BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Thuja plicata | Western Redcedar 



GENERAL BOTANICAL CHARACTERISTICS : 
Western redcedar is a large, native, long-lived, evergreen tree
[8,50,57,80].  At maturity it is generally 70 to 100 feet (21-30 m)
tall, sometimes 130 feet (40 m), with a tapering trunk 2 to 4 feet
(0.6-1.2 m) in diameter, sometimes 6 feet (1.8 m) or more.  On some
sites west of the Cascades, old-growth western redcedar often attains
basal diameters of 8 to 10 feet (2.4-3 m) and heights of 200 feet (61
m).  The largest known western redcedars are believed to be 1,000 years
old or more [8].

Western redcedar has a swollen or buttressed base, pointed conical
crown, and horizontal branches curving upward at the tips [80].  The
leaves are scalelike, flattened and 0.05 to 0.1 inches (1.5-3 mm) long.
The twigs are flattened, in fanlike sprays and slightly drooping.  The
bark is thin, fibrous and stringy or shreddy.  Thickness varies from 0.5
to 1 inch (1.3-2.5 cm) [51].  The cones are clusterd near the ends of
twigs and become turned up on short stalks [80].  Western redcedar
retains its lower limbs except when in densely crowded stands [8].

Western redcedar roots are extensive.  Tap roots are poorly defined or
nonexistent, but fine roots develop a profuse, dense network.  Root
systems tend to be shallower and less extensive on wet soils than on
deep, moderately dry soils.  When a thick duff layer is present, many
western redcedar roots lie in the duff rather than in the underlying
soil [50,51].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Seed production and dissemination:  Western redcedar reproduces from
seeds more readily in open, disturbed areas, such as clearcuts, than in
undisturbed stands [19].  Seed production normally begins when trees are
20 to 30 years old [73].  However, open-grown trees may produce seed by
age 10 [19,50].  Cones average about three to six seeds, but cones are
often numerous and heavy seed crops are common.  Average annual seed
crops vary from 100,000 to 1,000,000 seeds per acre
(247,000-2,470,000/ha) in coastal forests and from 22,000 to 111,000 per
acre (54,000-274,000/ha) in the interior [50].  Pure stands of western
redcedar may yield 60,704,168 seeds per acre (150,000,000/ha).  Poor
cone crops are rare [19].  Large seed crops occur every 3 to 4 years
[19,51].

Western redcedar seeds are small, 203,000 to 592,000 seeds per pound
(448,000-1,305/Kg) [8,50].  The seeds are dispersed primarily by wind.
However, the seeds have small wings and are not carried more than 400
feet (122 m) from the parent tree [8,48,50].

Germination:  Germination is epigeal.  Western redcedar seeds germinate
well without stratification and remain viable for at least 7 years
stored dry (5 to 8 percent moisture) at 0 degrees Fahrenheit (-18 deg C)
[50].  Stratification may improve the germination of some dormant seed
lots.  However, in others it may lower the germination capacity [51].
Haig [34] reported germination rates of 73 percent, and Schopmeyer [69]
reported germination rates of 34 to 90 percent.

Mineral soil has been found to be a better seedbed in many environments
than moss or duff, which may dry out rapidly [19,21,50].  Heavily shaded
seedbeds have been associated with the best germination of western
redcedar in British Columbia [19].  Rotten wood that is in contact with
the soil is the preferred seedbed in old western redcedar groves [50].
Graham [26] found that germination was best on burned surfaces.
 
Seedling development:  Western redcedar seedling survival is low [8,50].
Drought and high soil temperatures damage seedlings grown in full
sunlight [8,40].  Fungi, birds, insects, and smothering by fallen leaves
of deciduous shrubs are some other causes for the high mortality of
western redcedar seedlings [8,19].  Seedlings grow best in partial
shade, although they may fail on heavily shaded sites due to poor root
penetration [19].  Seedlings show high resistance to root flooding [47]
and respond well to removal of competition [57].  In one study, removal
of shrubs resulted in an increase in height growth of western redcedar
compared to unreleased trees [26].

Of all conifers in the northern Rocky Mountains, western redcedar and
western hemlock seedlings grow the slowest.  Annual height growth of
western redcedar seedlings is highly variable, from less than 0.39
inches (1 cm) in dense stands to over 7.5 inches (19 cm) in thinned
stands [26].

Vegetative reproduction:  Communities with closed canopies favor
vegetative reproduction over sexual reproduction [32].  Western redcedar
generally relies on vegetative reproduction in climax old-growth stands
with high soil moisture throughout the growing season [21,27].  The
frequent absence of adequate moisture in the upper soil layers of
well-drained sites often is responsible for western redcedar's reduced
ability to vegetatively reproduce on upland sites [28].  Three natural
types of vegetative reproduction occur:  (1) layering, (2) rooting of
fallen, living branches that have been torn off by wind or snow and have
fallen on wet soil; and (3) rooting along the trunks of fallen, living
trees [19,32,58].


SITE CHARACTERISTICS : 
Western redcedar grows best in maritime climates with cool, cloudy
summers and wet, mild winters.  In drier areas west of the Cascades,
western redcedar becomes abundant only on wet sites such as ravines,
along streams, or on poorly drained bottomlands.  Near its range limits
in the drier mountains east of the Cascade crest, western redcedar grows
almost exclusively in narrow canyons, where its roots are irrigated all
summer by a mountain stream [8].  In Glacier National Park and the
Selway-Bitterroot Wilderness in Idaho and Montana, western redcedar is
dominant in wet ravines and poorly drained depressions [50].

