[PDF]Silvics of North America, Vols 1 and 2

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Volume 1: Conifers



Table of Contents



The Tree and Its Environment

General Notes and Selected References



Scientific Name



Common Name



Abies

Abies amabilis
Abies balsamea
Abies concolor
Abies fraseri
Abies prandis
Abies lasiocarpa
Abies mapnifica
Abies procera



Fir

Pacific silver fir
balsam fir
white fir
Fraser fir
grand fir
subalpine fir
California red fir
noble fir



Chamaecyparis

Chamaecyparis lawsoniana
Chamaecyparis nootkatensis
Chamaecyparis thyoides



White-cedar

Port-Orford-cedar
Alaska-cedar
Atlantic white-cedar



Juniperus

Juniperus occidental is
Juniperus scopulorum
Juniperus silicicola
Juniperus virpiniana



Juniper

western juniper
Rocky Mountain juniper
southern redcedar
eastern redcedar



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Larix

Larix laricina
Larix lyallii
Larix occidentalis



Larch

tamarack
alpine larch
western larch



Libocedrus

Libocedrus decurrens



Incense-cedar

incense-cedar



Picea

Picea breweriana
Picea engelmannii
Picea plauca
Picea mariana
Picea pungens
Picea rubens
Picea sitchensis



Spruce

Brewer spruce
Engelmann spruce
white spruce
black spruce
blue spruce
red spruce
Sitka spruce



Pinus

Pinus albicaulis
Pinus banksiana
Pinus clausa
Pinus contorta
Pinus echinata
Pinus edulis
Pinus elliottii
Pinus flexilis
Pinus glabra
Pinus jeffreyi
Pinus lambertiana
Pinus monophylla
Pinus monticola
Pinus nigra
Pinus palustris



Pine

whitebark pine
jack pine
sand pine
lodqepole pine
shortleaf pine
pinyon
slash pine
limber pine
spruce pine
Jeffrey pine
sugar pine
singleleaf pinyon
western white pine
European black pine
lonqleaf pine



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Pinus ponderosa


ponderosa pine


Pinus punpens


Table Mountain pine


Pinus radiata


Monterey pine


Pinus resinosa


red pine


Pinus ripida


pitch pine


Pinus sabiniana


Digger pine


Pinus serotina


pond pine


Pinus strobus


eastern white pine


Pinus sylvestris


Scotch pine


Pinus taeda


loblolly pine


Pinus virpiniana


Virginia pine


Pseudotsuga


Douglas-fir


Pseudotsupa macrocarpa


bigcone Douglas-fir


Pseudotsupa menziesii


Douglas-fir


Sequoia


Redwood


Sepuoia sempervirens


redwood


Sequoiadendron


Giant sequoia


Sepuoiadendron pipanteum


giant seguoia


Taxodium


Baldcypress


Taxodium distichum var. distichum


baldcvpress (typical)


Taxodium distichum var. nutans


pondcypress


Taxus


Yew


Taxus brevifolia


Pacific yew


Thuja


Cedar


Thuja occidentalis


northern white-cedar


Thuja plicata


western redcedar



Torreya



Torreya



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Tor rev a taxi folia



Florida torreya



Tsuga

Tsuga canadensis
Tsuga heterophylla
Tsuga mertensiana



Hemlock

eastern hemlock
western hemlock
mountain hemlock



Glossary

Summary of Tree Characteristics

Checklist of Insects and Mites

Checklist of Organisms Causing Tree
Diseases

Checklist of Birds

Checklist of Mammals

Index of Authors and Tree Species



KSi



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Abies amabilis Dougl



Abies amabilis Dougl. ex Forbes

Pacific Silver Fir

Pinaceae — Pine family

Peggy D. Crawford and Chadwick Dearing Oliver



Pacific silver fir (Abies amabilis), also known as silver fir and
Cascades fir, has a gray trunk, a rigid, symmetrical crown, and
lateral branches perpendicular to the stem. It contrasts strikingly
with the more limber crowns, acute branch angles, and generally
darker trunks of its common associates Douglas-fir (Pseudotsuga
menziesii), western hemlock (Tsuga heterophylla), and mountain
hemlock (T. mertensiana). The species name, amabilis, means
lovely.

