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Reports of hybridization with Pinchot juniper (J. pinchotii) have been refuted by use of numerous chemical and morphologic characters. The two species have nonoverlapping pollination seasons [2,42].
Because research focused specifically on oneseed juniper is not abundant,
some information in this report is drawn from studies and reviews that pertain to
multispecies Southwestern juniper or pinyon (Pinus spp.)-juniper
(Juniperus spp.) woodlands. In this report "oneseed juniper" is used
where the study discussed focused on that species. "Juniper" or "pinyon-juniper"
describes studies broader in scope, but where oneseed juniper was usually
identified as component. When the pinyon species was identified it is included.
LIFE FORM:
Tree
FEDERAL LEGAL STATUS:
No special status
OTHER STATUS:
No entry
The Flora
of North America also provides distribution information on oneseed juniper
for North America.
ECOSYSTEMS [46]:
FRES21 Ponderosa pine
FRES29 Sagebrush
FRES30 Desert shrub
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES38 Plains grasslands
FRES40 Desert grasslands
STATES:
| AZ | CO | NM | OK | TX |
| MEXICO |
In northern Arizona overstory associates include Utah juniper (J. osteosperma) and Colorado pinyon (P. edulis). Associated plants include winterfat (Krascheninnikovia lanata), skunkbush sumac (Rhus trilobata), shrub live oak (Quercus turbinella), broom snakeweed (Gutierrezia sarothrae), rubber rabbitbrush (Chrysothamnus nauseosus), and Russian-thistle (Salsola kali). Associated grasses include galleta (Pleuraphis jamesii), black grama (Bouteloua eriopoda), blue grama (B. gracilis), Fendler threeawn (Aristida purpurea var. fendleriana), sideoats grama (B. curtipendula), tobosa (P. mutica), and bottlebrush squirreltail (Elymus elymoides). Other associated plants include freckled milkvetch (Astragalus lentiginosus), cholla and prickly-pear (Opuntia spp.), [59,74]. Occasionally oneseed juniper grows in extensive pure stands, such as those on the Coconino Plateau in northern Arizona. It is the dominant species in these stands and may exclude all other plants [64].
In southern Arizona oneseed juniper occurs with alligator juniper (J. deppeana), Mexican pinyon (P. cembroides), Emory oak (Q. emoryi), Arizona white oak (Q. arizonica), Mexican blue oak (Q. oblongifolia), and species of mesquite (Prosopis spp.) [12,92].
In New Mexico and western Texas common associates are Colorado pinyon, Pinchot juniper, alligator juniper,broom snakeweed, skunkbush sumac, winterfat, fourwing saltbush (Atriplex canescens), Bigelow sagebrush (Artemisia bigelovii), true mountain-mahogany (Cercocarpus montanus), gray oak (Q. grisea), catclaw mimosa (Mimosa biuncifera), lechuguilla (Agave lechuguilla), prickly-pear, sideoats grama, galleta, and blue grama [3,25,44,47,71,101,102,103].
Oneseed juniper is an indicator in a number of pinyon-juniper shrubland and desert grassland classification systems, including:
Arizona [15,121]
Colorado [54,69]
New Mexico [3,44,71,73,121]
Texas [27,83]
Oneseed juniper produces small, "berry-like", glaucous, globular staminate cones, and subglobose ovulate cones [42,127]. Mature cones are dark blue to purple or brownish, and succulent, or at least somewhat fleshy [50,127,132]. Seeds are generally 1 per fruit, more rarely 2, reddish-brown and ovoid to globose [50,127]. Juniper seeds are described as having a semipermeable and thick seed coat with a dormant embryo [41]. The cones are often referred to as "berries" in the literature.
Mature oneseed junipers have both tap and lateral root systems. The taproots in 1 study ranged from 18 inches (46 cm) to more than 12 feet (3.7 m) in length. Of 500 trees examined, 347 had well-developed taproots. Lateral roots were widespread, commonly being 2.5 to 3 times as long as the tree was tall. Most lateral roots were in the surface 3 feet (1 m) of the soil, most of those concentrated below the surface 6 inches (15 cm) [64]. The deep root system of mature oneseed junipers is adapted for growth on dry sites [51,64,107]. Foxx and Tierney [43] reported rooting depths ranging from 16 to 197 feet (5-60 m).
