BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Abies amabilis | Pacific Silver Fir 



GENERAL BOTANICAL CHARACTERISTICS : 
Pacific silver fir is a monoecious, long-lived, native conifer
[14,24,38,66,68].  At maturity, it can reach heights of 100 to 230 feet
(30-70 m) and diameters of 36 to 44 inches (90-110 cm) [24,26,38].  The
average maximum age for Pacific silver fir is 400 to 500 years on good
sites, and 250 to 350 years on more adverse sites.  The maximum recorded
age is 540 years [14,59].  As Pacific silver fir becomes older, growth
is commonly deformed [57].  The crown is rigid and symmetrical with
lateral branches perpendicular to the stem [14].  Young trees have
resin-filled blisters protruding from the smooth, thin bark.  The bark
of older trees is rough textured and flaky [6].

The needles grow from opposite sides of the branch, spreading
horizontally or brushed forward.  The top is flat, grooved, and
"lustrous green", and the underside is stomatiferous and silvery white
[6,38].  Pacific silver fir has a second type of foliage on the
uppermost, cone-bearing branches.  These needles are very sharp and
curved.  The cones are stiffly erect, barrel shaped, and 3.5 to 6 inches
(8.9-15.2 cm) long [6].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Pacific silver fir reproduces only from seed [14].  Seed production
begins at 20 to 30 years of age [14].  There are approximately 400 seeds
per cone; percentage of sound seed ranges from 6.3 to 35 percent
[14,24].  Good seed crops are generally produced every 2 to 3 years
[14,59], but intervals between good seed crops may be as long as 6 years
according to some reports [17,25].  Production of seed is poor due to
the high frequency of low pollen production years [14].  Complete crop
failures sometimes occur [59].

Pacific silver fir requires 2 years to complete its reproductive cycle
[63].  It is capable of self-fertilization [14,38].  Wind dispersion of
seed is inefficient because of seed size and cone disintegration [59].
Germination occurs in the spring.  Germination can occur on a variety of
substrates such as litter, rotten wood, moss, organic and mineral soils,
and fresh volcanic tephra.  Cool, moist sites are optimal for
germination, but full sunlight produces maximum growth [14].  Pacific
silver fir takes 9 years to reach breast height on average sites [14], 5
to 9 years on more favorable sites, and up to 80 years when severely
suppressed [36].


SITE CHARACTERISTICS : 
The climate throughout the range of Pacific silver fir is maritime to
submaritime [14,41].  Pacific silver fir is usually submontane to
subalpine [27,41].  It thrives in areas that receive a great deal of
precipitation.  Average annual precipitation ranges between 38 and 262
inches (965-6650 mm), mostly in the form of snow [14,22,27,42].  The
average winter temperature is 26 to 29.8 degrees Fahrenheit (-3.2 to
-1.7 deg C), and the average summer temperature is 57.2 to 58.8 degrees
Fahrenheit (14-14.9 deg C) [14,71].  Pacific silver fir is absent in
coastal areas with dry summers [59].  There is a correlation between
growth, snow-free period, days above a certain temperature, absence of
frost pockets, and preferable sites for Pacific silver fir [32].
Pacific silver fir has a mild frost tolerance and poor frozen soil
tolerance because of its need for water during the winter [22,51].

Pacific silver fir is an indicator of very moist soils.  It occurs on
soils in the orders Alfisols, Entisols, Inceptisols, Histosols, and
Spodosols [51,67].  Soil parent materials include basalt, glacial till,
volcanic ash, pumice, and sedimentary rock [31,51,52].  Pacific silver
fir can grow where the water table is near the surface during the
growing season if the soil is well aerated, thick, and/or with wood
accumulations on top of the mineral soil [59].  Growth is successful
with thick humus present [59].  Soils are generally shallow, but soil
depth varies from 1.2 to 12 inches (3-30 cm) [27].  Soils are acidic in
the rooting zone (pH 5) [41].  Whatever the soil type, an adequate,
year-round water supply is very important.  Often nitrogen and
occassionally sulfur are limiting elements in soils [32].  Soils rich in
magnesium and calcium indicate good sites for Pacific silver fir [42].