Habitat

Native Range

Pacific silver fir is found in southeastern Alaska, in coastal British
Columbia and Vancouver Island, and along the western and upper
eastern slopes of the Cascade Range in Washington and Oregon. It
also grows throughout the Olympic Mountains and sporadically in
the Coast Ranges of Washington and northern Oregon. Near Crater
Lake, OR, Pacific silver fir disappears from the Cascade Range
and then reappears at a few locations in the Klamath Mountains of
northwestern California. The major portion of its range lies
between latitudes 43° and 55° N. (35).



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Abies amabilis Dougl




- The native range of Pacific silver fir.

Climate

Climate throughout the range of Pacific silver fir is distinctly
maritime. Summers are cool, with mean daily temperatures of 13°
to 16° C (55° to 61° F), and winter temperatures are seldom lower
than -9° C (16° F) (35). Mean number of frost-free days ranges
from 40 near tree line to more than 250 at low elevations (26).



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Abies amabilis Dougl

Length of growing season also differs from year to year at a given
location. Mean annual precipitation varies greatly, ranging from
6650 mm (262 in) on the west coast of Vancouver Island to an
extreme low of 965 mm (38 in) on the eastern side of Vancouver
Island. Average annual precipitation in the Cascade Range is more
than 1500 mm (59 in); winter snowpacks are as much as 7.6 m (25
ft) deep (9). A summer dry season is characteristic of this region,
but Pacific silver fir is dependent on adequate soil moisture during
the growing season. It is most abundant on sites where summer
drought is minimal, such as areas of heavy rainfall, seepage, or
prolonged snowmelt.

Soils and Topography

Pacific silver fir grows on soils developed from nearly every type
of parent material found in the Northwest. Layering in soil profiles
caused by successive deposits of volcanic ejecta, colluvium, or
glacial till is especially common (1,43). The greatest known
growth rates for Pacific silver fir occur at low elevations on fine-
textured residual soils from sedimentary and basaltic rocks (16).
Growth is reduced on poorly drained or shallow rocky soils.

In northern Washington and British Columbia, podzolization is the
dominant process in well-drained soils under Pacific silver fir. A
typical podzol is characterized by strong acidity of organic (pH 3.3
to 4.0) and mineral horizons, moderate to thick (3 to 45 cm; 1 to
1 8 in) surface accumulations of organic matter, and moderate to
extremely low base saturation. In Oregon, podzolization is less
strongly expressed and soils are more shallow and rocky. Pacific
silver fir has been found on many soil suborders throughout its
range: Folists in the order Histosols; Aquents, Fluvents, Orthents
in the order Entisols; Andepts, Aquepts, Ochrepts, Umbrepts in the
order Inceptisols; and Aquods, Humods, and Orthods in the order
Spodosols (35).

At upper elevations in Washington, soils beneath Pacific silver fir
stands are generally low in available nitrogen, with availability
decreasing with age (44). External nutrient cycling is slow; a mean
nitrogen residence time as long as 120 years has been found in old-
growth forest floors (24). Nitrification has not been found to occur.
Availability of phosphorus tends to be low but availability of base
elements does not appear to limit plant growth (42). Internal
cycling meets much of the annual nutrient requirements. Foliar
nitrogen concentrations between 0.7 and 1.2 percent and foliar

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Abies amabilis Dougl

phosphorus concentrations of 0. 1 1 to 0.20 percent have been
reported (3,42,52). Pacific silver fir differs significantly from
western hemlock in its ability to accumulate specific elements (46).

Pacific silver fir grows at sea level along the coast from Alaska to
the Olympic Peninsula; farther inland, it is absent at lower
elevations. Its range in elevation is narrowest in Alaska, to 300
m (0 to 1 ,000 ft), and greatest in the western Cascade Range of
Washington, where Pacific silver fir may be found from 240 to
1830 m (800 to 6,000 ft). In British Columbia it is found from to
1525 m (0 to 5,000 ft) in elevation on western Vancouver Island
and from 180 to more than 1680 m (600 to more than 5,500 ft) on
the lower mainland. Pacific silver fir grows on the highest ridges
and peaks in the Coast Ranges of Washington, from 365 to 850 m
(1,200 to 2,800 ft). In the Olympic Mountains, it is the
predominant montane species up to 1400 m (4,600 ft), with lower
limits at sea level on the west side and at 360 m (1,200 ft) in the
central mountains. It is found between 610 and 1830 m (2,000 and
6,000 ft) in the Cascade Range in Oregon as far south as the divide
between the Rogue and Umpqua Rivers. On the east side of the
Cascade Range, it is confined to high elevations, down to 1 160 m
(3,800 ft) in Oregon and 1000 m (3,300 ft) in Washington (30,35).

