Western Redcedar
Thuja
plicata Donn ex D. Don
Cupressaceae - Cypress family
by
Don Minore
Western
redcedar (Thuja
plicata), also called
Pacific redcedar, giant-cedar, arborvitae, canoe-cedar, and
shinglewood, is the only Thuja
species native
to western North America. Extant redcedar volumes are
estimated to be 824 million m³ (29 billion ft³) in British
Columbia (43) and 228 million m³ (8 billion ft³) in the
United States (16). Most of this volume is in mature trees,
which have tapered, often-fluted bases, drooping branches,
thin fibrous bark, and small scalelike leaves arrayed in
flat sprays. Many have forked tops. They often reach ages
of 800 to 1,000 years. One particularly large specimen in
Washington has a d.b.h. of 592 cm (233 in), a height of
54.3 m (178 ft), and a crown spread of 16.5 m (54 ft). The
wood is valuable and extensively used in a wide variety of
products.
Habitat
Native Range
Western
redcedar grows along the Pacific coast from Humboldt
County, CA (lat. 40° 10' N.), to the northern and western
shores of Sumner Strait in southeastern Alaska (lat. 56°
30' N.). In California, it is common only in the lower Mad
River drainage and the wet region south of Ferndale in
Humboldt County; it is found elsewhere only in isolated
stands in boggy habitats (19). North of the
California-Oregon border, the coastal range broadens to
include the western slopes of the Cascade Range north of
Crater Lake and the eastern slopes north of about latitude
44° 30' N. (12). Optimal growth and development of western
redcedar are achieved near the latitudinal center of its
range- Washington's Olympic Peninsula.
North of the Olympic Peninsula and Vancouver Island, the
coastal range narrows again and is restricted to the Coast
Ranges and offshore islands. A few scattered stands are
found between the Coast Ranges and the Selkirk Mountains
near the southern border of British Columbia, but
redcedar's coastal range is essentially isolated from its
interior range.
The interior range extends south from the western slope of
the Continental Divide at latitude 54° 30' N. in British
Columbia through the Selkirk Mountains into western Montana
and northern Idaho (2). The southern limit is in Ravalli
County, MT (lat. 45° 50' N.). With the possible exception
of a few trees east of the Continental Divide near the
upper end of St. Mary Lake, Glacier County, the eastern
limit of the range of redcedar is near Lake McDonald in
Glacier National Park, MT.
Climate
Coastal western
redcedar receives from less than 890 mm (35 in) of annual
precipitation to more than 6600 mm (260 in), mostly as
winter rainfall; interior western redcedar, about 710 mm
(28 in) in the north, 810 to 1240 mm (32 to 49 in) farther
south-about half as spring and autumn rain, one-third as
winter snow (2).
Although western redcedar is abundant in many forested
swamps, it is sometimes found on sites that are too dry for
western hemlock (Tsuga
heterophylla) (12,39,42),
probably because the root penetration of the redcedar is
better. Redcedar leaves are not protected from excessive
transpiration by cutin and wax.
Trees tolerate stagnant winter water tables averaging less
than 15 cm (6 in) below the soil surface on the Olympic
Peninsula (32). The species dominates wet ravines and
poorly drained depressions in both Glacier National Park in
Montana and the Selway Bitterroot Wilderness in Idaho
(20,21).
Where sufficient precipitation is present, low temperature
appears to limit the species' range. Length of the
frost-free period abruptly decreases just above the tree's
upper elevation limits on Vancouver Island. The northern
limits of western redcedar lie between the 11.1° and 11.7°
C (52° and 53° F) mean summer temperature isotherms in
southeastern Alaska. Absolute minimum temperatures
experienced by western redcedar in British Columbia are
-10° to -30° C (14° to -22° F) in coastal populations, -14°
to -47° C (7° to -53° F) in the interior (28). Western
redcedar has a growing season of at least 120 frost-free
days along the coast but as few as 75 frost-free days in
some portions of its interior range. It is not resistant to
frost and is sometimes damaged by freezing temperatures in
late spring or early autumn.
