BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Picea glauca | White Spruce 



GENERAL BOTANICAL CHARACTERISTICS : 
White spruce is a native, coniferous, evergreen tree.  It typically
grows as a medium-sized upright tree with a long, straight trunk, and
narrow, spirelike crown.  Because of poor growing conditions at the
northern portion of its range, it may grow as a short, single-trunked
tree, or assume a mat or krummholz form [60].  In Alaska, white spruce
is typically 40 to 70 feet (12-21 m) tall and 6 to 18 inches (15-42 cm)
in diameter [60].  Throughout much of Canada, white spruce's average
height is about 80 feet (24 m) [36].  On good sites throughout the range
of white spruce, individual trees may grow to a height of 100 feet (30
m) or more and attain diameters of 24 to 36 inches (60-90 cm) [45].

The bluish-green needles are 0.75-inch-long (1.9 cm), stiff, and
four-sided [36].  Bark on mature trees is thin, usually less than 0.3
inch (8 mm) thick [53], scaly or smooth, and light-grayish brown.  White
spruce is shallow-rooted.  Rooting depth is commonly between 36 and 48
inches (90-120 cm), but taproots and sinker roots may descend to 10 feet
(3 m) [45].  On northern sites, large roots are usually concentrated
within 6 inches (15 cm) of the organic-mineral soil interface [45].
Trees often retain lower branches, but in dense stands lower branches
are gradually shed, so that eventually the crown occupies about one-half
of the tree's height [36].  Light-brown cones are about 2 inches (5 cm)
long and hang from the branches of the upper crown [36].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (mesophanerophyte)
   Burned or Clipped State:  Therophyte


REGENERATION PROCESSES : 
Cone and seed production:  Plants can begin producing seed at 4 years of
age but generally do not produce seed in quantity until they are 30
years of age or older [44].  Good to excellent seed crops occur every 2
to 6 years on good sites [45], but in many areas, good seed crops are
produced only every 10 to 12 years [46,65].  In natural stands cone
production occurs primarily on dominant and codominant trees, with
sporadic production from intermediate and suppressed trees [45].  Seeds
are about 0.12 inch (3 mm) long, with a 0.25- to 0.33-inch-long (6-9 mm)
wing [53].  There are approximately 226,000 seeds per pound [52].

Cone and seed predation:  Red squirrels can reduce cone crops
significantly.  In interior Alaska, they have harvested as much as 90
percent of a cone crop [45].  Their impact on cone and seed production
is greatest during poor or medium cone crop years [69].  Numerous
insects also reduce seed yields.  The spruce cone maggot, the fir cone
worm, and the spruce seed moth are responsible for most loss.  Following
dispersal, small mammals consume considerable amounts of seed off the
ground [45].

Dispersal:  The winged-seeds are dispersed by wind and travel primarily
in the direction of prevailing winds.  Most seed falls within about 300
feet (91 m) of a source, but seeds have been found as far as 1,300 feet
(400 m) from a seed source [6,66].  Seeds found considerable distances
from a source probably travel over crusted snow.  A study in Alaska
found that 50 percent of seed fell within 90 feet (27 m), and 90 percent
of seed fell within 210 feet (64 m) of a 60-foot-tall tree [65].  Red
squirrels disperse seeds also.  White spruce reproduction is common at
squirrel middens [62].

Viability and germination:  White spruce seeds remain viable for only
about 1 to 2 years.  Under natural conditions, seeds overwinter under
snow and germinate in the spring or summer when there is adequate
moisture and soil temperatures have warmed [45].  In Alaska seeds do not
begin germinating until temperatures become favorable, usually in
mid-May [69].  If June is a rainy month, most seeds will germinate.  If
June precipitation is low and seedbeds dry out, germination is delayed
until it rains in July and August [69].  Germanitive capacity is 50 to
70 percent [52].

Seedling establishment:  Seedling establishment is best on mineral soil.
White spruce may also establish on shallow organic seedbeds, but rarely
establish where organic layers are thicker than 2 to 3 inches (5-8 cm)
[55].  Seedlings are frequently found on rotten wood.

Growth:  Seedlings grow best in full sunlight, but are tolerant of low
light, and can withstand many years of suppression [6].  First-year
seedlings are normally less than 1 inch ( 2.5 cm) tall.  After 4 to 6
years, seedlings are less than 20 inches ( 50 cm) tall [45].