Associated Forest Cover

Western hemlock is a common associate throughout most of the
range of Pacific silver fir, in the Abies amabilis zone and portions
of the Tsuga heterophylla zone (9). Noble fir (Abies procera) is an
important associate in southern Washington and northern Oregon.
Other associates west of the Cascade Range are Douglas-fir,
western redcedar (Thuja plicata), and grand fir (Abies grandis),
with Sitka spruce (Picea sitchensis) and lodgepole pine (Pinus
contorta) important near the coast. At subalpine elevations in the
Tsuga mertensiana zone (9), Pacific silver fir is associated with
mountain hemlock, Alaska-cedar (Chamaecyparis nootkatensis),
and subalpine fir (Abies lasiocarpa). Toward the eastern limits of
its range, it grows with a mixture of coastal and interior species:
western larch (Larix occidentalis), western white pine (Pinus
monticola), lodgepole pine, subalpine fir, grand fir, and
Engelmann spruce (Picea engelmannii). Shasta red fir (Abies
magnifica var. shastensis) is an associate in the extreme southern
portion of its range. Extensive pure stands of Pacific silver fir have
been reported in the Mount Baker and Mount Rainier regions and
elsewhere in the southern Washington Cascade Range (40).

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Abies amabilis Dougl

Pacific silver fir is a major species in the forest cover type Coastal
True Fir-Hemlock (Society of American Foresters Type 226) (5).
It is also found in the following types:

205 Mountain Hemlock

206 Engelmann Spruce-Subalpine Fir

223 Sitka Spruce

224 Western Hemlock

225 Western Hemlock-Sitka Spruce

227 Western Redcedar- Western Hemlock

228 Western Redcedar

229 Pacific Douglas-Fir

230 Douglas-Fir- Western Hemlock

Shrubs associated with Pacific silver fir are primarily ericaceous.
Blueleaf huckleberry (Vaccinium delicto sum), Cascades azalea
{Rhododendron albiflorum), and rustyleaf menziesia (Menziesia
ferruginea) are common understory species at higher elevations;
copper bush (Cladothamnus pyrolaeflorus) is important in
subalpine British Columbia (2). Alaska huckleberry (Vaccinium
alaskaense), big huckleberry ( V. membranaceum), ovalleaf
huckleberry (V. ovalifolium), and devilsclub (Oplopanax
horridum) are widespread associates. At its lower limits of
elevation, Pacific silver fir is found with salal (Gaultheria shallon)
and Oregongrape (Berberis nervosa).

Common herbaceous associates are common beargrass
(Xerophyllum tenax), bunchberry (Cornus canadensis), twinflower
(Linnaea borealis), queenscwp (Clintonia uniflora), dwarf
blackberry (Rubus lasiococcus), strawberry leaf blackberry (R.
pedatus), rosy twistedstalk (Streptopus roseus), coolwort
foamflower (Tiarella unifoliata), and deerfern (Blechnum spicant).
Rhytidiopis robusta is a constant bryophyte associate.

Major habitat types include Abies amabilis-Tsuga mertensiana/
Vaccinium membranaceum-Rhododendron albiflorum on cold, wet
sites at high elevations and Abies amabilis/Xerophyllum tenax on
shallow coarse-textured soils at various elevations. Abies
amabilis / Vaccinium alaskaense is a widespread type on modal
sites. Abies amabilis/Rubus lasiococcus, Abies amabilis/Streptopus
roseus, Abies amabilis I Tiarella unifoliata, and Tsuga
heterophylla- Abies amabilis/Blechnum spicant are herb-dominated
types found in moist habitats. The Abies amabilis / Oplopanax

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Abies amabilis Dougl

horridum type occupies wet, alluvial habitats (2,9).

