Hans Nienstaedt and John C. Zasada
White spruce (Picea glauca), also known as Canadian spruce, skunk spruce, cat spruce, Black Hills spruce, western white spruce, Alberta white spruce, and Porsild spruce, is adapted to a wide range of edaphic and climatic conditions of the Northern Coniferous Forest. The wood of white spruce is light, straight grained, and resilient. It is used primarily for pulpwood and as lumber for general construction.
Picea glauca, white spruce, is a medium-sized to large evergreen coniferous tree in the Pinaceae (pine family that is widely distributed in the boreal and northern regions of North America. Also known as Canadian spruce, skunk spruce, cat spruce, Black Hills spruce (which is sometimes considered a subspecies, P. glauca subsp. densata, and is the state tree of South Dakota), western white spruce, Alberta white spruce, and Porsild spruce, it is adapted to a wide range of soil and climatic conditions. It is used primarily for pulpwood and as lumber for general construction.
White spruce has a straight trunk, reaching heights of 15–26 m (50–85 feet) and diameters of 30–60 cm (12–24 inches). Leaves are needle-shaped but blunt-tipped and stiff, typically 1–2 cm long but can be as short as 0.5 cm, and arranged spirally on the branches. When crushed, the leaves emit a disagreeable odor. Cones are slender and cylindrical, 2.5–5 cm long. In addition to reproducing from seed, vegetative reproduction from layering is common at some sites. Layering is most common in stands in which trees are open grown and the lower branches touch the ground. The branch roots when it is covered by moss, litter, or soil and organic material. Layering probably is an important means of maintaining the stand when sexual reproduction is limited or nonexistent because of climatic limitations.
White spruce grows from sea level to about 1520 m (5,000 ft) elevation, with a transcontinental range, from Newfoundland and Labrador west across Canada along the northern limit of trees to Hudson Bay, Northwest Territories, and Yukon. It almost reaches the Arctic Ocean at latitude 69° N. in the District of Mackenzie in the Northwest Territories. In Alaska, it reaches the Bering Sea at Norton Bay and the Gulf of Alaska at Cook Inlet.
White spruce is one of the most important commercial species in the boreal forest, commercially harvested for wood fiber and lumber products. The wood, which is light, straight-grained, and resilient, is also used for house logs, musical instruments, paddles, and various boxes and containers. White spruce forests have significant value in maintaining soil stability and watershed values and for recreation. The species is planted as an ornamental and in shelterbelts.
Historically, white spruce provided shelter and fuel for both Indians and white settlers of the northern forest. White spruce was the most important species utilized by natives of interior Alaska. The wood was used for fuel, but other parts of the tree also had a purpose; bark was used to cover summer dwellings, roots for lashing birchbark baskets and canoes, and boughs for bedding. Spruce pitch (resin) and extracts from boiled needles were used for medicinal purposes.
White spruce in Alaska experienced dramatic declines in the 1990s due to outbreaks of spruce bark beetle (Dendroctonus rufipennis) associated with unusually warm or longer summers, likely associated with global warming.
Excerpted and modified from Nienstaedt and Zasada 1994, with additional information from Barnes and Wagner 2004 and Juday 1998.
General: Pine Family (Pinaceae). Native trees grows to 25 (-50) meters tall, the crown broadly conic to spire-like, or the plants sometimes shrub-like near treeline; branches slightly drooping; twigs not pendent, slender, pinkish-brown, without hairs. Bark is gray-brown, thin scaly. Needles are evergreen, borne singly from all sides of the twig but often crowded on the upper side, (0.8-) 1.5-2 (-2.5) cm long, blue-green, 4-angled, often inwardly curved, stiff, sharp-pointed. Seed cones are light brown at maturity, 2.5-6 (-8) cm long, ellipsoid, pendent; cone scales fan-shaped, soft and flexible, the tip smooth-edged and extending 0.5-3 mm beyond seed-wing impression. The common name is derived from the white waxy layer on the foliage.
Variation within the species: White spruce is highly variable over its range and several varieties (apart from the typical) have sometimes been recognized.
P. glauca var. albertiana (S. Brown) Sargent – Canadian Rocky Mountains
P. glauca var. densata Bailey – Black Hills of South Dakota and adjacent Wyoming
P. glauca var. porsildii Raup – Alaska
The diagnostic characteristics of these variants are not well correlated and occur rather sporadically – some of the features may reflect interspecific hybridization and some may be phenotypic modifications. More study is needed, but recent taxonomic treatments do not formally recognize variants within white spruce. Most of the variation follows gradients of latitude and altitude.
Where they occur together, white spruce and Engelmann spruce regularly hybridize and intergrade completely, the hybrids occurring in intermediate elevation. Such trees are largely the basis for the description of P. glauca var. albertiana. White spruce also forms natural hybrids with Sitka spruce and black spruce.
Canada spruce, skunk spruce, cat spruce, single spruce, western white spruce (var. albertiana, Canadian Rocky Mts.), Porsild spruce (var. porsildii, Alaska), Black Hills spruce (var. densata, South Dakota); synonyms: Picea alba (Aiton) Link; Picea canadensis (Miller) B.S.P.
Widespread across northern North America, from Alaska, Yukon, and British Columbia continuously eastward to Nova Scotia, Newfoundland, New Brunswick, and Québec, in the northeastern United States and sporadically in the northern tier of states (Montana, Wyoming, South Dakota, Minnesota, Wisconsin, Michigan). For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.
Regularity: Regularly occurring
Regularity: Regularly occurring
Occurrence in North America
WY AB BC LB MB NB NF NS NT ON
PE PQ SK YT
Newfoundland, Labrador, and northern Quebec west across Canada along the
northern limit of trees to northwestern Alaska, south to southwestern
Alaska, southern British Columbia, southern Alberta, and northwestern
Montana, and east to southern Manitoba, central Minnesota, central
Michigan, southern Ontario, northern New York, and Maine. An isolated
population also occurs in the Black Hills of South Dakota and Wyoming
Regional Distribution in the Western United States
This species can be found in the following regions of the western United States (according to the Bureau of Land Management classification of Physiographic Regions of the western United States):
8 Northern Rocky Mountains
15 Black Hills Uplift
White spruce grows from sea level to about 1520 m (5,000 ft) elevation. It is found near 610 m (2,000 ft) on the central tableland of Labrador north of latitude 52° N. (108), and in Alaska white spruce forests approach 910 m (3,000 ft) at about latitude 68° N. in the Dietrich River Valley on the south slope of the Brooks Range (26). It reaches 1160 m (3,800 ft) in the timberline forest at latitude 61° N. in the Liard Range in the Northwest Territories (79), and farther south in the Rocky Mountains it is the dominant species from the edge of the plains at 1220 m (4,000 ft) to about 1520 m (5,000 ft). In interior British Columbia, white spruce grows at elevations as low as 760 m (2,500 ft) in the east Kootenay Valley (130).