Oneseed juniper is a slow-growing species. Lymbery and Pieper [80] reported an increase in height of approximately 6.3 inches (16 cm) per decade, with a corresponding increase in stem diameter of 0.5 inch (1.2 cm). Growth rate tends to vary according to site characteristics, however. On a hilly site in southwestern Texas, a oneseed juniper 35 years of age was 14 feet (4.3 m) in height with a diameter of 0.5 inch (1.3 cm) [23].
Oneseed juniper has the ability to stop active growth when moisture is limited but can resume growth when moisture availability improves [53]. This growth pattern may represent an important adaptation allowing junipers to survive on harsh, arid sites. Although small trees may be killed by drought, mature oneseed junipers are resistant to drought, especially in comparison to Colorado pinyon [64,107].Pollination: No information
Seed production: Trees first produce seed at 10 to 30 years of age, although maximum seed production generally does not occur until 50 to 200 years of age [66,115]. Trees as short as 18 inches (46 cm) in height can produce seed [64]. Oneseed juniper typically produces large seed crops at 2- to 5-year intervals [66].
Seed dispersal: Dispersal of oneseed juniper seeds may occur through water, gravity, or by any of a number of birds and mammals [10,64]. Animal dispersal may be particularly important, as digestive processes may enhance germination [13]. Most seed cones occur on the outer edges of trees where they are most visible and accessible to birds [110]. The brightly-colored, highly-visible cones persist on the trees for much of the year, providing a continually available food source for animals [13,34]. On some sites in New Mexico, as much as 95% of juniper reproduction could be attributed to bird dispersal [30]. Domestic sheep and cattle may also aid in seed dispersal [64].
Seed banking: According to Johnsen [64], "Since the seed is not harmed by long periods of dry storage, drought probably does not affect seed viability. Viable seed in the soil may endure prolonged drought and still germinate when conditions become favorable."
Germination: See Value for Rehabilitation of Disturbed Sites for detailed information about germination experiments with this species.
Seedling establishment/growth: Seedling establishment of oneseed juniper is often very poor even when good germination occurs [114]. The growth rate has been characterized as slow with medium vigor. Researchers in some areas have found that only approximately 3% of juniper seeds develop to the seedling stage. Shade may be important for good early growth of oneseed juniper [60]. Emergence appears to be somewhat greater under trees or shrubs than in interspaces where humidity and temperature fluctuations are more extreme [64]. In some areas, small junipers are particularly numerous under the canopy of pinyon or other trees [60,115]. Most seedlings occur some distance from the parent tree, although most seeds are located beneath the source tree [110]. Seedlings seldom establish beneath mature junipers, and an autopathic effect from litter is suspected [115].
Asexual regeneration:
Although oneseed juniper is usually regarded as a nonsprouter [135], limited sprouting,
mostly from older trees, has been observed [24,129]. Approximately 10% of living
oneseed junipers sprouted from the base following an Arizona fire [129].
SITE CHARACTERISTICS:
Oneseed juniper occupies xeric sites in semiarid
climatic zones [38,51,102]. A typical Arizona site occupied by oneseed juniper
receives 10 to 15 inches (250-380 mm) of precipitation annually, and has
an average growing season of approximately 120 days [95,134]. Unlike several
related species, the distribution of oneseed juniper does not appear to
be limited by temperature inversions [59].
Oneseed juniper grows on dry, rocky, open flats, and slopes [32,50,52]. It commonly occurs in canyons or on middle-elevation foothills [50,134]. In many areas this juniper occurs in a zone below ponderosa pine (P. ponderosa) or alligator juniper, but above oak (Quercus spp.)-mountain-mahogany (Cercocarpus spp.) shrublands [96,134].
Because soil moisture is limited on many oneseed juniper sites, competition with others species may significantly influence the occurrence of this tree on a particular site. Grasses can compete effectively with oneseed juniper seedlings for moisture and can limit its distribution in some areas [64,135]. Many oaks also compete for soil moisture, although oneseed juniper appears to be capable of outcompeting them on shallow soils [115]. Where oneseed juniper occurs with Colorado pinyon, junipers show much more adaptation to drought stress than do the pines [107]. These observations were based on tissue water potentials and metabolic activity during the hottest part of the day.
