Return to Native Trees of the Southern Rocky Mountains

Douglas fir is one of the primary forest trees in Colorado, in north, central and western Wyoming, and the mountains of northern New Mexico. It is found between 6000 and 10000 feet above sea level, especially in comparatively cool and moist locations. In the lower part of its range these locations are usually northern exposures.

Douglas fir are tall evergreens with a shape slightly broader than the spruces. The sight of Douglas fir on the shaded side of a valley and Ponderosa pine on the sunny slopes is common in canyons leading up into the mountains. Douglas fir is sometimes mixed with Ponderosa pine or aspen. Douglas fir is much more tolerant of shade than Ponderosa pine. Douglas fir is quite drought resistant.

Douglas Fir grows rapidly and can be a pioneer in burned areas. Large old trees are quite fire resistant because of the thick bark. Extensive forests of large Douglas fir once grew in the southern Rockies, though they have mostly been cut for timber. Smaller trees are still very common.

On the Pacific Coast Douglas fir grows to the second tallest tree in America. They also attain great age. The oldest tree is about 1300 years old and was discovered by David Douglas in 1825. It is 221 feet high and 45 feet around the trunk - over 12 feet in diameter. The Rocky Mountain variety is smaller. The largest example grows in Idaho and reaches 130 feet high and 19 feet trunk circumference. In Colorado this tree reaches a maximum size around 100 feet high and two to three feet in diameter. Colorado trees often live to 300 or 400 years.

Archibald Menzies of Scotland, physician and naturalist, discovered the tree now called Douglas fir in 1791 at Nootka Sound on Vancouver Island, British Columbia, while on the Vancouver expedition which was sent out to finish the British exploration of the Pacific remaining after Captain James Cook was killed on a previous voyage. David Douglas, also from Scotland, rediscovered the tree in 1825 and introduced it into England.

There was a long controversy about how to classify this tree. Douglas fir is not a true fir tree. It has needles similar to a fir (flat and soft), but the cones are more like spruce cones and not at all like fir cones. At one time the common name was Douglas spruce; hence the name of "Spruce Tree House" in Mesa Verde. Botanists finally decided this tree was actually closest to the hemlocks, especially a hemlock of Japan called Tsuga, and a new genus Pseudotsuga ("pseudo-hemlock") was devised for the Douglas fir and its relatives. In the end there is a sharing of the credit for recognizing this tree: the scientific name is Pseudotsuga menziesii , so Douglas gets the common name and the species name remembers Menzies.

The Douglas fir of Colorado is a variety of the species, Pseudotsuga menziesii . var. glauca . The variety name glauca refers to the whitish cast over the blue-green color which is slightly different from the green needles of the Douglas fir of the west coast.

Douglas fir wood is of very high quality; it is used for everything from house construction and traditional shipbuilding to fine furniture, paneling, and floors. It has both an attractive color and strength. Little is cut in the southern Rockies.

The seeds are eaten by grouse, squirrel, and chipmunk. The tree is occasionally browsed by mule deer and elk.

The western spruce budworm can defoliate entire Douglas fir trees. The moth form of the insect lays its eggs on the underside of needles in fall. They hatch in about ten days and overwinter under bark scales. In April and May the larvae begin feeding on new needles just released from buds. After about 40 days the larvae are mature. They pupate and new moths appear in about ten days, and the cycle starts all over again. Spruce budworm is a major pest, which afflicted the Rocky Mountains in the early 1980's, leaving large tracts of standing dead trees, notable by their dead, reddish-brown, needles. The needles are gone now and only the standing trunks remain.

Identifying features of Douglas fir

Cones

The Douglas fir cones are common and easy to recognize on the tree or forest floor litter, and absolutely distinctive. No other tree has cones like these. True fir cones are nothing like Douglas fir cones.

Mature cones are 1 1/2 to 4 inches long; hang down from the twigs, and fall intact from the trees when mature. They somewhat resemble spruce cones, except that long narrow papery strips with three points, called "three-pronged bracts," protrude from between the cone scales. This feature is a positive identifier for Douglas fir. The outer margin of the cone scales are a smooth round curve, unlike the ragged edges of Englemann spruce cone scales. Cones grow throughout the height of the tree, and may be abundant on a tree only 15 feet high. Not all trees have cones.

Needles

Single and flat, 3/4 to 1 1/4 inch long, dark green or blue-green to green with a very slight yellow tint. The needles narrow at the base into a short stalk, flaring back slightly into the twig. This stalk falls with the needle from the twig. This feature can be used to distinguish Douglas fir needles from true firs. Needles have a groove on the upper surface.

On some trees the year's new young growth may have the pale waxy coating on the needles which gives evergreens the whitish blue-green color commonly associated with the Blue spruce. This coating wears off quickly. Some trees never develop it. Two Douglas firs next to each other may have noticeably different color. Some Douglas fir even may be lighter in color than Ponderosa pine growing nearby.

Needles have a pleasant Christmas-tree-like scent when crushed. This tree is often grown commercially on private farms for Christmas trees.

Bark

Bark of young trees is smooth, gray or reddish brown, and thin, sometimes with resin blisters, resembling bark of true firs. When trunk diameter reaches about 5 inches the bark begins to crack vertically or into jigsaw pieces, at first with very thin cracks, or even pop off circular scales. When the grey outer bark splits the under bark shows reddish-brown. Some trunks may reach 12 inches diameter or more before the bark begins to split. On large mature trees the bark may be faded gray to gray-black, or pale brown to dark brown, furrowed into long, thick (up to 6 inches) solid or scaly ridges with an interwoven appearance. The distinctive pale brown color of mature Douglas fir trunks, free of any hint of red or orange, combined with the twisted furrows, is reminiscent of manila rope, and is not seen on other trees.