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Rocky Mountain Douglas-fir facts for kids

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Rocky Mountain Douglas-fir
A Douglas-fir in Thompson-Nicola, British Columbia, Canada
Scientific classification
Kingdom: Plantae
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Pinaceae
Genus: Pseudotsuga
Species: P. menziesii
Variety: P. menziesii var. glauca
Trinomial name
Pseudotsuga menziesii var. glauca
(Mayr) Franco
Species

P. menziesii subsp. glauca

The Pseudotsuga menziesii var. glauca, or Rocky Mountain Douglas-fir is a large evergreen tree in the genus Pseudotsuga in the plant family Pinaceae. The tree is native to British Columbia, Idaho and Colorado.

Characteristics

Rocky Mountain Douglas-fir is a large tree, typically reaching 35-45 m in height and 1 m in diameter, with exceptional specimens known to 67 m tall, and 2 m diameter. It commonly lives more than 500 years and occasionally more than 1,200 years. The bark on young trees is thin, smooth, gray, and covered with resin blisters. On mature trees, it is moderately thick (3-6 cm), furrowed and corky though much less so than Coast Douglas-fir.

Pseudotsuga glauca cones
Rocky Mountain Douglas-fir cones
Left: var. caesia, Shuswap Lake, British Columbia, Canada
Right: var. glauca, Chiricahua Mountains, Arizona, USA

The shoots are brown to gray-brown, smooth, though not as smooth as fir shoots, and finely pubescent with scattered short hairs. The buds are a distinctive narrow conic shape, 3-6 mm long, with red-brown bud scales. The leaves are spirally arranged but slightly twisted at the base to be upswept above the shoot, needle-like, 2-3 cm long, gray-green to blue-green above with a single broad stomatal patch, and with two whitish stomatal bands below. Unlike the Coast Douglas-fir, Rocky Mountain Douglas-fir foliage has no noticeable scent.

The male (pollen) cones are 2-3 cm long, and are typically restricted to or more abundant on lower branches. Pollen cones develop over 1 year and wind-dispersed pollen is released for several weeks in the spring.

The mature female seed cones are pendent, 4-7 cm long, 2 cm broad when closed, opening to 3-4 cm broad. They are produced in spring, purple (sometimes green) at first, maturing orange-brown in the autumn 5-7 months later. The seeds are 5-6 mm long and 3-4 mm broad, with a 12-15 mm wing. Both Coast and Rocky Mountain Douglas-fir produce abundant crops of seed approximately every 2-11 years. Seed is produced annually except for about 1 year in any 4-to-5-year period.

There are two varieties, which have proved distinct on genetic testing (Li & Adams, 1989):

  • 'Blue Douglas-fir' or 'Colorado Douglas-fir' (var. glauca) in the southern Rocky Mountains. Leaves strongly blue-green, 2-3 cm long. Cone scale bracts broader, often reflexed.
  • 'Gray Douglas-fir' or 'Fraser River Douglas-fir' (var. caesia) in the northern Rocky Mountains. Leaves gray-green to green above, 2-2.5 cm long. Cone scale bracts slender, not reflexed.

The oldest accurately-dated Rocky Mountain Douglas-fir, 1275 years old, is in New Mexico. This longevity is apparently an anomaly; growing on a relatively barren lava field has protected it from fire, animals, and humans. Growth typically slows dramatically between 90 and 140 years of age.

Interaction with Animals

In spring and winter (in British Columbia, Idaho, and Montana) elk browse on south- and southwest-facing Rocky Mountain Douglas-fir and Ponderosa pine stands, particularly when shrubs and/or grasses are productive. In summer, Elk generally are found at higher elevations (outside the Rocky Mountain Douglas-fir and Pacific Ponderosa Pine zones). During fall Elk use stands of Rocky Mountain Lodgepole Pine, Subalpine Fir, Western Larch, or Grand Fir with high canopy cover.

In parts of Yellowstone National Park, Elk browsing is so intensive that young Rocky Mountain Douglas-fir are stunted at 1-1.5 m (3-4.5 feet) in height, with live branches trailing very close to the ground, and branches on the upper two thirds of the tree dead. Low-elevation and south-facing open-structure Rocky Mountain Douglas-fir types are often important winter range for White-tailed Deer and Mule Deer. Moose winter in low-elevation Rocky Mountain Douglas-fir types in areas where willow thickets, the preferred winter habitat, are lacking; in such areas Rocky Mountain Douglas-fir is an important moose food.

Chipmunks, mice, voles, and shrews eat large quantities of conifer seeds from the forest floor, and clipped cones are a staple and major part of storage of red squirrels. These animals store a large amount of Rocky Mountain Douglas-fir cones or seeds. American Marten commonly den in hollow logs.

Numerous species of songbirds extract seeds from Douglas-fir cones or forage for seeds on the ground. The most common are the Clark's Nutcracker, Black-capped Chickadee, Mountain Chickadee, Boreal Chickadee, Red-breasted Nuthatch, Pygmy Nuthatch, Red Crossbill, White-winged Crossbill, Dark-eyed Junco, and Pine Siskin. Migrating flocks of Dark-eyed Juncos may consume vast quantities of seeds and freshly germinated seedlings. Woodpeckers commonly feed in the bark of Rocky Mountain Douglas-fir. Blue Grouse forage on needles and buds in winter; they and other birds rely heavily on Rocky Mountain Douglas-fir communities for cover.

The Douglas-fir is vulnerable to infestation by a woolly aphid, Adelges cooleyi that also infects the Cooley spruce to complete its lifecycle.

Uses

Rocky Mountain Douglas-fir is a valuable timber tree. The wood is exceptionally strong and is used for structural timber as well as poles, plywood, pulp, dimensional lumber, railroad ties, mine timbers, log cabins, posts and poles, fencing, and firewood. Other uses listed include "machine-stress-rated lumber", finger-jointed studs, glued-laminated beams, pallets, furniture, cabinets, doors, and window frames.

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