SPECIES: Juniperus occidentalis

INTRODUCTORY

SPECIES: Juniperus occidentalis
 
Western juniper/mountain big sagebrush woodland in Harney County, Oregon. Photo courtesy of the PRBO Conservation Science Shrubsteppe Monitoring Program.
AUTHORSHIP AND CITATION:

Tirmenstein, D. 1999. Juniperus occidentalis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

ABBREVIATION:

JUNOCC

SYNONYMS:

Juniperus occidentalis ssp. australis (Vasek) A. Holmgren & N. Holmgren
Juniperus occidentalis ssp. occidentalis [40,98]

NRCS PLANT CODE:

JUOC
JUOCA
JUOCO

COMMON NAMES:

western juniper
Sierra juniper

TAXONOMY:

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 [22].

LIFE FORM:

Tree

FEDERAL LEGAL STATUS:

No special status

OTHER STATUS:

No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Juniperus occidentalis
GENERAL DISTRIBUTION:

Western juniper occurs from southeastern Washington and Oregon southward to the upper slopes of the Sierra Nevada and San Bernardino Mountains of southern California [87]. It occurs along the western edge of the Great Basin in southwestern Idaho and northwestern Nevada [70].

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 [44]. It reaches its greatest extent in central Oregon east of the Cascade Range [103].

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 [29].

ECOSYSTEMS:

FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES26 Lodgepole pine
FRES28 Western hardwoods
FRES29 Sagebrush
FRES35 Pinyon-juniper

STATES:

CA    ID    NV    OR    WA 
BLM PHYSIOGRAPHIC REGIONS:

1  Northern Pacific Border
2  Cascade Mountains
3  Southern Pacific Border
4  Sierra Mountains
5  Columbia Plateau
6  Upper Basin and Range
KUCHLER PLANT ASSOCIATIONS:

K007  Red fir forest
K008  Lodgepole-pine-subalpine forest
K011  Western ponderosa forest
K023  Juniper-pinyon woodland
K024  Juniper steppe woodland
K030  California oakwoods

SAF COVER TYPES:

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
				<
SRM (RANGELAND) COVER TYPES:

107   Western juniper/big sagebrush/bluebunch wheatgrass
109   Ponderosa pine shrubland	
110   Ponderosa pine-grassland
201   Blue oak woodland
209   Montane shrubland	
210   Bitterbrush 
212   Blackbush
322   Curlleaf mountain-mahogany-bluebunch wheatgrass
412   Juniper-pinyon woodland	
415   Curlleaf mountain-mahogany	
	
HABITAT TYPES AND PLANT COMMUNITIES:

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 [25]
Plant communities and habitat types in the Lava Beds National Monument, California 1979 [30]
Great Basin pinyon and juniper communities and their response to management [33]
Plant communities of the Blue Mountains in eastern Oregon and southeastern Washington [41]
Plant associations of south Chiloquin and Klamath Ranger Districts, Winema National Forest [46]
Plant associations of the Fremont National Forest [47]
Vegetation types of the San Bernardino Mountains [49]
Plant associations of the Wallowa-Snake Province: Wallowa-Whitman National Forest [51]
Woodland classification: the pinyon-juniper formation [52]
Preliminary classification for the coniferous forest and woodland series of Arizona and New Mexico [58]
Forest/environment relationships in Yosemite National Park, California USA [76]
A vegetation classification system applied to southern California [79]


MANAGEMENT CONSIDERATIONS

SPECIES: Juniperus occidentalis
WOOD PRODUCTS VALUE:

Western juniper has been used since historic times for firewood, charcoal, corrals, poles, and fence posts [22]. The wood is extremely durable and resistant to rot [77]. 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 [14]. Western juniper dulls saws since wind-blown sand particles readily adhere to its shaggy bark [43].

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 [43]. It tends to be difficult to plane [22].

IMPORTANCE TO LIVESTOCK AND WILDLIFE:

Western juniper provides food and cover for a variety of bird and mammal species [94]. It is browsed to some extent by mule deer and elk [68]. 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 [86]. Western juniper is used primarily as an emergency food source by most classes of livestock and many big game species [77]. In California, it may be an important critical deer food source during severe winters; at these times, it is consumed in large quantities [59].