The elevation at which Pacific silver fir grows is quite variable.  It
is more common at higher elevations but grows faster at lower elevations
[59].  Pacific silver fir occurs at a maximum of 7,000 feet (2,120 m) in
the southern part of its range and at a maximum of 1,000 feet (330 m) in
the northern part of its range [14,22,24,27,51].

Overstory associates not mentioned in Distribution and Occurrence
include noble fir (Abies procera), Alaska cedar (Chamaecyparis
nootkatensis), Shasta red fir (Abies magnifica var. shastensis), and
western larch (Larix occidentalis) [9.14,27,51,60].  Shrub understory
includes huckleberry (Vaccinium spp.), Cascades azalea (Rhododendron
albiflorum), devils club (Oplopanax horridum), copper bush (Cladothanus
pyrolaeflorus), rustyleaf menziesia (Menziesia ferruginea), salal
(Gaultheria shallon), vine maple (Acer circatum), and Oregon-grape
(Berberis nervosa) [9,12,15,28,52].  Herbaceous species are beargrass
(Xerophyllum tenax), bunchberry (Cornus canadensis), twinflower (Linnea
borealis), queenscup beadlily (Clintonia uniflora), dwarf blackberry
(Rubus lasiococcus), rosy twistedstalk (Streptopus roseus), coolwort
foamflower (Tiarella unifoliata), deer fern (Blechnum spicant),
salmonberry (Rubus spectabilis), vanillaleaf (Achlys spp.), and
evergreen violet (Viola sempervirens) [9,12,14,28,52].


SUCCESSIONAL STATUS : 
Obligate Climax Species

Pacific silver fir is a late seral or climax species in most habitats
[41].  In the mountain hemlock zone, Pacific silver fir succeeds species
such as Shasta red fir, subalpine fir, and grand fir [27].

Pacific silver fir is very shade tolerant and has low spatial
requirements [14,15,22,26,71].  Pacific silver fir can survive in the
shade and emerge in stands that are uneven-aged [51].  Due to
ineffecient dispersion of seed by wind, migration is slow [56].

Following disturbance, Douglas-fir and noble fir become established.
Pacific silver fir is the last to invade, sometimes 400 to 500 years
after the disturbance.  After extensive forest fires, Pacific silver fir
may not become important among the large trees for 700 to 800 years
[61,69].  Eventually, Douglas-fir and noble fir fail to reproduce [27].
Often, almost all understory species are eliminated by shade, resulting
in an open forest floor [51].  Pacific silver fir is common in mixed
stands and rare in even-aged stands [59].


SEASONAL DEVELOPMENT : 
Pacific silver fir has a 2-year reproductive cycle.  In May of the first
year, buds are initiated; differentiation follows in July.
Megagametophytes and ovuliferous scales are initiated in mid-July and
mid-August, respectively.  Both are dormant by November and remain
dormant until April of the second year, at which time development of the
pollen-cone and seed-cone buds is resumed [63].  Pollination occurs in
May and is well synchronized with female receptivity [14,63].
Fertilization occurs in early July, 4 to 5 weeks after pollination.  In
early August, meristems and cotyledons of embryos develop and mature by
the end of the month.  Cones change from green to purple at maturity
[6,63].  As cones mature, they disintegrate before the seed can be
dispersed, which occurs in September and October [24,63].

Germination occurs in the spring [14].  Juvenile growth ranges from 4 to
16 inches (10-40 cm) per year [14].  Advance regeneration is quite
sturdy but grows slowly.  Terminal growth averages 19.9 (49.7 cm) per
year [14].

Related categories for Species: Abies amabilis | Pacific Silver Fir