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Limber Pine -
Pinus
flexilis
Limber pine is a slow growing, long-lived species, sometimes taking
several hundred years to reach maturity. Mature trees may exceed 1000
years of age. Limber pine grows across a wider range of elevations
that any other tree species in the central Rocky Mountains, inhabiting
some of the driest sites capable of supporting trees.
(4)
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Limber Pine -
Pinus
flexilis
This outstanding Morton Arboretum specimen is resident on Pine Hill |
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Limber pine is a
slow growing,
long-lived species,
sometimes taking
several hundred
years to reach
maturity. Mature
trees may exceed
1000 years of age.
Limber pine stands
are broadly
even-aged, though
populations also
occur in uneven-aged
stands and on very
harsh sites as
widely spaced,
isolated individuals
[96,102,112]. Trees
often have an
irregular or
multi-stem growth
form, and rarely
reach over 50 feet
(15 m). At high
elevations they
sometimes form
krummholz
(stunted, twisted
shrub-like
formations caused by
exposure to wind.
German for "twisted
wood"). Trunks may
reach 6.5 feet (2 m)
in diameter. The
species is cold and
drought tolerant.
Trees are
ectomycorrhizal,
have deep taproots,
and are very
windfirm. Limber
pine is often killed
by fire because of
its relatively thin
bark.
Limber pine grows
across a wider range
of elevations that
any other tree
species in the
central Rocky
Mountains,
inhabiting some of
the driest sites
capable of
supporting trees.
Cones of limber pine
are cylindrical, 3
to 6 inches (8-15
cm) long. They
release their seeds
if not preyed upon.
The seeds are large
(7-12 mm long) and
sometimes have a
vestigial wing.
Clark's nutcrackers
have co-adapted an
important mutualism
with limber pine and
are the primary
harvester and
disperser of its
seeds. Limber pine
regeneration on
burns is largely
from germinants of
Clark's nutcrackers
seed caches. The
birds begin
harvesting seeds in
late August, while
the cones are still
green and slightly
closed. They remove
the cones by pecking
them loose, fly them
to perches, and peck
between the scales
to remove the seeds.
As cones begin to
open on the trees in
September, Clark's
nutcrackers remove
exposed seeds. An
individual bird can
store as many as 125
seeds in its
sublingual pouch,
then flies to a
cache area and
deposits numerous
caches from its
pouchful of seeds.
In a burned-over
area in northern
Utah, Clark's
nutcrackers cached
an estimated 12,140
seeds per acre
(30,000/ha) in 1
year.
The wood of limber
pine has little
commercial value.
Its potential for
timber and fuelwood
production is low,
because the trees
are slow growing
with irregular form.
Limber pine has been
used locally for
mine props and
railroad ties.
(4)
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Limber pine has a dense
branching habit
IMPORTANCE TO
LIVESTOCK AND
WILDLIFE:
The large, wingless
seeds of limber pine
have high energy
content. Pine "nuts"
provide critical
food for rodents and
birds, which cache
the seeds for later
use. Other small
mammals and birds
benefit from these
caches. Bears also
feed from caches.
Sites with limber
pine provide key
winter range for
deer and elk.
Bighorn sheep use
open stands on
ridges. Difficult
access and low grass
production result in
low forage value of
limber pine stands
for livestock.
Because of its slow
growth, limber pine
has been used only
to a limited extent
in land reclamation
projects. Vegetation
recovery is slow on
the exposed, hot,
dry, rocky sites
where it is found,
and soil erosion can
prevent complete
restoration.
However, limber
pine's drought
tolerance and
ability to survive
at high elevations
indicate that it has
potential for use in
revegetation
projects.
Management of limber
pine forests
associated with
Douglas-fir
typically favors the
growth of the
economically
important
Douglas-fir. Of
primary management
importance in these
areas is watershed
protection and
enhancement. The
slow rate of
vegetation recovery
in areas where
limber pine occurs
requires dispersed,
low-impact
recreation to
maintain the
aesthetic appeal of
these forests.
Forage productivity
can be increased by
periodic surface
fires..
Limber pine trees
are infected and
killed by white pine
blister rust
(Cronartium
ribicola) throughout
the tree's range.
Ribes species are
obligate alternate
hosts of the rust.
