Douglas-fir (Pseudotsuga menziesii)

• Needles are yellowish-green, 1-inch-long and arranged in a spiral around the branchlets, like a bottlebrush.
• Cones are oblong, 2 to 4 inches long with three-pointed bracts and are located primarily in the upper crown.
• Bark on young trees is thin, smooth, and gray, with numerous resin blisters. On mature trees the bark is thick (4 to 12 inches) and corky.

Douglas-fir is not a true fir at all, nor a pine or spruce. It is a distinct species named after its discoverer Archibald Menzies and a botanist, David Douglas. A major characteristic that distinguishes it from true firs is its cone which falls from the tree intact.

Douglas-fir is one of the world's most important and valuable timber trees. It grows across a larger portion of western North America, from 19 to 55 degrees North in latitude, than any other commercially used conifer. 

• Diameter: > 11 1/2 feet (Coos County, Oregon)
• Height: 330 feet (Little Rock, Washington)
• Age: 1400 years (Mount Vernon, Washington)

 Range

RANGE: There are two varieties of Douglas-fir, the coast Douglas-fir and the Rocky Mountain Douglas-fir. Coast Douglas-fir grows from west-central British Columbia southward to central California. In California, it is found in the Klamath Mountains and Coast ranges as far south as the Santa Cruz Mountains, and in the Sierra Nevada as far south as Yosemite. The Rocky Mountain variety does not grow in California.

The tree grows under a wide variety of climatic conditions, including the mild maritime climate of the coast and the more severe weather of the Sierra Nevada.

Elevation range of the Douglas-fir in California:
Area	Elevation
Northern Sierra Nevada	2,000 to 6,000 feet
Southern Sierra Nevada	up to 7,500 feet
River valleys & canyon bottoms	800 to 900 feet

Climate in Douglas-fir's natural range
		Sierra Nevada	Coast
Average temp:	July	72• to 86•	68• to 81•
	January	15• to 28•	28• to 37•
Frost free days	days	80 to 180	195 to 260
Precipitation	inches	24 to 120	34 to 134
Snowfall	inches	4 to 120	0 to  24 inches

Douglas-fir grows best on well-drained deep soils and will not thrive on poorly drained or compacted soils. Along the coast it is mostly found where marine sandstones and shales have weathered deeply to fine-textured, well drained soils. Douglas-fir is found on a wide variety of soils in the Sierra Nevada.

The principal limiting factors are temperature in the north and moisture in the south. Douglas-fir is found on south facing slopes in the northern part of its range (on warmer sites) and north facing slopes in the southern part (on moister sites).

Douglas-fir reproduces by seeds which form on cones. Trees start to bear seed at about age 20. Cones are fertilized in the spring and ripen in the fall, dropping seeds in fall, winter and spring. Seed crops occur at irregular intervals, with one heavy and one moderate crop every seven years. Even during heavy crop years, only about a quarter of trees produce many cones. Old growth trees produce the majority of cones.

Each cone produces up to 50 seeds. Seeds on California trees are light (23,000 of them in a single pound), and may be blown as far as a mile away, although most fall within 300 feet of the source. Seeds are eaten by the Douglas squirrel, chipmunks, mice, voles, and birds. Seeds germinate in the spring and grow relatively slowly in the first year.

Douglas-fir seedlings grow best on bare mineral soil but can tolerate a thin litter layer. First year seedlings, especially those on dry sites, actually survive and grow best in light shade, although older seedlings require full sun. Lack of summer moisture triggers young seedlings to go dormant until the following spring.

Full shade and moisture competition caused by competing vegetation such as understory hardwoods, woody shrubs, and grasses can kill Douglas-fir seedlings. Many of these plants grow much more quickly on disturbed sites than young Douglas-fir trees. This results in difficulties regenerating the species without weed control. Fire also will favor Douglas-fir by destroying other species that would compete with and outgrow young seedlings.

Along the coast, height growth starts to accelerate after five years, and reaches its maximum at age 20 to 30, although the species can grow rapidly for up to 200 years.

In loose soils, Douglas-fir roots grow quickly, forming a taproot and reaching almost their entire length in the first ten years. The tree's rooting habit is not particularly deep. The roots of young coast Douglas-fir tend to shallower than roots of the same aged ponderosa pine, sugar pine, or incense-cedar. Some roots are commonly found in organic soil layers or near the mineral soil surface. The spread of the roots generally conforms to the width of the tree's crown.

In the Klamath and Coast ranges, Douglas-fir either grows in nearly pure stands, or in the mixed evergreen forest, while in the Sierra Nevada it is a component of the mixed conifer forest. Wherever Douglas-fir grows in mixture with other species, the amount of the species varies greatly and depends on aspect, elevation, soil and fire history of the areas.

