|Tree of var. occidentalis, Lava Beds National Monument|
Juniperus occidentalis (Western Juniper and Sierra Juniper) is a shrub or tree native to the western United States, growing in mountains at altitudes of 800-3,000 m (rarely down to 100 m).
The Juniperus occidentalis shoots are of moderate thickness among junipers, 1-1.6 mm diameter. The leaves are arranged in opposite decussate pairs or whorls of three; the adult leaves are scale-like, 1–2 mm long (to 5 mm on lead shoots) and 1-1.5 mm broad. The juvenile leaves (on young seedlings only) are needle-like, 5–10 mm long. The cones are berry-like, 5–10 mm in diameter, blue-brown with a whitish waxy bloom, and contain one to three seeds; they are mature in about 18 months. The male cones are 2–4 mm long, and shed their pollen in early spring.
The cones are an important food for several birds, including American Robin, Phainopepla and Cedar Waxwing; these digest the fleshy cone scales and disperse the seeds in their droppings. The plants often bear galls caused by the Juniper Tip Midge Oligotrophus betheli (Bibionomorpha: Cecidomyiidae); these are violet-purple fading to brown, 1–2 cm diameter, with dense modified spreading scale-leaves 6–10 mm long and 2–3 mm broad at the base.
Juniperus occidentalis usually occurs on dry, rocky sites where there is less competition from larger species like Ponderosa Pine and Coast Douglas-fir. In very exposed positions at high altitude, they can assume a krummholz habit, growing low to the ground even when mature with a wide trunk (see image at left). Hybrids with Juniperus osteosperma are occasionally found.
Media related to Juniperus occidentalis at Wikimedia Commons
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