Soils
and Topography
Western
redcedar can tolerate a wide range of soil proper-ties in
most localities. Soils on which it is most commonly found
are in the orders Inceptisols, Ultisols, and Histosols. It
is found on all landforms, soil textures, and parent
materials on Vancouver Island (39). In southwestern Oregon,
it grows on sedimentary, metasedimentary, gabbroic,
dioritic, granodioritic, and occasionally even serpentinite
and peridotite parent materials (24). Coarse sandy soils
are not well suited to establishment and growth of redcedar
in northern Idaho and northeastern Washington, but rocky
slopes with limited soil development support redcedars in
southeastern Alaska. Poorly drained organic soils also
support redcedar south of Petersburg, AK. It grows on
loams, clays, sands, chalk downland, and
Molina-Juncus peat in
England, but is most competitive on fine-textured lowland
soils there. It grows well on shallow soils over chalk and
can tolerate both acid and alkaline soil conditions (45).
Western redcedar seems able to survive and grow on soils
that are low in nutrients and is found on such soils over
much of its natural range. Site index is positively
correlated with foliar nitrogen, sulfur, copper, boron, and
chlorophyll. However, productivity may be improved by
fertilization (44). When grown in well watered soil
fertilized with nitrogen, phosphorus, and potassium,
redcedar seedlings outgrow the seedlings of
Douglas-fir (Pseudotsuga
menziesii), grand
fir (Abies
grandis), Sitka
spruce (Picea
sitchensis), western
hemlock, and ponderosa pine (Pinus
ponderosa). Available
nitrogen,
calcium, and water appear to be the most important factors
affecting growth and establishment of redcedar. Established
redcedars tend to raise soil cation exchange capacities,
pH's, and amounts of exchangeable calcium (1) and thus
benefit the soils in which they grow.
Western redcedar grows from sea level to 910 m (3,000 ft)
in southeastern Alaska. In British Columbia, the
elevational range is higher-from sea level to 1190 m (3,900
ft). Redcedar is found in the interior from 320 m (1,050
ft) to 2130 m (7,000 ft).
The greatest range in elevation occurs in Oregon, where the
species occurs from sea level to 2290 m (7,500 ft) at the
rim of Crater Lake.
Associated
Forest Cover
Pure stands of
western redcedar cover some small areas, but it is usually
associated with other tree species. Along the coast these
include black cottonwood (Populus
trichocarpa), bigleaf
maple (Acer
macrophyllum), western
hemlock, mountain hemlock (Tsuga
mertensiana), Sitka spruce,
western white pine (Pinus
monticola), lodgepole
(shore) pine (P.
contorta), Port-Orford-cedar
(Chamaecyparis
lawsoniana), Alaska-cedar
(C.
nootkatensis), incense-cedar
(Libocedrus
decurrens), Douglas-fir,
grand fir, Pacific silver fir (Abies
amabilis), red
alder (Alnus
rubra), Pacific
madrone (Arbutus
menziesii), and Pacific
yew (Taxus
brevifolia). Several of
these species (black cottonwood, western hemlock, western
white pine, Douglas-fir, grand fir, and Pacific yew) are
also associated with western redcedar in the interior.
Subalpine fir (Abies
lasiocarpa), western
larch (Larix
occidentalis), Engelmann
spruce (Picea
engelmannii), white
spruce (P.
glauca), lodgepole pine,
and ponderosa pine are also associated with redcedar in the
interior.
