Western Juniper

''Juniperus occidentalis'', known as the western juniper, is a shrub or tree native to the Western United States, growing in mountains at altitudes of and rarely down to . It is listed as Least Concern on the IUCN Red List because it is a widespread species with an increasing population.

Description

''Juniperus occidentalis'' is a shrub or small tree tall. Exceptionally tall specimens can be found in the John Day area of Oregon in excess of tall.

The shoots are of moderate thickness among junipers, at diameter. The juvenile leaves (on young seedlings only) are needle-like and long. Arranged in opposite decussate pairs or whorls of three, the adult leaves are scale-like, 1–2 mm long (5 mm on lead shoots) and 1–1.5 mm broad. The cones are berry-like, 5–10 mm in diameter, blue-brown with a whitish waxy bloom, and mature in about 18 months. The male cones are 2–4 mm long and shed their pollen in early spring. The plants are about half monoecious (with both sexes on the same plant) and half dioecious (producing cones of only one sex).

The cones contain 1–3 seeds, the majority of which germinate in springtime. In Oregon, where most of the species resides, seeds germinate in April and the foliage emerges in June. Seed dispersal is conducted by water runoff, gravity, and animals.

Western juniper (14149478156).jpg, Form
Juniperus occidentalis 8249.jpg, Berry-like female cones
Western juniper berries.JPG, Leaves and cones

Taxonomy

Further to the south, '' Juniperus grandis'' (the Sierra juniper) is sometimes treated as a variety of ''J. occidentalis'' (as ''J. occidentalis'' var. ''australis''). ''J. grandis'' is tall with a trunk up to in diameter. The cones are wide. Most plants are dioecious, but about 5–10% are monoecious. The two plants are also chemically distinct. ''J. grandis'' can be found in California and westernmost Nevada, south of 40° 30' N latitude in the Sierra Nevada and San Bernardino Mountains. The oldest and largest specimen of ''J. grandis'' is tall and wide, perhaps 3,000 years old, and located in California's Stanislaus National Forest.

Distribution and habitat

''J. occidentalis'' can be found in the Western United States—specifically southeast Washington, eastern and central Oregon, southwest Idaho, northeastern California and extreme northwest Nevada, north of 40° 30' N latitude, east of the Cascade Range.

It usually occurs on dry, rocky sites where there is less competition from larger species like ponderosa pine and coast Douglas-fir. Annual precipitation can be as low as . In very exposed positions at high altitude, it can assume a ''krummholz'' habit, growing low to the ground even when mature with a wide trunk. Hybrids with '' J. osteosperma'' are occasionally found.

In the John Day area of Oregon, it competes for sunlight among ponderosa pines at the bottom of some deep side canyons. However, it more commonly reaches with a bushier growth habit on open and barren ground.

Ecology

The cones are an important food for several birds, including American robin, Clark's nutcracker, 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''. These are violet-purple fading to brown, in diameter, with dense modified spreading scale-leaves long and 2–3 mm broad at the base.

Fire ecology

In the past two decades, sagebrush steppe

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