Oneseed juniper grows on a variety of soil textures including gravelly, rocky, or sandy soils [50]. Parent materials include basalt, limestone, and sandstone [38]. Soil characteristics, combined with temperature, moisture and topography influence the upper and lower elevational extent of oneseed juniper [18,134]. Elevational ranges of oneseed juniper reported in the literature are:
Arizona 3,000 to 7,000 feet (914-2,130 m) [32,72]
Colorado 4,000 to 7,600 feet (1,220-2,315 m) [52]
New Mexico > 5,000 to 7,500 feet (1,525-2,285 m) [125]
SUCCESSIONAL STATUS:
Populations of oneseed juniper have been classified as climax [54,113], seral [44],
late seral [27], and postclimax [64]. Schott and Pieper [113,115] examined secondary
succession in pinyon-juniper several decades following cabling and concluded that
re-established stands of pinyon and oneseed juniper were climax. Johnsen [64] concluded
that within northern Arizona grasslands are numerous postclimax oneseed juniper stands with
soil and microclimate conditions different from adjacent grasslands. The oneseed
junipers maintain themselves on these areas but are not invading the surrounding grassland.
Francis [44] described 4 seral phyto-edaphic community types in northwestern
New Mexico where oneseed juniper is a codominant indicator species.
According to Gottfried [48] junipers are the 1st to return in secondary succession but are often followed and replaced by pinyon. "Habitat type affects the successional pathway following a disturbance. Succession on a site is influenced by the severity and size of the disturbance, and by the composition, longevity, and density of any surviving plants and propagules within the disturbed area and the characteristics of plant communities in adjacent undisturbed areas. Climatic conditions also influence the nature and speed of succession."
See Other Management Considerations for an analysis of a drought-induced ecotone shift of oneseed junipers into a declining ponderosa pine forest in Arizona.
New Mexico studies comparing plant growth in zones extending out from the boles of
oneseed juniper and pinyon pine showed differences between the zones and also between the
two tree species [6,112]. Grasses and other plants were consistently sparser beneath the
tree canopies. The author's review of possible explanations includes allelopathy,
shade, precipitation interception by the canopy, and litter cover forming a physical
barrier to germinating plants. Other explanations offered to explain the reduced
under-canopy vegetation include root competition for soil moisture, and possible
chemical properties of oneseed juniper litter [9,62].
SEASONAL DEVELOPMENT:
Based on a study conducted near Flagstaff Arizona, annual leader elongation of oneseed
juniper generally begins in April [53]. Detailed phenological development from that study is:
| phenological state | date |
| bark begins to slip | March 25 |
| pollen shedding and female flowers open | March 25 |
| approximate start of leader elongation | April 20 |
| 1st conspicuous formation of male flowers | April 19 |
| leader elongation ceases | October 26 |
Flowering generally occurs in March or April [50,66], but can occur as early as January or as late as June, depending on geographic location [41]. Fruit matures in 1 season, ripening from August through November [64,66]. Seed may remain on the tree for 1 to 2 years [66]. Lymbery and Pieper [80] reported that in the northern Sacramento Mountains, flowering occurred from March to April, fruit ripening from August to September, and seed dispersal from October to November.
In some areas, juniper is protected from fire by site factors. For example, junipers frequently grow on rocky breaks or escarpments where fire frequency is low. Wright [134] reported that nonsprouting juniper species often occupy isolated topographic breaks which may be surrounded by grasslands that are more susceptible to fire.
Fire adaptations: Postfire reestablishment is primarily through seed and is relatively slow [63]. Most establishment is from seed dispersed from off-site by birds and mammals, but some establishment may occur from seeds buried on-site and protected from the heat of fire by overlying soil layers. Establishment may be relatively poor even when good germination occurs, and growth is typically very slow [115].
Oneseed juniper is usually regarded as a nonsprouter [134], but older trees have been known to sprout infrequently after fire [24,128]. This mode of regeneration appears to be relatively unimportant, however.Fire regimes: Past fire regimes in southwestern pinyon-juniper woodlands were mixed, having both surface and crown fires, and are a reflection of variable intensity and frequency depending on site productivity [48,98]. "Productive sites could sustain patchy fires at intervals of 10 to 50 years, and could have attained densities sufficient to carry crown fires at intervals of 200 to 300 years. In open stands, where grass cover was continuous, fire intervals might have been 10 years or less, and probably maintained grasslands and savannas [48]."