Domestic goats consume foliage and bark of western juniper [35].

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 [21]. 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 [90].

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 [84]. Western juniper cone-berries are the primary food source of the dusky-footed woodrat [68].

PALATABILITY:

Western juniper is palatable browse for elk, mule deer, mountain cottontails, porcupines and black-tailed jackrabbits [68]. However, palatability of western juniper varies by individual tree [87] and Rosentreter and Jorgensen [82] 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 [68]. Western juniper cone-berries are at least moderately palatable to wintering birds such as the American robin and Townsend solitaire [28].

NUTRITIONAL VALUE:

Western juniper is fairly nutritious for mule deer and other large 
mammals, but is not highly digestible [60].

Crude protein (%) is as follows [10]:

	January	6.9
	February	5.6
	March		7.2
	April		7.0
	May		8.3
	August	7.5
	October	7.8
	November	8.5
	December 	7.0

Nutritive values vary by season and plant part.  Protein and ash 
content (%) is as follows [35]:

	                   crude protein   ash 
	green foliage	  8.1		      3.9
	cured foliage	  7.6		      4.2
	bark               3.2	            7.1

COVER VALUE:

Western juniper provides perching and nesting sites for at least 27 species of birds, as well as cover and hibernation sites for small mammals [68]. 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 [101]. Western juniper also provides shade for domestic livestock [22].

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 [68]. Lewis' woodpecker and the northern flicker nest in western juniper [54,90].

VALUE FOR REHABILITATION OF DISTURBED SITES:

Western juniper can be propagated from cuttings or by layering [22,87]. Trees have been used as riprap for stabilizing streambanks [22].

OTHER USES AND VALUES:

Western juniper has been cultivated as an ornamental since 1840 [50]. 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 [43]. 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 [77].

The essential oils of western juniper are used for flavoring or scenting agents in medicines, beverages, condiments, aerosols, insecticides, soaps, and men's cosmetics [43]. The cone-berries of western juniper are edible and taste best when dried [48]. Western juniper foliage has been added to chicken feed to produce gin-flavored eggs for human consumption [43].

Some Native American peoples traditionally used western juniper wood in making bow staves [100].

OTHER MANAGEMENT CONSIDERATIONS:

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 [13]. At least 3 years of rest from grazing is suggested after seeding in western juniper [82].

Fire suppression, overgrazing, and climatic factors have led to an expansion of western juniper into adjacent grass and shrublands [70]. 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 [105].

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 [31].


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Juniperus occidentalis

Western juniper is a tree that typically grows 15 to 30 feet (4.6 to 9.1 m) [87]. 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) [12]. Trees develop full crowns and heavy limbs at maturity [22].

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 [98].

Bark is furrowed and shreddy [31]. Taproots average 51 inches (130 cm) in depth [55]. Root-to-shoot ratios decrease with age giving western juniper the ability to outcompete species such as big sagebrush [55].

Western juniper is slow growing and long lived [31]. Individuals can survive for 1,000 years or longer [87]. 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 [28]:

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

RAUNKIAER LIFE FORM:

Phanerophyte

REGENERATION PROCESSES:

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 [50]. Cone-berries contain 1 to 4 (more rarely up to 12) brownish seeds [69]. Western juniper is monoecious or dioecious [92]. 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 [28].

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 [73]. Western juniper produces an abundance of seed cones nearly every year after maturity [87].

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" [104]. Specific information on germination characteristics is available [50,104]. Tueller [91] 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 [92].

Seed of western juniper is dispersed by birds, mammals, water, and gravity [69]. 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 [19]. The seeds of many juniper species are thought to germinate faster after the seed cone has been consumed by animals [88]. 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 [84] 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 [19] 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 [28]. Seed establishment is favored in deeper valleys or in areas rich in forbs [19].

Western juniper seedlings establish more rapidly under big sagebrush, bunchgrasses, or under existing trees. In a central Oregon study, seedlings established as follows [28]:

with big sagebrush - 47%
with western juniper - 15%
with bunchgrasses - 14%
in the open - less than 1%

Burkhardt and Tisdale [19] 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 [22].


