BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Thuja occidentalis | Northern White-Cedar 



GENERAL BOTANICAL CHARACTERISTICS : 
Northern white-cedar is a monoecious, native, evergreen tree with a
narrow, almost columnar crown.  Branches on open-grown trees extend to
the ground.  The trunk is often divided into two or more secondary
trunks of equal size.  Northern white-cedar has scalelike foliage and
fibrous, sometimes shredding bark [25,26].

At maturity northern white-cedar is 40 to 50 feet (12-15 m) tall and 12
to 24 inches (30-60 cm) in d.b.h.  Infrequently it reaches heights of 70
to 80 feet (21-24 m) and diameters of 48 to 60 inches (120-150 cm) [26].
This species is extremely slow growing; after 50 years, it might reach
40 feet (12 m) in height on good sites, but only 15 feet (4.6 m) or less
on poor sites [27].

Northern white-cedar reaches ages in excess of 800 years [5,32].  Two
trees on the Niagara Escarpment in southern Ontario were dated at 935
and 1,032 years [32].

Seedlings develop deep roots in well-drained soil and shallow roots in
saturated soil.  With age, northern white-cedar develops a widespreading
root system which is well adapted to secure water and nutrients from
cracks in rocks [26].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual reproduction:  Northern white-cedar begins producing cones as
young as 6 years of age and begins producing large quantities by age 30.
The best production occurs after age 75.  Good crops occur at 2- to
5-year intervals with intervening years having fair to medium crops.
Seeds have lateral wings and are disseminated by wind.  Seeds are
dispersed a distance of 150 to 200 feet (45-60 m) from the source tree
[13,14,26].

Germination occurs when daytime temperatures reach about 84 degrees
Fahrenheit (29 deg C) [21].  Northern white-cedar germinates on a
variety of substrates including both mineral and organic soils, but
seedling establishment is limited to sites with a constant moisture
supply [26].  Drought is a major cause of seedling mortality [14].
Seedlings that germinate on old stumps are likely to die when the stumps
dry out in late summer, and seedlings that germinate in fast-growing
sphagnum moss (Sphagnum spp.) may be smothered [13].  Seedlings prosper
on recently burned sites [26].

Seedling growth is slow.  Annual height growth averages 3 inches (8 cm)
in the first few years.  Partial light is needed for continued seedling
growth [26].  

Vegetative reproduction:  Under favorable moisture conditions, northern
white-cedar reproduces vegetatively by layering.  Seedlings may
reproduce by layering at age 5 or earlier.  Layering accounts for a
considerable amount of northern white-cedar reproduction.  It is common
in swamp forests where trees often fall or tip slowly.  Trees
established on logs and stumps may fall as their weight increases and
the substrate rots [13,14,26].

Branches on a fallen tree that still has functional roots may begin
growing vertically.  Eventually, with the increased weight of new
growth, the stem will contact the soil and put out adventitious roots
[13].


SITE CHARACTERISTICS : 
Northern white-cedar grows on both uplands and lowlands.  The uplands
are primarily seepage areas, old fields, and limestone cliffs and
boulder fields.  The lowland sites include swamps, streambanks, and
lakeshores.  Northern white-cedar occurs from near sea level to more
than 2,000 feet (600 m) in elevation.  It grows up to 4,270 feet (1,300
m) in the Adirondack Mountains in New York on sites where water is
flowing over rocks [26].

On lowland sites, northern white-cedar generally grows where there is a
strong flow of moderately mineral-rich soil water of near neutral pH
(minerotrophic and weakly minerotrophic swamps) and where the organic
peat is moderately to well decomposed.  The peat is ususally 1 to 6 feet
(0.3-1.8 m) thick and contains rotten wood.  Northern white-cedar grows
best where soils are neutral to moderately alkaline [19,24,26].

On upland sites, northern white-cedar grows primarily in calcareous
soils including calcareous clays and shallow loam overlying broken
limestone [26].