According to a 1962 review of oneseed juniper by Johnsen [64] (and references therein), fires were reported to have been widespread and destructive before the juniper woodlands were heavily used by settlers. A 1904 publication cited by Johnsen reported that 5% of the junipers on the Coconino National Forest had been struck and killed by lightning. Johnsen indicated that "lightning strikes are still common, but fires started in this way are usually confined to the tree struck, for only in the very dry hot periods with strong winds in the late spring will a fire carry through even a dense juniper stand".
The following table provides some fire return intervals for communities where oneseed juniper may occur. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".
| Community or Ecosystem | Dominant Species | Fire Return Interval Range (years) |
| desert grasslands | Bouteloua eriopoda and/or Pleuraphis mutica | 5-100 |
| grama-galleta steppe | Bouteloua gracilis-Pleuraphis jamesii | < 35 to < 100 |
| cheatgrass | Bromus tectorum | < 10 [98] |
| basin big sagebrush | Artemisia tridentata var. tridentata | 12-43 [111] |
| mountain big sagebrush | Artemisia tridentata var. vaseyana | 15-40 [8,21,88] |
| juniper-oak savanna | Juniperus ashei-Quercus virginiana | < 35 |
| Ceniza shrub | Larrea tridentata-Leucophyllum frutescens-Prosopis glandulosa | < 35 |
| pinyon-juniper | Pinus-Juniperus spp. | < 35 [98] |
| Mexican pinyon | Pinus cembroides | 20-70 [91,123] |
| Colorado pinyon | Pinus edulis | 10-49 [98] |
| Arizona pine | Pinus ponderosa var. arizonica | 2-10 [7] |
| mesquite | Prosopis glandulosa | < 35 to < 100 |
| mesquite-buffalo grass | Prosopis glandulosa-Buchloe dactyloides | < 35 |
| oak-juniper woodland (Southwest) | Quercus-Juniperus spp. | < 35 to < 200 [98] |
Average mortality following a low-severity June wildfire in oak-juniper woodlands of Arizona was 76% [68]. Researchers observed 92% mortality after a stand of small, bushy oneseed juniper were burned [17]. Springfield [118] noted 70 to 100% of oneseed junipers less than 4 feet (1.2 m) in height were killed by fire. Mortality ranging from 30 to 100% has been reported in trees 5 to 6 feet (1.5-1.8 m) in height.
Researchers have found that 100% juniper mortality results when 60%
of the crown is scorched [61]. Temperatures lethal to oneseed
juniper tissue are also related to the degree of desiccation, and
thus season of burn may also influence the amount of damage the plant
sustains. Laboratory experiments have shown that temperatures lethal to oneseed
juniper ranged from 140 degrees Fahrenheit to 176 degrees Fahrenheit
(61.8o to 80oC). Lethal temperatures
tend to be lowest during late spring and summer [58].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No entry
PLANT RESPONSE TO FIRE:
Regeneration of oneseed juniper is usually from seed when
aboveground vegetation has been killed or seriously damaged by fire. Older
oneseed junipers can occasionally sprout from the base after fire. In a
southern Arizona burn, 10% of oneseed junipers resprouted. In
contrast 42% of alligator juniper resprouted [68]. However, in most cases,
sprouting appears to be a relatively unimportant mode of regeneration.
The length of time required for postfire recovery of oneseed juniper has
not been well documented. Oneseed juniper did not become prominent after a
severe wildfire in Utah until postfire year 40. This species did not regain
dominance on this site until 70 years after the fire [128]. Evidence
suggests that factors such as soil type and preburn community
composition may significantly influence the length of time required for recovery
[114]. Seedling establishment may be favored in the shade of
dead vegetation, including other oneseed junipers [24]. Once established,
oneseed juniper can bear seed as early as 10 years of age on some sites
[114].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
No entry
FIRE MANAGEMENT CONSIDERATIONS:
Historically, periodic fire is believed to have played an important role in
maintaining juniper savannas [64,98,132]. Mueggler [93] reported that a
fire-free period of 85 to 90 years was required for formation of a "well-developed"
juniper woodland. Recent decades of fire suppression have probably contributed to
encroachment of juniper into grasslands [78,94].
In some instances, forage production has increased after oneseed juniper and other species were removed by fire. On 1 "notable" Colorado pinyon-juniper site, Aro [11] reported increased forage production from 100 pounds per acre (45 kg/ha) before treatment to 500 pounds per acre (227 kg/ha) following fire. However, in other instances little long-term increase in forage production has been noted. According to Payson and others [98], most of the control operations failed to meet managers' objectives.
