J. Edward Dealy
Western juniper (Juniperus occidentalis) is also called Sierra juniper. There are two subspecies separated geographically, occidentalis in the northern part and australis in the southern part of its range. Unless specifically identified, both are included in the following discussion. One of the largest western junipers recorded grows on the Stanislaus National Forest in California. It measures 414 cm (163 in) in d.b.h., is 26.5 m (87 ft) tall, and has a crown spread of 15.5 m (51 ft).
Regularity: Regularly occurring
Western juniper occurs from southeastern Washington and Oregon southward to the upper slopes of the Sierra Nevada and San Bernardino Mountains of southern California . It occurs along the western edge of the Great Basin in southwestern Idaho and northwestern Nevada .
The subspecies J. occidentalis var. australis occurs most commonly in the subalpine zone to forested uplands of the northern Coast Ranges and the Sierra Nevada Mountains of California, southward to California's San Bernardino, San Gabriel and various desert mountain ranges westward into Nevada [44,98,103,106]. The variety J. occidentalis var. occidentalis occurs from the Cascade Range through the Modoc Plateau into adjacent parts of Washington, Oregon, and Idaho, and southward into northwestern Nevada . It reaches its greatest extent in central Oregon east of the Cascade Range .
During the past 150 years, western juniper has extended its range and now occupies approximately 42 million acres (17 million hectares) in the Intermountain West [16,36]. It grows over approximately 4 million acres (1.6 million hectares) in the Pacific Northwest .
Regional Distribution in the Western United States
This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):
1 Northern Pacific Border
2 Cascade Mountains
3 Southern Pacific Border
4 Sierra Mountains
5 Columbia Plateau
6 Upper Basin and Range
Occurrence in North America
CA ID NV OR WA
- The native range of western juniper.
Western juniper is a tree that typically grows 15 to 30 feet (4.6 to 9.1 m) . It rarely exceeds 60 feet (18.3 m) in height. The largest recorded specimen is 86 feet tall (26 m), with a circumference of 480 inches (1,219 cm) and crown spread of 58 feet (18 m) . Trees develop full crowns and heavy limbs at maturity .
Varieties differ with respect to growth characteristics. The variety Juniperus occidentalis var. australis reaches an average height of 26 feet (7.9 m), with a maximum height of 50 feet (15.2 m), whereas J. occidentalis var. occidentalis typically grows to 23 feet (7.0 m) in height, and rarely grows over 40 feet (12.2 m). Average circumference of the largest stem 5 feet (1.5 m) above the ground of J. occidentalis var. australis is 84 inches (213 cm), while only 42 inches (107 cm) for J. occidentalis var. occidentalis .
Bark is furrowed and shreddy . Taproots average 51 inches (130 cm) in depth . Root-to-shoot ratios decrease with age giving western juniper the ability to outcompete species such as big sagebrush .
Western juniper is slow growing and long lived . Individuals can survive for 1,000 years or longer . The Bennett juniper, which grows near Sonora Pass, California, is believed to be 3,000 to 6,000 years old [4,12]. Annual growth of mature western juniper is as follows :
Stand Height Diameter
inch cm inch cm
Open, dominant 3.5 9 0.3 0.8
Closed, subdominant 3.5 9 0.1 0.4
Closed, young 1.2 3 0.05 0.2
Highest rate 4.3 11 0.5 1.3
Catalog Number: US 280590
Collection: Smithsonian Institution, National Museum of Natural History, Department of Botany
Verification Degree: Verified from the card file of type specimens
Preparation: Pressed specimen
Collector(s): D. Douglas
Locality: Base of Rocky Mts., the Columbia., Washington, United States, North America
- Type material: Hooker, W. J. 1838. Fl. Boreali-Amer. (Hooker). 2: 166.
Habitat and Ecology
Western juniper occurs in open stands on mountain slopes and high plateaus . It grows as scattered individuals on rimrock or rock outcrops and in higher densities along streams, on scablands, and lower slopes where water has dispersed the seed . It has remained dominant in shifting sand dune communities of south-central Washington where fire is unlikely .
The growth of western juniper is favored by long, dry summers and cold winters with little moisture . Western juniper often occurs in a zone between desert, shrub-steppe, or grassland below and ponderosa pine (Pinus ponderosa) or sagebrush (Artemisia spp.) desert above [37,87]. Cold winter temperatures may restrict its occurrence at higher elevations . It occurs in the most xeric tree-dominated zone of the Pacific Northwest . Soil, climate, topography, fire, and biotic factors all contribute to the distribution of western juniper, but moisture is thought to be the primary determinant .
Average annual precipitation ranges from approximately 10 to 13 inches (250-330 mm), with the bulk occurring as winter snow. Temperature ranges from 36 to 105 degrees Fahrenheit (2-41oC), with an average July temperature of 66 degrees Fahrenheit (19oC). The growing season rarely exceeds 130 days .