- The native range of white spruce.
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 . In Alaska, white spruce
is typically 40 to 70 feet (12-21 m) tall and 6 to 18 inches (15-42 cm)
in diameter . Throughout much of Canada, white spruce's average
height is about 80 feet (24 m) . 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) .
The bluish-green needles are 0.75-inch-long (1.9 cm), stiff, and
four-sided . Bark on mature trees is thin, usually less than 0.3
inch (8 mm) thick , 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) . On northern sites, large roots are usually concentrated
within 6 inches (15 cm) of the organic-mineral soil interface .
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 . Light-brown cones are about 2 inches (5 cm)
long and hang from the branches of the upper crown .
Habitat and Ecology
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 . Across northern Alaska, white spruce grows at the northern
limit of tree growth where it forms open communities on dry exposed
sites . At arctic timberline, white spruce grows in well-drained
soils, often along streams where permafrost has been melted away by
flowing water . 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 . 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 widespread. 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 .
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 , and in
Maine, with red spruce .
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 . 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) .
Stand characteristics: In Alaska and western Canada, climax stands are
usually closed, except near treeline . 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
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 . 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 . 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 . 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 .
Key Plant Community Associations
Climax white spruce forests are widespread across Alaska and
northwestern Canada. They consist almost entirely of white spruce, but
may have scattered black spruce, paper birch (Betula papyrifera), aspen
(Populus tremuloides), and balsam poplar (P. balsamifera) present .
Climax stands are often broken up by extensive seral communities
resulting from forest fires.
In eastern Canada and the northeastern United States, white spruce
occurs as a climax species in pure or mixed stands. Within the fog belt
of Quebec and Labrador, white spruce forms pure stands near the seaboard
. At climax, it often codominates or forms a significant part of
the vegetation in mixed stands with red spruce (Picea rubens), balsam
fir (Abies balsamea), and black spruce.
In the Black Hills, white spruce habitat types occur at high elevations
and in cool canyon bottoms .
Published classifications listing white spruce as an indicator species
or dominant part of the vegetation in habitat types (hts), community
types (cts), or ecosystem associations (eas) are presented below:
Area Classification Authority
AK general veg. cts Viereck & Dyrness 1980
nw AK general veg. cts Hanson 1953
interior AK postfire cts Foote 1983
SD, WY: Black Hills forest hts Hoffman & Alexander 1987
AB general veg. cts Moss 1955
w-c AB forest cts Corns 1983
general veg. eas Corns & Annas 1986
BC: Prince Rupert Forest
Cedar-Hemlock Zone general veg. eas Haeussler & others 1985
Prince Rupert Forest
Spruce Zone general veg. eas Pojar & others 1984
PQ: Gaspe Peninsula forest veg. cts Zoladeski 1988
ON forest eas Jones & others 1983
Habitat: Cover Types
This species is known to occur in association with the following cover types (as classified by the Society of American Foresters):
1 Jack pine
5 Balsam fir
12 Black spruce
15 Red pine
18 Paper birch
21 Eastern white pine
24 Hemlock - yellow birch
25 Sugar maple - beech - yellow birch
27 Sugar maple
30 Red spruce - yellow birch
31 Red spruce - sugar maple - beech
32 Red spruce
33 Red spruce - balsam fir
37 Northern white cedar
39 Black ash - American elm - red maple
107 White spruce
201 White spruce
202 White spruce - paper birch
203 Balsam poplar
204 Black spruce
206 Engelmann spruce - subalpine fir
218 Lodgepole pine
251 White spruce - aspen
252 Paper birch
253 Black spruce - white spruce
254 Black spruce - paper birch
Habitat: Plant Associations
This species is known to occur in association with the following plant community types (as classified by Küchler 1964):
K012 Douglas-fir forest
K093 Great Lakes spruce - fir forest
K095 Great Lakes pine forest
K096 Northeastern spruce -fir forest
K102 Beach - maple forest
K106 Northern hardwoods
K107 Northern hardwoods - fir forest
This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):
FRES10 White - red - jack pine
FRES11 Spruce - fir
FRES18 Maple - beech - birch
FRES19 Aspen - birch
FRES23 Fir - spruce
FRES28 Western hardwoods
Soils and Topography
Mature northern white spruce stands have well-developed moss layers that significantly affect the mineral soil. The layer is most highly developed in regions with adequate moisture conditions and is dominated by feather mosses (e.g., Hylocomium splendens, Pleurozium schreberi, Ptilium cristacastrensis, and Dicranum spp.) rather than Sphagnum species (92,159). In the far north, total depth of the live moss-organic mat frequently is from 25 to 46 cm (10 to 18 in) or more. Development is, in part, regulated by flooding and stand composition. Stands in which hardwoods are mixed with white spruce tend to have shallower, discontinuous moss layers. The layer is a strong competitor for nutrients and an effective insulator that reduces temperature in the rooting zone. The temperature reduction varies with latitude and climatic regime. In Alaska, Yukon, and the Northwest Territories, soil temperatures can reach the point at which permafrost is developed and maintained (53,158,161).
Podzolic soils predominate over the range of the species, but white spruce also grows on brunisolic, luvisolic, gleysolic, and regosolic soils. On sandy podzols, it is usually a minor species, although white spruce is common on sand flats and other coarse-textured soils in the Georgian Bay area. It grows on shallow mesic organic soils in Saskatchewan, and in central Yukon on organic soils with black spruce (85,134,149).
White spruce is able to grow on extremely diverse sites but to achieve the best development it is generally more demanding than associated conifers. The range of sites supporting the species becomes more limited northward with increasing climate severity (149).
In the Algoma District of Ontario, the species is a major component of the stands on calcareous podzol loams and clays and shows exceptionally good development on melanized loams and clays. In Saskatchewan, it does best on moderately well-drained clay loams (84); in Alberta Mixedwoods, the best development is on well-drained lacustrine soils (60). Further north in Canada and Alaska, particularly productive stands are found on moist alluvial soils along rivers (78,79,90,162) and on south-facing upland sites (41,158).