Redcedar is a major component of two forest cover types
(11): Western Redcedar (Society of American Foresters Type
228) and Western Redcedar-Western Hemlock (Type 227). It is
a minor component of the following types:
210 Interior Douglas-Fir
212 Western Larch
213 Grand Fir
215 Western White Pine
218 Lodgepole Pine
221 Red Alder
222 Black Cottonwood-Willow
223 Sitka Spruce
224 Western Hemlock
225 Western Hemlock-Sitka Spruce
226 Coastal True Fir
229 Pacific Douglas-Fir
230 Douglas-Fir-Western Hemlock
231 Port-Orford-Cedar
232 Redwood
Some associated shrub species are listed in table 1
[excluded here]. Several occur in both interior and coastal
environments, but Rocky Mountain honeysuckle
(Lonicera
utahensis) and
clematis (Clematis
columbiana) are associated
with redcedar only in the interior, whereas
salmonberry (Rubus
spectabilis) and red
huckleberry (Vaccinium
parvifolium) are found only
on the Pacific slope. Pacific rhododendron
(Rhododendron
macrophyllum) is an abundant
associate in coastal California, Oregon, and Washington,
but it is rare and confined to isolated locations in
south-coastal British Columbia. Salal (Gaultheria
shallon) also is an
abundant associate. Its range extends farther south than
that of redcedar, but the northern limits of salal are
nearly the same as the northern limits of western redcedar
in coastal Alaska.
Some
associated herb species are listed in table 2 [excluded
here]. Many are common in both coastal and interior
environments. However, slough sedge (Carex
obnupta) and Pacific
water-parsley (Oenanthe
sarmentosa) are limited to
moist habitats west of the Cascades, whereas wild
sarsaparilla (Aralia
nudicaulis) and
goldthread (Coptis
occidentalis) occur with
redcedar only in the interior.
Coastal
redcedar plant communities in British Columbia have been
classified into 24 associations under 9 alliances in
the Thuja-Rubus
spectabilis order (35).
Communities listed in less detailed coastal classifications
include redcedar/swordfern, redcedar/devilsclub/maidenhair
fern, redcedar/maidenhair fern-ladyfern, redcedar-western
hemlock/devilsclub/ladyfern, redcedar-grand fir/mountain
boxwood, redcedar-grand fir/swordfern,
redcedar-Douglas-fir/Oregongrape, redcedar-Sitka spruce-red
alder/skunkcabbage-slough sedge, and redcedar/skunkcabbage
(12,28).
The redcedar/skunkcabbage plant community also occurs in
the interior; where redcedar/devilsclub,
redcedar/devilsclub/coolwort (Tiarella
trifoliata), redcedar/queenscup
(Clintonia
uniflora), and
redcedar/maidenhair fern are found (7,28,42).
Life
History
Reproduction and Early Growth
Flowering and Fruiting- When grown in
the open, western redcedars begin to produce strobili at 10
years of age and usually every other year thereafter.
Strobilus development can be artificially induced at
younger ages and increased in mature trees by girdling or
treating with gibberellin (8). The species is monoecious;
male and female strobili are produced on different branches
of the same tree, at different heights-the reddish male
strobili on lower branches and the green female strobili
nearer the treetops and farther from the trunk (38,52).
Anthesis and pollination occur during March and April in
southern stands near the coast. They occur during May and
June in coastal Alaska and interior stands (47).
Seed
Production and Dissemination- Each mature
strobilus usually produces only 3 to 6 seeds (8), but the
strobili are often numerous and heavy seed crops are
common. In dry years, conebearing stands in the interior
tend to be on high, moist sites (14). Average annual seed
crops vary from 247,000 to 2,470,000 seeds per hectare
(100,000 to 1 million/acre) in coastal forests and from
54,000 to 274,000/ha (22,000 to 111,000/acre) in the
interior. Major seedfall occurs during October and November
in both ranges (2). Gibberellin-treated, containerized seed
orchards should permit efficient management of seed
production and harvesting (8).
Seeds are small- 448,000 to 1,305,000/kg (203,000 to
592,000/1b) (47). They fall faster and do not fly as far as
the seeds of western hemlock, Sitka spruce, and
Douglas-fir, but dissemination is adequate within 100 m
(330 ft) of a seed source (4,30). The seeds usually
germinate well without stratification, and they retain
their initial viability for at least 7 years when stored
dry (5 to 8 percent moisture) at -18° C (0° F) (8).