Life History

Reproduction and Early Growth

Flowering and Fruiting- Pacific silver fir is monoecious; self-
fertilization is possible because times of pollen dispersal and seed
cone receptivity overlap on the same tree. Flowers differentiate
from axillary buds of current- year lateral shoots in early July of
the year before seed development (32). When receptive to
pollination, the seed cones appear purple, erect, and 8 to 16 cm (3
to 6 in) tall on the upper surfaces of 1 -year-old branches in the
upper parts of tree crowns. Just before pollination, the pollen cones
appear red, pendent, and usually abundant on the lower surfaces of
the branches somewhat lower on the crowns than the seed cones.
Cone buds burst the following May, and pollination occurs about 2
weeks later-before vegetative bud burst. The pollen does not
germinate and begin forming its pollen tube until 4 to 5 weeks
later, resulting in a 6-week delay between pollination and
fertilization (7,33).

Initiation of phenological events varies with latitude, altitude,
aspect, weather, and snowpack and is apparently related to mean
soil and air temperatures. For example, pollination may occur in
mid-May at 900 in (2,960 ft) in central Washington but is delayed
until mid- June at 1600 in (5,250 ft) and until late May in southern
British Columbia (7,32,33).

Seeds are fully mature in late August, and dissemination begins in
mid-September- one of the earliest dispersal times for Pacific
Northwest conifers. Initiation of dispersal is apparently
independent of altitude or latitude (7); most seeds are shed by the
end of October but may be shed until the following April (21,33).

Seed Production and Dissemination- Cone production begins at
years 20 to 30 (33,37). Good seed years vary from region to
region; a good seed crop generally occurs every 3 years (8).
Pacific silver fir is not considered a good seed producer; this
condition is attributed to frequent years of low pollen, the
extended period between pollination and fertilization, and
archegonial abortion producing empty seeds (33). Percentage of
sound seed varies, with reports of 6.7 to 35 percent and 51 percent

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Abies amabilis Dougl

in one location (4). Germinative capacity varies widely from 3 to
70 percent- but averages 20 to 30 percent. Cleaned seeds range
from 17,200 to 45,860/kg (7,800 to 20,800/lb) (37).

The seeds are heavier than seeds of most Pacific Northwest
conifers except noble fir. Seeds each contain a single wing but
often fall from the upright cone axis by pairs on ovuliferous scales,
as the bracts contort and tear themselves from the cone-a process
that does not require wind. When the seeds are dispersed by the
wind, they do not carry far; unsound seeds are carried farther than
sound seeds. In one study, only 9 percent of the sound seeds were
found more than 1 14 in (375 ft) from the stand edge, compared
with 41 percent at the stand edge and 34 percent more than 38 m
(125 ft) (4).

Seedling Development- Pacific silver fir germinates in the spring
after overwintering under snow. Germination is epigeal (37).
Seedlings germinating on snow because of early snowfall or late
seed fall are generally short lived. Germination can occur on a
variety of media: on litter humps and in moist depressions in the
subalpine zone; on edges of melting snowpack in subalpine
meadows; and in litter, rotten wood, moss, organic soils, mineral
soils, and fresh volcanic tephra (2,1 1,25). Survival is better on
mineral seedbeds than on organic seedbeds. Early mortality of
seedlings is attributable more to germination on snow, adverse
climatic effects, and competing vegetation than to disease (18).

Cool, moist habitats are best for germination, but full sunlight
produces maximum subsequent growth. Seedlings can also grow
under dense shade; seedlings 8 to 12 years old and about 10 cm (4
in) tall can frequently be found beneath older, closed forest
canopies. Seedlings that survive continue to grow very slowly,
existing as advance regeneration that can be 65 to 110 years old
and only 45 to 200 cm tall (18 to 80 in). When existing as advance
regeneration, Pacific silver fir has flat-topped crowns caused by
slow height growth relative to lateral branch growth.

Seedlings are sturdy and erect and resist being flattened by litter
and heavy, wet snow. Survival of Pacific silver fir as advance
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