Individual tree burning was used on some pinyon-juniper woodlands [61,118]. Mechanical methods, such as chaining and cabling in pinyon-juniper woodlands, were often followed by the piling and burning of slash. Burning these high fuel concentrations generated high heat levels that damaged soil and site productivity. Surface soils in many of these piled areas were degraded and remained free of vegetation 20 years later [98,125].
Oneseed juniper does not survive in grasslands where fires occur frequently [134]. Broadcast burns may effectively control oneseed juniper if the species is well represented, weather conditions are favorable, and sufficient fuels are present. Dense stands (400 or more/ac (990/ha)) with a flammable understory are most suitable for broadcast burning [59,128]. In areas with a past history of heavy grazing where little fuels remain and few residual grasses occur, burning may be difficult and ineffective. Burns tend to be most successful when carried out in June when temperatures are high and humidity low [11,104]. Unfortunately, risk of escape may be great during this time period [11], and the window for burning very narrow [104].
Currently, prescribed fire in pinyon-juniper woodlands is used to reduce accumulations of slash from fuelwood harvesting or to reduce or eliminate tree cover to increase range productivity and biodiversity. Prescribed burning to dispose of slash is less desirable in partially harvested stands because residual trees are damaged and advance regeneration is killed. Established, smaller trees are particularly important for the next rotation because of the difficulty of achieving adequate regeneration of these relatively slow growing trees. Payson and others [98] provide recommendations relevant to fire management in pinyon-juniper ecosystems.
Parent material: Basic basalt exposed along ridges, covered by cinders 1 to 4 inches (2.5-10.2 cm) deep on uplands and deeper in drainage areas. Calcareous silt tends to cement the cinders.
Moisture patterns: Little surface runoff, low evaporation, subsurface is often moist.
Average annual precipitation: 11.6 inches (300 mm) (60% as summer thunderstorms).
Grazing history:
"badly overgrazed" by 1907. Grazing levels reduced in recent years. (Numbers in
parentheses below refer to individual burn sites.) (1) January and (2) March burn sites -
light domestic sheep grazing for at least 20 years prior to the study.
(3) June burn site - lightly grazed by cattle in winter.
FIRE DESCRIPTION:
(1) January 5 fire:
Air temperature: 49 to 54 degrees Fahrenheit (9-12oC)
Relative humidity: 44% at 49 degrees F (9oC).
Wind: from northeast, gusts to 6 to 8 miles per hour (10-13 km/hr).
Fires were set from 12:45 to 3:45 p.m., burned 60 out of 90 acres (24 out of 36 ha).
Fire slowed down or died as it moved toward the junipers.
(2) March 19 fire:
Air temperature: 70 degrees Fahrenheit (21oC).
Relative humidity: 44%.
Wind: from southwest at 15 to 20 miles per hour (24-32 km/hr).
Fire burned close to trees because prevailing winds had piled Russian-thistle and
other debris under the larger trees. The southwest wind caused debris to ignite.
(3) June 28 fire:
Wildfire started by lightning, conditions were very dry.
Wind: from the southwest at 10 to 15 miles per hour (16-24 km/hr).
Air temperature: 97 degrees Fahrenheit (36oC).
Relative humidity: 17 to 25%.
FIRE EFFECTS ON TARGET SPECIES:
On the 3 burns, 380 oneseed junipers were examined along randomly located
compass lines. Mortality of trees less than 4 feet (1.2 m) tall ranged from
70 to 100% and 30 to 40% in trees 5 to 6 feet tall (1.5-1.8 m). The March
and June burns caused the death of 60 to 90% of the oneseed junipers 8 to
10 feet (2.4-3.1 m) tall. Mortality data for this height group in the January
burn was not presented. The authors attributed much of the mortality in the
taller oneseed junipers to the accumulation of flammable debris around the
base of the trees. When the fires moved with the prevailing winds,
Russian-thistle ignited and tree mortality was relatively high (60-90%).
When fires moved against the prevailing winds, flammable understory
debris did not ignite and few (< 10%) large oneseed junipers were killed.