Germination is epigeal.
Seedling
Development- Most seeds
escape rodent and bird predation, but seedling mortality is
high during the germination period (15). Where moisture and
temperature conditions are favorable, germination can occur
in the autumn, winter, or spring. Almost no germination
occurs after the first year, however. Seedbed quality may
be critical.
Throughout the range of western redcedar, disturbed mineral
soil seedbeds seem to be a major requirement for
regeneration from seed (41). Although unburned soil
benefits redcedar more than soil that has been scorched,
slash burning favors redcedar by creating more mineral soil
surfaces in cutover areas. Rotten wood that is in contact
with the soil is the preferred seedbed in old redcedar
groves (41). Partial shade is beneficial because drought
and high soil temperature damage seedlings in full
sunlight, and poor root penetration causes damage from
drought in full shade (48).
Direct seeding in the autumn is successful where soil
moisture is available, but large quantities of seed may be
required to obtain adequate stocking. In the nursery,
spring sowing is best; half-shaded seedbeds are recommended
(47). Pelleting the seeds makes them more compatible with
automated nursery sowing machinery (8). Containerized
nursery seedlings can be produced in 7 months. They survive
as well or better than bare-root stock when planted in
coastal Oregon, Washington, and British Columbia, but
2-year-old bare-root stock tends to be most cost effective
in the coastal range (6). When bare-root stock is planted,
recently lifted dormant seedlings with low shoot/root
ratios should be used and cold storage avoided whenever
possible. Containerized stock planted in the spring appears
to perform better than bare-root stock in the interior
(18). Natural regeneration is important in the northern
Rocky Mountains, where it is most frequently successful on
westerly and northerly aspects in western redcedar habitat
types (18).
Western redcedar seedlings are less tolerant of high soil
temperature and of frost than are the seedlings of
Engelmann spruce, grand fir, and Douglas-fir. The exposed
upper foliage of young redcedars often sunburns severely
(31). Roots of seedlings grow more slowly than the roots of
Douglas-fir and incense-cedar, but they outgrow the roots
of seedling western hemlock and Sitka spruce. Shoots have a
longer growth period than any associated conifer. Non-rigid
leaders are produced, and neither lateral nor terminal
shoots form dormant buds. Lateral shoot growth is vigorous,
amounting to at least 80 percent of terminal shoot growth
in young redcedars (31). Seedlings account for most of the
western redcedar regeneration in clearcuts and other
disturbed areas. On good coastal sites, they grow as tall
or taller than Douglas-fir, western hemlock, and Sitka.
spruce seedlings during the first 5 years (6,51). The
redcedars are subsequently overtaken by Douglas-fir (by age
10) and western hemlock (by age 15).
Vegetative
Reproduction- Three types of
natural vegetative reproduction occur: layering, rooting of
fallen branches, and branch development on fallen trees.
The resulting "veglings" are more abundant than seedlings
in mature Idaho stands (40). Saplings that have been
knocked down in the western Cascades often regenerate when
their branches root.
Redcedar clones are easily propagated by the rooting of
stem cuttings. Although untreated cuttings will root, a
1-minute dip in a 3,000 ppm solution or a 4-hour soak in a
200 to 400 ppm solution of indolebutyric acid improves
rooting speed, the number of cuttings rooted, and the total
length of roots per cutting. Ramets for seed orchards can
be produced by treating cuttings with indolebutyric acid,
then rooting them in a 1-to-1 mixture of peat and perlite
(8). Young fragmented stems can be induced to bud after
being soaked in a cytokinin solution, and the resulting
buds can be rooted on a culture medium that contains
napthalineacetic acid and kinetin (33).
