BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pinus longaeva | Great Basin Bristlecone Pine 



GENERAL BOTANICAL CHARACTERISTICS : 
Great Basin bristlecone pine is a long-lived, native species,
characteristic of treeline in the high desert ranges of eastern
California, Nevada, and Utah.  It is ectomycorrhizal and may be nitrogen
fixing.  Trees usually have a contorted and multistemmed appearance.
The first leader on a tree often does not persist.  Branches are
pendulous or twisted [3].  In the White Mountains of California, trees
remain erect even at the extreme upper limit of tree growth at 12,000
feet (3,659 m); however, at treeline in the Snake Range of eastern
Nevada trees are stunted and form krummholz [2].

The sparse crowns of twisted trees are supported by a narrow strip of
cambium, the living tissue of a tree.  The effects of sand- and
ice-blasting by wind are seen in older trees with a double "pick-a-back"
growth form.  Here the windward trunk is dead, but a narrow strip of
cambium supports branches on the leeward side of the tree, the "piggy
back" [13,40].

Trees retain needles for 30 to 40 years.  They usually reach 30 to 40
feet (9-12 m) in height and are 1 to 2 feet (0.3-0.6 m) in diameter,
although some do attain considerable breadth [4,12,27,28].  The Patriarch
tree, in the Schulman Grove in the White Mountains has a d.b.h of 12
feet (3.8 m), is 37 feet (11 m) in circumference, and 47 feet (14 m) in
height [2].

In the Schulman Grove trees growing at 9,300 feet (2,835 m) on
south-facing slopes were found to take 200 to 250 years to expand 1 inch
(2.54 cm) in radial growth.  One specimen from this area was 3 feet (1
m) high, 3 inches (8 cm) in diameter, and 700 years old [2].

Highly sensitive to its environment, Great Basin bristlecone pines
exhibit slow, but highly variable, growth rates within and among stands
[16].  Bristlecone pines are known for their longevity.  One individual
on Wheeler Peak in eastern Nevada lived at least 4,900 years by count of
annual growth rings and was estimated to be 5,200 years old.  It is
difficult to determine the exact age of these trees because of
asymmetric growth and heartwood decay.  Growth rates and ages
can be estimated with increment bores [28].

In the Schulman Grove there are several trees growing above 10,000 feet
(3,050 m) in elevation that are estimated to be in excess of 4,000 years
of age.  The Methuselah tree is estimated to be over of 4,600 years old.
Pine Alpha was the first tree to be estimated to have a longevity
exceeding 4,000 years [2,4].

Great Basin bristlecone, Rocky Mountain bristlecone (Pinus aristata),
and foxtail pine (P. balfouriana) share many characteristics [7,12,27]:

 (1)  occurrence at the upper limits of tree growth and a reduced rate of
      growth
 (2)  a capacity for long life
 (3)  continued growth after loss of large areas of tissue from drought,
      stress, wind injury, and soil erosion
 (4)  heavy, dense, resin-impregnated wood with small, closely arranged,
      water-conducting cells (tracheids) which provide resistance to
      moisture and decay
 (5)  survival in an environment of drought, low temperatures, short
      growing seasons, daily temperature extremes, and poor soils
 (6)  retention of needles for several years, which reduces the need for
      moisture and nutrients, in addition to carrying a tree over several
      years of stress
 (7)  relative safety from ground fire due to sparse ground cover and
      litter scarcity


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
The environmental and physiological factors contributing to the
longevity of the Great Basin bristlecone pine also work to lower its
regeneration potential.  Trees are intolerant of shade, grow slowly, and
are locally scattered in distribution.  Reproduction is sparse.
Bristlecones characteristically occur in old to moderately old open
stands and form the vegetative climax.  This species may also act like a
pioneer species in recently disturbed areas where, under favorable
conditions, its growth is vigorous and fast.  However, for the most
part, seedlings are slow growing [8,32].

The longevity of the species evidently enables it to bridge relatively
long unfavorable periods.  The sampling of a stand at 10,600 feet (3,232
m) on the headwaters of Poison Creek east of Campito Mountain in the
White Mountains of California revealed very few trees 12 inches (31 cm)
in diameter and none under 3.7 inches (9.4 cm) in diameter [7].


