Juniperus occidentalis

Common Names

Western, Sierra or yellow juniper; yellow or western red cedar (Peattie 1950).

Taxonomic notes

Two varieties, occidentalis (syn: Sabina occidentalis (Hooker) Antoine (Adams 1993)) and australis.

In northwestern Nevada, where the two species overlap, J. occidentalis var. occidentalis hybridizes with J. osteosperma (Miller et al. 2005).

Description

"Trees monoecious or dioecious, to 20(-30) m, single-stemmed; crown rounded to conical. Bark red-brown to brown, exfoliating in thin strips, that of small branchlets (5-10 mm diam.) smooth, that of larger branchlets exfoliating in scales or flakes. Branches spreading to ascending; branchlets erect, 3-4-sided in cross section, ca. 2/3 or less as wide as length of scalelike leaves. Leaves green, abaxial glands ovate to elliptic, conspicuous, with yellow or white exudate, margins denticulate (at 20×); whip leaves 3-6 mm, not glaucous adaxially; scalelike leaves 1-3 mm, not overlapping, rounded, apex acute to obtuse, appressed. Seed cones maturing in 2 years, of 2 distinct sizes, with straight peduncle, ovoid, 5-10 mm, blue to blue-black, glaucous, fleshy and resinous, with 2(-3) seeds. Seeds 2-4 mm" (Adams 1993).

For var. occidentalis only: "Bark red-brown. Plants often (50%) monoecious. Seed cones (5-)7.5(-9) mm" (Adams 1993). In eastern Oregon, cones are fertilized in April or May and mature during their first winter (Bedell et al. 1993).

Range

USA: Washington, Oregon, Idaho, Nevada and California (Silba 1986). See also Thompson et al. (1999).

The following discussion applies to variety occidentalis:

J. occidentalis var. occidentalis represents the northwestern portion of the piñon and juniper region in the Intermountain West. It has a range extent of approximately 3.6 million hectares (Miller et al. 2005). It is found at elevations of 0-3000 m, mostly on dry rocky slopes (Adams 1993).

Life history: Western junipers primarily regenerate from seed, but trees less than about 60 years of age can also resprout from stems cut near the ground surface. Seeds are cast starting in their first winter and may be spread by gravity, wind, water, or a variety of animals, chiefly the common robin (Turdus migratorius) and Townsend's solitaire (Myadestes townsendi). Seedlings establish primarily in protected microenvironments under woody shrubs. They produce a deep taproot in the first decade of life, and thereafter send out long lateral roots that may extend as much as five times the height of young (<40 years) trees. Growth is slow until the trees are above the shrub layer (commonly 15-25 years) and then accelerates to up to 15 cm per year. Trees normally become fully reproductive when 2.5 to 3 m tall, commonly at about 75 years old. Sex expression is influenced by genome and stress; normally about 10% of trees produce only male cones, 40-50% produce only female cones, and the remainder have mixed composition. Stressed trees produce no cones or predominantly male cones, while in exceptionally benign conditions trees primarily produce female cones (Bedell et al. 1993).

Juniper Invasion: Beginning in ca. 1870, western juniper woodlands in eastern Oregon and adjacent Idaho, Nevada and California began a rapid expansion into former shrub and grass dominated communities, and by the end of the 20th century had increased their range to more than three times the estimated coverage in the mid-1800s (Bedell et al. 1993). The time required for a new woodland to achieve stand closure is 70-90 years on cool wet sites and 120-170 years on dry warm sites (Miller et al. 2005). Various causes of this expansion have been suggested, including an optimal climate from about 1870 to 1915, and long-term overgrazing by cattle and sheep and suppression of natural fire regimes. The increased cover by juniper woodlands causes reduced cover by shrubs and herbs and a proportional increase in exposed soil. This has been tied to significantly increased rates of soil erosion - four times as great as on good condition grasslands, and about 15% more than on sagebrush lands (Bedell et al. 1993). Other ecological changes related to the expansion of juniper woodlands include reduced stream flows; reduced forage production; altered wildlife habitat; changes in plant community composition, structure, and biodiversity; and the replacement of mesic and semi-arid plant communities with woodlands (Miller et al. 2005). This has been very distressing to ranchers, who see juniper as a direct competitor to grass on an increasingly degraded range, and thus extensive efforts have occurred to "control" (i.e. kill) the invasive junipers with bulldozers, chains (a very large chain or cable dragged across the landscape between two bulldozers, uprooting all trees in its path), chainsaws, mechanical shears and whole tree chippers, and prescribed fire (Miller et al. 2005). These efforts have been controversial, partly because some of the control methods are perceived as highly destructive on the landscape, and partly because control is perceived as temporary and questionably effective either ecologically or economically (or both). Miller et al. (2005) provide a very responsible review of the many different sides to the question of whether juniper invasion should be controlled, and if so, then how to do it.

Big Tree

See variety australis.

Oldest

The very oldest specimens are of variety australis. The oldest sampled specimen of the type variety is 1600 years old, and is still alive (see Dendrochronology, below).

Dendrochronology

Both varieties have been used in climate studies. Var. occidentalis has proved particularly useful in dendroclimatology; many collections are tabulated in (Holmes et al. 1986). Rick Miller, researcher out of Oregon State University, reports (e-mail 30-Jul-1999) "The oldest western juniper (var. occidentalis) we have aged to date is 1600 yrs (solid to pith). We have aged around a dozen that are between 1,000 and 1,500 years. These are living trees and have been working with the tree ring lab at Univ. of Ariz. to develop a master chronology. There are probably older trees but it is very difficult to find old trees solid enough to age to the pith. Working with Chris Baisan and Dave Meko from the lab we have cross dated standing dead trees with pith dates going back to around 100 BC. These trees have been dead for 500 to 600 years."

Ethnobotany

"There are some commercial uses of juniper but profit margins are often marginal. To date, products include firewood, chips for particle-flake board and animal bedding, decking, interior paneling, doors, cabinetry, rustic furniture, picture frame molding, small gifts, Christmas decorations, and the female cones are used as flavoring for gin" (Miller et al. 2005). Recently, it has also been chipped for biomass-based electricity generation (Miller et al. 2005).

Observations

Var. occidentalis can be seen widely in the West, notably at the Juniper Dunes Wilderness in WA (its N range limit) and throughout much of E Oregon, SW Idaho and NW Nevada.

Remarks

Citations

Bedell, T.E., L.E. Eddelman, T. Deboodt, and C. Jacks. 1993. Western Juniper -- Its Impact and Management in Oregon Rangelands. Publication EC 1417, Oregon State University Extension Service. 16pp.

Miller, R.F., J.D. Bates, T.J. Svejcar, F.B. Pierson, and L.E. Eddleman. 2005. Biology, Ecology, and Management of Western Juniper (Juniperus occidentalis). Oregon State University Agricultural Experiment Station Technical Bulletin 152. 82pp. (Highly recommended. Can be found on the Web.)

See Also

Burns and Honkala (1990).

Elias (1987).

Lanner (1983).

Farjon (2005) provides a detailed account, with illustrations.

Little (1980).