Juniperus occidentalis subsp. occidentalis
Western juniper (Peattie 1950).
The type was collected in 1826 by David Douglas, near the Columbia River. He described it as "Common on the higher parts of the Columbia, at the base of the Rocky Mountains." This collection was nearly at the northern limit of the species' range (Farjon 2005).
Synonymy (Farjon 2005):
See Juniperus occidentalis. Subsp. occidentalis is often (50%) monoecious. Branchlets mostly have 3 scale leaves per whorl. Mature seed cones average 7.5 mm diameter. Seedlings mostly have 2 cotyledons (Adams 1993, Farjon 2005).
In eastern Oregon, cones are fertilized in April or May and mature during their first winter (Bedell et al. 1993).
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), occurring at elevations of (185-)670-1525(-2500) m (Dealy 1990).
Climate is semi-arid continental, with dry hot summers, cold winters, and precipitation of 230 to 355 mm falling from fall to spring as rain or snow. The average temperature in January is -1°C and in July, 18°C, with extremes as much as 20° colder or hotter. Summer lightning storms are common and result in natural fires which have historically had a major influence on the species' distribution. Soils are highly variable but are generally of silicate origin, often weakly developed and stony; carbonate, where present, is usually depositional due to the dry climate. Soils in mature stands have elevated levels of Ca, K, and pH, factors that apparently confer a competitive advantage (Dealy 1990).
Western juniper often forms pure stands, or is associated with Pinus ponderosa or Cercocarpus ledifolius. Near its upper elevation limits, common associated trees include Abies concolor, Pinus contorta subsp. latifolia, Pinus ponderosa subsp. ponderosa, and Pseudotsuga menziesii subsp. glauca. The most common shrub associate is Artemisia tridentata (sagebrush); other common shrubs include Chrysothamnus nauseosus, C. viscidiflorus, Purshia tridentata, Ribes cereum, and Tetradymia spp. (Dealy 1990).
Life history: Normally pollen is released in May, with cones maturing in September of the second season. A good cone crop is produced almost every year, so most trees bear two years' worth of cones. Seeds are dispersed during the fall and winter, and germinate in April (Dealy 1990). 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.
Death and Destruction: Historically, fire was likely the principal agent of mortality. Prior to maturity, the species is highly vulnerable to fire, and invasive stands of this age are most easily controlled by prescribed fire. Mature trees have some resistance to fire because they have little fuel near the stem and relatively thick bark, and because foliage is fairly high above the ground. The oldest stands, though, occur in relatively fireproof locations where sufficient fuels do not accumulate and the wide spacing betweent trees retards the spread of fire (Dealy 1990 and pers. obs.). Insect infestation has not been intensively studied in this species because it has relatively little commercial value, and severe infestations have seldom been observed. The juniper bark beetle (Phloeosinus serratus) can cause mortality, particularly to trees in a weakened condition, such as during drought. Gall midges feed on western juniper and produce galls (Dealy 1990). The principal fungal diseases include a white trunk rot (Pyrofomes demidoffii) that attacks living trees and an unidentified brown cubicle rot usually found in the basal portions of the trunk (Dealy 1990). I have observed that these fungi are common in fast-growing trees growing on relatively moist sites, but are rare in trees on severely dry sites. Fungi known to attack foliage include endophytic fungi Retinocyclus abietis anamorpha and Hormoneme sp. Infection rates increase with age, density, and purity of stands, but in general, western juniper is minimally susceptible to infection (Petrini and Carroll 1981 in Dealy 1990). Two mistletoes, Phoradendron ligatum and P. densom, cause lower vigor, deformity of branches, and brooming of the foliage. Brooming of foliage can also be caused by the stem rusts Gymnosporangium kernianum and G. betheli (Herbst 1978 in Dealy 1990).
No data as of 2009.
The oldest sampled specimen of the type variety is 1600 years old, and is still alive (see Dendrochronology, below).
This subspecies has proved particularly useful in dendroclimatology; many collections are tabulated by Holmes et al. (1986). Rick Miller, researcher out of Oregon State University, reports (e-mail 1999.07.30) "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."
"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).
Western juniper 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. Once you are north or west of the range of Juniperus osteosperma, it is by far the most common juniper on the landscape.
Adams, Robert P. 1993. Juniperus. Flora of North America Editorial Committee (eds.): Flora of North America North of Mexico, Vol. 2. Oxford University Press. This document is available online. Go to http://www.efloras.org, click on "Flora of North America," and search for "Juniperus."
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.
Dealy, J. E. 1990. Western juniper, in Burns and Honkala (1990).
Herbst, John R. 1978. Physical properties and commercial uses of western juniper. P. 169-177. in R.E. Martin, J.E. Dealy, and D.L. Caraher (eds.), Proceedings, Western Juniper Ecology and Management Workshop. General Technical Report PNW-74. Portland, OR: Pacific Northwest Forest and Range Experiment Station.
Hooker, William Jackson. 1838. Flora Boreali-Americana 2 (10): 166.
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.)
Petrini, Orlando, and George Carroll. 1981. Endophytic fungi in foliage of some Cupressaceae in Oregon. Canadian Journal of Botany 59:629-636.
Johnson, D.D. and R.F. Miller. 2006. Structure and development of expanding western juniper woodlands as influenced by two topographic variables. Forest Ecology and Management 229(1-3): 7-15.
Last Modified 2017-12-29