Douglas-fir is a component of the redwood forest type, but as sites become drier farther inland, redwood gives way to mixed evergreen forests which are codominated by Douglas-fir, Pacific madrone, and tanoak. Canyon live oak, giant chinkapin, sugar pine, ponderosa pine, and incense-cedar are also found along with these dominant species.

Associates in the mixed-conifer zone include ponderosa pine, Jeffrey pine, sugar pine, incense-cedar, California black oak and white fir. Douglas-fir's abundance in the mixed-conifer zone tends to decrease and that of ponderosa pine increase from north to south within this zone.

Douglas-fir is classified as an intermediate shade intolerant after its first few years. It is, however, more tolerant than most associates including ponderosa pine, Jeffrey pine, sugar pine, western white pine, lodgepole pine, incense-cedar, noble fir, and red alder, but less than white fir. On drier sites, Douglas-fir tends to be more shade-tolerant.

Douglas-fir is more fire resistant than many of its associates because of it grows rapidly and is covered with a thick corklike bark along its stem and roots. In addition, the tall trees have their foliage concentrated on the upper bole, which makes it difficult for fire to reach the crown.

Regeneration of Douglas-fir is favored by fire. Since it is shade intolerant, new Douglas-fir trees are not established under current forests without fires to kill more shade tolerant competition. Forest fires therefore allow Douglas-fir to continue to be a dominant presence in the forest.

Douglas-fir is typically regenerated using even-aged management methods. Clear cutting with planting is most common. Shelterwood systems are also used since young seedlings can tolerate partial shade. Because young seedlings which grow from naturally falling seeds are so unevenly spaced, planting of new trees is often required. Young Douglas-fir respond well to release from brush or overstory trees if they have not been too suppressed.

Nitrogen is typically the limiting nutrient in forest soils that restricts growth of Douglas-fir. Application of nitrogen fertilizer has been used in combination with thinning to increase growth.

Trees 5 to 6 feet in diameter and 250 feet or more in height are common in old-growth stands. Self-pruning is generally slow and trees retain their lower limbs for a long period.

Douglas-fir is grown as a Christmas tree on harvest rotations ranging from 4 to 7 years. Attempts to grow Douglas-fir as a Christmas tree outside its native range have failed, due to frost and needle cast diseases. Coastal Douglas-fir will not tolerate frost below 14 degrees Fahrenheit for more than a week, even if the ground is well protected against freezing by snow cover.

Douglas-fir seedlings in nurseries may be killed by various species of fungi. Young trees in plantations are vulnerable to root rot which weakens them allowing them to blow over. Several heart rot species infect trees at their knots or scars after fire, lightning, or mechanical damage causing decay and reducing commercial value. Mistletoe occurs throughout its rare.

The Douglas-fir beetle is the most damaging insect and often attacks fire-killed or fire-weakened trees. Tussock moths and spruce budworm attack trees of all ages and often cause defoliation. Several species of insects are capable of reducing the seed crop but are not generally a problem for regeneration. Many small mammals depend upon the seeds for food and are capable of destroying virtually all unprotected seed. Browsing by deer, elk, and rodents can be a major problem in plantations.

 Uses

Coast Douglas-fir forest is one of the world's best timber producers and yields more timber than any other forest type in North America. Coast Douglas-fir is used extensively in landscaping and as a Christmas tree.

Douglas-fir is unique among all softwood species in that it is dimensionally stable without being dried, meaning that it does not shrink or twist significantly. Many builders prefer to cut, nail and fasten it in the "green" or unseasoned condition, allowing it to air dry during construction. For millwork, remanufacturing applications or glued products, Douglas-fir is dried in temperature and humidity-controlled kilns or stacked and air dried until its moisture content reaches the desired level for an intended purpose.

Douglas fir's appearance and stability make it ideal for joinery, doors, millwork, window and door casings, mantels, stairs and baseboards, paneling, and flooring. Treated pilings and decking are used in marine structures. The wood is also made into railroad ties, mine timbers, house logs, posts and poles, flooring, veneer, pulp, and furniture.

This text was largely summarized from an article originally by Richard K. Hermann, Professor of Forest Ecology (retired), Oregon State University Corvallis and Denis P. Lavender Department Head. Faculty of Forestry, University of British Columbia, Vancouver. that appears in Burns, Russell M., and Barbara H. Honkala, tech. coords. 1990. Silvics of North America: 1. Conifers. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC. vol. 1, 675 p.

Interested readers are referred to the original article for more detailed and technical information and references. Publication of this series was in part funded by California Department of Forestry and Fire Protection under Contract numbers 8CA96027 and 8CA96028