BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juniperus pinchotii | Pinchot Juniper 



GENERAL BOTANICAL CHARACTERISTICS : 
Pinchot juniper is a native, evergreen large shrub or small tree, not
usually over 25 feet (8 m) tall, more often not over 18 feet (5.5 m)
tall [20,47,55].  It usually has lengthy lateral stems and spreads
considerably, with a broad, flattened to dish-shaped crown [20].  The
bark is gray to reddish brown and peels off in shaggy strips [55].
Pinchot juniper forms a berrylike "fruit" that contains one or rarely
two seeds [55].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual reproduction:  Pinchot juniper is typically dioecious, though
most populations have a small percentage of monoecious individuals
[47,55].  Pinchot juniper reproductive maturity is correlated more
strongly with tree height (r = 0.59) than with age (r = 0.35 or r = 0.50
site dependent) [35].  Average height at reproductive maturity is 3 to 4
feet (1-1.2 m); average age at maturity is 25 years.  Height and age
were found to be highly correlated (r = 0.93); however, a few
individuals produce strobili as young as 12 years if they are tall
enough [35].  Seeds are dispersed by mammals and birds.  Rabbits can
carry seed up to one mile.  Some seed is carried by rainfall runoff
[17].

Pinchot juniper requires 2 years of above average precipitation for good
seedling establishment; the first year for good seed production and the
second for good germination [48].  Germination of Pinchot juniper seeds
declines with a decrease in moisture availability.  Optimal soil
temperature for germination is 64 degrees Fahrenheit (18 deg C), with no
emergence at 50 degrees Fahrenheit (10 deg C) and limited emergence at
81 degrees Fahrenheit (27 deg C) [48].  Seedling densities of more than
800 per acre (2,000/ha) were found on sites where mature Pinchot juniper
had been tree-dozed.  Seedling densities can also be high beneath
canopies of live oak and honey mesquite trees, due to dispersal of seed
by birds [39,52].

Asexual reproduction:  Pinchot juniper sprouts from meristematic tissue
at the base of the stem following injury or top removal [48].


SITE CHARACTERISTICS : 
Pinchot juniper occurs on open flats, on dry hillsides, in canyons,
caprock regions, and talus slopes.  It is usually found on limestone or
gypsiferous soils [18,47,55].  Pinchot juniper-mixed grass habitats are
most widely developed on rough breaks and shallow range sites along the
high plains escarpment and adjacent rolling plains of western Texas
[51].  On the redbed soils of the Permian formation, Pinchot juniper
forms dense clumped stands 15 to 20 feet (4.6-6 m) in height.  On gypsum
soils it can form thickets of very low (3 feet [0.9 m] tall) shrubs that
cover hundreds of acres [47].  Pinchot juniper is drought resistant; its
range extends into the Chihuahuan Desert region, and it is associated
there with xeric shrubs such as creosotebush (Larrea tridentata),
lecheguilla (Agave lecheguilla), sotol (Dasylirion leiophyllum), catclaw
acacia (Acacia greggii), and mariola (Parthenuim incanum) [56,57].

Overstory or shrub associates not previously mentioned include Texas
persimmon (Diospyros texana), Shumard oak (Quercus shumardii), lotebush
(Ziziphus obtusifolia), catclaw mimosa (Mimosa biuncifera), yucca (Yucca
spp.), netleaf hackberry (Celtis reticulata), algerita (Mahonia
trifoliolata), littleleaf sumac (Rhus microphylla), skunkbush (R.
aromatica), feather dalea (Dalea formosa), and elbowbush (Forestiera
pubescens) [33,36,39,51].

Understory/herbaceous associates not previously mentioned include common
curlymesquite (Hilaria belangeri), buffalograss (Buchloe dactyloides),
little bluestem (Schizachyrium scoparium), silver bluestem (Bothriochloa
saccharoides), perennial threeawn (Aristida wrightii, A. purpurea, A.
longiseta), sideoats grama (Bouteloua curtipendula), red grama (B.
trifida), hairy grama (B. hirsuta), hairy tridens (Erioneuron pilosum),
slim tridens (Tridens muticus), Texas wintergrass (Stipa leucotricha),
sedges (Carex spp.), Arizona cottontop (Trichachne californica), chloris
(Chloris spp.), tumblegrass (Schedonnardus paniculatus), and fall
witchgrass (Leptoloma cognatum) [33,36,51].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Following top removal, Pinchot juniper sprouts are only slightly
affected by competition from herbaceous species in terms of reproductive
succcess, growth rate, and survival.  Competition from neighboring
herbaceous plants has a greater effect on the growth and survival of
seedlings, and may delay reproductive maturity [35,36].  Shrub density
and cover, however, have no effect on reproductive maturity [35].

The encroachment of Pinchot juniper onto adjacent grasslands is
attributed to disturbances such as grazing, reduced fire frequency, and
climatic changes over the last 50 to 300 years [6].  Grazing thins or
removes the grass cover, providing Pinchot juniper seeds a "safe spot"
to become established.  Blue grama (Bouteloua gracilis) will suppress
Pinchot juniper seedling growth [48].  Johnsen [63], however, found that
in years of above normal moisture, Pinchot juniper seedlings may become
established in even the best stands of grass.

The maintenance of continuous Pinchot juniper stands depends on at least
2 consecutive years of cooler and wetter than average weather occurring
during the lifespan of the trees in a stand.  This is not usually an
obstacle, since Pinchot juniper can live more than 100 years [38].

In closed-canopy stands, Pinchot juniper can exclude essentially all
herbaceous vegetation [37].  The litter and foliage extracts of some
juniper species have allelopathic effects on some associated grasses and
browse [22].  Some woody species were present only in the shade of large
Pinchot juniper plants; shrub densities may increase as Pinchot juniper
approaches reproductive maturity [35].  Pinchot juniper significantly (p
< 0.01) affected total production and grass production on both grazed
and ungrazed sites, with a linear inverse relationship on ungrazed sites
and a inverse logarithmic relationship on grazed sites [37].  McPherson
and Wright [37] determined that herbaceous composition and productivity
are altered for at least 5 years following cessation of grazing, from
which they inferred that succession following grazing will proceed
slowly or be unpredictable.

Pinchot juniper is apparently tolerant of some shade, as it can
establish under the canopies of live oak and honey mesquite [39,51].
The relationship is not reciprocal; honey mesquite does not establish
under Pinchot juniper canopies.  Pinchot juniper does, however,
facilitate the establishment of algerita, littleleaf sumac, and catclaw
mimosa [39].


SEASONAL DEVELOPMENT : 
Pollination occurs in September and October, and the fruiting cones
mature the following fall [4].

Related categories for Species: Juniperus pinchotii | Pinchot Juniper