Western juniper generally grows on soils that are shallow, stony, and low in organics [82,95]. Western juniper grows on soils derived from basalt, andesite, rhyolite, pumice, volcanic ash, tuff, welded tuff, colluvial, alluvial, or eolian mixtures . In the Sierra Nevada, Sierra juniper grows on granitic crevices on windswept ridges . Surface soils supporting western juniper are often slightly acid to moderately acidic sandy loams or coarse sands with little organic matter (1 to 4%) [37,95]. Western juniper also grows on finely-textured calcareous soils . Levels of calcium, potassium, and pH are higher under mature western juniper than in the interspaces [22,23]. Soil depth ranges from 10 to 15 inches (25-38 cm) to more than 48 inches (122 cm). The subsoil is typically broken and indurated with cracked bedrock below . Western juniper is best adapted to soils exhibiting rapid infiltration, deep percolation, low evaporation, and low soil moisture tension . Western juniper is often found on a perched water table .
Western juniper grows from near sea level to more than 10,000 feet (3050 m) . Elevational ranges are as follows [42,87]:
3,000 to 10,000 feet (915-3050 m) in California
3,000 to 7,500 feet (915-2288 m) in central Oregon
600 to 1,800 feet (183-549 m) in eastern Washington
Key Plant Community Associations
Western juniper is an indicator of climax in a variety of sagebrush (Artemisia spp.) grassland, shrub-steppe, and dry coniferous habitat types. It occurs as a codominant with singleleaf pinyon (Pinus monophylla), big sagebrush (A. tridentata), gray low sagebrush (A. arbuscula ssp. arbuscula), stiff sagebrush (A. rigida), curlleaf mountain-mahogany (Cercocarpus ledifolius), antelope bitterbrush (Purshia tridentata), rubber rabbitbrush (Chrysothamnus nauseosus), green rabbitbrush (C. viscidiflorus), arrowleaf balsamroot (Balsamorhiza sagittata), Sandberg bluegrass (Poa secunda), Idaho fescue (Festuca idahoensis), bluebunch wheatgrass (Pseudoroegneria spicata), smilo grass (Piptatherum micranthum), and Thurber needlegrass (Achnatherum thurberiana). Western juniper also occurs with spiny hopsage (Grayia spinosa), gray horsebrush (Tetradymia canescens), junegrass (Koeleria macrantha), needle-and-thread grass (Hesperostipa comata), bottlebrush squirreltail (Elymus elymoides), and other grasses [27,37,87].
Western juniper has been described as an indicator or dominant in the following published classifications:
A relict area in the central Oregon juniper zone 
Plant communities and habitat types in the Lava Beds National Monument, California 1979 
Great Basin pinyon and juniper communities and their response to management 
Plant communities of the Blue Mountains in eastern Oregon and southeastern Washington 
Plant associations of south Chiloquin and Klamath Ranger Districts, Winema National Forest 
Plant associations of the Fremont National Forest 
Vegetation types of the San Bernardino Mountains 
Plant associations of the Wallowa-Snake Province: Wallowa-Whitman National Forest 
Woodland classification: the pinyon-juniper formation 
Preliminary classification for the coniferous forest and woodland series of Arizona and New Mexico 
Forest/environment relationships in Yosemite National Park, California USA 
A vegetation classification system applied to southern California 
Habitat: Rangeland Cover Types
This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):
107 Western juniper/big sagebrush/bluebunch wheatgrass
109 Ponderosa pine shrubland
110 Ponderosa pine-grassland
201 Blue oak woodland
209 Montane shrubland
322 Curlleaf mountain-mahogany-bluebunch wheatgrass
412 Juniper-pinyon woodland
415 Curlleaf mountain-mahogany
This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):
FRES21 Ponderosa pine
FRES26 Lodgepole pine
FRES28 Western hardwoods
Habitat: Cover Types
This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):
205 Mountain hemlock
207 Red fir
208 Whitebark pine
211 White fir
218 Interior Douglas-fir
237 Interior ponderosa pine
238 Western juniper
247 Jeffrey pine
250 Blue oak-gray pine
256 California mixed subalpine
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
K007 Red fir forest
K008 Lodgepole-pine-subalpine forest
K011 Western ponderosa forest
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K030 California oakwoods
Soils and Topography
Under mature western juniper trees in central Oregon, soil Ca, K, and pH are higher than in inter-space soils and soils under young trees. These changes appear to increase the ability of western juniper to compete with other vegetation (7).
Soils supporting juniper at high densities are frequently Mollisols. Argixerolls, Haploxerolls, and Haplaquolls are common great groups. Soils supporting scattered juniper are commonly Aridisols-including Camborthids, Durargids, and Haplargids however, Argixerolls are also common. Other soils on which western juniper can be found are Durixerolls and Cryoborolls of the order Mollisols, Torriorthents of the order Entisols, and Chromoxererts of the order Vertisols (5,6).
