About Juniperus occidentalis Hook.
Juniperus occidentalis Hook. is most often a shrub or small tree that grows 4 to 15 meters (13 to 49 feet) tall. Exceptionally large specimens growing taller than 26 to 28 meters (85 to 92 feet) can be found in the John Day area of Oregon. Its shoots are moderately thick for a juniper, with a diameter of 1 to 1.6 millimeters (1⁄32 to 1⁄16 inch). Only young seedlings produce juvenile leaves, which are needle-like and 5 to 10 mm (3⁄16 to 13⁄32 inch) long. Adult leaves are scale-like, arranged in opposite decussate pairs or whorls of three; they are typically 1 to 2 mm long, reaching up to 5 mm on lead shoots, and 1 to 1.5 mm broad. The species produces berry-like cones that are 5 to 10 mm in diameter, blue-brown with a whitish waxy bloom, and mature in around 18 months. Male cones are 2 to 4 mm long and shed their pollen in early spring. Around half of all Juniperus occidentalis plants are monoecious, bearing both sexes on the same plant, while the other half are dioecious, producing cones of only one sex. Each cone holds 1 to 3 seeds, and most of these seeds germinate in spring. In Oregon, where most of the species' population grows, seeds germinate in April and new foliage emerges in June. Seeds are dispersed by water runoff, gravity, and animals.
Juniperus occidentalis is native to the Western United States, where it occurs specifically in southeast Washington, eastern and central Oregon, southwest Idaho, northeastern California, and extreme northwest Nevada, located north of 40° 30' N latitude and east of the Cascade Range. It most commonly grows on dry, rocky sites, where it faces less competition from larger species such as ponderosa pine and coast Douglas-fir. It can grow in areas with annual precipitation as low as 20 centimeters (7+7⁄8 inch). In very exposed high-altitude locations, mature Juniperus occidentalis may develop a krummholz growth habit, staying low to the ground even when it has a thick, wide trunk. Hybrids between Juniperus occidentalis and Juniperus osteosperma are occasionally found. In the John Day area of Oregon, the species grows and competes for sunlight alongside ponderosa pines at the bottom of some deep side canyons, but it more often grows to 4–15 m (13–49 ft) with a bushier habit on open, barren ground.
For ecology, Juniperus occidentalis cones are an important food source for several bird species, including the American robin, Clark's nutcracker, phainopepla, and cedar waxwing. These birds digest the fleshy cone scales and disperse the plant's seeds in their droppings. Juniperus occidentalis plants often develop galls caused by the juniper tip midge Oligotrophus betheli. These galls are violet-purple when young, fading to brown as they age, 1 to 2 cm (3⁄8 to 13⁄16 inch) in diameter, and covered in dense, modified spreading scale-leaves that are 6 to 10 mm (1⁄4 to 3⁄8 inch) long and 2 to 3 mm broad at the base.
Regarding fire ecology, sagebrush steppe ecosystems across the western United States have seen an expansion of Juniperus occidentalis over the past two decades. This vegetation shift is linked to decreased fire frequency, livestock overgrazing, and climate change that has resulted in a wetter, milder climate. Dated fire scar data shows that the expansion of western juniper began between 1875 and 1885, with the peak growth rate occurring between approximately 1905 and 1924. Since the 1990s, the use of prescribed fires to control the species' expansion has increased, and this practice has been shown to have a positive effect on local plant communities.
For uses, like other junipers, Juniperus occidentalis produces cone crops commonly called juniper berries. While original European gin was flavored with berries from Juniperus communis, several distilleries (especially in Bend, Oregon) use locally harvested western juniper berries to flavor their gin. Western juniper is not a common lumber source, but Oregon State University has sponsored research into using it for commercial applications such as sign posts and guard rails. Western juniper lumber is known for its durability and high compression strength.
