BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pinus ponderosa var. ponderosa | Pacific Ponderosa Pine 



GENERAL BOTANICAL CHARACTERISTICS : 
Pacific ponderosa pine has the potential for achieving large dimensions.
Stems of 103.5 inches (263 cm) in d.b.h. and 232 feet (70.7 m) in height
have been recorded.  Diameters at breast height of 30 to 50 inches
(76-127 cm) and heights of 90 to 130 feet (27.4-39.6 m) are common
throughout its range [5].  Trees often reach ages of 300 to 600 years
[48].  Needles are typically in bundles of three.  They are 5 to 10
inches (12.5-25.0 cm) long and form tufts at the end of each branch.
Cones are oval and 3 to 6 inches (7.5-15.0 cm) long.  The bole is
typically straight and at maturity is clear of lower branches.  The bark
of mature trees is composed of broad, irregular scaly-plates that fit
together like jigsaw puzzle pieces.  The crown is conical and composed
of stout branches [38,48].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Pacific ponderosa pine reproduces sexually.  It does not regenerate
naturally by vegetative methods.  It can be propagated by rooting and
grafting, but success decreases rapidly when scions are taken from trees
older than 5 years [48].

Seedling development:  Successful natural regeneration of Pacific
ponderosa pine is accomplished by a combination of heavy seed crops,
favorable weather during the growing season, soil texture, low
competition, and exposed mineral seedbeds [26,39].  Moisture-stress
reduces seed germination as well as initial seedling survival and
development.  Pacific ponderosa pine has the capacity for root growth in
relatively dry soil.  Nursery stock removed in January from California
had appreciable root elongation even when planted in soil with very low
water potential.  Shrub competition reduces the height and diameter
growth of seedlings planted in northern California and Oregon.  On the
western slopes of the Sierra Nevada, growth starts noticeably later with
each 2,000 foot (610 m) increase in elevation.  Rates of height and
radial growth do not vary with elevation during the growing season [48].

Seed production and dissemination:  Seed production varies with
geographic distribution.  There are generally 6,900 to 23,000 clean
ponderosa pine seed per pound (6,210-20,700 per kg) [36].  In California
west of the Sierra Nevada, medium seed crops are borne on an average of
every 2 to 3 years.  The average interval between heavy cone crops is 8
years; in the Pacific Northwest it is every 4 to 5 years.  Twenty-three
years of data show Pacific ponderosa pine to be a poor seeder in western
Montana.  It bears cones as early as 7 years and continues to produce
good cone crops up to at least 350 years.  Optimum seed viability is
produced by trees 60 to 160 years old.  In California, trees greater
than 25 inches (64 cm) d.b.h. were the most dependable seed producers.
Recommended cold stratification period is 30 to 60 days for stored seeds
at 33 to 41 degrees F (1-5 deg C).  Pacific ponderosa pine seeds do not
naturally disseminate beyond about 100 feet (31 m) from the seed source.
In central Oregon, the amount of seeds reaching the ground at 132 feet
(40 m) into a clear-cut was only 22 percent that of those measured at
the timber's edge.  At 528 feet (161 m) it was only 8 percent.  Nearly
all seeds are disseminated by early November.  In a good seed year, as
many as 345,080 seeds per acre (852,050 seeds per hectare) may reach the
ground [48,79].

Seedling mortality and predation:  Many variables are responsible for
seedling mortality.  Seedlings younger than 36 days old are more
susceptible to minimum night temperatures cooler than 23 degrees F (-5
deg C) than are lodepole pine (Pinus contorta) seedlings.  During
winters with little snowcover, 1- and 2-year-old seedlings may suffer
damage and frost kill.  Also, 1- to 3-month-old seedlings are killed by
stem temperatures of 130 degrees F (54 deg C) and higher.  Pacific
ponderosa pine seeds are consumed by a number of birds and small
mammals.  Squirrels and porcupines clip many of the cone-bearing twigs,
hence destroying flowers and conelets.  Rabbits and hares injure or kill
many seedlings by nibbling young stems, while pocket gophers may
decimate an entire population of seedlings.  Repeated browsing by deer
may stunt seedling growth for up to 50 years [13].  Livestock also
damage seedlings and saplings by trampling, bedding, and browsing.  Many
species of insects and disease affect Pacific ponderosa pine.  See
MANAGEMENT CONSIDERATIONS for futher discussion [48].


SITE CHARACTERISTICS : 
Throughout its range, Pacific ponderosa pine is dependent upon several
site variables such as soils, elevation, and climate [68].  Soil
moisture is the variable most often limiting growth, especially in the
summer months when rainfall is deficient [48].