Western juniper is found on all exposures and slopes. In central Oregon, it is common in large continuous stands on level to gentle topography. In other areas, it grows less continuously on terraces, moderately sloping alluvial fans, canyon slopes, and steep, rocky escarpments (5,6,8). Elevations at which western juniper is found range from about 185 m (600 ft) along the Columbia River to more than 3050 m (10,000 ft) in the Sierra Nevada (24). In central Oregon, there are large, continuous stands between 670 and 1525 m (2,200 and 5,000 ft) (8).
Although western juniper grows in extensive stands in a narrow range of precipitation (230 to 355 mm; 9 to 14 in) in central Oregon, it is a minor species in many upper elevation areas of higher precipitation. The latter areas have shallow, rocky soils too droughty to support other more common upper-slope conifers.
Associated Forest Cover
Western juniper is recognized in five forest cover types (9). It is the dominant species in Western Juniper (Society of American Foresters Type 238); an associate species in Interior Ponderosa Pine (Type 237) and Jeffrey Pine (Type 247); and a minor or occasional species in Blue Oak-Digger Pine (Type 250) and California Mixed Subalpine (Type 256).
Big sagebrush (Artemisia tridentata) is the most common shrub species associated with western juniper throughout its range. Other shrubs common to western juniper communities in the northern portion of its range are gray rabbitbrush (Chrysothamnus nauseosus), green rabbitbrush (C. viscidiflorus), antelope-brush (Purshia tridentata), wax currant (Ribes cereum), and horsebrush (Tetradymia spp.). Less common shrubs are low sagebrush (Artemisia arbuscula), stiff sagebrush (A. rigida), spiny hopsage (Atriplex spinosa), broom snakeweed (Gutierrezia sarothrae), prickly phlox (Leptodactylon pungens), and desert gooseberry (Ribes velutinum) (2,5,8).
Common grass or grasslike species in northern areas are bluebunch wheatgrass (Agropyron spicatum), cheatgrass (Bromus tectorum), Idaho fescue (Festuca idahoensis), prairie Junegrass (Koeleria cristata), Sandberg bluegrass (Poa sandbergii), bottlebrush squirreltail (Sitanion hystrix), and Thurber needlegrass (Stipa thurberiana). Less common are threadleaf sedge (Carex filifolia), Ross sedge (C. rossii), sixweeks fescue (Festuca octoflora), needle-and-thread (Stipa comata), and western needlegrass (S. occidentalis). Forb species common to northern communities include western yarrow (Achillea millefolium), milkvetch (Astragalus spp.), littleflower collinsia (Collinsia parviflora), obscure cryptantha (Cryptantha ambigua), lineleaf fleabane (Erigeron linearis), woolly eriophyllum (Eriophyllum lanatum), spreading groundsmoke (Gayophytum diffusum), lupine (Lupinus spp.), a suffrutescent wild buckwheat (Eriogonum spp.), and tufted phlox (Phlox caespitosa). Less common associates are sulfur eriogonum (Eriogonum umbellatum), small bluebells (Mertensia longiflora), and Hooker silene (Silene hookeri) (2,5,8).
Major western juniper associations in central Oregon include Juniperus/Artemisia/Festuca, Juniperus/Artemisia/Festuca-Lupinus, Juniperus/ Festuca, Juniperus/Artemisia/Agropyron-Chaenactis, Juniperus/ Artemisia/Agropyron, Juniperus/Artemisia/Agropyron-Astragalus, Juniperus/Artemisia-Purshia, Juniperus/Agropyron, and Juniperus/ Agropyron-Festuca (8).
In one treatment of vegetation types in the conterminous United States, western juniper is considered the dominant species in the Juniper Steppe Woodland (Juniperus-Artemisia-Agropyron), number 24, and is a secondary species in the Juniper-Pinyon Woodland (Juniperus-Pinus), number 23 (8,10,17).
Diseases and Parasites
Because the species has relatively little commercial value, little attention has been given to the identification or effect of insects that attack western juniper. Serious damage in western juniper by insects is infrequent. The juniper bark beetle (Phloeosinus serratus) can cause mortality, particularly to trees in a weakened condition, during a drought (24). Gall midges feed on western juniper and produce galls; however, their effect on productivity has not been studied. Although termites are not considered a problem in use of products made from western juniper wood, an unidentified species of termite has been observed in dead material on lower portions of overmature trees, as well as in juniper fenceposts in central Oregon.
The principal damaging agents to western juniper are a white trunk rot (Pyrofomes demidoffii) that attacks living trees and an unidentified brown cubicle rot usually found in the basal portions of the trunk (24). These rots cause high losses and have prevented the use of western juniper wood for pencils. A single sporophore in evidence usually indicates a tree is unmerchantable. The endophytic fungi Retinocyclus abietis anamorpha and Hormoneme sp.have been found on the foliage of western juniper. Infection rates increase with age, density, and purity of stands. In general, western juniper is minimally susceptible to infection (22). Two mistletoes, identified as constricted mistletoe (Phoradendron ligatum) and dense mistletoe (P. densom), cause lower vigor, deformity of branches, and brooming of the foliage (12). A third mistletoe, R. juniperinum (Viscaceae), also occurs on western juniper (25). Brooming of foliage is also caused by the stem rusts Gymnosporangium kernianum and G. betheli. One other rust of the same genus has been reported (12). Except for the white trunk rot and the unidentified brown one, none of the diseases that attack western juniper has been assessed.