FIRE MANAGEMENT IMPLICATIONS:
The objective of the prescribed burns was to test grass fires as a means of
controlling juniper encroachment into grasslands. The amount of flammable
material present at a given site and wind conditions greatly influenced mortality
in larger junipers. Mortality was relatively high when winds ignited Russian-thistle
and other debris accumulated beneath the crowns. A high percentage of smaller oneseed
junipers (< 4 feet (1.2 m)) can also be killed by fire. The authors concluded that
grass fires at frequent intervals killed oneseed junipers less than 4 feet (1.2 m)
tall. Larger trees were much more resistant to fire except where significant
flammable material was present beneath the crown.
Slope: 0 to 9%
Elevation: 6,014 to 6,514 feet (1,829-1,981 m)
Average annual precipitation: 15.5 inches (390 mm), with approximately 61.8% occurring from June to October
Soils: Mostly very fine sandy loam "developed on recent alluvium
derived from the San Andres Formation and mixed material of Guadalupe age."
FIRE DESCRIPTION:
The fire was a 935 acre (378 ha) wildfire that started at 1:45 p.m. on April 10th.
It was controlled approximately 3 hours later. The fire did not move through the
crowns of the trees. Other conditions were as follows:
Relative humidity: low
Wind: warm, dry, from the south, (speed not recorded)
Soil, litter, and grass fuel: very dry
Rate of spread: 1,250 feet per hour (381 m/hr)
Available fuel in open grasslands: 750 pounds per acre (670 kg/ha)
FIRE EFFECTS ON TARGET SPECIES:
The total number of oneseed junipers in the burn was 120. All those less than
4 feet (1.2 m) tall were killed by fire. The foliage of many of the smaller trees
extended close to the ground and ignited readily. Larger junipers were found to be
somewhat more resistant to surface fire. Many trees did not show
the extent of fire damage until 1 or 2 years after the fire. After 2 years,
approximately 24% of oneseed junipers had died (while only 13.5% of the pinyon
pines were killed). At that time some of the larger trees that had been defoliated
by fire were surviving. Thirteen % of oneseed junipers were unharmed by the fire.
FIRE MANAGEMENT IMPLICATIONS:
The broad objective of data collection following the wildfire was to examine
the effects of fire on the grama-pinyon-juniper vegetation type. Reduction in
herbage caused by the fire was 30% in October of the same year. Litter production
was also reduced following the fire. Small cholla cacti (Opuntia spp.)
were also killed by the fire. The findings suggest that low
severity surface fires may be effective in reducing numbers of small (< 4 feet (1.2 m))
oneseed junipers and cholla cacti. Larger oneseed junipers and cacti are somewhat
resistant to such fires. Fine fuels tended to be sparse under
the large junipers, and the authors conclued that more juniper and pinyon
would have been killed if more grass fuel had been present.
Browse: Deer utilize the foliage of oneseed juniper [26,59,84]. Mahgoub and others [82] observed heavy utilization in parts of south-central New Mexico where juniper can represent up to 20% of the annual diet of mule deer. Oneseed juniper foliage is reported to be a major mule deer food item from January through March in parts of southeastern New Mexico [108]. Pronghorns also browse oneseed juniper, and in some areas, winter use may be heavy [20,122]. Bighorn sheep and elk may consume small amounts of juniper browse [108]. The foliage of oneseed juniper is of little value to domestic livestock. Domestic sheep and goats utilize this species to a limited extent [26,59].
Fruit: The succulent, berrylike cones of oneseed juniper serve as an abundant and readily available food source for a wide range of wildlife species. The bright cones tend to remain on the tree and can provide food year-round [34,110], but become dry and leathery by the 2nd winter [109].
It is estimated that avian population densities may be 70% greater during years with abundant juniper "berry" crops (generally every 2 to 5 years) [13]. Studies with captive birds have revealed that an average Townsend's solitaire can consume approximately 240 "berries" per day, or 36,000 to 84,000 per winter [13,110]. In some areas at least 97% of the Townsend's solitaire's winter diet may be made up of oneseed juniper "berries" [109]. Robins also consume large numbers of the berrylike cones. An individual bird can eat 220 "berries" per day or 33,000 per winter. Birds and mammals serve as important dispersal agents for seeds of oneseed juniper. Many bird species disperse seed up to 6.3 miles (10 km) or more from the seed source. Sheep and domestic cattle can also facilitate dispersal of oneseed juniper [13,64]. Salomonson [110] reported the following animals as juniper seed consumers and dispersers:
| birds | mammals |
| northern flicker | desert cottontail |
| Steller's jay | black-tailed jackrabbit |
| mountain chickadee | cliff chipmunk |
| plain titmouse | rock squirrel |
| sage thrasher | golden mantled ground squirrel |
| American robin | deer mouse |
| Townsend's solitaire | Mexican woodrat |
| western bluebird | coyote |
| evening grosbeak | gray fox |
| Cassin's finch |
Other wildlife species known to consume oneseed juniper berries include
mule deer, western chipmunk, antelope ground squirrel, squirrels, bear,
javelina, pocket mouse, rabbits, and raccoon [,64,108,119].