Sapling
and Pole Stages to Maturity
Growth and Yield- Intermediate
redcedars are distinguishable from dominants by age 5 on
good sites. Codominants usually can be differentiated from
dominants by age 25. Mean annual height growth of the
dominants is 0.5 m (1.64 ft) in 40- to 60-year-old, pure,
second-growth stands on moist sites in western Washington
(36). Annual radial increments of 10 mm or even 20 mm (0.4
to 0.8 in) occur on the best moist sites in the south coast
region of British Columbia (39).
Pure, even-aged stands can attain volumes comparable to
pure Douglas-fir stands by age 50 on high-quality upland
sites in western Washington (37), Plantations should be
dense (about 2,470 trees per hectare or 1,000/acre), and
intermediate crown classes should be removed in a light
thinning to reduce side shade at about age 25 (22,36).
Stands of 370 to 430 crop trees/ha (150 to 175 crop
trees/acre) at time of harvest may allow maximum diameter
growth without causing poor form (36). Maintaining a nearly
closed canopy at all times will benefit form because
open-grown redcedars tend to develop excessively large
limbs and multiple tops. Faster growing trees of acceptable
quality can be grown at wide spacings if their lower holes
are pruned (50), but percentages of latewood decrease
significantly (49).
Volumes of 379 to 825 m³/ha (5,418 to 11,782 ft³/acre) were
measured in 40- to 60-year-old pure second-growth stands on
moist sites in western Washington (36). A yield model on
medium sites in British Columbia indicates yields of 70
m³/ha (1,000 ft³/acre) at age 40, 350 m³/ha (5,000
ft³/acre) at age 115, and 595 m³/ha (8,500 ft³/acre) at age
270; maximum current annual increment occurs at 82 years
and maximum mean annual increment at 130 years (34).
In Great Britain, the cumulative volume produced by normal
western redcedar stands on poor sites is 50 m³/ha (714
ft³/acre) at age 20 and 953 m³/ha (13,620 ft³/acre) at age
80. On good sites, cumulative volume produced is 232 m³/ha
(3,315 ft³/acre) at age 20 and 1839 m³/ha (26,268 ft³/acre)
at age 80. The average age of maximum mean annual increment
is 72 on poor sites and 58 on good sites in these British
stands (22). At ages 20 and 50, cumulative volume
production is lower for western redcedar than for
Douglas-fir and Sitka. spruce in Great Britain, but by age
80 the redcedar volume production is higher than that of
Douglas-fir and spruce (45).
Growth is often much slower. Suppressed redcedar trees that
are 200 years old but only 7.6 cm. (3 in) in d.b.h. and 7.6
m (25 ft) tall are not unusual. Survival for such long
periods of suppression may be due to the ability of the
species to produce new root growth in full shade. It may
also be a result of frequent root grafting. Dominant trees
often support growth of the root systems and lower boles of
suppressed trees (9).
Rooting
Habit- Tree roots are
extensive. Redcedars made up only 17 percent of the basal
area but accounted for 82 percent of the root length in a
mixed-species stand in northern Idaho (29). Tap roots are
poorly defined or nonexistent, but fine roots develop a
profuse, dense network.
Western redcedar roots usually are deeper than the roots of
western hemlock but shallower than the roots of western
larch, western white pine, grand fir, and Douglas-fir (30).
The soils on which these species usually grow may be
responsible, however, because western redcedar, western
hemlock, and Douglas-fir trees of similar size growing on
similar soils have roots that penetrate to similar depths
and extend over similar areas (10). Shallow root systems
are most frequent where soil bulk density is high. Redcedar
roots cannot grow in dense soils penetrated by the roots of
Douglas-fir, red alder, lodgepole pine, and Pacific silver
fir (30). Redcedar root systems also tend to be shallower
and less extensive on wet sites than they are on deep,
moderately dry soils.
Where a thick duff layer is present, many redcedar roots
lie in the duff rather than in the underlying soil. Root
grafting is common (9). Western redcedar mycorrhizae are of
the vesicular-arbuscular type, and redcedar seedlings are
more responsive to mycorrhizal inoculation than are the
seedlings of redwood (Sequoia
sempervirens), incense-cedar
(Libocedrus
decurrens), and giant
sequoia (Sequoiadendron
giganteum) (27).