Fire Management Considerations
Western juniper sites with less than 1,322 pounds per acre (600 kg/ha) of fine fuels are difficult to burn
. As the crown of an established western juniper expands over time,
herbaceous production declines from the combined effects of shading, litter accumulation,
and soil moisture . Trees create their own fine fuel break,
so these stands may be virtually "fireproof" except under the "most severe burning conditions"
Many western juniper woodlands have advanced to a point where prescribed fire is no longer
a viable management option. For example, in extremely dense stands, prescribed burning would be
both hazardous and expensive. In some cases, weedy annuals prevent the establishment of more
desirable perennial species after fire .
However, prescribed burning can in some instances be used to reduce western juniper
and may offer the best means of control.
in areas of western juniper invasion. Fall and spring prescribed fires in in a basin big sagebrush community in
east-central Oregon, for example, killed 100% of western juniper seedlings on
study plots . See the Fire Case Study and Research Project Summary of this study for more information on fire effects
on western juniper and 60 additional shrubs, grasses, and forbs.
Warm dry conditions are necessary for fire to carry in western juniper woodlands.
Often mature open stands can be used as fuel breaks. Steady winds greater than 5 miles per hour (8.1 k/h), temperatures of at least 68 degrees Fahrenheit (20oC), and relative humidity of less than 25% are generally required for a successful burn . Generally, where tree cover is greater than 30%, there is so little herbaceous understory that extremely high winds are needed to support a burn . Thirty- to 50-year-old western junipers under 10 feet (3.1 m) in height and with an understory are fairly easy to burn, as are dense, uneven-aged mature stands .
Western juniper slash can be burned where fine fuels average 400 to 700 pounds per acre (181-318 kg/ha), and where slash fuel Â¼ to 3+ inches (0.6->8 cm) totals at least 4 tons per acre (11 Mg/ha). For best results, trees should retain their needles and fuels should be fairly continuous. A rest from grazing followed by a late summer to fall burn can produce better results due to more continuous fine fuels .
Western juniper tends to have more resinous foliage than many other species. Ash and heat content values are as follows :
foliage litter cones woody fuel
average ash content (%) 4.26 5.31 3.42 1.35-2.80
average heat content
with ash (mJ/kg) 23.64 22.53 23.68 20.04-20.27
average heat content
without ash (mJ/kg) 24.70 23.79 24.51 20.31-20.66
Van Wagtendonk and others  recommend adjusting fire spread models for use with Sierra Nevada conifers. If standard fuel models are used, they suggest adjusting fire front with the following "correction factors:"
heat per Unit Area fireline intensity flame length
0.98 0.95 0.98
Western juniper-low sagebrush communities that have been invaded by medusahead (Taeniatherum caput-medusae) are often extremely "fire hazardous" .
Broad-scale Impacts of Plant Response to Fire
Recovery time depends on the size of burn, location of seed source, stand maturity, and presence of animal dispersers . Postburn succession in western juniper communities depends on season of burn, postfire mortality, and on seed of associated species present in the preburn community. Postfire succession is also related to the effects of competition from herbaceous species and shrubs as well as drought. Large burns and long distances from seed sources slow recovery rates. According to Bunting and others  "because these factors vary widely early seral community composition is highly variable." Fire scars have been observed on western junipers found growing in fire-resistant low sagebrush communities lacking perennial grass cover .
Plant Response to Fire
Mature trees are somewhat resistant to fire if the crown is not scorched, so some larger trees may survive low-severity fires and serve as a seed source . Western juniper first becomes dominant 30 to 50 years after fire . Reoccupation of a site occurs fairly slowly through dispersed seed [19,25].
Broad-scale Impacts of Fire
Western juniper foliage is not easily ignited and/or scorched when moist . Western junipers under 4 to 6 feet (1.2-1.8m) tall are readily killed by fire [64,17]. A more severe fire is necessary to kill taller trees .
Immediate Effect of Fire
Western juniper is a nonsprouter that is generally killed by severe fires . Younger trees have thin bark and are readily killed by surface fires . Older trees with thicker bark, little fuel near the stem, and higher foliage are moderately resistant to fire [38,87]. Fire may not carry in open stands of mature trees with sparse understory vegetation .
Tree without adventitious bud/root crown
Initial off-site colonizer (off-site, initial community)
Secondary colonizer - off-site seed
Young western junipers have thin bark and are readily killed by surface fires. "Older" trees with thicker bark are described as "moderately resistant" to fire . In general, the taller the juniper, the greater the severity of the fire required to kill it . Western juniper does not sprout . Reestablishment is through seed that is dispersed fairly slowly by water and animals.