PALATABILITY:
The fruits of oneseed juniper are palatable to
many birds and mammals [110]. They appear to remain palatable even when
dry. The foliage is relatively unpalatable to most species, although it
is reported to be somewhat more palatable than that of most other junipers [26].
The palatability of oneseed juniper to livestock and
wildlife species in 2 western states has been rated [28]:
| CO | UT | |
| Cattle | poor | poor |
| Domestic sheep | poor | fair |
| Horses | poor | poor |
| Pronghorn | - | fair |
| Elk | - | fair |
| Mule deer | - | fair |
| Small mammals | - | good |
| Small nongame birds | - | good |
| Upland game birds | - | good |
| Waterfowl | - | poor |
| CO | UT | |
| pronghorn | - | good |
| elk | - | good |
| mule deer | fair | good |
| white-tailed deer | fair | - |
| small mammals | good | good |
| small nongame birds | good | good |
| upland game birds | - | good |
| waterfowl | - | poor |
VALUE FOR REHABILITATION OF DISTURBED SITES:
Oneseed juniper is rated as having low overall value for short-term
rehabilitation but high value for long-term rehabilitation [28]. It was not widely
used in the past for rehabilitation projects because of
unreliable seed germination. Fertilizers, wood chips, straw mulch, plastic mesh
protection against rodents, and drip irrigation can all contribute to
increased survival on disturbed sites. Oneseed juniper has been
successfully planted on surface coal and uranium mines in
the Southwest. Improved techniques have resulted in survival rates
as high as 99% [40,41].
In a New Mexico study of planted seed, drip irrigation was more effective than mulch, while triple-superphosphate aided growth more than slow-release fertilizers. On these sites, July planting dates produced best results at higher elevations, whereas August plantings were most successful on low elevation sites [40].
Transplanting containerized seedlings onto disturbed sites has also been a successful technique [39,40,41]. In New Mexico, survival is best when trees are planted after the June drought but before the ground freezes. Survival of transplants is heavily dependent on moisture availability. Mulch aids in water conservation and can enhance survival on dry sites. Drip irrigation may be necessary on the most arid sites. Researchers suggested that fertilizer may improve survival on some sites particularly when combined with irrigation [40,41]. In another New Mexico study of rehabilitation of surface-mined land, survival of transplanted containerized seedlings was improved by wood chip mulch and animal protection using rigid mesh. In this study, fertilizer provided no benefit and decreased oneseed juniper survival where seeded grasses were able to outcompete. Competition from weeds also reduced juniper growth and survival [39].
Germinating juniper seeds is difficult. Seeds may require a period of afterripening [41]. Pack [97] found that high temperatures, alternating temperatures, freezing and thawing, removal of the seed coat, application of hydrogen peroxide, dilute acids, carbon dioxide, or light had little influence on germination of juniper seeds. Cold stratification may improve germination in oneseed juniper [66]. Fischer and others [41] found that germination improved when seeds were leached 48 hours with hydrogen peroxide, or treated with ethephon or hydrogen peroxide plus gibberellic acid followed by cold stratification .
Experiments suggest that exposure to sunlight may have relatively little effect on
germination. Johnsen [64] observed average germination of 44% for seeds grown
in the dark, and 52% for seeds exposed to sunlight. Soil moisture may be an important
factor influencing germination. Germination appears to be best in moist but not saturated
soil. Seeds of oneseed juniper do not germinate well on the soil
surface which is subject to rapid desiccation. Juniper seeds appear to be
resistant to drought when buried in the soil [63,64]. Buried seeds can often retain
viability and germinate when moisture conditions become favorable. Approximately
54% of oneseed juniper seed stored for 21 years germinated [63].
