BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pseudotsuga macrocarpa | Bigcone Douglas-Fir 



GENERAL BOTANICAL CHARACTERISTICS : 
Bigcone Douglas-fir is a native evergreen conifer from 50 to 100 feet
(15-30 m) in height and 22 to 62 inches (56-155 cm) in DBH.  Its growth
form is straight and pyramidal.  The deeply ridged bark is composed of
thin, woodlike plates separating heavy layers of cork [3,10]; bark of
trees over 40 inches (102 cm) in DBH is from 6 to 8 inches (36-64 cm)
thick [31].  Main branches are long and pendulous, spreading from 20 to
50 feet (6-15 m) [1,3,15,18,21].  Side branches are few.  The needles,
from 0.8 to 1.2 inches (2-3 cm) long, are shed about every 5 years
[10,24].  Female cones are from 4 to 7 inches (10-18 cm) long [28,24].
Seeds are large and heavy, each having a short rounded wing [18].  Roots
are described as strong and spreading [18].  The largest known bigcone
Douglas-fir is 91 inches (231 cm) DBH, 173 feet (53 m) tall, and is
estimated to be from 600 to 700 years of age [10].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual:  The male strobili of an individual tree usually sheds pollen
before female strobili open, preventing self-pollination [10].  Seed
production begins at about 20 years of age; full seed production occurs
at about age 40.  Insect larvae destroy some immature seed.  At times,
they will destroy most of the crop.  Heavy seed crops are rare.  Seeds
fall under the parent tree and only during high winds is wider seed
dissemination possible [18].  Rodents and birds play a minor role in
seed dispersal.  Deer mouse, Merriam chipmunk, California ground
squirrel, and western grey squirrel consume considerable portions of the
seed crop [10].  Seed quality tends to be poor.  In one laboratory test,
seeds given cold-stratification treatment for 28 days proved 31 percent
viable [18].

Seedbed requirements are broad.  Seeds will germinate successfully on
bare mineral soil or deep litter, although some seedling mortality from
damping-off fungi occurs in deep litter.  Germination is epigeal [18].
Bigcone Douglas-fir does not reproduce well where fires are frequent
[3,18].  It reproduces best in locales undisturbed for at least 50
years, where emergents are shaded by canyon live oak.  Survival is low
on open sites unless soil remains moist, but seedlings surviving on
these open sites attain top growth more rapidly than shaded seedlings
[18,31].  With time, continuous shade becomes a liability.  A span of 40
to 70 years commonly is required for bigcone Douglas-fir to penetrate
through 16.5- to 27-foot (5-9 m) overstories of canyon live oak.
Seedlings on higher elevation south or west slopes, however, enter the
sapling-size class within 3 to 5 years [10].

Vegetative:  Vegetative reproduction occurs after injury.  Bigcone
Douglas-fir does not sprout from the root crown, but intermediate-aged
trees will sprout from the bole.  In the Santa Ana Mountains, coppice
sprouts developed in trees that were 5 to 45 inches (13-114 cm) in DBH
and 25 to 300 years old [3].  Pole- and sawtimber-sized trees often
regrow burned crowns (see Plant Response to Fire).  Seedlings and
saplings appear to have this ability as well [23].  Sprouting in young
trees is not well documented, however.  Some authorities claim that
seedlings and saplings are not usually capable of sprouting following
injury [14,18].


SITE CHARACTERISTICS : 
Climate:  Bigcone Douglas-fir grows in a mediterranean climate,
characterized by hot summers and wet, mild winters.  Annual rainfall
during a 30-year period on a bigcone Douglas-fir site in the San Gabriel
Mountains averaged 30 inches (762 mm) and ranged from 10 to 49 inches
(254-1,245 mm).

Elevation:  Bigcone Doulgas-fir occurs between 2,000 and 8,000 feet (610
and 2,720 m) [10,24].

Soil and topography:  Bigcone Douglas-fir grows in a wide variety of
soil types [10].  At low elevation, it occurs near streams in moist,
shaded canyons and draws where aspects are mostly north and east.  At
elevations from 4,440 to 5,600 feet (1,350-1,700 m), aspects include
south- and east-facing slopes.  At these elevations, bigcone Douglas-fir
also grows on sloping hillsides, ridges, and benches.  At higher
elevations, it occurs on south and west aspects on all types of terrain.
The average angle of slope on which bigcone Douglas-fire grows is 34.5
degrees.  Slope angles range from 2 to 90 degrees, although these
extremes are uncommon [3].

Plant associations:  The number of plant associates in bigcone
Douglas-fir communities is usually small [14].  Common overstory
associates not listed under SAF Cover Types or Habitat Types and Plant
Communities include bigleaf maple (Acer macrophyllum), California bay
(Umbellularia californica), Digger pine (Pinus sabiniana), and white
alder (Rhombus rhombifolia) [1,4,7,10,19].  Shrub associates include
bigpod ceanothus (Ceanothus megacarpus), red shank (Adenostoma
sparsifolium), Eastwood manzanita (Arctostaphylous glandulosa), toyon
(Heteromoles arbutifolia), white sage (Salvia apiana), black sage (S.
mellifera), purple sage (S. leucophylla), and California scrub oak
(Quercus dumosa) [5,10].  Ground cover is usually sparse and may include
California buckwheat (Eriogonum fasciculatum), wild onion (Allium spp.),
scarlet beardtongue (Penstemon ternatus), chainfern (Woodwardia
fimbriata), and western brackenfern (Pteridium aquilinium var.
pubescens [10].


SUCCESSIONAL STATUS : 
Obligate Climax Species

Bigcone Douglas-fir eedlings are shade tolerant, while mature trees are
intolerant [18].  The bigcone Douglas-fir forest is a climax type.  In
the absence of fire or other disturbance, bigcone Douglas-fir invades
and dominates surrounding chaparral and oak communities [19].  Chaparral
shrubs remain the dominant vegetation type of their zone because
succession is constantly interrupted by drought accompanied by fire.
Trees usually do not grow large enough during the fire-free period to
become fire resistant [3,13].  Return of bigcone Douglas-fir to
chaparral sites following disturbance probably requires centuries [14].


SEASONAL DEVELOPMENT : 
Bigcone Douglas-fir undergoes the following seasonal development:

     cone buds form:  September to October [10]
     pollination:  early March to mid-April [18]
     seed germination:  March to May [10]
     cones mature:  August to September [18]
     seed released:  September to October {18}
     needles fall:  September to October [10]

Related categories for Species: Pseudotsuga macrocarpa | Bigcone Douglas-Fir