FIRE REGIMES in western juniper communities: When fires occurred at 10 to 25 year intervals, western juniper was restricted to protected microsites . Belsky  reports that "at current levels of livestock grazing and fire control, western juniper woodlands represent the final phase of vegetative succession in parts of Oregon, California, and Idaho." In climax western juniper communities, all age classes are typically represented from seedlings to trees several hundred years in age .
Fire return intervals in western juniper communities range from 7 to 25 years to more than 100 years . Mean fire interval for western juniper within the Columbia River Basin is estimated at 52 years . Fire return intervals within western juniper communities have been reported as follows:
California: 7-17 years
southwestern Idaho: 25 years
Nevada: 15-20 years 
southwestern Oregon: < 20 years 
In western juniper woodlands of the San Bernardino Mountains of California, infrequent canopy fires produce a mosaic of fairly small scattered patches within uniform stands .
FIRE REGIMES in other communities: The range of fire intervals reported for some species that dominate communities where western juniper occurs are listed below. To learn more about the FIRE REGIMES in those communities refer to the FEIS summary for that species, under "Fire Ecology or Adaptations."
Pacific ponderosa pine (Pinus ponderosa var. ponderosa): 2-42 years
red fir (Abies magnifica var. magnifica): 10-65 years
(Abies magnifica var. shastensis): 70-130 years
More info for the terms: climax, fire frequency, fire suppression, frequency, invasive species, shrub, tree
Western juniper is a highly competitive invasive species . It is found on all exposures and slopes but is relatively intolerant of shade [22,23]. This long-lived species has been expanding its range into adjacent shrub-steppes, grasslands, and savannas during the past 100 to 150 years . It has doubled its range in central and eastern Oregon during the past 80 to 100 years . Expansion into low sagebrush communities has been slower than into big sagebrush communities . Expansion into shrub steppe communities in Nevada has reduced understory diversity and productivity . Western juniper expansion has been attributed to livestock grazing and associated reductions in fine fuels, climatic changes (mild temperatures and above average precipitation in the late 1880s and early 1900s), and reduction in fire frequency due to fire suppression and cessation of Native American burning [8,29,74,75].
Climax stands are generally restricted to rimrock and the edges of mesas, whereas seral communities can dominate slopes and valley bottoms adjacent to older western juniper stands . Old growth western juniper is generally found in "firesafe" spots . This tree was formerly restricted to rocky ridges and outcrops, deep pumice soils and on fractured bedrock. Western juniper remains a climax dominant in rimrock and similar sites due to the rocky substrate and lack of fuels needed to carry an intense fire [1,18]. Western juniper is an indicator of climax in a number of sagebrush-grassland, shrub-steppe, and drier conifer habitat types. Some communities represent topo-edaphic climaxes .
Western juniper survives on harsh sites and is increases in many early seral communities. In seral communities near Prineville, Oregon, young classes of western juniper predominate with a maximum age of nearly 100 years in these seral stands. In non-seral communities western junipers are at least several hundred years in age .
Western juniper regenerates through seed. Green pistillate megastrobili form seed cones in abundance [87,92]. Female cones first develop 2 weeks after the male cones, and seed cones remain on the tree for 2 years until mature [72,84]. Seed cones generally ripen in mid-September. Seed cones are blue-green prior to ripening, and bluish-black and glaucous when ripe . Cone-berries contain 1 to 4 (more rarely up to 12) brownish seeds . Western juniper is monoecious or dioecious . Many plants have the capacity to shift their sex from year to year, depending on conditions. Trees bordering roads or clearings typically produce much greater numbers of female cones than do trees within stands .
Seed production typically begins at 20 years of age or more, but few seed cones are produced until the tree reaches 50 to 70 years of age [28,29]. Full reproductive potential is achieved at 50 years or older . Western juniper produces an abundance of seed cones nearly every year after maturity .
The germination of most species of juniper is delayed due to embryo dormancy, impermeable seedcoats, or temperature constraints. Western juniper seed is dormant when freshly harvested. Germination of juniper seed has been described as "erratic and unpredictable" . Specific information on germination characteristics is available [50,104]. Tueller  reports that germination in junipers (Juniperus spp.) "is not a straight-forward process, but one that requires a specific sequence of environmental conditions for natural germination and seedling establishment." Mineral soil may be required for best seedling establishment .