Habeck [50] has suggested that northern white-cedar growing in limestone
uplands is an ecotype distinct from wet lowland northern white-cedar.
Specimens growing on cliffs tend to be deformed with multiple leaders
and twisted trunks, whereas those in wet lowlands tend to be more erect
with well-defined trunks.  However, four studies that looked at tree
morphology [8], seed morphology [7], growth patterns [36], and xylem
water potential [12] found no evidence of ecotypic variation.  There
tended to be more variation within a single site than between lowland
and upland sites.  Seedlings, from seeds collected from the two
contrasting habitats, were grown under different moisture conditions.
Xerically grown seedlings had significantly (p<0.05) more negative xylem
water potential than did seedlings grown under moist conditions,
independent of seed origin.  The seedlings acclimated to the conditions
and demonstrated that northern white-cedar has broad physiological
tolerance to habitat moisture [12].

Overstory associates not mentioned in DISTRIBUTION AND OCCURRENCE
include white spruce (Picea glauca), quaking aspen (Populus
tremuloides), balsam poplar (P. balsamifera), and bigtooth aspen.  Shrub
associates on good sites include speckled alder, mountain maple (Acer
spicatum), red-osier dogwood (Cornus stolonifera), and American fly
honeysuckle (Lonicera canadensis).  Labrador-tea ledum (ledum
groenlandicum), blueberries (Vaccinium spp.), and wintergreen
(Gaultheria procumbens) occur on poorer sites.  Creeping wintergreen (G.
hispidula) occurs on both good and poor sites [26].

Herbs that occur in swamps with northern white-cedar include dwarf red
blackberry (Rubus pubescens), Canada mayflower (Maianthemum canadense),
woodfern (Dryopteris spp.), bunchberry dogwood (Cornus canadensis),
false Solomons-seal (Smilacina spp.), and pitcherplant (Sarracenia
purpurea) [26].  Dwarf lake iris (Iris lacustris), a federally threatened
species endemic to the northern shores of Lake Michigan and Lake Huron,
is found in association with narrow beach strands of northern
white-cedar [43].

The groundcover in northern white-cedar swamp forests includes sphagnum
and other mosses, liverworts, decaying logs, and litter [26].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Although northern white-cedar is generally considered shade tolerant, it
is not as tolerant as balsam fir or sugar maple (Acer saccharum).
Seedlings may only be intermediate in shade tolerance [13,26].  They can
survive severe suppression for several years, but if not released, they
die [26].  Vegetative shoots are more tolerant than seedlings.  Although
some authors [6,30,31] consider northern white-cedar a climax species
because of its longevity and shade tolerance, it cannot reproduce by
seed under dense shade to any marked extent [13].

Northern white-cedar will invade and form even-aged stands in old
fields, openings created by windfall or cutting, and recently burned
swamp sites.  It replaces speckled alder thickets that form in swamps
after fire or after changes in water levels [19,26].  Northern
white-cedar is a pioneer on limestone cliffs and talus slopes.  The
roots grow in small pockets of organic material between rocks [49].
Northern white-cedar succeeds less tolerant, shorter lived species such
as balsam poplar, tamarack (Larix laricina), and black spruce (Picea
mariana) [26].

An uneven-aged old-growth northern white-cedar community occurs on the
Niagara Escarpment in southern Ontario.  This self-sustaining population
occurs in a 3.3 to 16.4-foot (1-5 m) wide strip on the limestone cliff
edge and face [32].  Uneven-aged stands also form on poor lowland sites
where vegetative reproduction is the primary mode of reproduction [26].

Northern white cedar is often succeeded by sugar maple and other more
shade-tolerant species [1,17].  Replacement is usually tree by tree, but
major disturbance (excluding fire) can accelerate succession by
releasing shade-tolerant species [balsam fir, sugar maple, black ash
(Fraxinus nigra)] growing in the understory [1,19].


SEASONAL DEVELOPMENT : 
Flower buds form in autumn and expand the following spring.  Pollen is
dispersed from late April to June.  Cones are full grown by mid-August,
ripen in August and September, and open 7 to 10 days after ripening.
Seeds germinate the following spring or early summer when sufficiently
high temperatures occur [26].

Related categories for Species: Thuja occidentalis | Northern White-Cedar