Juniperus scopulorum, the Rocky Mountain juniper, is a species of juniper native to western North America, from southwest Canada to the Great Plains of the United States and small areas of northern Mexico. They are the most widespread of all the New World junipers. They are relatively small trees, occasionally just a large bush or stunted snag. They tend to be found in isolated groves or even as single trees rather than as the dominant tree of a forest. Though they can survive fires, they are vulnerable to them especially when young and this is one of the factors that can limit their spread into grasslands. Rocky Mountain junipers provide habitat and food for wildlife. They provide cover to a range of species, from small birds and mammals to deer and bighorn sheep. Their berry-like cones are eaten by many animals and their scaly leaves and small twigs are browsed in small amounts by large herbivores. The primary human use is in landscaping for aesthetic purposes, to shelter habitations, or attract fruit-eating birds. They are also used in small amounts for their insect repellent and rot-resistant wood or as firewood for heating.
Description Juniperus scopulorum is a small evergreen tree that in favorable conditions may reach as much as 20 metres (66 feet) in height. However, on sites with little water or intense sun it will only attain shrub height, and even those that reach tree size will more typically be 4.6–6.1 metres (15–20 feet) tall in open juniper woodlands. Younger trees have a narrow pyramidal shape, but develop into a rounded, oval, or spreading and irregular crown when older. They may either have a single trunk or multiple stems. Trunks can be large on mature trees, 38–76 centimetres (15–30 inches) in diameter. When the subsoil is difficult to penetrate and lacks moisture the roots of Juniperus scopulorum spread out. They are numerous and fibrous in the upper part of the soil. When soils are deep and well drained they will grow to a greater depth. On twigs between 5 and 10 millimetres (3⁄16 and 13⁄32 in) in diameter the bark is smooth. On larger twigs and branches it becomes rough, coming off in thin strips. Juniperus scopulorum has red-brown bark on branches that can weather to grey on the trunk. The texture of the bark is rough and comes away in shreds on the trunk with brown bark showing in the cracks at times. Branches tend to grow outwards a short distance and then curve to growing upwards (ascending). In sheltered to somewhat shady locations the branches may hang downwards and be quite slender. The very ends, the branchlets, can either stand upright or hang down.
Young shoots are very slender. All the leaves are light to dark green, but are often covered in a waxy coating that gives a blue or white cast to the leaves (glaucous) making them appear blue-gray or blue. On immature trees they will be covered in sharp needle like "whip leaves" 3–6 millimetres (1⁄8–1⁄4 in) long that stick out from the shoots. The needles will not have the waxy coating on their upper surface. What appear to be green scales on the shoots of adult trees are the mature leaves which clasp the shoot in opposite pairs with the next pair down or up the shoot rotated a quarter turn (90°) around it (decussate). Occasionally they will be turned one third to make the shoot three sided. The scales either do not overlap or overlap for at most one-fifth of their length of 1–3 millimetres (1⁄32–1⁄8 in).
The seed cones are berry-like that are round to somewhat irregular in shape with two lobes (globose to bilobed) and 5–9 mm (3⁄16–11⁄32 in) in diameter. They are dark blue-black in color, but will be pale blue-white when covered in natural wax. The berries most often contain two seeds, but may contain one or three; they are mature in about 18 months. The pollen cones are 2–4 mm (3⁄32–5⁄32 in) long, and shed their pollen in early spring, generally in April. It is usually dioecious, producing cones of only one sex on each tree, but is occasionally monoecious.
Chemistry Rocky Mountain juniper is an aromatic plant. Essential oil extracted from the trunk is prominent in cis-thujopsene, α-pinene, cedrol, allo-aromadendrene epoxide, (E)-caryophyllene, and widdrol. Limb essential oil is primarily α-pinene and leaf essential oil is primarily sabinene. Experiments with deer have found that oxygenated monoterpenes, like sabinene, inhibit the gut bacteria of ruminants and deer show the expected preference for foliage lower in these chemicals.
Similar species Juniperus scopulorum is closely related to eastern redcedar (Juniperus virginiana), and often hybridizes with it where their ranges meet on the Great Plains. It will also form hybrids with alligator juniper (Juniperus deppeana), creeping juniper (Juniperus horizontalis), oneseed juniper (Juniperus monosperma), and Utah juniper (Juniperus osteosperma). The population of juniper trees in Mexico near the former site of Colonia Pacheco, Chihuahua is a hybrid with Juniperus blancoi. There is some disagreement whether hybrids are formed with the oneseed juniper in the wild.
Taxonomy
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