Precipitation and temperature:  Western redcedar occurs on sites that
receive from 35 inches (890 mm) of annual precipitation to more than 260
inches (6,600 mm), mostly as winter rainfall [50].  Western redcedar is
not resistant to frost and is sometimes damaged by freezing temperatures
in late spring or early autumn.  When sufficent precipitation is
present, low tempertures appear to limit western redcedar's range.  The
northern limits of western redcedar lie between the 52 and 53 degree
Fahrenheit (11.1-11.7 deg C) mean summer temperature isotherms in
southeastern Alaska [50].  Bottomland frost pockets in northern Idaho
are commonly occupied by subalpine fir (Abies lasiocarpa) rather than
western redcedar [51].

Soils:  Western redcedar can tolerate a wide range of soil.  It is found
on all soil textures and parent materials on Vancouver Island.  Coarse
sandy soils are not well suited to the establishment and growth of
western redcedar in northern Idaho and northeast Washington, but rocky
slopes with limited soil development support western redcedars in
southeastern Alaska.  Poorly drained organic soils support redcedar
south of Petersburg, Alaska.  It grows well on shallow soils over chalk
and can tolerate both acid and alkaline soils conditions.  It is able to
survive and grow on soils that are low in nutrients and is found on such
soils over much of its natural range.  However, productivity may be
improved by fertilization [50].

Elevation:  Elevational ranges of western redcedar have been reported as
follows [19,50,51]:

        Alaska - 0 to 3,000 feet (0-910 m)
        British Columbia - 0 to 3,900 feet (0-1,190 m)
        Oregon - 0 to 7,500 feet (0-2,290 m)        
        northern Rocky Mountains - 2,000 to 5,900 feet (610-1,798 m)

In coastal regions, western redcedar is commonly associated with the
following shrub and herb species:  dwarf Oregon grape (Mahonia nervosa),
stink currant (Ribes bracteosum), Alaska blueberry (Vaccinium
alaskaense), box blueberry (V. ovatum), Pacific rhododendron
(Rhododendron macrophyllum), salal (Gaultheria shallon), threeleaf
anemone (Anemone deltoidea), deerfern (Blechnum spicant), slough sedge
(Carex obnupta), and evergreen violet (Viola sempervirens) [50,51].

In interior regions western redcedar is commonly associated with the
following shrub and herb species:  mountain alder (Alnus incana spp.
tenuifolia), Oregon grape (Mahonia repens), common juniper (Juniperus
communis), red raspberry (Rubus idaeus), blue huckleberry (Vaccinium
globulare), Rocky Mountain honeysuckle (Lonicera utahensis), gold thread
(Coptis occidentalis), roundleaf alumroot (Heuchera cylindrica), pine
drops (Pterospora andromedea), and green pyrola (Pyrola chlorantha)
[35,50,51,61].

Common shrub and herb associates of both coastal and interior regions
are as follows:  western serviceberry (Amelanchier alnifolia),
thimbleberry (Rubus parviflorus), oceanspray (Holodiscus discolor),
Devil's club, common snowberry (Symphoricarpos albus), lady fern,
western swordfern (Polystichum munitum), prince's-pine (Chimaphila
umbellata), bunchberry dogwood (Cornus canadensis), false Solomon's-seal
(Smilacina stellata), and Pacific trillium (Trillium ovatum) [50,51].


SUCCESSIONAL STATUS : 
Obligate Climax Species

Western redcedar is very shade tolerant [8,21,50,51].  It is one of the
most shade tolerant species growing in cedar-hemlock ecosystems of the
northern Rocky Mountains [25].  It is usually considered a climax or
near climax species, but it can be found in all stages of forest
succession.  It invades disturbed areas as widely distributed seeds but
regenerates vegetatively in undisturbed areas, tolerating competition in
both [50].  Moisture and soil conditions strongly influence the
successional status of western redcedar.  It is climax on wet sites in
the Lake McDonald region of Glacier National Park and on calcium-rich
seepage habitats in British Columbia [51].  In Glacier National Park,
western redcedar enters pioneer communities.  The seedlings develop
rapidly in open stands of lodgepole pine (Pinus contorta) and western
larch (Larix occidentalis)[32].  It can survive as a late-seral or
coclimax tree on western-hemlock-dominated sites [21].  In Idaho,
western white pine (P. monticola) stands are slowly replaced by a
western hemlock-western redcedar climax [51].


SEASONAL DEVELOPMENT : 
The reproductive cycle of western redcedar occurs over approximately 16
months.  Phenology varies between coastal and interior regions.  For
trees in the middle of the coastal distrubution on Vancouver Island,
pollen and seed cones develop in early June.  Pollen forms in late
February or early March of the second season.  Pollination occurs within
1 to 2 weeks usually in March but may begin as early as mid-February in
mild coastal areas or as late as early April at higher elevations.
Pollination in March is most common [57].  Fertilization occurs in late
May.  Cones mature in October.  West of the Cascade Range, cone maturity
is usually reached in 5 months, but in northern Idaho it takes 3 months.
Major seedfall occurs during October and November in both the interior
and coast range [50].  Dry warm weather can cause earlier seed release.
Some seeds may be retained in the cones and gradually shed throughout
the winter [19].  Where moisture and temperature conditions are
favorable, germination can occur in the autumn, winter, or spring [50].
Along the coast region, seeds generally germinate in either fall or
spring [8].

Related categories for Species: Thuja plicata | Western Redcedar