Vegetative reproduction:  At the northern treeline in Alaska and much of
Canada, white spruce reproduces almost exclusively by layering [19,45].
In these far north habitats, seed viability is at best low, and
seedlings are rare or absent [19].  Layering may also occur further
south when the lower branches touch the ground and become covered with
moss, litter, or soil.


SITE CHARACTERISTICS : 
White spruce occupies boreal forests.  It is largely confined to
well-drained uplands or river terraces and floodplains.  In interior
Alaska and the Northwest Territories, white spruce forests are usually
found on stream bottoms, river terraces and lake margins, and on warm,
well-drained, south-facing slopes within 5 miles (8 km) of major river
valleys [24,45].  Seral stands of white spruce and aspen, and white
spruce and birch, are common on relatively dry slopes with a south or
southwest exposure, and on dry, excessively drained outwash or deltaic
soils [41].  Across northern Alaska, white spruce grows at the northern
limit of tree growth where it forms open communities on dry exposed
sites [57].  At arctic timberline, white spruce grows in well-drained
soils, often along streams where permafrost has been melted away by
flowing water [73].  In British Columbia and Alberta, white spruce is
widely distributed, occupying floodplains, foothills, and mountains from
2,500 to 5,000 feet (762-1,524 m) in elevation [43,45].  In northeastern
Alberta, open, parklike white spruce forests occur on high ridges, stony
beaches, and dune habitats [43].  In eastern Canada, the Lake States,
and the northeastern United States, white spruce occurs in many
coniferous and mixed coniferous-hardwood forests.  Pure stands or mixed
stands where it is dominant are not widespead.  Conifers, including
white spruce, tend to occupy shallow outwash soils on upper slopes and
flats, while hardwoods or mixtures of hardwoods and spruce are found on
deep glacial till soils of lower slopes [72].

Associated trees:  Alaska associates include paper birch, quaking aspen,
black spruce, and balsam poplar.  In western Canada, associates include
subalpine fir (Abies lasiocarpa), balsam fir, Douglas-fir (Pseudotsuga
menziesii), jack pine (Pinus banksiana), and lodgepole pine (P.
contorta).  In eastern Canada and the northeastern United States
associates include black spruce, paper birch, quaking aspen, red spruce,
balsam fir, northern white-cedar (Thuja occidentalis), yellow birch
(Betula alleghaniensis), and sugar maple (Acer saccharum) [22,45].  In
Wisconsin, white spruce commonly grows with balsam fir [14], and in
Maine, with red spruce [22].

Understory:  In Alaska and across much of western Canada, climax stands
have understories dominated by a well-developed layer of feather mosses.
The total depth of the live moss-organic mat is frequently 10 to 18
inches (25-46 cm) or more [45].  Mixed stands of white spruce and seral
hardwoods have shallower moss layers.  Understory shrubs include green
alder (Alnus viridis ssp. crispa), willows (Salix spp.), mountain
cranberry (Vaccinium vitis-idaea), prickly rose (Rosa acicularis),
highbush cranberry (Viburnum edule), bog birch (Betula glandulosa),
twinflower (Linnaea borealis), black crowberry (Empetrum nigrum),
bearberry (Arctostaphylos uva-ursi), and soapberry (Shepherdia
canadensis) [22,45].  In the Prairie Provinces, common understory shrubs
include snowberry (Symphoricarpos albus), red-osier dogwood (Cornus
stolonifera), serviceberry (Amelanchier alnifolia), and western
chokecherry (Prunus virginiana) [45].

Stand characteristics:  In Alaska and western Canada, climax stands are
usually closed, except near treeline [22].  White spruce stands can be
either even-aged or uneven-aged.  Even-aged stands result from rapid
invasion of white spruce into burned areas.  Uneven-aged stands result
from the slow invasion of spruce seedlings into seral birch or aspen
stands [41].

Soil:  White spruce grows on a wide variety of soils of glacial,
lacustrine, marine, or alluvial origin.  It grows well on loams, silt
loams, and clays, but rather poorly on sandy soils [22].  It is somewhat
site demanding, and often restricted to sites with well-drained, basic
mineral soils.  White spruce grows poorly on sites with high water
tables and is intolerant of permafrost [22].  In the Lake States and
northeastern United States, it grows mostly on acid Spodosols,
Inceptisols, or Alfisols, with a pH ranging from 4.0 to 5.5 [72].  In
the Northeast, it grows well on calcareous and well-drained soils but is
also found extensively on acidic rocky and sandy sites, and in some fen
peatlands in coastal areas [22].


