BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juniperus scopulorum | Rocky Mountain Juniper 



GENERAL BOTANICAL CHARACTERISTICS : 
Rocky Mountain juniper is a long-lived erect shrub or small tree which
reaches 20 to 50 ft (6.1-15.3m) in height [15].  Crown shape is conical,
with trunk diameter reaching up to 17.8 in (45cm).  Bark is reddish-gray
to brown, furrowed, and shreddy [33].  Blue-green, scalelike leaves are
.04-.16 in (1-4mm) long, and mostly opposite.  Twigs are slender.

Rocky Mountain juniper is generally monoecious although rarely
dioecious.  Brown, staminate cones are .08-.12 in (2-3mm) in length
[33].  Female flowers form strobili or "berries," which reach .16-.32 in
(4-8mm) in diameter at maturity [15,33].  Prior to ripening, the fruit
is green with a bloom [15].  Ripe fruit is blue with a white waxy bloom
and contains two yellow to light brown seeds [27].  Heavy berry crops
are produced at 2 to 5 year intervals [6].

Rocky Mountain juniper is characterized by a long lifespan and slow
growth rate.  It grows fairly uniformly to age 40 when the plant
averages 13-14 ft (4.0-4.3m) in height.  After age 40 growth rate
declines, with growth averaging .55 ft (.17m) per decade.  Eighty year
old trees average 18 ft (5.5m) and 300 year old plants typically grow to
30 ft (9.2m).  Diameter growth averages .79 in (2.0cm) per decade until
170 years when growth slows to .255 in (.65cm) per decade.  The diameter
of 300 year old trees averages 17 in (43.2cm) at 1 ft (.31m) above the
ground [6].  The average lifespan of Rocky Mountain juniper is believed
to be from 250 to 300 years [27].  However, some plants can survive much
longer.  An individual growing in Logan Canyon in northern Utah is
estimated to be more than 3,000 years old [6].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Regeneration in Rocky Mountain juniper is through seed.  Green female
flowers form strobili or "berries" which are generally produced in
abundance [27].  Ripe ovulate cones contain two small seeds, averaging
.16-.32 in (4-8mm) in diameter, and are blue with a white waxy bloom
[15].  Brown, staminate cones are .08-.12 in (2-3mm) in length, and grow
terminally on short branches [27].

Pistillate flowers develop during late summer and open the following
April when pollen is shed from the staminate flowers [6].  Fruit ripens
from September-December of the second year after pollination and remains
on the tree until the following March or April [6,15].  Seed can persist
for two to three years [15].

Rocky Mountain juniper begins seed production at 10-20 years of age
although maximum seed production is not attained until 50 to 200 years
[6,15].  Heavy seed crops occur at two to five year intervals.
 
Germination occurs during or after the second spring [27].  Seed can
remain viable for some time.  Germination after 3 1/2 years was found to
be 30% [15].  An afterripening period of 14-16 months may be important
for good germination [6].  Warm stratification at 68 degrees F (20
degrees C) (night) and 86 degrees F (30 degrees C) (day) for 45-90 days,
followed by cold stratification may induce germination [15].

Seed of Rocky Mountain juniper is dispersed primarily through birds and
large or small mammals.  Seed is often cached by rodents or dispersed
more widely by Bohemian waxwings and other small birds [6].  Gravity and
water can also serve as dispersal agents.  Rocky Mountain juniper does
not reproduce vegetatively.


SITE CHARACTERISTICS : 
Rocky Mountain juniper occurs throughout the drier lower mountains and
foothills of the Rocky Mountains and northern plains from glaciated
valleys of British Columbia to mesas of the southwest [6].  It is a dry,
or more rarely, moist, subhumid plant which grows well on open, exposed
bluffs, rocky points, or ridgetops, on southern exposures and in ravines
or canyons [6,31].  Rocky Mountain juniper occurs at a wide range of
sites which vary significantly in soils, elevation, and climatic
factors.  Stand structure and associated plant species are also highly
variable.

Rocky Mountain juniper grows best on calcareous or alkaline soils [31].
Soils are commonly derived from limestone, sandstone, shale, and basalt.
The species is found on limestone cliffs, foothills, lava beds, or on
stony, shallow limy-cemented subsoils which can be subject to rapid
erosion.  It also grows in deep soils along drainages in the central and
southern part of the range [6].

Rocky Mountain juniper grows best on sites with average minimum
temperatures of from -10 degrees F (-23 degrees C) to -5 degrees F (-21
degrees C) [6].  It can however, survive temperatures of -35 degrees F
(-37 degrees C) to more than 100 degrees F (38 degrees C) [31].  Typical
average July temperatures range from 60 degrees to 75 degrees F (16
degrees to 24 degrees C), with average January temperatures of from 15
to 40 degrees F (-9.4 to 4.4 degrees C) [6].  Growing season length is
from 140 to 230 days [31].  Average annual precipitation ranges from
12-26 in (305-660mm) and annual average snowfall is from 5 to 150 in
(12.7-381cm).  Rocky Mountain juniper is said to be less
drought-resistant than other western species of juniper [6].

Rocky Mountain juniper grows from near sea level in the Pacific
Northwest to 11,000 ft (3,355m) in the Intermountain Region.  It is
abundant within a narrow elevational band of 6,300 to 6,500 ft
(1,922-1,983m), along the east slope of the Rocky Mountains [6].
Elevational ranges are as follows [3,6]:

               from  5,000 to 9,000 ft (1,525 to 2,745m) in AZ
                     4,000 to 11,000 ft (1,220 to 3,355m) in CO
                     2,000 to 5,000 ft (610 to 1,525m) in n. ID
                     1,900 to 8,500 ft (580 to 2,593m) in MT
                     5,000 to 9,000 ft (1,525 to 2,745m) in NM
                     3,500 to 7,400 ft (1,068 to 2,257m) in NV
                     3,500 to 7,400 ft (1,068 to 2,257m) in UT
                     4,000 to 10,000 ft (1,220 to 3,050m) in WY


SUCCESSIONAL STATUS : 
Rocky Mountain juniper is an indicator of climax in a number of ponderosa
pine, mountain brushland, and sagebrush-grassland habitat types.  Because
of its ability to survive where many other species cannot, it is also
considered to be a pioneer species in some earlier seral communities [31].


SEASONAL DEVELOPMENT : 
Pistillate flowers first develop during late summer of the first year
and open during the following April when staminate flowers shed pollen
[6].  Fruit ripens from mid-September to mid-December during the second
year after pollination and remains on the plant until March or April of
the following spring [6,15].  Seed germinates during the second spring
after maturity following an afterripening period of 14-16 months [27].

Rocky Mountain juniper begins to bear seed at 10 years of age but does
not reach optimum seed production until 50 to 200 years [27].  Large
seed crops are produced at two to five year intervals [15].

Flowering dates are as follows [3]:

   State           Earliest Date of Flowering      Latest Date of Flowering
     MT                     May                              June
     ND                     April                            May
     WY                     April                            May

Related categories for Species: Juniperus scopulorum | Rocky Mountain Juniper