UTILIZATION:
Oneseed juniper is used locally for fuel, fenceposts, poles, and
Christmas trees [100]. Native Americans relied on oneseed juniper for many
purposes. Wood was used for bows and arrows by the Kiowa, Comanche,
Cheyenne, and Apache [51]. The "berries" were eaten whole or ground into flour
for bread [22,31]. Prayer sticks were made from wood, and dye, fibrous mats,
and saddles were fashioned from the bark [,31]. Parts of the tree were also
used as building materials and for medicinal purposes [64]. Foliage was used as
domestic sheep food during extreme winters [31]. Oneseed junipers were used by
settlers for fenceposts, fuel, and mine timbers. Oneseed juniper has also been used
in the production of cellulose and chemical products [34,64]. Springfield [118] noted
that many species of juniper may have potential value for the production of charcoal,
pulp, particleboard, chip products, fiber, or in certain chemicals. Oneseed
juniper was first cultivated in 1900 [66].
OTHER MANAGEMENT CONSIDERATIONS:
In parts of the Southwest, juniper species including oneseed juniper
have encroached into adjacent grasslands, or increased in stand density
[48,59,78,93,133]. Explanations include fire suppression, a decrease in
light fuels from overgrazing, reduction of grass competitiveness by overgrazing,
spread of seed by livestock, and climatic change [4,64,78,89,106,132]. Past management
efforts focused on halting the juniper invasion through mechanical or chemical means.
Mechanical control: A number of methods of mechanical removal were tried with limited success. Cabling, chaining, bulldozing, and various means of hand removal were used in attempts to convert pinyon-juniper woodlands to grasslands. Neither the single chaining nor double chaining method effectively eliminated trees less than 10 feet (3.1 m) in height. In treatment areas heavily stocked with young trees, reinvasion may be rapid [11,65,104,114,118].
Chemical control: The foliage of junipers tends to be resistant to herbicides, and leaves have little surface area for absorption [65], though juniper can be killed with chemicals. See Springfield [118] and Johnsen [65] for details.
Production: Herbage production values are variable in pinyon-juniper woodlands. Springfield [118] reported an inverse relationship between tree canopy and average herbage production:
| tree canopy | average herbage production |
| 0% | 600 lbs per acre |
| 20% | 300 lbs per acre |
| 80% | 50 lbs per acre |
Fertilization: The diameter of oneseed juniper was found to be largely unaffected by the addition of nitrogen fertilizer in a New Mexico study, although growth of lateral branches and apex was enhanced [108].
In a 1998 study in northern New Mexico, Allen and Breshears [4] concluded that the ecotone between a semiarid ponderosa pine forest and Colorado pinyon-oneseed juniper woodland shifted extensively (1.2 miles (2 km)) and rapidly (within < 5 years) through drought-induced ponderosa pine mortality and associated expansion of the pinyon-juniper population. The Bandelier Wilderness site was chosen in part for its minimal history of human disturbance and extensively documented fire history. They used a Geographic Information System and a series of aerial photographs taken from 1935 to 1975. Their analysis showed that the shift coincided with the culmination of a 1950s drought, which was one of the most severe of the past 500 years. The shift has persisted for at least 40 years. The authors acknowledge that fire suppression since the 1800s allowed the Colorado pinyon and oneseed juniper to become more densely established in proximity to the ponderosa pines prior to the 1950s drought. They also note that the shift was amplified by bark beetle mortality in the ponderosa pine and more efficient water use in pinyon and juniper. They assert drought was the driving factor in the shift, in part because widespread ponderosa pine mortality ceased when the drought broke.
A number of other studies and reviews have examined the relatively recent changes in stand density or areal extent of juniper or pinyon-juniper woodlands [33,48,55,67,89]. Evidence and arguments are presented for both expansion and reduction of the woodlands. The studies do not focus on oneseed juniper specifically, but provide relevant perspectives.
In a recent discussion of the problem of pinyon-juniper expansion, Lanner [78] provided the following perspective: "Despite the decades old alarm occasioned by juniper encroachment into rangelands, very little research has been undertaken to establish its cause or causes... The lumping of pinyon pines with junipers, despite their very different biologies, is a further confusing factor in understanding the behavior of these coniferous woodlands in which the species may occur together, or singly... At present woodland eradication in the pinyon-juniper zone is nearly an abandoned practice, partly because it is controversial, but mainly because it is almost always a prohibitively expensive way to grow grass."
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