Limber pine appears
to have less
resistance to
blister rust than
other North American
white pines
(Strobi), with
greenhouse infection
levels as high as 98
to 100% [45,113]. In
a 3-year greenhouse
study of relative
seedling
susceptibility to
blister rust, limber
pine mortality was
75% (n=348). In
comparison,
mortality in
whitebark pine was
33% (n=207) and 86%
in southwestern
white pine (n=323).
Limber pine is
susceptible to
numerous other
fungal diseases. It
can be heavily
infected or killed
by limber pine
dwarf-mistletoe (fig
2.) (Arceuthobium
cyanocarpum),
and is susceptible
to infestation by
mountain pine
beetles, cone
beetles, coneworms,
and budworms.
(4)
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Limber Pine Foliage
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Limber pine dwarf mistletoe (Arceuthobium
cyanocarpum)
is a damaging parasite of limber pine, whitebark
pine (P. albicaulis Engelm.), Rocky Mountain
bristlecone pine (P. aristata Engelm.) and Great
Basin bristlecone pine (P. longaeva D.K. Bailey).
Limber pine dwarf mistletoe occurs in the Rocky
Mountains from southern Montana to southern Colorado
and Utah. It also occurs in widely scattered
populations in the Great Basin (southern Idaho,
western Utah and Nevada), and in the southern Sierra
Nevada Mountains.
Limber pine dwarf mistletoe is a small, parasitic
flowering plant. The external (aerial) shoots are
yellow-green, have inconspicuous scale-like leaves
at the nodes, and are perennial. Plants are
typically densely clustered around infected tree
branches. On the average, plants are only 1 inch (3
cm) tall, but they are sometimes as tall as 3 inches
(7 cm) (Figure 2). Aerial shoots arise from a
network of root-like, absorbing strands imbedded in
host tissues. This network, called the endophytic
system, consists of cortical strands growing within
the bark and sinkers within the wood. The endophytic
system extracts nutrients and water from the host
tree. The endophytic system lives as long as
adjacent host tissues are alive. The mistletoe is
dependent upon its host for water and nutrients. The
aerial shoots do contain chlorophyll, but they
produce minor amounts of carbohydrates. |
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Figure 3. Witch's Brooms |
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The first symptom of dwarf
mistletoe infection is the appearance of slight
swellings at infection sites. Swellings become
visible 1 to 2 years after infection occurs. The
presence of aerial shoots is the most obvious visual
sign of dwarf mistletoe infection. If the plants
have dropped, small brown shoot remnants, called
basal cups, often remain attached to the bark.
Porcupines and squirrels often preferentially feed
on bark associated with mistletoe infections, and
this chewing activity can make the infection sites
more visible.
The most striking symptoms of dwarf mistletoe
infection are witches' brooms. Witches' brooms are
variously shaped clumps of branches caused by an
abnormal proliferation of tree branches and twigs
(figure 3). Brooms caused by limber pine dwarf
mistletoe are usually small and compact. Severely
infested stands typically have many trees with
multiple brooms, trees with significant branch
mortality, and dead trees.
Dwarf mistletoe flowers, shoots
and fruits are food for insects, birds, and mammals.
The witches' brooms produced in severely infected
trees may be used for hiding, thermal cover, and
nesting sites by birds and other animals. The
mortality caused by dwarf mistletoe, either directly
or by predisposing trees to other agents, provides
snags as habitat for cavity-nesting birds and,
eventually, coarse woody debris on the forest floor.
Dwarf mistletoe may also have negative consequences
for some animals. Animals which depend on limber and
whitebark pine seeds will be impacted by the reduced
seed and cone production and mortality of
cone-bearing trees. The loss of limber pine in the
range-forest interface zone will impact animals such
as deer and elk which rely on the trees for hiding
and thermal cover.(1)
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References:
1.
Limber Pine Dwarf Mistletoe
Forest Insect and Disease Leaflet 171 1999
Jane E. Taylor1 and Robert L. Mathiason
2.
USDA, ARS, National Genetic Resources Program.
Germplasm Resources Information Network - (GRIN)
3. Limber Pine Dwarf Mistletoe photos courtesy
Rocky Mountain Research
Station/Forest Pathology Archive, USDA Forest
Service, Bugwood.org
4.
U.S. Forest Service Fire Effects Information
Pinus flexilis
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