SITE CHARACTERISTICS:

Western juniper occurs in open stands on mountain slopes and high plateaus [87]. 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 [28]. It has remained dominant in shifting sand dune communities of south-central Washington where fire is unlikely [1].

The growth of western juniper is favored by long, dry summers and cold winters with little moisture [87]. 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 [73]. It occurs in the most xeric tree-dominated zone of the Pacific Northwest [37]. Soil, climate, topography, fire, and biotic factors all contribute to the distribution of western juniper, but moisture is thought to be the primary determinant [23].

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 [87].

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 [23]. In the Sierra Nevada, Sierra juniper grows on granitic crevices on windswept ridges [87]. 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 [3]. 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 [23]. Western juniper is best adapted to soils exhibiting rapid infiltration, deep percolation, low evaporation, and low soil moisture tension [5]. Western juniper is often found on a perched water table [37].

Western juniper grows from near sea level to more than 10,000 feet (3050 m) [87]. 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

SUCCESSIONAL STATUS:

Western juniper is a highly competitive invasive species [81]. 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 [8]. It has doubled its range in central and eastern Oregon during the past 80 to 100 years [81]. Expansion into low sagebrush communities has been slower than into big sagebrush communities [2]. Expansion into shrub steppe communities in Nevada has reduced understory diversity and productivity [7]. 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 [95]. Old growth western juniper is generally found in "firesafe" spots [103]. 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 [65].

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 [96].

SEASONAL DEVELOPMENT:

In Oregon, leaf elongation begins in June with 15 to 20% annual leaf turnover [72]. 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 [50]. Cones may persist on the trees for 2 to 3 years [69]. Most germination occurs during the spring [87]. In Oregon, most natural germination occurs during April [22].


FIRE ECOLOGY

SPECIES: Juniperus occidentalis
FIRE ECOLOGY OR ADAPTATIONS:

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 [87]. In general, the taller the juniper, the greater the severity of the fire required to kill it [64]. Western juniper does not sprout [19]. 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 [1]. Belsky [8] 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 [96].

Fire return intervals in western juniper communities range from 7 to 25 years to more than 100 years [2]. Mean fire interval for western juniper within the Columbia River Basin is estimated at 52 years [6]. Fire return intervals within western juniper communities have been reported as follows:

California:   7-17 years
southwestern Idaho:   25 years
Nevada:   15-20 years [1]
southwestern Oregon:   < 20 years [19]

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 [99].

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

POSTFIRE REGENERATION STRATEGY:

Tree without adventitious bud/root crown
Initial off-site colonizer (off-site, initial community)
Secondary colonizer - off-site seed


FIRE EFFECTS

SPECIES: Juniperus occidentalis
IMMEDIATE FIRE EFFECT ON PLANT:

Western juniper is a nonsprouter that is generally killed by severe fires [11]. Younger trees have thin bark and are readily killed by surface fires [87]. 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 [15].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

Western juniper foliage is not easily ignited and/or scorched when moist [17]. 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 [64].

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 [67]. Western juniper first becomes dominant 30 to 50 years after fire [15]. Reoccupation of a site occurs fairly slowly through dispersed seed [19,25].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Recovery time depends on the size of burn, location of seed source, stand maturity, and presence of animal dispersers [19]. 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 [17] "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 [103].

FIRE MANAGEMENT CONSIDERATIONS:

Western juniper sites with less than 1,322 pounds per acre (600 kg/ha) of fine fuels are difficult to burn [16]. 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 [1]. Trees create their own fine fuel break, so these stands may be virtually "fireproof" except under the "most severe burning conditions" [1,103]. 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 [16].

However, prescribed burning can in some instances be used to reduce western juniper dominance [20,66] 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 [83]. 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 [15]. Generally, where tree cover is greater than 30%, there is so little herbaceous understory that extremely high winds are needed to support a burn [70]. 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 [15].

Western juniper slash can be burned where fine fuels average 400 to 700 pounds per acre (181-318 kg/ha), and where slash fuel 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 [63].

