BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pinus albicaulis | Whitebark Pine 



GENERAL BOTANICAL CHARACTERISTICS : 
Whitebark pine is a slow growing, long-lived, ectomycorrhizal, native
conifer characteristic of treeline.  Trees often reach 400 to 700 years
of age.  The oldest known cored tree is 750 years old and is in Mount
Robson Provincial Park, British Columbia [2,3,13,18,19,37].

Trees in well-developed stands are 50 to 70 feet (15-20 m) tall and 24
to 36 inches (60-90 cm) in d.b.h.  Growing at the uppermost limits of
growth, trees usually are dwarfed or contorted.  At upper treeline this
species takes on a spreading krummholz growth form and grows in isolated
cushions of "alpine scrub" 1 to 3 feet (0.3-1 m) tall [3,39].

In Crowsnest Forest, Alberta, the largest whitebark pine is at 107 feet
(37 m) high and 31 inches (79 cm) in d.b.h. [12].  The largest reported
whitebark pine in the United States is in the Sawtooth Range of central
Idaho and is 69 feet (21 m) in height and 9.5 feet (2.9 m) in d.b.h.
[3,41].  On good sites in the Flathead National Forest of Montana,
dominant whitebark pines are often 80 to 100 feet (24-30 m) tall [Arno
pers. comm. 1987].

Whitebark pine trees commonly have two or more trunks that are often
partially fused at the base.  Electrophoretic evidence reveals that two
or more trunks of what appears to be a single tree are indeed separate
trees with distinct genotypes.  This supports the idea that several
mature trees can arise from single seed caches [36] and that seeds
cached by Clark's nutcrackers are instrumental in the establishment of
trees [48].  Trees develop a deep and spreading root system on most
sites [3,19].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
The minimum seed-bearing age of whitebark pine trees is between 20 and
30 years, and the interval between large seed crops is 3 to 5 years.  On
most sites significant amounts of seed occur only on trees greater than
80 years of age [47,Arno pers. comm. 1987].  Large seed crops are
produced at irregular intervals, interrupted by smaller crops and crop
failures [32].  Cone production fluctuates widely between years, and
variations in seed crops may play an important role in the intial
establishment of a stand.

Greater than 95 percent of the whitebark pine seed crop is harvested by
animals [Arno pres. comm. 1987].  The primary disperser of seeds is the
Clark's nutcracker.  The seed-caching activities of nutcrackers in the
Sierra Nevada are reported in detail by Tomback [44,45,46,47] and in the
Absaroka and Teton Ranges of Wyoming by Lanner [33,22].  Evidence for
nutcrackers facilitating the regeneration and spread of whitebark pine
includes the rapid regeneration of trees on burned or clearcut areas,
the clumping of seedlings, and the disjunct occurrence of populations.

Besides Clark's nutcrackers, other vertebrates also harvest, feed on,
and cache whitebark pine seeds.  However, they do not possess the
behavior to systematically disperse and cache the seeds.  Rodents
disperse fewer seeds than nutcrackers, in shorter distances from parent
trees, and in sites less suitable for germination.  Also, seed caches of
rodents are larger and have lower potential for successful tree
establishment.  In addition, not many seeds are left to germinate from
rodent caches because the olfactory sense of rodents may allow them to
find and use caches more efficiently than nutcrackers [3,30,45,46,47].

Clark's nutcrackers are effective dispersers of seeds in part because of
the long distances they travel [45].  A nutcracker can carry as many as
150 seeds in its sublingual throat pouch and can store 850 seeds per
day, usually in caches of four to five seeds.  Over a 42-day period one
bird may cache 32,000 seeds.  They bury the seeds to 1.2 inches (3 cm)
in depth, which is suitable for germination.  Nutcrackers store three to
five times their energetic requirements, so more seeds are buried than
are recovered.  These seeds, along with abandoned caches, can germinate
and produce new trees.

Squirrel pressures on seed crops and blister rust damage have caused a
reduction in whitebark pine populations in Idaho and Washington [11].
Regeneration of whitebark pine is sporadic.  In addition to consistant
losses from vertebrates, Eggers [14] reported that in the Rocky
Mountains those seeds that do survive have low germination rates.  In
contrast, Tomback [46] reported a good survival rate of seeds from
caches in the Sierra Nevada, with 56 percent for the first year and 25
percent by the fourth year.  Seedling survival rate after a fire was 25
percent [46].

At treeline in Jasper National Park, Alberta, it was found that higher
than average mean minimum summer temperature is one of the main factors
triggering seedling establishment for whitebark pine.  In contrast,
there was little association between mean summer precipitation and
seedling germination [24].  Seeds from high-elevation krummholz stands
of whitebark pine have less germination capacity than do those from
lower elevations [48].

The viable period for seeds in cold storage, 0 to 5 degrees Fahrenheit
(-17 to 15 deg C), is 8 years [30].  Cold stratification of 90 to 120
days for fresh seeds is recommended by some researchers [32].  A
germination success of about 30 percent has been reported for seeds
soaked in cold water for 1 to 2 days, then stored damp in plastic bags
at 33 to 41 degrees Fahrenheit (0.5-5.0 deg C) for 90 to 120 days [15].