White spruce grows on both acid and alkaline soils and acidity (pH) values from 4.7 to 7.0 and perhaps higher are probably optimum (10,141,149,176). On the floodplains of the northern rivers, pH may vary from 5.0 to 8.2 (194). In the Northwest Territories, the species grows in the alpine fir forest on strongly acid soils with a surface pH of from 4.0 to 4.5, increasing with depth to pH 5.5 at 15 cm (6 in); but at somewhat lower elevations, the mixed coniferous forest soils have a pH of 4.0 at the surface with pH 8.0 at 38 cm (15 in) depth. Good growth of white spruce on alkaline soils has also been reported in Mixedwoods in the Prairie Provinces (141). In New York, one factor common to most white spruce locations is an abundant calcium supply. Of the wide range of sites and soils on which white spruce grows, soils in the orders Alfisols and Inceptisols are most common.
The species also tolerates a range of fertility levels. On the alluvial soils along northern rivers, nitrogen may vary from 0.2 to 0.01 percent and phosphorus from 10 to 2 p/m. On adjacent upland soils derived from loess parent material, nitrogen may vary from 0.1 to 0.4 percent and phosphorus from 10 to 3 p/m (194).
Good growth requires a dependable supply of well-aerated water, yet the species will tolerate a wide range of moisture conditions. It will not tolerate stagnant water that reduces the rooting volume. On the other hand, white spruce will grow on dry sites if they are fertile.
Soil fertility, soil moisture, and physical properties are interrelated. Moisture alone will not improve yields unless it is associated with increased fertility (149). Nor will increased moisture be beneficial if soil structure is less than optimum. In Riding Mountain, Manitoba, for example, lower yields on the moist sites have been attributed to the higher clay content and massive structure when wet and columnar structure in dry conditions (73).
Other soil factors that must be carefully considered include the depth to ground water, permeability (especially of surface layers), presence of hardpans or claypans, and the mineralogical composition of the parent material.
Minimum soil-fertility standards for white spruce are higher than for other conifers commonly planted in the Lake States (176) (table 1).
Table 1- Minimum soil fertility standards for planting Wisconsin native conifers (146)¹ Item Jack pine Red pine White pine White spruce Approx. site index² m 16 17 18 16 ft 53 57 60 52 Approx. optimum range of pH³ 5.0 to 7.0 5.2 to 6.5 4.7 to 7.3 4.7 to 6.5 Silt and clay, pct 7.0 9.0 15.0 35.0 Organic matter, pct 1.0 1.3 2.5 3.5 Exchange capacity, meq/100g 2.5 3.5 5.7 12.0 Total N, pct 0.04 0.05 0.10 0.12 Available P kg/ha 13.4 28.0 33.6 44.8 lb/acre 12 25 30 40 Available K kg/ha 56.0 78.5 112.1 145.7 lb/acre 50 70 100 130 Exchangeable Ca, meq/100g 0.50 0.80 1.50 3.00 Exchangeable Mg, meq/100g 0.15 0.20 0.50 0.70 ¹Minimum is an amount sufficient to produce 126 to 157 m³/ha (20 to 25 cords/acre) at 40 years. All nutrients are given in terms of elements, not oxides.
²Base age 50 years.
³Data for values above pH 6.5 are insufficient; the range is strongly influenced by climatic conditions. Fertility requirements for white spruce based on foliar analyses are in percent of dry matter: nitrogen 1.50 to 2.50; phosphorus 0.18 to 0.32; potassium 0.45 to 0.80; magnesium 0.10 to 0.20; and calcium 0.15 to 0.40. At the lower end of the range, plants will respond to fertilizer. These data are from sand-culture experiments and are definitely provisional (152); however, except for calcium, they are in line with values published for 3-year-old seedlings in the nursery (71).
Little specific information is available on the effects of fertilizer in natural stands or plantations of white spruce, but growth gains have been reported after treatments to overcome nutrient deficiencies (141). Response of established older stands and new plantations to fertilization can occur within a year of treatment (9,156). Observations in progeny test plots in northern Wisconsin suggest that a hand application of 10-10-10 fertilizer may shorten the period of planting shock. In a nursery in which prolonged use may have depleted exchangeable bases and probably micronutrients, an application of micronutrient and major nutrient fertilizers resulted in a greatly increased volume of root systems and their absorbing capacity, and in a decreased top-root ratio. But indiscriminate use of micronutrient fertilizers together with nitrogen fertilizers may reduce seedling quality, making plants succulent, with a high top-root ratio (71).
White spruce stand development can significantly affect forest floor composition and biomass and mineral soil physical and chemical properties. The magnitude of these effects will vary with site conditions and disturbance history of the site. On sites in Alaska, organic layers accumulate to greater depths in mature spruce stands than in hardwood stands growing on similar sites. As a result, soil temperatures decrease and, in extreme cases, permafrost develops (161,163). Acidity of the mineral soil in spruce plantations established on abandoned farmland in Ontario decreased by 1.2 pH units over a 46-year period (10). Soil conditions under 40-year-old white spruce differed significantly in some respects from that under aspen, red pine, and jack pine growing on the same soil type; relative differences among species varied with specific nutrients (2).
In the north, the position of the tree line has been correlated to various factors, including the 10° C (50° F) isotherm for mean July temperature, cumulative summer degree days, position of the Arctic front in July, mean net radiation (especially during the growing season), and low light intensities (see review 39). None of the variables strictly define the northern limit of spruce, and in northern Alaska the presence of mountainous topography makes it difficult to determine controlling factors (26). Other biotic and abiotic variables affecting the northern and altitudinal distribution include lack of soil, low fertility, low soil temperature, fire, insects, disease, human impact, soil stability, and others (39,158,159).
The southern limit of the belt in which white spruce forms more than 60 percent of the total stand roughly follows the 18° C (64° F) July isotherm. The association is particularly close northeast of Lake Superior; in the Prairie Provinces, the species' limit swings north of the isotherm.
At the northern limit of the species' range, climatic extremes are significant. For example, -54° C (-65° F) in January and 34° C (94° F) in July were recorded extremes in one study area (102,158). Mean daily temperatures of -29° C (-20° F) for January are recorded throughout the species' range in Alaska, Yukon, and Northwest Territories, while mean daily July temperatures range from about 21° C (70° F) in the extreme southeastern area of distribution to 13° C (55° F) throughout much of Alaska and Canada. Maximum temperatures as high as 43° C (110° F) have been recorded within the range in Manitoba. Mean annual precipitation ranges from 1270 mm (50 in) in Nova Scotia and Newfoundland to 250 mm (10 in) through the Northwest Territories, Yukon, and parts of Alaska. Conditions are most severe, however, along the southern edge of distribution through Alberta, Saskatchewan, and Manitoba, where a mean annual precipitation of from 380 to 510 mm (15 to 20 in) coincides with mean July daily temperature maxima of 24° C (75° F) or more.
