Juniperus scopulorum

Rocky Mountain juniper

Cupressaceae

The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Coniferophyta (conifers). Class - Pinopsida. Order - Pinales. Family - Cupressaceae (cypress). Genus - Juniperus L. Species - Juniperus scopulorum Sarg.

Ecology: Of 11 junipers native to the United States normally reaching tree size, Rocky Mountain juniper is the most widely distributed in western North America. Rocky Mountain juniper is usually found in long-term seral or near-climax vegetation. It is relatively shade-tolerant during the seedling and sapling stages, but it later becomes more intolerant and is unable to endure as much shade as eastern redcedar-its eastern counterpart. Rocky Mountain juniper requires top light for height growth and crown development, and trunk branches die out when it develops in overly dense, pure stands or under deep shade of other tree species. In the northern Rocky Mountains, it is considered less tolerant of shade than ponderosa pine, limber pine, or lodgepole pine but is reported to endure considerable shade from broadleaf trees in protected canyons and sheltered sites on the Pacific coast. Overall, it is most accurately classed as a very shade-intolerant species. It is often found as a climax species in juniper, pinyon-juniper, and pinyon associations in the Rocky Mountain region, and tends toward dominance at higher elevations. It is a minor component of climax or a seral species in Gambel oak and ponderosa pine associations. The species may also be climax with Douglas-fir, or it may occur as a "pioneer" tree species in Douglas-fir succession. In pinyon-juniper habitats, Rocky Mountain juniper is often the first to return after a disturbance, and it may invade sagebrush (Artemisia spp.) stands. In both habitats pinyon may follow and eventually replace it.

Identification

Trees dioecious, to 20 m, single-stemmed (rarely multistemmed); crown conic to occasionally rounded. Bark brown, exfoliating in thin strips, that of small branchlets (5--10 mm diam.) smooth, that of larger branchlets exfoliating in plates. Branches spreading to ascending; branchlets erect to flaccid, 3--4-sided in cross section, ca. 2/3 or less as wide as length of scalelike leaves. Leaves light to dark green but often glaucous blue or blue-gray, abaxial gland elliptic, conspicuous, exudate absent, margins entire (at 20 and 40); whip leaves 3--6 mm, not glaucous adaxially; scalelike leaves 1--3 mm, not overlapping to overlapping by not more than 1/5 their length, keeled to rounded, apex obtuse to acute, appressed or spreading. Seed cones maturing in 2 years, of 2 distinct sizes, generally with straight peduncles, globose to 2-lobed, 6--9 mm, appearing light blue when heavily glaucous, but dark blue-black beneath glaucous coating when mature (or tan beneath glaucous coating when immature), resinous to fibrous, with (1--)2(--3) seeds. Seeds 4--5 mm. 2 n = 22. (Flora of North America)

Threats

Fire effects: Due to its thin bark and compact crown, Rocky Mountain juniper trees up to 0.9-1.2 m tall are easily killed by fire. Since the species grows slowly, trees are especially susceptible to fire for their first 20 years or more. As trees mature, they develop thicker bark and a more open crown, allowing them to survive surface fires if the low, spreading branches do not carry fire to the crown. A severe fire, however, may damage or kill such trees. High volatile oil content, especially in the lower branches, also makes the trees more flammable.

Reproduction

Flowering and Fruiting- Rocky Mountain juniper is dioecious. Both pistillate and staminate flowers are small and are borne on the ends of short branchlets or along the branchlet from mid-April to mid-June. The greenish-yellow female flowers usually contain one or two ovules and become more conspicuous during late summer, opening the following spring before pollination. Pollen is disseminated primarily by wind from inconspicuous yellow male flowers on short branchlets, each flower usually containing six stamens. Female flowers are composed of three to eight pointed scales which become fleshy and fuse to form small indehiscent strobili, commonly called "berries".

Seed Production and Dissemination- Rocky Mountain juniper may begin bearing seed at 10 years of age, under favorable conditions. The optimum age for seed production is 50 to 200 years. Trees that are open grown, stunted, or under stress often are prolific seed producers. Rocky Mountain juniper is rated as a good to prolific seed producer throughout most of its range, but in parts of Idaho and Montana, production is reported as only fair. The interval between heavy seed crops varies from 2 to 5 years, but some seed is produced almost every year. Rocky Mountain juniper is as good a seed producer as its other tree associates, with the possible exception of Utah juniper and singleleaf pinyon. It is a better producer than common or creeping juniper

Seedling Development - Under natural conditions, Rocky Mountain juniper seedlings become established more readily on moist sites under partial shade; in fact, the characteristic sparseness of Rocky Mountain juniper regeneration is due partly to its inability to establish itself on drier sites. The moist sites favored by Rocky Mountain juniper often are conducive to frost-heaving, however, which can take a heavy toll of seedlings. In nurseries, seedlings are best established on mulched seedbeds under partial shade. The seedlings, characterized by acicular foliage (sharp-pointed leaves), develop slowly under natural conditions. Seedlings in the juvenile stages are sometimes confused with common juniper seedlings, but they do not have the basally jointed leaves of that species.

Vegetative Reproduction- Rocky Mountain juniper does not reproduce naturally by sprouts or layering.

Species Distribution

Citation

USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

Flora of North America
Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

Silvics of North America
Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

USGS Plant Species Range Maps
Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97. Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.