Reaction
to Competition- Only Pacific
silver fir, western hemlock, and Pacific yew are more
tolerant of shade than western redcedar (30). Its relative
tolerance may be higher in warm than in cool areas, but
redcedar is very tolerant wherever it grows, and it may be
"the species of choice" for reforesting high, brush-risk
areas near the coast (6). Often present in all stages of
forest succession, redcedar occupies pioneer, seral, and
climax positions (39). Multiple attributes seem to be
responsible-redcedar invades disturbed areas as widely
distributed seeds but regenerates vegetatively in
undisturbed areas, tolerating competition in both (26).
Nevertheless, it is usually considered a climax or near
climax species.
Western redcedar is best managed on moist sites
characterized by the presence of ladyfern, queenscup,
mountain woodfern, oakfern (Gymnocarpium
dryopteris), or
thimbleberry. On poorly drained sites of lower quality,
fertilizing with nitrogen appears to benefit growth (37).
Urea seems to be a better source of that nitrogen than
ammonium nitrate (54). Redcedar can be grown in stands of
mixed species where uneven-aged management is practiced or
when redcedar poles are to be produced under normal
even-aged management regimes. But pure stands are more
suitable for the long rotations needed to produce large
sawtimber, shingles, and shakes.
Where western redcedar is managed in mixed-species or
uneven-aged stands, its excellent shade tolerance and long
life should be considered. Redcedar is usually overtopped
by Douglas-fir, grand fir, western hemlock, and western
white pine. It tolerates understory conditions in
mixed-species stands but often grows slowly there. In
uneven-aged stands, western redcedar can maintain
acceptable growth rates over long periods, but it should
not be given excessive crown space. Thinning from above may
release the redcedars in mixed-species stands; thinning
from below is preferable in uneven-aged stands of western
redcedar. In the northern Rocky Mountains, growth response
to release is best on large, young redcedars with
green-yellow foliage growing on northerly aspects (17).
Redcedars probably should not be released when overtopped,
however, because much of the increased growth after their
release often occurs in large branches and a spreading
crown rather than stem wood (37).
Most western redcedars are harvested by clearcutting the
mixed-species stands in which they grow. Because of steep
terrain, decay, and breakage, redcedar harvesting costs are
high and lumber recovery is low (55). Redcedars should not
be left as scattered seed trees, however; even those along
clearcut margins may be lost to windthrow or exposure.
Effects of slash-burning vary with site conditions, but
low-impact spring burns tend to benefit the mycorrhizal
colonization of seedlings (6).
Damaging
Agents- Western
redcedar is less susceptible than its associates to most
damaging agents, but, as it is longer lived, damaged trees
are common. Although they are as windfirm as Douglas-fir on
dry sites, redcedars, are often windthrown in wet
environments and are not resistant to windthrow on the
moist sites where growth and yield are highest. Fire
resistance also varies with environment. Redcedar is more
severely damaged by fire than any of its associates along
the coast but is less susceptible than Engelmann spruce,
western hemlock, and subalpine fir in the interior (30).
Western redcedar suffers little damage from insects, but it
is a host for several economically important insect species
(13). One of the most important is the gall midge,
Mayetiola
thujae, which sometimes
seriously damages redcedar seeds in Oregon, Washington, and
British Columbia. Newly planted seedlings are occasionally
damaged by a weevil (Steremnius
carinatus) in British
Columbia, and larger trees are killed by a bark
beetle (Phloeosinus
sequoiae) on poor sites
in southeastern Alaska. The western cedar borer
(Trachykele
blondeli) causes degrade
and cull in sawtimber.
More than 200 fungi are found on western redcedar, but it
is less susceptible to pathological attacks than are most
of its associates. Indeed, redcedar may be a suitable
alternative species on coastal Douglas-fir and western
hemlock sites where soils are infected with
Phellinus
weiri, Fomes annosus, or
Armillaria
spp.