The growing season ranges from about 180 days in parts of Maine to about 20 days in parts of Canada. Generally, however, white spruce grows in regions where the growing season exceeds 60 days (108).
Photoperiod varies continuously over the range of the species from approximately 17 hours at summer solstice along the southern edge of the species' distribution to 24 hours north of the Arctic Circle in Alaska and parts of northern Canada.
Habitat & Distribution
Adaptation: In muskegs, bogs, and river banks, to montane slopes; at 0-1000 (-2100) meters elevation. White spruce is a dominant tree of interior forests in Canada and Alaska and often an early colonizer in succession. White spruce co-occurs with black spruce (Picea mariana) over a wide range – the two species have evolved a complex competitive relationship (habitat partitioning) involving contrasts in water tolerance, vegetative reproduction, flowering times, and rate of early growth. Picea glauca grows best on well-drained mineral soils with deep or no permafrost, while P. mariana is more tolerant of sites with flooding, permafrost, and high soil acidity.
Planting: Cone crops have been reported for trees as young as 4 years, but seed production in quantity begins at age 30 or older for most natural stands. Good years of seed production may be 2-12 years apart.
Germination under established or mature stands commonly occurs on a variety of seedbeds – particularly on rotted logs and moss beds, but exposed mineral soil after windthrow and floods is the best seedbed. Large numbers of white spruce may become established immediately following disturbance. Seedling growth is greatest at full light intensity, but white spruce is capable of reproducing under mature stands of spruce and early succession tree species. Because seedling and juvenile growth of white spruce is slower than its early successional associates, it remains in the understory for 50 to 70 years.
Trees 100-250 years old are common on good sites; older trees (250 to 300 years) are frequently found in areas protected from fire and in relatively wet upland situations. As in other species, maximum age appears to occur on stress sites at latitudinal or elevational treeline. Trees 500-1000 years old are known from such sites.
aecium of Chrysomyxa pirolata parasitises cone scale of Picea glauca
In Great Britain and/or Ireland:
Foodplant / saprobe
superficial, clustered, hypophyllous pycnidium of Rhizosphaera coelomycetous anamorph of Rhizosphaera kalkhoffii is saprobic on dead needle of Picea glauca
Remarks: season: late winter to early spring
Other: major host/prey
Foodplant / saprobe
erumpent, shortly stalked apothecium of Tryblidiopsis pinastri is saprobic on dead, attached twig of Picea glauca
Remarks: season: 5-7
Associated Forest Cover
The type is minor and confined to abandoned fields in New England and the Maritime Provinces, and within the fog belt farther north in Quebec and Labrador. It is more widespread elsewhere in eastern Canada and as far north as the tree line in Ungava and along Hudson Bay.
In northern Quebec, the lichen (Cladonia) woodland, the feathermoss forest, and the shrub forest with bog birch (B. nana) and heath species are common white spruce communities.
White spruce is an associated species in the following Eastern Forest cover types:
Boreal Forest Region
1 Jack Pine
5 Balsam Fir
12 Black Spruce
18 Paper Birch
Northern Forest Region
15 Red Pine
21 Eastern White Pine
24 Hemlock-Yellow Birch
25 Sugar Maple-Beech-Yellow Birch
27 Sugar Maple
30 Red Spruce-Yellow Birch
32 Red Spruce
33 Red Spruce-Balsam Fir
37 Northern White-Cedar
39 Black Ash-American Elm-Red Maple
In three of these types, Aspen (Type 16), Paper Birch (Type 18), and Red Pine (Type 15), white spruce attains increasing importance in the stand composition as the succession progresses and more tolerant species take over.
Western Forest- White Spruce (Type 201) is the pure white spruce forest in the West. In Alaska and the Northwest Territories, the type is largely confined to stream bottoms, river floodplains and terraces, and warm, south-facing upland sites. Farther south in British Columbia and Alberta, it has broader distribution from as low as 760 m (2,500 ft) to 1520 m (5,000 ft).
Associated tree species in Alaska include paper birch, quaking aspen, black spruce, and balsam poplar (Populus balsamifera). In Western Canada, subalpine fir (Abies lasiocarpa), balsam fir, Douglas-fir (Pseudotsuga menziesii), jack pine (Pinus banksiana), and lodgepole pine (P. contorta) are important associates.
The type varies little and generally comprises closed stands. White spruce plant communities in interior Alaska include white spruce/feathermoss; white spruce/dwarf birch/feathermoss; white spruce/ avens (Dryas)/moss; and white spruce/alder (Alnus spp.)/blue-joint (Calamagrostis canadensis) (32,43, 61). Two communities are common in northwestern Canada and in Alaska: (1) white spruce/willow (Salix spp.)/buffaloberry (Shepherdia spp.)/northern goldenrod (Solidago multiradiata)/crowberry (Empetrum spp.) and (2) white spruce/willow/buffaloberry/huckleberry (Gaylussacia spp.)/dewberry (Rubus spp.)/peavine (Lathyrus spp.).
In White Spruce-Aspen (Type 251), either species may be dominant, but each species must make up at least 20 percent of the total basal area. Paper birch and black spruce may also be represented in Alaskan stands along with balsam fir and lodgepole pine in Canadian stands. The type is common throughout western Canada at lower elevations and in all of interior Alaska. Associated shrubs in Alaska are American green alder (Alnus crispa), willows, common bearberry (Arctostaphylos uva-ursi), soapberry, highbush cranberry (Viburnum edule), and mountain cranberry (Vaccinium vitis-idaea). Associated shrubs in the Prairie Provinces are common snowberry (Symphoricarpos albus), red-osier dogwood (Cornus stolonifera), western serviceberry (Amelanchier alnifolia), and western chokecherry (Prunus virginiana var. demissa).
White Spruce-Paper Birch (Type 202) is defined similarly to White Spruce-Aspen in that either spruce or birch may be dominant as long as each species makes up at least 20 percent of the basal area. Aspen, lodgepole pine, subalpine fir, and black spruce are associated species. The type is common in Western Canada and in Alaska from the Arctic Circle to the Kenai Peninsula. Undergrowth species include willow, American green alder, highbush cranberry, prickly rose (Rosa acicularis), mountain cranberry, bunchberry (Cornus canadensis), and Labrador-tea (Ledum groenlandicum).