Seed of western juniper is dispersed by birds, mammals, water, and gravity . In a southwestern Idaho study, western juniper seed dispersed an average of 4.7 feet (1.42 m) downslope and 2.0 feet (0.60 m) upslope during a 4-month summer period, and an average of 4.2 feet (1.29 m) during a 6-month winter period. More distant seed dispersal in summer is due to animals. Most, if not all, uphill seed movement can be attributed to animal dispersal. Livestock may aid in dispersal by kicking or rolling seeds . The seeds of many juniper species are thought to germinate faster after the seed cone has been consumed by animals . Rabbits, ground squirrels, woodrats and other rodents, mule deer, elk, coyotes, and domestic livestock are all dispersal agents for western juniper [19,84]. Schupp and others  report that although rabbits, deer, and other mammals consume cone-berries; coyotes are the most important of the mammalian dispersers.
Wintering birds such as the American robin, Stellar's jay, scrub jay, and Townsend solitaire eat and disseminate large numbers of western juniper cone-berries [28,68,75]. Burkhardt and Tisdale  maintain that the proportion of long-range seed dispersal, at least in southwestern Idaho, is low as evidenced by the lack of disjunct stands of western juniper.
Water dispersal accounts for a large percentage of downslope seed movement. Spring runoff traveling across frozen soil compacted by livestock may account for high densities of western junipers along waterways . Seed establishment is favored in deeper valleys or in areas rich in forbs .
Western juniper seedlings establish more rapidly under big sagebrush, bunchgrasses, or under existing trees. In a central Oregon study, seedlings established as follows :
with big sagebrush - 47%
with western juniper - 15%
with bunchgrasses - 14%
in the open - less than 1%
Burkhardt and Tisdale  found that most seedlings established on the north side of existing trees where the young plants were protected from intense solar radiation. Seedlings are often found along fences, hedges, or under taller trees where large numbers of birds perch [69,87,103].
Western juniper does not reproduce vegetatively .
Growth Form (according to Raunkiær Life-form classification)
Reaction to Competition
Western juniper is intolerant of fire and historically was kept in restricted sites by natural fires. Since the advent of effective fire control and intensive livestock grazing (reducing ground fuel and understory competition), regeneration and establishment of western juniper have expanded into suitable sites previously dominated by mountain big sagebrush (Artemisia tridentata spp. vaseyana). This expansion of young stands is common in Oregon, Idaho, and northeastern California (2,3,5,6).
Life History and Behavior
More info for the term: natural
In Oregon, leaf elongation begins in June with 15 to 20% annual leaf turnover . Western juniper cones develop from mid-April to mid-May and pollen is shed in May [50,72,87]. Seed cones ripen in mid-September after the second growing season . Cones may persist on the trees for 2 to 3 years . Most germination occurs during the spring . In Oregon, most natural germination occurs during April .
Bare mineral soil seedbeds are reported as best for successful germination of seed and establishment of seedlings (24). Young plants are normally vigorous, single stemmed, and have pyramidal forms.
Western juniper is very hardy in the early growth stage, resists disease and insect attacks well, and is not preferred as a food item by domestic or wild animals. Considerable browsing, however, occurs on deer winter ranges when other forage is limited; heavy use results in a hedged growth form.
Seed Production and Dissemination
Seeds are disseminated during the fall, primarily by birds and mammals. Animals ingest the fruit but do not digest the seeds. Dissemination of seeds by animals is evidenced by seed-filled droppings, particularly from robins and coyotes. Western juniper is often found growing along fence rows, seeds having been deposited there by perched birds (14,19,24).
Fruit can be collected after it has fallen from the tree or by handpicking it from the tree. Care must be taken when collecting fruit directly from the tree because the new, unripe crop and the 2-year-old, ripe crop are mixed. Fruit should be collected as soon after ripening as possible to prevent removal by animals. It should be stored in shallow trays or piles to prevent excessive heating until seeds are extracted.
Seeds of western juniper may be extracted from fruit by use of a macerator or hammermill in conjunction with water. Because of its resinous nature, pulp is more easily removed from the seeds if berries are presoaked in a lye solution consisting of 1.25 grams of sodium hydroxide or potassium hydroxide per liter (1 teaspoon to 1 gallon) of water for 1 to 2 days. After they are cleaned, seeds should be washed to remove the lye and then stored dry in sealed containers at -2° to 4° C (29° to 40° F) and with a moisture content of approximately 10 percent (14).
Flowering and Fruiting
In Oregon and Washington, western juniper flowers in spring and sheds pollen in May. Yellowish-brown staminate cones are terminal, ovoid, and 3 to 4 mm (0. 12 to 0. 16 in) long. They have 12 to 15 microsporophylls. Ovulate cones are 6 to 8 mm. (0.24 to 0.31 in) long, subglobose to ellipsoid, bluish-black when mature, and very glaucous. Ovulate cones, referred to as berries, have resinous pulp and mature in September of the second season in Oregon, Washington, and Idaho. Ovulate cones commonly have two to three developed seeds, rarely one. The seed has a thick, bony outer coat and a thin, membranous inner coat. The membranous coat surrounds a fleshy endosperm within which a straight embryo with cotyledons occurs (4,14,24,26).