Western juniper tends to have more resinous foliage than many other species. Ash and heat content values are as follows [97]:

                        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 [97] 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	
(reaction intensity)
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" [103].

FIRE CASE STUDIES

SPECIES: Juniperus occidentalis
FIRE CASE STUDY CITATION:

Tirmenstein, D., compiler. 1999. Spring and fall prescribed burning of western juniper in basin big sagebrush in east-central Oregon. In: Juniperus occidentalis. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [ ].

REFERENCE:

Sapsis, David B. 1990. Ecological effects of spring and fall prescribed burning on basin big sagebrush/Idaho fescue--bluebunch wheatgrass communities. Corvallis, OR: Oregon State University. 105 p. Thesis. [83].

SEASON/SEVERITY CLASSIFICATION:

Fall (9/25/87) /severity not specified
Spring (5/24/88) /severity not specified

STUDY LOCATION:

The study was located approximately 5 miles (10 km) west of Dayville in east-central Oregon. The site was located in John Day Fossil Bed National Monument in T 11 S R 26 E , sections 31 and 32.

PREFIRE VEGETATIVE COMMUNITY:

Preburn vegetation was a basin big sagebrush (Artemisia tridentata subsp. tridentata)-Idaho fescue (Festuca idahoensis)-bluebunch wheatgrass ((Pseudoroegneria spicata) community. Dominant understory species included Idaho fescue, bluebunch wheatgrass, yarrow (Achillea millefolium) and threadstalk milkvetch (Astragalus fillipes). Western juniper (Juniperus occidentalis) did not occur as a dominant or codominant in the prefire vegetative community. Western juniper presumably grew as scattered individuals (many of which were seedlings). Prefire cover of western juniper was 369 stems/ha.

TARGET SPECIES PHENOLOGICAL STATE:

Not specified

SITE DESCRIPTION:

Aspect - north
Slope - 20-65%
Elevation - 2,297-2,625 feet (700-860 m)
Soils - very stony, clay-loams
Annual precipitation - 10-14 inches (250-360 mm)

FIRE DESCRIPTION:

Both burns were ignited with drip torches using a strip-head firing pattern. Pretreatment fuel loads ranged from 5-12 Mg/ha. Fuel loads in fall treatment units averaged 10.5 Mg/ha and in spring treatment units, fuel loads averaged 6.2 Mg/ha. Large amounts of herbaceous fuels (> 3 Mg/ha) were present.

Burning Conditions:
Fall Spring
Time of burn 9:35-13:45 12:35-15:26
Temperature (oC) 15-18 23-25
Relative humidity (%) 41-48 21-24
Windspeed (km/h) 0-15 0-17
Soil m.c. (moisture content, %) 2.90 3.21
Dead herbaceous m.c.* 8.88 7.36
10-hr timelag m.c. 4.59 4.99
Sagebrush foliage m.c.* 97.19 186.02
Live grass m.c. n/a 142.60


Fire Behavior:
Fall Spring
Flame length (m)* 4.14 1.74
Fireline intensity (kW/m)* 6441 883
Reaction intensity (heat release rate, kW/m2) 2.17 1.12
Flame depth (m)* 10.35 2.56
Rate of spread (m/s)* 1.57 0.23
Heat/area in flaming front (kJ/m2) 3253 3935
Total energy (flaming & smoldering, kJ/m2) 18,119 9267
Residence time (s)* 6.92 11.66
Fuel consumption (Mg/ha)* 9.80 5.23
n/a=not available
*significant difference between fall and spring burning (p<0.05)

FIRE EFFECTS ON TARGET SPECIES:

Both spring and fall treatments killed all western juniper:

Treatment Density (stems/ha)
1987 1988 1989
fall 456 0 0
spring n/a 369 0
control 733 733 1,040
(difference between treatments not significant at p<0.1)

Western juniper frequency (%):
1987 1988 1989
4 0 0

FIRE MANAGEMENT IMPLICATIONS:

Prescribed fire was effective in limiting the abundance of western juniper. Prescribed fire may represent an effective and economical management tool for rangelands.


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