Whereas White Spruce-Aspen and White Spruce-Paper Birch are successional stages leading to the pure White Spruce type, Black Spruce-White Spruce (Type 253) may be a climax near the altitudinal and northern treeline. But black spruce may be replacing white spruce on some intermediate sites on older river terraces (160). Black Spruce-White Spruce is the lichen-woodland type from Hudson Bay to northwestern Alaska along the treeline as well as in open stands at alpine treeline sites in interior Alaska and northwestern Canada. It is also found on sites intermediate to the two species, such as older terraces above the floodplain. Paper birch, tamarack (Larix laricina), balsam poplar, aspen, and balsam fir may be found within the stands. In open stands near the treeline, resin birch (Betula glandulosa), alder, and willows may form a continuous shrub cover that on drier sites may be replaced by mats of feathermosses and Cladonia lichens. Labrador-tea, bog blueberry (Vaccinium uliginosum), mountain cranberry, and black crowberry (Empetrum nigrum) are other common shrubs within the type.
In addition to these three tree cover types in which white spruce is a major component, the species is an associate in the following Western Forest cover types:
203 Balsam Poplar
204 Black Spruce
206 Engelmann Spruce-Subalpine Fir
218 Lodgepole Pine
237 Interior Ponderosa Pine
252 Paper Birch
254 Black Spruce-Paper Birch
Several of these types are intermediate in the succession. Paper Birch may advance through White Spruce-Paper Birch to pure White Spruce. Balsam Poplar (Type 203) is eventually overtopped and replaced by white spruce; on some sites the process is very slow. Aspen often precedes the more tolerant spruce and fir forests, and lodgepole pine may be replaced by white spruce in northern latitudes.
In the Canadian boreal spruce-fir forest, American green alder is the most widespread tall shrub, with littletree willow (Salix arbusculoides), gray willow (S. glauca), and Bebb willow (S. bebbiana) important in the western range. Mountain maple (Acer spicatum), showy mountain-ash (Sorbus decora), and American mountain-ash (S. americana) are important in the East. Highbush cranberry, red currant (Ribes triste), prickly rose, and raspberry (Rubus idaeus) are the most common medium to low shrubs. The most wide-ranging members of the herb-dwarf shrub stratum are fireweed (Epilobium angustifolium), one-sided wintergreen (Pyrola secunda), one-flowered wintergreen (Moneses uniflora), northern twinflower (Linnaea borealis), naked bishops-cap (Mitella nuda), bunchberry, dwarf rattlesnake-plantain (Goodyera repens), stiff clubmoss (Lycopodium annotinum), and horsetail (Equisetum spp.) (91).
An average of 24 bryophytes (17 mosses and 7 liverworts) occur in Canadian white spruce-fir stands (92). The most common mosses are Pleurozium schreberi, Hylocomium splendens, Ptilium cristacastrensis, Dicranum fuscescens, and Drepanocladus uncinatus. The most common liverworts are Ptilidium pulcherrimum, R. ciliare, Lophozia spp., and Blepharostoma trichophyllum. Some common lichens are Peltigera apthosa, P. canina, Cladonia rangiferina, C. sylvatica, C. alpestris, C. gracilis, and Cetraria islandica.
Diseases and Parasites
Fire frequency, intensity, and severity, and not simply the presence of fire, determine white spruce distribution and growth. Fire frequency may range from 10 years or less to more than 200 years; most commonly, it is from 60 to 200 years. If fires occur at short intervals (less than 40 or 50 years), the source of white spruce seed can be eliminated. The reduction in depth of organic matter depends generally on fire severity and is a critical factor because the organic substrate that remains following fire makes a poor seedbed. In general, even severe fires do not expose mineral soil on more than 40 or 50 percent of a burn, and this area is usually distributed in small patches.
On floodplains in the northwestern part of the range, floods and silt deposits provide a seedbed for germination and seedling establishment. Flooding is detrimental to young seedlings, however, and establishment of spruce stands may be prevented until the flooding frequency declines. Fifty years may be required after initial sandbar formation before sedimentation rate declines enough for white spruce to colonize (104). As much as 20 percent of the seedlings may be killed on moist and wet sites that have been scarified by tractor and bulldozer blade (94).
Slow initial root growth makes young seedlings and transplants particularly susceptible to frost heaving. The severity of damage generally is greatest on fine-textured and wet soils where water is adequate for ice crystal formation in the surface soil. Late fall and winter seeding and spring field planting are best in most cases (141). White spruce roots respond vigorously to pruning (146); spring planting with root pruning is likely to be of some protective value against frost heaving.
Depending on soil texture and drainage, white spruce may be prone to windthrow. Windthrow is common along stand edges and in heavily thinned stands on shallow or poorly drained soils where root systems are surficial. On soils where a strong taproot, strong descending secondary roots, or multi-layered root systems develop, the species is much more windfirm. In mixed stands in which white spruce is overtopped by hardwoods, the leader and upper stem of spruce are frequently damaged by hardwood branches whipping in the wind.
Snow and ice can break up to 70 percent of white spruce in stands and hail can cause defoliation, stem lesions, and leader or terminal bud mortality (31,52,156).
White spruce vegetative and reproductive growth are particularly susceptible to frost damage at the time of flushing (116,181). The risk of frost damage is less for late flushing genotypes (110,116). Damage by fall frost is uncommon but has been observed in 1-year-old seedlings, when plantations heavily damaged by spring frost have responded with regrowth in August. Damage from spring frost is less serious after trees reach from 4 to 6 m (13 to 19 ft) in height. Because the species is so susceptible to frost damage, sites exposed to late spring frost should be avoided in all white spruce regeneration efforts.
Young seedlings are damaged by rodents. The snowshoe hare can be a significant pest, but white spruce is not a preferred animal food (4,12).
Environmental factors such as frost, mammals, birds, insects, and disease reduce the number of cones and the number of dispersed seeds (101,181). The impact of squirrels can be substantial. In Alaska, they may harvest as much as 90 percent of the cone crop (144,193). Small mammals such as deer mice, red-backed and meadow voles, chipmunks, and shrews can be an important cause of failure of natural regeneration and artificial regeneration by direct seeding. Seed consumption by individual animals can be very high-2,000 white spruce seeds per day for caged animals of the species mentioned- and the population density substantial but highly variable. Estimates range from 7 animals per hectare (3/acre) to as high as 44/ha (18/acre). Even at the low density, the impact on regeneration would be unacceptably high (126,141). The impact on seed varies with the time of seeding: 50 percent for spring-sown seeds as compared to 19 percent or less for winter-sown seeds. Coating seeds with repellent is effective and has little influence on seed germination even when coated seeds have been stored for 5.5 years (125,127).
