BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juniperus monosperma | Oneseed Juniper 



GENERAL BOTANICAL CHARACTERISTICS : 
Oneseed juniper is a native, perennial evergreen which grows as a shrub
or small tree [73].  Although it can grow up to 49 feet (15 m) in
height, 7 to 13 feet (2-4 m) is more typical [75,78].  In extremely arid
areas trees may reach only 3 to 4 feet (0.9-1.2 m) at maturity [40].
Most oneseed junipers have multiple stems at or below ground level [75].
Oneseed juniper is characterized by a rounded or low spreading bushlike
crown [73,75].

Branches are stout and grayish to reddish-brown [27].  Gray to brown
twigs are scaly or shreddy [75].  The bark is ashy gray to gray, thin,
fibrous, and furrowed or shreddy [27,75,78].  The inner bark is
reddish-brown [82].  Foxx and Tierney [22] reported the following
rooting depths:
        
        average rooting depth (cm)              range (cm)
                2,438                           579-6,096

The relatively deep root system is well adapted for growth on sites with
low soil-water content [28].

Foliage is described as "bunched" [3].  The yellow-green, scalelike
leaves are mostly opposite, although sometimes occur in whorls of three
3 [75,82].  Juvenile leaves are sharp and awl-shaped [78].

Oneseed juniper is dioecious with small glaucous, brown, globular
staminate cones, and subglobose ovulate cones [75].  Mature cones are
dark blue to purple or brownish, and succulent, or at least somewhat
fleshy [27,75,78].  Seeds are generally one per fruit, more rarely two,
reddish-brown and ovoid to globose [27,75].

Oneseed juniper is a slow-growing species.  Lymbery and Pieper [49]
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) [11].  The taproot extended to 3.5 feet (1.1 m) in depth [11].

Oneseed juniper has the ability to stop active growth when moisture
conditions are limited but can resume growth when moisture availability
improves [30].  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 quite
resistant to drought [40].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Oneseed juniper is dioecious with seed persisting for 1 to 2 years
[40,42].  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 [42,67].  Trees as short as 18 inches (46 cm) in height can
produce seed [40].  Oneseed juniper typically produces large seed crops
at 2- to 5-year intervals [42].

Germination of most species of juniper is relatively poor [59].  Seeds
generally require a specific period of rest and afterripening [59].
Pack [59] found that high temperatures, alternating temperatures,
freezing and thawing, removal of the seedcoat, application of hydrogen
peroxide, dilute acids, carbon dioxide, or light had little influence on
the germination of juniper seeds.  Juniper seeds are described as having
a semipermeable and thick seed coat with a dormant embryo [59].

Oneseed juniper seed should generally be cold-stratified prior to
planting [42].  Germination was found to improve after a 48-hour water
soak and stratification at 41 degrees Fahrenheit (5 deg C) for 30 to 120
days [21].  Under laboratory conditions germination results were best
when seeds were exposed to an 8-hour photoperiod; 16 hours at 68 degrees
Fahrenheit (20 deg C), and 8 hours at 106 degrees Fahrenheit (30 deg C)
[21].  Seed should be leached with water at 68 to 75 degrees Fahrenheit
(20-24 deg C) and cold stratified for 90 days, or treated with water and
GA3 or ethephon applied 30 days prior to cold stratification [21].
Exposure to sunlight appears to have relatively little effect on
germination [40].  Johnsen [40] observed average germination of 44
percent for seeds grown in the dark, and 52 percent for seeds exposed to
sunlight [40].  Soil moisture may be an important factor influencing
germination.  Germination appears to be best in moist but not saturated
soil [40].  Seeds of oneseed juniper do not germinate well on the soil
surface which is subject to rapid desiccation.  Seed emergence by depth
is as follows [40]:

        depth                           % emergence
       (inches)                     uncovered       covered
          0                             0             44
         1/4                           44             40
         1/2                           52             38
          1                            48             48
          2                            28             30
          4                             0              0

Juniper seeds appear to be resistant to drought when buried in the soil
[39].  Buried seeds can often retain viability and germinate when
moisture conditions become favorable [39].  Approximately 54 percent of
oneseed juniper seed stored for 21 years germinated [39].  Natural
germination generally occurs during the first spring after dispersal
[75].

Seedling establishment is often very poor even when good germination
occurs [69].  Researchers in some areas have found that only
approximately 3 percent of juniper seeds develop to the seedling stage
[36].  Shade may be important for good early growth of oneseed juniper
[36].  Emergence appears to be somewhat greater under trees or shrubs
than in interspaces where humidity and temperature fluctuations are more
extreme [40].  In some areas, small junipers are particularly numerous
under the canopy of pinyon or other species [36,67].  Most seedlings
occur some distance from the parent tree, although most seeds are
located beneath the source tree [64].  Seedlings seldom establish
beneath mature junipers, and an autopathic effect from litter is
suspected [67].

Dispersal of oneseed juniper may occur through water, gravity, or by any
of a number of birds and mammals [3].  Animal dispersal may be
particularly important, as digestive processes may actually actually
enhance germination [5].  Most berries occur on the outer edges of trees
where they are most visible and accessible to birds [64].  The brightly
colored highly visible berries remain on the trees for much of the year
and provide a constantly available food source for animals [5,16].  It
is estimated that on certain sites in New Mexico, 90 to 95 percent of
juniper reproduction could be attributed to bird dispersal [25,60].
Domestic sheep and cattle also aid in seed dispersal [40].  Trampling by
livestock can apparently reduce competition with grasses and help to
"plant" the seeds [40].