Growth and Yield
Height of mature trees ranges from 4 to 10 in (13 to 33 ft), with exceptions at both ends of the spectrum, depending on site conditions. Occasionally, trees reach exceptional heights, such as one recorded as 26.5 in (87 ft) tall and 396 cm (156 in) in d.b.h.; and another, 26.5 in (87 ft) tall and 414 cm (163 in) in d.b.h. (4,21). Boles of mature trees are massive and more tapered than those of many conifer species, and the butt section is often slightly fluted. This species commonly develops full crowns and heavy limbs at maturity and, in the overmature stage, has a ragged, dead-topped, gnarled appearance. Western juniper is a long-lived and ruggedly picturesque species, reaching ages estimated to be more than 1,000 years (24). Old-growth stands in central Oregon are between 200 and 400 years old.
Molecular Biology and Genetics
Western juniper may be hybridizing with Utah juniper where the two species grow together in northwestern Nevada east of California's Warner Mountains. Two relict individuals in the White Mountains of California may be hybrids of western juniper and Utah juniper (26).
Barcode data: Juniperus occidentalis
Statistics of barcoding coverage: Juniperus occidentalis
Public Records: 3
Specimens with Barcodes: 3
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
In western juniper woodlands, wet to moderately wet soils grazed during the early spring are subject to damage through increased soil compaction. Grazing on dry or frozen soils causes fewer negative effects . At least 3 years of rest from grazing is suggested after seeding in western juniper .
Fire suppression, overgrazing, and climatic factors have led to an expansion of western juniper into adjacent grass and shrublands . This juniper invasion has dramatically reduced the understory and thus the forage base in many areas. From 1940 to 1960, when heavy emphasis was placed on livestock management, individual tree removal, cabling, chaining, and herbicides were widely used in an attempt to reduce western juniper woodlands [8,71]. Various means of mechanical control have been examined in detail [102,105]. For mechanical control to be effective, the heavy support roots must be broken and the tree uprooted .
Detailed information on chemical control is available [32,71,102].
Detailed information on silvicultural methods pertaining to western juniper harvest has been examined. Both even and uneven-aged methods have been used, but no one method is best suited for all situations and it is important to consider local needs and conditions .
Relevance to Humans and Ecosystems
Value for rehabilitation of disturbed sites
Western juniper provides perching and nesting sites for at least 27 species of birds, as well as cover and hibernation sites for small mammals . In southeastern and south-central Oregon western juniper provides excellent hiding and thermal cover for mule deer [61,62]. In parts of Nevada, it also provides some cover for pronghorn . Western juniper also provides shade for domestic livestock .
Decadent trees provide nesting cavities for mountain chickadees and mountain bluebirds, and hibernation sites for several species of bats. Thirty percent of these species nest in cavities while 70 percent nest in open nests . Lewis' woodpecker and the northern flicker nest in western juniper [54,90].
Western juniper is palatable browse for elk, mule deer, mountain cottontails, porcupines and black-tailed jackrabbits . However, palatability of western juniper varies by individual tree  and Rosentreter and Jorgensen  describe overall palatability as "low."
Western juniper cone-berries provide food for coyotes, and small mammals such as deer mice, yellow-pine chipmunks, and golden-mantled ground squirrels . Western juniper cone-berries are at least moderately palatable to wintering birds such as the American robin and Townsend solitaire .
Importance to Livestock and Wildlife
Western juniper provides food and cover for a variety of bird and mammal species . It is browsed to some extent by mule deer and elk . In parts of California, mule deer feed on small amounts of western juniper during winter and spring [10,59]. In the high desert of Oregon, western juniper is an important winter pronghorn food . Western juniper is used primarily as an emergency food source by most classes of livestock and many big game species . In California, it may be an important critical deer food source during severe winters; at these times, it is consumed in large quantities .
Domestic goats consume foliage and bark of western juniper .
Western juniper seed cones or cone-berries are an important winter food source for migratory birds such as the American robin and Townsend solitaire [28,26]. In Oregon, blue grouse feed on western juniper cone-berries during the fall . Lewis' woodpecker, scrub jay, and Stellar's jay feed on the cone-berries [54,29]. The northern flicker nests and feeds in western juniper communities of the Blue Mountains of Oregon .
The foliage and cone-berries of western juniper are important foods for a number of mammals. Mule deer, elk, mountain cottontail, and coyote consume western juniper cone-berries . Western juniper cone-berries are the primary food source of the dusky-footed woodrat .
Wood Products Value
Western juniper has been used since historic times for firewood, charcoal, corrals, poles, and fence posts . The wood is extremely durable and resistant to rot . Juniper wood splits easily, burns clean and produces little ash [22,43]. Western juniper woodlands can produce 8 to 11 cords of firewood per acre. However, it is estimated that 7 hours of labor are required per cord to cut, limb, pile slash, and gather the wood . Western juniper dulls saws since wind-blown sand particles readily adhere to its shaggy bark .