The impact of birds feeding on seeds is small compared to that of rodents (126), but chickadees, grosbeaks, crossbills, juncos, and sparrows feed on coniferous seeds.
Seed losses from insects can be a serious problem. The spruce cone maggot (Hylemya (Lasiomma) anthracina), the fir coneworm (Dioryctria abietivorella), and the spruce seed moth (Laspeyresia youngana) are most important. Hylemya leaves the cone in midsummer and, as a result, Laspeyresia is blamed for the damage it does; however, where the infestation is severe, Hylemya may destroy 100 percent of the seed (59). Damage by D. abietivorella is particularly severe in years of heavy cone crops and appears to be found when cones develop in clusters. The following insects also attack seeds and cones but do less damage: the spruce cone axis midge (Dasineura rachiphaga), the spruce seed midge (Mayetiola carpophaga), the seed chalcids (Megastigmus atedius and M. picea), the cone cochylid (Henricus fuscodorsana), and the cone moth (Barbara mappana) (59). The only disease associated with cone production is the cone rust Chrysomyxa pirolata (151). Seeds produced from infected cones are about half the weight but the same size as healthy seeds. Seeds are fragile because seed coats are poorly developed, and seed mortality is almost 100 percent in severely affected cones (101,151). Even if viable seeds are produced, they are not readily dispersed because cone malformation and resinosis prevent efficient opening of the cone scales (151).
White spruce seedlings are affected by disease during the dormant and growing seasons. Snow blight (Phacidium infestans) causes damage in nurseries and the field. Various species of Pythium, Rhizoctonia, Phytophthora, and Fusarium have been shown to be moderately to highly pathogenic to spruce seedlings in both pre- and post-emergent conditions (65). Pythium and Fusarium as well as Epicoccum and Phoma can also injure seedlings in cold storage; many of these damaged seedlings die when they are field planted (67). Nematodes have been shown to cause winterkill and reduce seedling vigor.
Needle and bud rusts are common throughout the range of white spruce. The most important rust causing premature defoliation in Canada is Chrysomyxa ledicola. Losses of up to 90 percent of the current year's needles have been observed in Western Canada. Other needle rusts that infect white spruce are C. weiri, C. empetri, C. ledi, and C. chiogenis. The witches' broom rust (C. arctostaphyli) frequently causes dead branches, abnormally proliferating branches, deformed boles, and reduced growth. A bud rust (C. woroninii) is more prevalent in far northern areas and infects seedlings and vegetative and female buds of mature trees (65,101,195).
Stem diseases of white spruce are not of major importance. A canker caused by Valsa kunzei has been reported. One of the most conspicuous and common stem and branch deformities is a tumor-like growth of unknown origin. These tumors occur throughout the range and may reach 0.6 to 0.9 m (2 to 3 ft) in diameter. In a small test of grafts of tumored and tumor-free trees, tumor growth was transmitted to some, but not all, ramets in some clones of tumored trees (44).
Root diseases of white spruce affect both seedlings and mature trees. Inonotus tomentosus is a major cause of slow decline and death of white spruce in patches of 0.4 ha (1 acre) or more in Saskatchewan. The disease has been called the "stand-opening disease." It develops slowly over a period of 20 to 30 years but the impact can be substantial- 87 percent of white spruce in mixed stands either dead or heavily rotted at the butt. Stand openings occur on soils of all textures but rarely on alkaline soils (174). Trees planted in infected areas are also damaged (175). Other root-rot fungi associated with white spruce are Coniophora puteana, Scytinostroma galactinium, Pholiota alnicola, Polyporus guttulatus, P. sulphureus, and Phaeolus schweinitzii.
Trunk rots affecting white spruce include Haematostereum sanguinolentum, Peniophora septentrionalis, and Phellinus pini. These species produce rot development beyond the tree base. Coniophora puteana, Fomitopsis pinicola, and Scytinostroma galactinium are associated only with butt rot. In general, cull percentage in white spruce caused by rot is low, particularly for trees less than 100 to 120 years old. Most trees older than 200 years have significant amounts of rot, however.
Although most spruce species are seriously injured by the European strain of scleroderris canker (Gremmeniella abietina), white spruce suffers only from tip dieback and eventually recovers (137). Dwarf mistletoe (Arceuthobium pusillum) is usually associated with black spruce, but it has killed white spruce in Minnesota (3), along the coast of Maine, and in the Maritime Provinces.
White spruce is attacked by a number of bark beetles in the genera Dendroctonus, Ips, Trypodendron, Dryocoetes, Scolytus, Polygraphus, and others. Although most of these species attack trees of low vigor, dying trees, windthrows, and slash, the spruce beetle (Dendroctonus rufipennis) attacks trees of normal vigor and has killed large areas of white and other spruces. In areas with transition maritime climates, such as western and south-central Alaska, prolonged extreme cold (-40° C or -40° F) kills large numbers of beetles. Where spruce beetle outbreaks are common, resistance of trees is greater in mature stands with stocking levels of 18m²/ha (80 ft²/acre) or less because of wide tree spacing and rapid growth (58). Dense stocking contributes to cold soils in the spring and thus tree moisture stress, which predisposes the trees to beetle attack (57). Bark beetles bore or mine in the phloem. or inner bark and girdle the tree. Symptoms of beetle attack are pitch flow tubes and fine wood particles on the bark or at the base of the tree. The foliage of the attacked tree changes color and dies, but this may not occur until after the beetle has left the tree. The best method of preventing beetle outbreaks is to remove or destroy desirable habitat such as slash and damaged trees; trees weakened by budworms are particularly susceptible.
Wood-boring insects (Monochamus spp., Tetropium spp., and Melanophila spp.) attack weakened or dead white spruce and are particularly attracted to burned areas. They can attack trees almost before the fire cools. The intensity of attack is determined by the condition of the individual tree (173). Lumber recovery from heavily infested trees declines rapidly because of extensive tunneling.
The spruce budworm. (Choristoneura fumiferana) and the western spruce budworm (C. occidentalis) feed and mine in old foliage, in developing reproductive and vegetative buds, and in new foliage of the expanding shoot. True firs are the principal hosts, but spruces are readily attacked and injured. Budworms are the most destructive conifer defoliators; severe defoliation for 2 years reduces growth, and sustained outbreaks have killed all spruce in some stands (48,81). Plantations are not usually subject to serious damage until they are about 6 m (20 ft) tall (141).