Climate:  Pacific ponderosa pine is typically found on warm, dry sites.
The climate is characterized by a short growing season and minimal
summer precipitation.  The mean annual precipitation ranges from 11 to
17 inches (28-43 cm), with summer precipitation averaging 5 to 10 inches
(13-25 cm).  Average annual precipitation ranges from about 14 to 30
inches (35-75 cm) on Pacific ponderosa pine sites in Oregon and
Washington, and is typically in the form of snow [18].  The western
slope of California's northern Sierra Nevada may be the wettest area
supporting Pacific ponderosa pine, with an annual rainfall reaching 69
inches (173 cm).  In contrast, this species occupies areas in California
where extreme rainfall deficiencies occur [July and August precipitation
about 1 inch (2.5 cm) or less] [48].

Soil and topography:  Pacific ponderosa pine occurs on a wide variety of
soils ranging from glacial till, glacio-fluvial sand and gravel, dune,
basaltic rubble, colluvium, to deep loess or volcanic ash.  This pine
develops best on wet, deep, sandy gravel and clay loams with pH between
6.0 and 7.0.  Throughout its extensive range, however, it will most
often be found on a variety of loams, loamy sand, and gravel; with a pH
from 4.9 to 9.1 [68,74].  Many studies have shown better survival and
growth rates on coarse-textured clayey soils where extensive root
proliferation is possible [18].  In Oregon, Pacific ponderosa pine soils
are typically less than 40 inches (100 cm) deep and formed from loess
and basalt colluvium and bedrock materials.  Surface layers have silt
loam to silty clay loam textures with greater than 35 percent rock
fragments by volume.  Surface rocks usually exceed 10 percent cover
[33].  Pacific ponderosa pine has been found on a variety of sites from
steep slopes in the plateau region of northern Idaho and Oregon to the
flat coastal plains of California [7,48].

Elevation:  Elevational ranges of Pacific ponderosa pine are as follows
[68]:

State              Mean ft (m)                Range ft (m)
-----             -------------        -----------------------------
California        3,242   (988)         348 to 6,520  (106-1,987 m)
Oregon (eastern)  5,400 (1,646)       1,800 to 9,000  (549-2,743 m)
Oregon (western)  2,800   (853)       2,200 to 3,400  (670-1,036 m)
Washington        2,625   (800)         330 to 4,950  (100-1,510 m)

Associated forest cover:  Pacific ponderosa pine is associated with a
rich variety of tree species.  Only five of these, however, western
juniper (Juniperus occidentalis), Rocky Mountain juniper (J. scoparium),
quaking aspen (Populus tremuloides), lodgepole pine, and Oregon white
oak (Quercus garryana), are common associates in climax stands [18].
Understory associates can be catagorized into two groups: a shrub- and
forb-rich group and a drier bunchgrass-dominated group.  The climax
shrub-dominated undergrowth generally includes ninebark (Physocarpus
malvaceus), common snowberry, and bitterbrush.  Seral site shrubs
generally include blue huckleberry (Vaccinium globulare) and bearberry
(Arctostaphylos uva-ursi) [9,49,63].


SUCCESSIONAL STATUS : 
Historically, fire has played the greatest role in the successional
status of Pacific ponderosa pine.  See FIRE ECOLOGY for further
discussion.

In many areas of the Pacific Northwest, the first zone above the
grasslands is the Pacific ponderosa pine climax.  This tree species is
shade intolerant and grows most rapidly in near full sunlight [18,74].
There is a strong tendancy for climax pine stands to be even-aged in
small groups rather than being truly uneven-aged.  Heavy grazing induces
effects opposite those of fire.  Removal of the grass cover by grazing
tends to favor shrub communities.  Logging is usually done by a
selection-cut method.  Older trees are taken first, leaving younger,
more vigorous trees as growing stock.  This method substantially
accelerates the successional trend toward a more climax dominant tree
species.  Logging also impacts understory species by machine trampling
or burial by slash.  Clear-cutting generally results in dominance by
understory species present before logging, with invading species playing
only a minor role in postlogging succession [18,39].

The successional status of Pacific ponderosa pine can be expressed in
terms of its successional role, which ranges from seral to climax
depending on specific site conditions.  It plays a climax role on sites
toward the extreme limits of its environmental range and becomes
increasingly seral with more favorable conditions.  On sites with more
favorable moisture, pine encounters greater competition and must
establish itself opportunistically.  On moist sites it is usually seral
to Douglas-fir and the true firs (mainly grand fir and white fir).  On
severe sites it is climax by default because other species cannot
establish.  On such sites, establishment is likely to be highly
dependent upon the cyclical nature of large seed crops and favorable
weather conditions [62].



SEASONAL DEVELOPMENT : 
In California, Pacific ponderosa pine flowers from April to June; cone 
ripening and seed dispersal occur from August to September [48].

Related categories for Species: Pinus ponderosa var. ponderosa | Pacific Ponderosa Pine