SITE CHARACTERISTICS : 
The distribution of Great Basin bristlecone pine is related to the
diversity of associated species.  Where conifer diversity is high, it is
restricted to poor sites.  However, where conifer diversity is
relatively low, Great Basin bristlecone pine increases in area,
altitudinal range, and types of habitats it dominates.  It forms stands
on sites with low moisture and nutrients available because there is less
competition from other conifers [4].

Great Basin bristlecone pine ranges in elevation from 7,500 to 11,200
feet (2,300-3,400 m) and is characteristic of treeline for high desert
ranges [8,13,21].  The habitat is characterized by a short growing
season and little available moisture.  Precipitation ranges from 10 to
30 inches (25-75 cm).  Great Basin bristlecone pine is outcompeted by
other conifers below its natural lower elevational limits, where more
moisture and nutrients are available.  Although the lower limit for it
appears to be precipitation sensitive, the upper limit is temperature
sensitive [3,13].

Stands of Great Basin bristlecone pine usually are pure, even-aged, and
open.  They occur on rocky outcrops of southern or southwestern slopes
with limited soil, intense sunlight, and rapid runoff.  Trees reach
their greatest density on north-facing dolomitic slopes and at times mix
with limber pine [4,7,40].

The nature of geological substrates greatly affects the development of
this species.  It competes best on limestone and dolomite substrates.
These light-colored soils reflect sunlight better then darker granitic
and sandstone ones.  In addition, they have lower soil temperatures
during the growing season, which reduces moisture stress [3].
Bristlecone pines are not successful in competing with other conifers on
granite, quartzite, or sandstone substrates [4,21,28].  On dolomitic
soils in the White Mountains of California, Great Basin bristlecone
dominates with an occasional limber pine; however, just to the north on
granitic soil, the situation is reversed [3,13].
 
Bristlecones are intolerant of shading and occur in areas of sparse
ground cover.  In the White Mountains they provide 29.1 percent of the
cover in an area with 35.5 percent total cover.  Sheet erosion of fine
particles is severe, due to steep slopes, summer convection storms, and
minimal ground cover.  Winter snowpack accumulations are reduced by high
insolation and wind [4,5,34,41].

Since big sagebrush (Artemisia tridentata) is an important competitor of
the bristlecone pine in California and Nevada, the distributions of
these two are complementary.  The Great Basin bristlecone pine favors
dolomitic soils and north slopes, but big sagebrush is best developed on
sandstone and granitic soils, especially on south-facing slopes [40].

Plants of big sagebrush are more drought tolerant and occur on more
xeric substrates than bristlecone pine.  However, big sagebrush is
intolerant of the low nutrient availability of dolomitic soil.  Thus,
bristlecone pines are best developed on dolomitic soils due to a
combination of greater moisture availability and a lack of competition
[2,3,13,40].


SUCCESSIONAL STATUS : 
Great Basin bristlecone pine is a climax species and persists at
treeline for hundreds to thousands of years in the absence of
disturbance and competition.  It is highly adapted to its habitat of
very shallow soils, slow primary succession, short growing season, and
avalanches [27].  There is no evidence for the expansion or recession of
the range of Great Basin bristlecone pine, so it is considered a
senescent species [30].  However, stands in Utah and Nevada were found
to be maintaining or increasing in numbers.


SEASONAL DEVELOPMENT : 
Bristlecone pines flower from July to August and cones start ripening
about mid-September.  The period of flowering and cone opening is
uniform for Great Basin and Rocky Mountain bristlecone pines, as well as
for foxtail pine [8,13].

Bristlecones store half of their carbohydrates from the growing season
for use during the winter.  In an experiment in the White Mountains of
California at 10,150 feet (3,090 m), winter rates of photosynthesis and
respiration were measured.  With the coming of severely cold
temperatures, net photosynthesis decreased sharply and remained at zero
until early spring.  Respiration rates were high until late winter, but
decreased significantly in early spring.  By the end of winter, there
was a negative carbon dioxide balance resulting from high respiration
and negative photosynthetic rates [34].

Related categories for Species: Pinus longaeva | Great Basin Bristlecone Pine