The yellowheaded spruce sawfly (Pikonema alaskensis), another defoliator, is not important in closed stands but can seriously reduce growth or kill plantation-grown trees if defoliation continues for 2 or more years (141). A number of other sawflies including the European spruce sawfly (Diprion hercyniae), also damage the species.
Spruce spider mites (Oligonychus spp.) build up in damaging numbers in early spring and summer and sometimes in fall. They are also common on young white spruce plants growing in greenhouses. Their feeding destroys the chlorophyll-bearing cells of the needle surface, causing a bleached look. Continuous attacks weaken and eventually kill the tree (81).
The European spruce needleminer (Epinotia nanana) causes unsightly webbing and kills needles on spruces in the Eastern United States. Heavy attacks cause severe defoliation, and weakened trees succumb to secondary pests. Other needleminers of less importance are in the genera Taniva and Pulicalvaria (122). Other insects damaging spruce needles include needle worms, loopers, tussock moths, the spruce harlequin, and the spruce bud scale.
The gall-forming adelgids (Adelges spp.), of which the eastern spruce gall adelgid (A. abietus) is the most prevalent, cause cone-shaped galls on the shoots. Other gall-forming insects belong to the Pineus and Mayetiola genera (122). Although not important for forest trees, these galls can deform and stunt the growth of seedlings, saplings, and ornamental trees (48,81).
Spruce buds are damaged by bud moths, Zeiraphera spp., the bud midge (Rhabdophaga swainei), and bud and twig miners (Argyresthia spp.). None of these insects causes serious damage (122), but killing of the terminal leader by Rhabdophaga results in multiple leaders and thus poor tree form.
White spruce is considered lightly susceptible to damage by the white pine weevil (Pissodes strobi) and certainly is much less damaged than either black or Norway spruce (Picea abies). However, an ecotype of the insect, sometimes called the Engelmann spruce weevil, is an important pest in plantations in interior British Columbia and on natural regeneration in British Columbia and Alberta (141).
Warren's collar weevil (Hylobius warreni) does cause appreciable damage on spruce. Small trees may be girdled and killed; on older trees, the wounds are entries for root rots such as Inonotus tomentosus (122). In controlled experiments, 4-year-old white spruce has shown high radio-sensitivity when exposed to chronic gamma irradiation. The trees were most sensitive in mid-July when the central mother-cell zone was enlarging.
Fire Management Considerations
Broadcast burning can be used for fuel reduction and site preparation
following logging of white spruce . Survival and early growth of
planted white spruce is enhanced by burning. Four years after
outplanting of container-grown stock in northeastern British Columbia,
leader length was 36 percent longer on burned versus unburned sites;
however, foliar nutrient content was much lower. Improvements in growth
on burned sites have been observed for 15 years .
Frequent fires can eliminate white spruce from an area because it does
not produce seed in quantity until it is 30 years old or older.
Broad-scale Impacts of Plant Response to Fire
White spruce seedling establishment is rapid following fall wildfires
that expose mineral soil but do not burn into the tree crowns. These
hot surface fires usually kill the trees, but the mature seeds are not
harmed and soon begin dispersing onto the mineral soil. One year
following a late-August wildfire of this type in interior Alaska, white
spruce frequency was 100 percent, and seedling density was 12,150 per
acre (30,000/ha) . White spruce is less likely to regenerate
following high-severity, low-intensity surface fires in the spring or
summer, because seeds will not develop on the fire-killed trees.
However, if not all trees are killed, some seed will develop over the
summer. This occurred on portions of a late May-early June burn in
interior Alaska. One year following this fire, white spruce seedlings
were numerous on portions of the burn where underburning consumed most
of the forest floor, but crowning did not occur. Although the trees
were severely injured, seeds matured within the cones, so that by fall
1,100 viable seeds were dispersed per square meter. Seedling frequency
was 100 percent, and density 290 per square meter one growing season
after the fire .
In British Columbia and Alberta, in areas where white spruce or white
spruce x Engelmann spruce hybrids are abundant and lodgepole pine
scarce, spruce will establish quickly following fire if sufficient
numbers of seed trees survive or are near the burn. If lodgepole pine
is present before burning, it usually seeds in aggressively and assumes
a dominant role, quickly overtopping any spruce seedlings [16,35].
However, because of its shade tolerance, white spruce can establish
under a developing pine canopy. Day  sampled lodgepole pine-white
spruce x Engelmann spruce hybrid stands in southern Alberta that
initiated from fires that occurred 29 and 56 years before sampling. He
found that both pine and spruce initiated large numbers of seedlings
immediately after the fire. Pine, however, established greater numbers
of seedlings, which rapidly outgrew the spruce and formed a canopy that
was 3 to 4 times the height of the spruce. Pine seedling establishment
ceased about 30 years after fire, but the shade-tolerant spruce
continued to establish. Given a sufficient disturbance-free interval,
white spruce will eventually dominate sites where spruce and pine seed
in together following fire.
The Research Project Summary of Van Wagner's  study provides information
on prescribed fire use and postfire response of plant community species,
including white spruce, that was not available when this species review
was originally written.
Plant Response to Fire
surviving trees in protected pockets or from trees in adjacent unburned
areas. Within a few years after a fire, white spruce reproduction is
often localized and centered around areas of surviving trees.
Establishment is quite variable, depending on the proximity of surviving
cone-producing trees, seed production during the year of the fire and
immediate postfire years, and amount of mineral soil exposed by the
fire. Under most circumstances, it can rapidly invade burned sites only
when (1) fire consumes the organic mat and exposes mineral soil and (2)
surviving trees provide a seed source. When these conditions are met,
white spruce begins to establish seedlings 1 or 2 years after fire.
Broad-scale Impacts of Fire
Viereck and Schandelmeier  reported that most fires in spruce stands
in interior Alaska are either crown fires or ground fires intense enough
to kill overstory trees. The needles of white spruce trees often remain
green following ground fires, but the boles are usually scorched to the
extent that most trees die . In interior Alaska, 100 percent of 40-
to 140-year-old white spruce were killed by a high-severity,
low-intensity surface burn that consumed the entire organic mat,
estimated to be 1 to 5 inches (3-13 cm) thick .
Following a late May-early June wildfire in Interior Alaska, Zasada
 observed that fire effects on white spruce varied considerably
depending upon fire intensity and severity. This fire occurred when
white spruce flowering was complete, but fertilization was not. Fire
effects varied as follows:
Crowns destroyed - within the zone of the highest fire intensity, crowns
were completely destroyed by fire.