Seed immaturity and physical dormancy were cited for poor germination in
seeds collected near Cranbrook, British Columbia, at 7,200 feet (2,200
m).  The growing season is short at high elevations, leaving little time
for seeds to mature.  The lack of development of embryos was partially
overcome by exposing hydrated seeds to a temperature of 68 degrees
Fahrenheit (20 deg C) for 30 to 60 days.  A temperature of 36 degrees
Fahrenheit (2 deg C) for 60 to 90 days broke dormancy.  It was found
that poor germination resulted from the restraint imposed by the seed
coat which inhibited the protrusion of the radicle root.  These
researchers concluded that it was not an inability of seeds to imbibe
water [35].

Removal of seed coats did not confer an advantage in germination, as
germination was 30 percent regardless of whether the coats were clipped
or entirely removed [35].  Sterilization only slightly increased
germination of seeds which received cold stratification.  Germination
was significantly improved with a combined warm and cold treatment [35].

In another study, researchers found conflicting evidence, where the
limiting factor for germination could indeed be the restriction of water
uptake by the seed coat.  When seeds were cut and exposed to germination
paper the germination rate was 61 percent.  The rate was increased to 91
percent with cold stratification plus clipping [41].


SITE CHARACTERISTICS : 
Whitebark pine grows on dry rocky sites on high mountains between 6,000
and 10,000 feet (1,800 and 3,030 m).  It is characteristic of treeline
where it forms dense krummholz thickets.  In Banff and Jasper National
Parks at treeline about 6,500 to 7,500 feet (2,000-2,300 m), whitebark
pine trees are dwarfed and isolated on dry exposed sites.  Here at the
northern end of its range, it is a minor component of treeline.
Whitebark pine is an important component of high-elevation forests in
Idaho, Montana, and Wyoming between 5,900 and 10,500 feewt (1,800-3,200
m).  In high-elevation forests in the Cascades of southern Oregon and
northern California between 8,000 and 9,500 feet (2,440 and 2,900 m),
whitebark pine is a major component of treeline [2,3].

Whitebark pine occurs at elevations as low as 5,000 feet (1,470 m) in
British Columbia and in the Cascades of Washington.  The lowest reported
natural occurrence of whitebark pine is 3,600 feet (1,100 m) on Mt.
Hood in Oregon.  In the southern Sierra Nevada, it commonly occurs up to
11,500 feet (340 m) in elevation [Arno pers. comm. 1987].

The dispersal of whitebark pine seeds by Clark's nutcrackers strongly
affects the distribution and abundance of this species.  Trees occur on
dry rocky, subalpine slopes, and exposed ridges.  Stands are generally
open with an undergrowth of low shrubs, forbs, and grasses [2,9,23].
Sites where whitebark pine occurs as a climax are drier than those where
it is seral.

Whitebark pine is important in areas where the mean annual precipitation
is 24 to 70 inches (600-1,800 mm) [3].  The climate is characterized by
cool summers and cold winters with deep snowpack.  Trees have high frost
resistance and low shade tolerance.

Trees are found predominately on acidic substrates, although they also
have been reported on calcareous ones.  Most soils under whitebark pine
stands are Inceptisols.  The growth of whitebark pine in Montana and
Wyoming is reported as good on sandy-loam and loam, fair on gravels and
clay loams, and poor on clay [3,13,14,19,43].



SUCCESSIONAL STATUS : 
In upper elevation subalpine forests, whitebark pine is generally seral
and competes with and is replaced by more shade-tolerant trees.
Subalpine fir, a very shade-tolerant species, is the most abundant
associate and most serious competitor of whitebark pine.  Although
whitebark pine is more shade tolerant than lodgepole pine and subalpine
larch (Larix lyallii), it is less shade tolerant than Engelmann spruce
and mountain hemlock (Tsuga mertensiana).  Whitebark pine is the
potential climax species on high exposed treeline sites and
exceptionally dry sites [2,3,14,47].  It sometimes acts as a pioneer
species in the invasion of meadows and burned areas [17,19].  On dry,
wind-exposed sites, the regeneration of whitebark pine may require
several decades, even though it is often the first tree to become
established [3,15,17,48].

The distribution of seral whitebark pine is strongly affected by the
dispersal of seeds by Clark's nutcrackers.  The fact that bird
dispersion of seed occurs allows whitebark pine to be more widespread as
a seral species.  The dispersal of seeds by them throughout subalpine
habitats is partly responsible for the status of whitebark pine as a
pioneer and postfire invader [43].


SEASONAL DEVELOPMENT : 
Whitebark pine produces pollen during June and July.  Cones mature in
late August and September of the second year.  Female cones remain
closed until they fall to the ground, where they disintegrate by decay
and predation by animals.  Few cones are available to fall, as most are
harvested in the trees by Clark's nutcrackers and red squirrels [3,14].

Related categories for Species: Pinus albicaulis | Whitebark Pine