True firs are about 40 species of conifer trees in the genus Abies, occurring in cool-temperate, boreal, and montane forests of the northern hemisphere. Firs are members of the pine family (Pinaceae).
Firs are characterized by flattened needles, usually having two white lines running the length of the leaf. Firs do not have a petiole joining the needles to the twigs, and after the foliage is shed large scars are left on the twigs. Fir cones are held upright, and they shed their scales soon after the winged seeds have been dispersed, leaving a spikelike axis on the twig. Fir trees generally have a dense spirelike crown. The bark of most species is rather smooth on younger trees, becoming somewhat scaly on older ones. Many species develop resin-containing blisters on the surface of their bark. Firs are not a prime species for sawing into lumber, but they are excellent as a source of pulp-wood for the manufacturing of paper, and are also cultivated as Christmas trees and as ornamentals.
Douglas firs (Pseudotsuga spp.) are a closely related group of six species that occur in western North America and eastern Asia. Douglas firs are distinguished from true firs by their small, raised leaf scar, a petiole joining the leaf to the twig, and the distinctive, three-pointed bracts (scalelike leaves) that occur immediately below and close to the scales of their oval-shaped, hanging cones.
Nine species of true firs grow naturally in North America. The most widespread is balsam fir (Abies balsamea ), a prominent tree in boreal and north-temperate forests of eastern Canada and the northeastern United States. On moist sites with a moderate climate, this species grows as tall as 65 feet (20 m). In some places, balsam firs occur above the timberline in a depressed growth-form known as krummholtz. Balsam fir is highly intolerant of fire, and it tends to be a relatively short-lived tree. Balsam fir is the major food species of the spruce budworm (Choristoneura fumifer-ana ), a moth that periodically causes extensive forest damage in northeastern North America. Fraser fir (A. fraseri ) is closely related to balsam fir, but occurs in montane forests of the southern Appalachians.
The other seven species of true firs in North America all occur in western forests. The subalpine fir (Abies lasiocarpa ) grows in montane forests from southern Alaska to northern Texas, sometimes occurring past the timberline in a krummholtz growth form. Grand fir (A. grandis ), Pacific silver fir (A. amabilis ), and white fir (A. concolor ) are species of moist, western rain forests, growing on sites of moderate altitude, and achieving heights of as much as 164 feet (50 m). Species with relatively restricted distributions in the western United States are bristlecone fir (A. bracteata ), noble fir (A. procera ), and California red fir (A. magnifica ).
Boreal —This refers to the conifer-dominated forest that occurs in the sub-Arctic, and gives way to tundra at more northern latitudes.
Krummholtz —A stunted, depressed growth form that some conifers develop above the tree-line on mountains, in the arctic, and sometimes along windy, oceanic coasts. Krummholtz trees are extremely slow-growing, and can be quite old, even though they are small in diameter and less than 3 feet (1 m) tall.
Montane —A conifer-dominated forest occurring below the alpine tundra on high mountains. Montane forest resembles boreal forest, but is affected by climate changes associated with altitude, rather than latitude.
The Douglas fir (Pseudotsuga menziesii ) is a common, fast-growing, and valuable timber species in western North America, where it can grow as tall as 262 feet (80 m) and attain a diameter of more than 6.5 feet (2 m). Some taxonomists divide the species into two races, the coastal Douglas fir (P. m. menziesii ), which grow in humid western forests, and the Rocky Mountain or interior Douglas fir (P. m. glauca ), which grows in drier forests further to the east. The big-cone Douglas fir (Pseudotsuga macrocarpa ) is a locally occurring species in extreme southern California and northern Baja.
The most important use of true firs is for the production of pulp for the manufacturing of paper. All of the abundant firs are used in this way in North America, especially balsam fir and white fir.
True firs are used to manufacture a rough lumber, suitable for framing buildings, making crates, manufacturing plywood, and other purposes that do not require a fine finish. The Douglas fir is an important species for the manufacturing of a higher-grade lumber.
Canada balsam is a viscid, yellowish turpentine that is secreted by balsam fir, and can be collected from the resinous blisters on the stems of these trees. Canada balsam is now a minor economic product, but it used to be important as a clear-drying, mounting fixative for microscope slides, and as a cement for optical lenses. Oregon balsam, collected from Douglas fir, was similarly used.
Some species of firs are grown as ornamental trees around homes and in public parks. White, grand, and Douglas firs are native species commonly used in this way. The European white fir (Abies alba ) and Himalayan silver fir (A. spectabilis ) are also sometimes cultivated as ornamentals in North America.
Firs are highly desirable for use as Christmas trees, and in some areas they are grown on plantations established for this purpose. They can be pruned to develop a thick canopy with a pleasing shape, and firs retain their foliage for a rather long time, even inside dry homes during the winter.
See also Pines.
Hosie, R.C. Native Trees of Canada. Ottawa: Canada Communications Group, 1985.
Judd, Walter S., Christopher Campbell, Elizabeth A. Kellogg, Michael J. Donoghue, and Peter Stevens. Plant Systematics: A Phylogenetic Approach. 2nd ed. with CD-ROM. Suderland, MD: Sinauer, 2002.
Petrides, G.A. A Field Guide to the Trees and Shrubs of North America. New York: Houghton Mifflin, 1986.
Van Gelderen, D.M., and J.R.P. Van Hoey Smith. Conifers. Eugene, OR: Timber Press, 1989.
Oregon State University. “True Fir Species Descriptions” <http://oregonstate.edu/trees/con/spp/trfirspp.html> (accessed November 24, 2006).