for larch.

Our species is named for Archibald Menzies, Scottish naturalist with the Vancouver Expedition, who first collected it in 1792. These grand trees occur from British Columbia to the highlands of northern Mexico, although our Rocky Mountain version of Douglas-fir (the hyphen reminds us it’s not a true fir) is sometimes considered to be a distinct variety, called glauca for its bluish color. A second American species, bigcone Douglas-fir (Pseudotsuga macrocarpa) occurs in southern California.

The accepted common name honors another Scotsman, David Douglas, pioneer explorer-botanist of the Pacific Coast, who collected the seeds of Douglas-fir and also discovered many other new conifers in California and the Pacific Northwest. He once wrote to William Jackson Hooker, recipient of the many specimens he sent to England:“You will begin to think that I manufacture pines at my pleasure.” New species were, in those days, more abundant than botanists.

Through all the confusion of nomenclature, the trees have, of course, not changed perceptibly—nor has their utility been compromised by botanical uncertainties. If this tree was tough to categorize, it was easy to appreciate. In the temperate rainforests where Douglasfir was first “discovered,” its size, abundance, and the quality of its wood were all that mattered, and few cared what you called it. When you hear “old-growth forest” on the evening news, this coastal Douglas-fir is the tree in question. It comprises almost 90% of those forests.

From the Blue Ox to the Spotted Owl, Douglas-fir is part of our lore and landscape and more. For a century and a half, Douglas-fir has literally formed the foundation of our history and development.

In Oregon and Washington, Douglas-firs may reach 300 feet in height and 15 feet in diameter. Who could resist such timber? No one did. Its contributions to western civilization have been both mundane and monumental: from the humble 2x4s that hold up our roofs to the massive beams of the Mormon Tabernacle, from the railroad ties and telephone poles that knit the growing West together to new (in 1925) masts for the U.S.S. Constitution, Douglas-fir has served our needs. Its popularity was assured, in part, by the demise of virgin eastern white pine, which had provided the Constitution’s original masts in 1798, but no longer grew tall enough to do so. That species had dominated the lumber market from the late 1700s until its virgin stands were logged beyond effective use a century later. (Eastern white pine still occupies its original range, but it has not yet returned to its original glory.) Logging firms from the east shipped their lumberjacks (and sometimes their entire operations, mill and all) west to the new frontiers of timber, to the great forests of Douglas-fir.

Here in the Rocky Mountains, our trees do not grow nearly as big or as quickly. They can reach diameters of three feet and heights of 130 feet at maturity; about half the height of large scale coastal Douglas-fir. Our trees are, by necessity, better able to withstand drought and are less shade tolerant than those in the Northwest. Rocky Mountain trees are also valuable as timber, though less so than their coastal cousin. Douglas-fir makes up about 10 percent of Colorado’s forest acreage, but only accounts for about 5 percent of the harvested wood.

Never mind the differences—you’ll recognize Douglas-fir wherever you find it. The 3-pronged bracts between the cone scales are unique to Pseudotsuga. In fact, it’s often easiest to recognize Douglas-fir along the trail by the squirrel-cut cones you see on the ground; the leafy tops are often too tall to distinguish. You’ll find its needles are flat but blunt, giving it a softer feel than spruces; its twigs are somewhat roughened—not as much as in spruces, but more than those of true firs. The graceful presence of Douglas-fir illuminates our woodlands from the foothills to the upper montane, but it rarely occurs in large, single-species stands. At its lower elevations, it often accompanies ponderosa pine, replacing it on the cooler north-facing slopes. In southern Colorado, it’s likely to be found with white fir (Abies concolor).

In addition to its value to us humans, Douglas-fir provides many services to wildlife. Its branches provide cover and nesting sites; its seeds provide nourishment, but keep critters busy in the process. With 20 to 30 seeds per cone, a bushel of cones yields about half a pound of seeds. That’s the entire production of an average tree in a good year. At that rate, by my clumsy calculation, it would take about 12 Douglas-fir trees to support one hungry squirrel through winter—if he can get all the seeds. (In real life, it probably takes even more trees. Squirrels might do better on ponderosa pine seeds, which have more calories, but they’ll have to work harder to get them out of the tougher cones.)

So how does a tree make sure some seeds survive to grow new trees? By tricking those pesky squirrels, and anyone else who’s looking for lunch. Douglas-fir, and a number of other trees, have “learned” to do this by starving the squirrels (or forcing them to look for food elsewhere) during most years, then overwhelming them with a massive seed crop in an occasional good year. Because the squirrels can’t take advantage of this sudden wealth, seeds have a better chance to escape and some will grow. Douglas-fir generally has one complete failure and two or more light crops between heavy, or “mast,” years. After each the squirrels must be prepared for a few lean ones ahead.

Copyright © 2012 Sally L. White