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Bigcone Douglas-fir
Pseudotsuga macrocarpa
Pseudotsuga menziesii
  (Mirb.) Franco
Chinese Douglas-fir
Pseudotsuga sinensis
  Owner:   C. Michael Hogan    

Coast Douglas-fir in a stressed condition, Annadel State Park, California.

Pseudotsuga menziesii

C. Michael Hogan
September 17, 2008

The latitude span of P. menziesii surpasses that of any other commercial western North American conifer. Lumber of this species is prized for its commercial utility, and the species holds the world record for the tallest individual tree ever occurring. The species is not a true fir, and it is a separate species from three others in Mexico, Japan and China, all of which are also called by the common name Douglas-fir. The species was first recorded on Vancouver Island by naturalist Archibald Menzies.

Two subspecies occur in western North America: P.m. menziesii and P.m.glaucescens. P.m.menziesii (Coast Douglas-fir) occurs from west-central British Columbia south to central California. In Oregon and Washington the range is continuous from the Cascades west to the Pacific Ocean. In California, it ranges from the Klamath and Coast ranges south to the Santa Cruz Mountains, and in the Sierra Nevada as far south as Yosemite National Park. P.m.glaucescens (Rocky Mountain Douglas-fir) occurs east of the Sierra Nevada and Cascade Mountain Ranges. The distribution extends east to the Rocky Mountains and north to Calgary, Alberta, Canada.

Douglas-fir is monoecious; with strobili production commencing at about age twelve. Primordia of pollen, stroboli and leaves appear in spring, but the egg-shaped pollen cone buds cannot be distinguished even microscopically until July, and not visibly until September. Pollen cone primordia are usually clustered at the shoot base, whereas the larger seed cone structures lie singly at the acropetal extreme of the shoot.(Allen) Frost during cone anthesis or herbivory by insects can render cones unviable The yellow to deep red male strobili measure approximately two cm in length, whilst the deep green to red female counterparts are roughly 50 percent longer, and manifest sizable trident bracts ready for to pollination soon after emergence. (Owston) Length of mature cones is eight to ten cm. Bracts become brown after seeds mature.

Coast Douglas-fir cones mature and seeds ripen from August in California and southern Oregon to mid-September in northern Washington and southern British Columbia. Seedfall takes place rapidly following cone maturity with most of the total crop hitting ground by the late October. Other seeds fall even lasting until spring. Seedfall east of the Coast Ranges occurs more rapidly than in coastal North America.

In the case of Rocky Mountain douglas-fir flowering is similar to Coast Douglas-fir, with Colorado flowering commencing in April and May in Idaho. Cone ripening starts in July at the lower elevations in Montana and later at more northern latitudes, and higher dispersal of seed for Rocky Mountain Douglas-fir begins in September at higher elevations in Montana.

Seedlings flourish with a moderate amount of soil moisture in light shade and may attain a first year height of six to ten cm. In most areas seedling growth is inhibited by high densities of leaf litter and forest floor detritus. By age eight, young trees may have sprout extensions exceeding one meter.per annum. In the Rockies, P.m.menziesii suffers limitation of distribution due to low precipitation and evaporative stress. As with most perennial woody plants, Douglas-fir relies on a mycorrhizal relationship for uptake of minerals and water. Around 2000 species of fungi are symbionts with Douglas-fir, ectomycorrhizal and ectendomycorrhizal structures both having been recorded on Douglas-fir. (Trappe) Mature Douglas-fir reach heights of 40 to 100 meters, with the tallest recorded tree of any species being a 126,5 m individual in Lynn Valley at Vancouver, British Columbia; a slightly smaller 120 m Douglas-fir was recorded at Mineral, Washington. The tallest extant P. menziesii is a 100.3 m specimen at Coos Bay, Oregon.

P. menziesii are food plants for larvae of certain Lepidoptera such as Bordered White, Autumnal, Turnip, Engrailed and Pine Beauty Moths, as well as many species within the moth family Gelechiidae, especially of the Chionodes genus. Avafauna consuming Douglas-fir seeds include siskins, grouse and crosbills. Chickadees, nuthatches, brown creepers, and woodpeckers devour insects found in the trunk, branches and twigs. Foliage herbivory is noted by pine white butterfly larvae, silver-spotted tiger moth larvae, and many other moths. Squirrels and chipmunks eat P.menziesii seeds. Foliage and twigs are browsed by beavers, porcupines, deer and elk.

In mixed oak woodlands of California, Douglas-fir is becoming an increasingly common tree, due to the use of widespread fire suppression in modern times. In many Coast Range venues Douglas-fir threatens to take over dominant status.due to its ability to reach greater heights than its associate oak and madrone species, when fire does not interrupt in a natural time frame. Therefore, many oak woodland ecosystems which have been associated with certain locations at least through the Holocene are transforming (in many cases) to pure stands of Douglas-fir. This process leads to habitat alteration that may ultimately reduce biodiversity by denying niches to the greater number of species that depend upon oak woodlands.. In many locations, such as Annadel State Park in California, resource managers are combating this effect by selectively girdling Douglas-firs as they encroach into oak dominant forests. These biodiversity threats are magnified by planting vast tracts with Douglas-fir to meet commercial demand for lumber.

* George S. Allen and John N. Owens (1972) The life history of Douglas-fir. Environment Canada, Canadian Forestry Service, Ottawa, Ontario. 139 p.
* James M. Trappe, (1977). Selection of fungi for ectomycorrhizal inoculation in nurseries. Annual Review of Phytopathology 15:203-222
* Peyton W. Owston and William I. Stein (1974) Pseudotsuga Carr. Douglas-fir. In Seeds of woody plants in the United States. p. 674-683. C. S. Schopmeyer, tech. with. U.S. Department of Agriculture, Agriculture Handbook 450. Washington, DC

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