SUCCESSIONAL STATUS : 
White spruce is a long-lived climax tree that gradually replaces pine,
aspen, birch, and/or poplar on well-drained sites.  Less frequently it
occurs as an early successional species, forming pure stands or mixing
with seral hardwoods immediately after fire.  Its ability to
successfully establish following fire depends on fire severity and
intensity, and seed production during the year of the fire [see Plant
Response to Fire].

Following stand destroying fires, dense stands of aspen, birch, and/or
poplar tend to develop quickly, and these successional species are often
scattered throughout all but the oldest white spruce stands [56].  White
spruce seedlings establish under these seral hardwoods, develop and grow
slowly, and eventually replace them.  White spruce-aspen, white
spruce-birch, and white spruce-balsam poplar are common mid-successional
communities that, with the continued absence of fire, will gradually be
replaced by essentially pure stands of white spruce.  Foote [24]
outlined six postfire successional stages for sites capable of
supporting climax white spruce stands in interior Alaska:

  1.  Newly burned (0-1 year after fire) - Following stand destroying
      fires, shoots of prickly rose, highbush cranberry, willows,
      quaking aspen, and birch appear within a year.  White spruce
      seedlings are rare.

  2.  Moss-herb stage (1-5 years after fire) - Herbs cover about 30
      percent of the ground; fireweed (Epilobium angustifolium) is the
      most common.  Mosses cover about 30 percent of the ground.
      Quaking aspen and paper birch each average about 12,150 stems per
      acre (30,000 stems/ha), originating from both sucker shoots and
      seedlings.  Limited white spruce establishment occurs at this
      time.

  3.  Tall shrub-sapling stage (3-30 years after fire) - Tall shrubs or
      tree saplings dominate the overstory, with herbs, tree seedlings
      and litter below.  White spruce seedlings are often present at
      this stage, but not conspicuous.

  4.  Dense tree stage (26-45 years after fire) - Young trees, mostly
      aspen and/or birch dominate the overstory.  The understory is
      dominated by highbush cranberry, prickly rose, twinflower,
      mountain-cranberry, and Labrador-tea.  Willows and herbs decline.

  5.  Hardwood stage (46-150 years) - This stage has well developed
      stands of quaking aspen, paper birch, or mixtures of hardwoods and
      hardwood-white spruce.  As the hardwoods begin to die, codominant
      or understory white spruce form the overstory.

  6.  White spruce stage (150-300+ years) - White spruce eventually
      replaces the hardwoods to form an open to closed canopy.  Some
      hardwoods remain, but the oldest stands tend to be nearly pure
      spruce.

Following fire in upland spruce-fir stands in New England, early seral
stages are dominated by aspen and birch, sometimes pine, and
occasionally pure white spruce [6].  White spruce has invaded much
abandoned agricultural land in this region, forming essentially
even-aged stands.  In northwestern Quebec, white spruce is considered a
long-lived, shade-tolerant climax species.  However, probably due to
spruce budworm outbreaks, white spruce often declines after about 200
years, while paper birch remains abundant [7].  In Wisconsin, white
spruce commonly replaces trembling aspen and paper birch.  White spruce
and balsam fir are the major dominants of the oldest boreal forest
stands in Wisconsin [14].

White spruce is a climax species on the floodplains of large rivers of
interior Alaska and northwestern Canada.  Willows are the first to
colonize siltbars and are in turn replaced by the mid-successional
balsam poplar.  The long-lived white spruce becomes established in low
numbers early on and survives to dominate the climax stage [10,49].  The
climax type on river terraces in southeastern British Columbia is
dominated by white spruce and trembling aspen [25].

In Glacier National Park, white spruce x Engelmann spruce hybrids have
invaded ponderosa pine (Pinus ponderosa) savannas as a result of fire
exclusion [27].


SEASONAL DEVELOPMENT : 
Pollen shedding may occur in May, June, or July, with southern areas
having earlier dispersal than northern areas.  Pollen shedding is
temperature dependent and may vary yearly by as much as 4 weeks at any
given location.  Cones ripen in August or September, about 2 to 3 months
after pollen shed. Timing of seedfall varies yearly depending on
climatic conditions.  Cool, wet weather delays seedfall, but under warm
and dry conditions cones open and seeds disperse early [45,69].  In
general seedfall begins in late August or September [45].  Nienstadt and
Teich [44] reported that most seeds are shed within about 5 weeks after
cones open; however,, Zasada and others [69] reported that over several
years in interior Alaska, 90 percent of white spruce seeds were
dispersed by late December.  Following dispersal, cones remain on the
tree for 1 to 2 years.

Related categories for Species: Picea glauca | White Spruce