In recent times, western juniper has been used for paneling, interior studs, particleboard, veneer, plywood, and other lumber products. Western juniper logs brought to mills are short with a rapid taper. Most logs are limby and bark inclusions extend deep into the wood. Western juniper wood requires slow and careful kiln drying to prevent warping . It tends to be difficult to plane .
Other uses and values
Western juniper has been cultivated as an ornamental since 1840 . The wood is used in toys, sporting goods, jewelry boxes, suitcase and closet liners, inlay products, clocks, decorative items, and pencils [43,77]. Pipe bowls are made from the roots of western juniper, and pet bedding from the shavings . Juniper boughs have been used for Christmas wreaths and other decorations. Over 100 tons of boughs from central Oregon were sold in 1983 at 1 to 2 cents per pound .
The essential oils of western juniper are used for flavoring or scenting agents in medicines, beverages, condiments, aerosols, insecticides, soaps, and men's cosmetics . The cone-berries of western juniper are edible and taste best when dried . Western juniper foliage has been added to chicken feed to produce gin-flavored eggs for human consumption .
Some Native American peoples traditionally used western juniper wood in making bow staves .
Western juniper is fairly nutritious for mule deer and other large
mammals, but is not highly digestible .
Crude protein (%) is as follows :
Nutritive values vary by season and plant part. Protein and ash
content (%) is as follows :
crude protein ash
green foliage 8.1 3.9
cured foliage 7.6 4.2
bark 3.2 7.1
Western juniper logs are difficult to process. They are rough, limby, short, and have rapid taper. They also have bark inclusions deep in the wood. Juniper is reputed to be difficult to cure because it twists and warps while drying, and to be difficult to plane, splitting easily. The reputation is undeserved-local specialty manufacturers have been air-drying this wood successfully for many years (12). Thin boards can be kiln-dried successfully without checking. In fact, any slow drying process works well. Local manufacturers use western juniper for making furniture, novelty items, toys, tongue-and-groove interior paneling, fenceposts, and firewood. Products experimentally manufactured that are considered commercially feasible include hardboard, particle board, veneer, and exposed and decorative interior studs. Research in extracted essential oils indicates that cedrol, used in scenting and flavoring, could be extracted in quantities and would be of a quality to be commercially competitive with cedrol from other juniper species (1,12).
Western juniper is valuable for wildlife cover, food (primarily berries), and nest sites, and as shade for livestock (16,19). Also, management agencies use harvested trees as riprap for stabilizing streambanks. Natural stands in developing areas are highly valuable for landscaping homesites, but the species has not been popular for horticultural uses.
Juniperus occidentalis (western juniper or Sierra juniper) is a shrub or tree native to the western United States, growing in mountains at altitudes of 800–3,000 metres (2,600–9,800 ft) and rarely down to 100 metres (330 ft).
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, 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 (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 var. occidentalis Western Juniper. 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. A shrub or small tree 4–15 m tall. Exceptionally tall specimens can be found in the John Day area of Oregon well in excess of 26–28 m tall (80–90 feet+) competing for sunlight among ponderosa pines at the bottom of some deep side canyons, but on open and barren ground 4–15 m with a bushier growth habit is more common. Cones 7–10 mm diameter. About 50% of plants are monoecious with both sexes on the same plant, 50% dioecious, producing cones of only one sex.
- Juniperus occidentalis var. australis Sierra juniper. California and westernmost Nevada, south of 40° 30' N latitude in the Sierra Nevada and San Bernardino Mountains. A medium-sized tree 12–26 m tall with a stout trunk up to 3 m diameter. Cones 5–9 mm diameter. Most plants dioecious, but about 5-10% are monoecious.
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.
- Adams, R. P. (2004). Junipers of the World: The genus Juniperus. Trafford Publishing ISBN 1-4120-4250-X
- Chase, J. Smeaton (1911). Cone-bearing Trees of the California Mountains. Chicago: A. C. McClurg & Co. p. 99. LCCN 11004975. OCLC 3477527. LCC QK495.C75 C4, with illustrations by Carl Eytel - Kurut, Gary F. (2009), "Carl Eytel: Southern California Desert Artist", California State Library Foundation, Bulletin No. 95, pp. 17-20 retrieved Nov. 13, 2011
- Conifer Specialist Group (1998). Juniperus occidentalis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
Names and Taxonomy
Comments: Comprised of two varieties (FNA 1993; Kartesz 1999), which perhaps have hybrid populations in some Nevada mountain ranges (Charlet 1996).
The scientific name of western juniper is Juniperus occidentalis Hook. (Cupressaceae) [44,45,53]. The following varieties of western juniper are recognized:
J. occidentalis var. australis (Vasek) A. Holmgren & N. Holmgren (Sierra juniper) [44,106]
J. occidentalis var. occidentalis
Western juniper may hybridize with Utah juniper (J. osteosperma) where the two species occur together in northwestern Nevada east of California's Warner Mountains. Relict individuals in the White Mountains of California may also be hybrids of western and Utah juniper .