(37).
Nevertheless, many attacks occur during the long lives of
some redcedar trees, and the heartwood extractives that
provide decay resistance are eventually detoxified through
biodegradation by a series of invading fungi (25). As a
result, the volume of accumulated decay in living trees is
greater for western redcedar than for any other major
conifer in British Columbia (25), and hollow old trees are
common in the interior (7).
The major seedling disease, Didymascella
thujina, is a leaf
blight that infects 2nd- and 3rd-year nursery seedlings. As
much as 97 percent of the natural redcedar reproduction may
also be killed when this blight reaches epidemic
proportions (2). Epidemics are rare in North America,
however, and Didymascella
is not as damaging
here as it is in Europe, where the disease seriously
limited production of planting stock until cycloheximide
fungicides were developed (3,52).
In North America, the most important fungi attacking
redcedar are root, butt, and trunk rots (23). The root and
butt rots include Phellinus
weiri, Armillaria mellea, and
Poria
subacida. Poria asiatica and
P.
albipellucida are the most
important trunk rots near the coast; P.
asiatica and
Phellinus
weiri are most
important in the interior range of western redcedar (2).
These rots are most evident in old stands, where much of
the standing volume is often defective and unmerchantable.
Redcedar seedlings and saplings are often severely browsed
by deer, elk, or rodents, and browse damage may be the most
important stand-establishment problem (6).
Western redcedar is damaged more than Sitka spruce by salt
spray. Its foliage is more severely damaged by sulfur
dioxide than is the foliage of Douglas-fir, western
hemlock, and Sitka spruce and less damaged than the foliage
of subalpine fir and grand fir. Redcedar is damaged less
than Douglas-fir by airborne fluorides and ozone (30).
Special
Uses
Shingles and
shakes constitute the most important special use of
redcedar. Attractive appearance, durability, lightness, and
superior insulation qualities probably are responsible for
its popularity as a roofing material. Wood is also used in
utility poles, fenceposts, piling, paper pulp, clothes
closets and chests, caskets, crates, boxes, beehives, and
fishtrap floats. Perfumes, insecticides, medicinal
preparations, veterinary soaps, shoe polishes, and
deodorants are made from cedar leaf oil. Redcedar
extractives and residues are used in lead refining,
boiler-water additives, and glue extenders (31). When
properly trimmed, redcedars make excellent hedges. Their
drooping branches, thin fibrous bark, and flat sprays of
scalelike leaves make redcedars attractive ornamental
trees. The leaves are a major winter food for big game in
the northern Rocky Mountains, and deer browse redcedar all
year along the coast.
Genetics
Population Differences
Western
redcedar seems to vary less than other northwestern conifer
species. Lack of isoenzyme variation in newly germinated
seedlings from western Oregon and eastern and western
Washington indicates that redcedar populations contain
little genetic polymorphism (5). Isoenzyme variability is
also low in British Columbia (56). Leaf oil terpene
composition is similar in populations at both low and high
elevations in British Columbia, Washington, Oregon, Idaho,
and Montana; but small differences between coastal and
interior populations were recently detected by discriminant
analysis of the chemical data (53). Seedlings from
different seed sources usually have remarkably similar
forms and growth rates when grown in the same environment.
Inland populations are more tolerant of frost than those
from coastal populations, however (46), and plantation
trials indicate that provenances from Alaska are inferior
to those from Oregon and Idaho when grown in Poland (31).
Seed orchards have been established in Denmark, where
resistance to leaf blight and frost have been shown to be
homozygously recessive (52).
Races
Several
horticultural varieties of western redcedar are grown in
North America. They include atrovirens,
fastigiata, and
pendula.
Haploid and
triploid varieties have been studied in Germany (31).
Hybrids
Thuja
plicata x
Thuja
standishii hybrids are
resistant to the leaf blight caused by Didymascella
thujina (52).
Literature
Cited
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