Although oneseed juniper is generally described as a nonsprouter [83].,
limited sprouting, mostly from older trees, has been observed in some
areas [12,76].  Approximately 10 percent of living oneseed junipers
sprouted from the base following an Arizona fire [76].


SITE CHARACTERISTICS : 
Oneseed juniper is an important species throughout much of the
pinyon-juniper woodlands of the Southwest [8,49,].  It forms woodlands
with true pinyon, singleleaf pinyon (Pinus monophylla), Mexican pinyon
(P. cembroides), Utah juniper , and alligator juniper throughout much of
its range [54,82], and occasionally occurs in pure stands at lower
elevation sites too dry for pinyon [47,80].

Oneseed juniper typically occupies fairly xeric sites in semiarid
climatic zones [19,28].  The distribution of this tree may be largely
confined to the Arizona monsoon area or regions which receive summer
rains [57].  A typical Arizona-Utah site occupied by oneseed juniper
receives 10 to 15 inches (25-38 cm) of precipitation annually, and has
an average growing season of approximately 120 days [80].  Tree density
is believed to be related to leaf water potential [6].  Unlike several
related species, the distribution of oneseed juniper does not appear to
be limited by temperature inversions [35].

Oneseed juniper grows on dry, rocky, open flats, and slopes [27,29].  It
commonly occurs in canyons or on middle elevation foothills [27,80].  In
many areas this juniper occurs in a zone below ponderosa pine or
alligator juniper, but above oak (Quercus spp.)-mountain-mahogany
(Cercocarpus spp.) shrublands [58,80].  Common shrub, forb, and grass
associates of oneseed juniper include:  skunkbush sumac , turbinella oak
(Quercus turbinella), broom snakeweed, mountain-mahogany, big sagebrush
(Artemisia tridentata), black sagebrush (A. nova), antelope bitterbrush
(Purshia tridentata), winterfat, rabbitbrush (Chrysothamnus spp.),
mesquite (Prosopis glandulosa), Mormon-tea (Ephedra spp.), yucca (Yucca
spp.), pricklypear (Opuntia spp.), scarlet globemallow, blue grama,
sideoats grama, bottlebrush squirreltail (Sitanion hystrix), prairie
junegrass, western wheatgrass, muhlys (Muhlenbergia spp.), and galleta
[3,45,55,69].

Because soil moisture is so 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 [40,83].  A number of oaks also compete
for soil moisture, although oneseed juniper appears to be capable of
outcompeting them on shallow soils [67].

Oneseed juniper grows on a variety of soil textures including gravelly,
rocky, or sandy soils [27].  Parent materials include basalt, limestone,
and sandstone [19].  Generalized growth potential by soil type is rated
as follows [14]:

        gravel:         fair
        sand:           fair to poor
        sandy loam:     good
        loam:           good
        clay loam:      fair to good
        clay:           good to poor
        dense clay:     fair to poor
        organic:        poor
        acidic:         poor
        saline:         fair
        sodic:          poor
        sodic-saline:   poor

Soil characteristics, temperature, and topography combine to influence
the upper and lower elevational extent of oneseed juniper [80].
Elevational range of oneseed juniper by state is as follows [14,49]:

     from: 2,951 to 6,885 feet (900-2,100 m) in Arizona and New Mexico
           4,000 to 7,600 feet (1,220-2,318 m) in Colorado
           3,500 to 3,500 feet (1,068-1,068 m) in Utah


SUCCESSIONAL STATUS : 
The successional status of oneseed juniper has not been well documented.
This long-lived species apparently occurs as climax vegetation in some
areas [12,31] but as a seral species in others [12,23,67,68].  According
to some researchers, oneseed juniper is the most water-stressed plant in
certain climax communities of New Mexico, and although it persists, it
typically does not replace itself [67,68].  In these communities it is
probably best thought of as a late seral species [67,68].  Francis [23]
reported that oneseed juniper occurs in a variety of low to high seral
communities of New Mexico, suggesting that this species may have a wide
successional role in some areas of the Southwest.

Topographic factors can significantly influence the successional role of
oneseed juniper.  Nonsprouting junipers such as oneseed juniper are
susceptible to fire and are consequently not considered to be a climax
species in grasslands subject to frequent fires [83].  On rocky breaks
or escarpments where fires do not occur or are infrequent oneseed
juniper grows as a climax species [83].


SEASONAL DEVELOPMENT : 
Annual leader elongation of oneseed juniper generally begins in April.
Detailed phenological development is as follows [30]:

     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 varies with geographic location but can occur from January
through June [21].  Flowering generally occurs in March or April
[27,42].  Fruit matures in one season and ripens from August through
November [40].  Most fruits ripen in August or September [42].  Seed may
remain on the tree for 1 to 2 years with dispersal in October or
November [42].  Lymbery and Pieper [49] 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.

Related categories for Species: Juniperus monosperma | Oneseed Juniper