Crowns scorched - near the intense zone tree crowns were scorched by the
heat of the fire. All these trees were killed. Small cones did not
develop any further.
Boles scorched or girdled - where underburning consumed most of the
forest floor, tree crowns were hardly affected, but trees received so
much damage to the bole that most died by the end of the first or second
summer after the fire. Although these trees were severely injured, the
cones and seeds continued to develop. When seed matured, viability was
about equal to seed from adjacent unburned stands.
Immediate Effect of Fire
White spruce is easily killed by fire. Its thin bark provides little
insulation for the cambium, and the shallow roots are susceptible to
soil heating. Surface fires can burn deep into litter and duff,
charring or sometimes consuming roots up to 8 to 9 inches (20-23 cm) in
diameter . Surface fires often spread to white spruce crowns
because the highly flammable fine fuels concentrated under the trees
often produce flames that reach the low-growing, flammable,
lichen-draped branches [1,37].
White spruce seeds on the ground are usually killed by fire because they
have little or no endosperm to protect the embryo from high temperatures
. Cones are not necessarily destroyed by summer fires, but immature
seeds will not ripen on fire-killed trees.
Plant adaptations to fire: White spruce relies on wind-dispersed seeds
which readily germinate on fire-prepared seedbeds to colonize burned
sites. However, it is not adapted to colonize large burns because (1)
most fires in boreal regions occur in the summer before white spruce
seeds are mature, and thus little or no seed is available for fall
dispersal, and (2) seeds in cones on surviving trees are dispersed over
relatively short distances [55,65]. Since fire-killed trees generally
do not contribute to seedfall, seed for colonizing burns must come from
nearby surviving trees. Survivors include the occasional mature tree
which survives fire damage, trees escaping fire in small, unburned
pockets, and trees adjacent to burned areas . Occasionally trees
that are severely injured by a summer fire will continue to develop and
disperse viable seed in the fall, even though the trees will die within
1 to 2 years . Because seeds in trees are mature and ready for
dispersal by fall, white spruce can quickly invade areas after fall
burns, especially during good seed crop years .
Many researchers report that white spruce is not well adapted to
regenerate following fire because it has nonserotinous cones
[1,2,41,65]. Nearly all seed is dispersed in the fall or winter, but
cones remain on trees for 1 to 2 years after this peak dispersal period
. However, in northern Saskatchewan, Archibold [3,4] found that
some seed remains in cones for up to 2 years and is an important factor
in postfire seedling establishment. In these studies, an April wildfire
burned through a mixed spruce-hardwood stand containing 1,080 white
spruce trees per acre (2,667/ha) averaging 40 years old. During the
first postfire year, fire-killed white spruce trees released 540,000
seeds per acre (1,338,000/ha). During the 2nd postfire year, these dead
trees released 50,000 seeds per acre (123,500/ha), of which 70 percent
germinated in the laboratory.
Fire regime: Across its range, few white spruce stands are older than
200 years. The oldest are floodplain white spruce stands, some of which
are older than 300 years . Fire frequency in white spruce forest
types is generally between 60 and 200 years . In Alaska, Foote 
observed that fire in white spruce forest types was less common than in
black spruce types. She found numerous white spruce stands older than
100 years, but most black spruce stands sampled were less than 100 years
White spruce stands typically have well-developed organic soil layers.
The depth to which this organic mat is consumed varies depending on the
type of fire. Sometimes the organic mat is consumed, and mineral soil
More info for the terms: climax, cover, fire severity, hardwood, litter, severity, shrubs, tree
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 . 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 
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
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
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 . 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 . 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 .
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 .
In Glacier National Park, white spruce x Engelmann spruce hybrids have
invaded ponderosa pine (Pinus ponderosa) savannas as a result of fire
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 . Good to excellent seed crops occur every 2
to 6 years on good sites , 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 . Seeds
are about 0.12 inch (3 mm) long, with a 0.25- to 0.33-inch-long (6-9 mm)
wing . There are approximately 226,000 seeds per pound .
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 . Their impact on cone and seed production
is greatest during poor or medium cone crop years . 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
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 . Red
squirrels disperse seeds also. White spruce reproduction is common at
squirrel middens .
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 . In Alaska seeds do not
begin germinating until temperatures become favorable, usually in
mid-May . 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 .
Germinative capacity is 50 to
70 percent .
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)
. 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 . 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 .
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 . Layering may also occur further
south when the lower branches touch the ground and become covered with
moss, litter, or soil.
Growth Form (according to Raunkiær Life-form classification)
More info for the terms: phanerophyte, therophyte
Undisturbed State: Phanerophyte (mesophanerophyte)
Burned or Clipped State: Therophyte
Reaction to Competition
Large numbers of white spruce may become established immediately following disturbance and form even-aged stands. Because seedling and juvenile growth of white spruce is slower than its early successional associates, it remains in the understory for 50 to 70 years (25,104,160,169). Although white spruce survives this period of suppression, growth will be significantly reduced (139). White spruce shows a significant response to release resulting from natural causes or silvicultural treatment; ages of trees exhibiting good growth after release range from very young to 200 or more years (6,22,45, 139,185).
White spruce also forms multi-aged pure stands or is a component of multi-aged, late-succession stands mixed with the true firs, maple, beech, and other species. In such stands, age ranges from 200 to 250 years in Alberta (25) and from 300 to 350 years in British Columbia (104) and at treeline in northern Alaska (26). Natural stands occurring within relatively small areas can show markedly different age structures depending on age of the site, stand history, soil conditions, and other variables (83). The distribution of ages is not continuous but consists of several groups of ages separated by periods when no white spruce become established.
Depth of rooting in white spruce is commonly between 90 and 120 cm (36 and 48 in), but taproots and sinker roots can descend to a depth of 3 m (10 ft). Eighty-five percent of the root mass was in the top 0.3 m (1 ft) on sites in Ontario, but on the most northern sites, large roots are heavily concentrated within 15 cm (6 in) of the organic-mineral soil interface. Lateral spread of the root system was reported to be as much as 18.5 m (61 ft) on sandy soils in Ontario, and lateral root extension was estimated at 0.3 m (1 ft) per year (141,145,148).
Fine-root production in a Maine plantation was 6990 kg/ha (6,237 lb/acre); 87 percent of this material was located in the top 15 cm (6 in) of soil (136). In an Ontario plantation, fine roots 0.25 cm (0.10 in) in diameter and smaller comprised about 10 percent (2670 kg/ha or 2,382 lb/acre) of the total root biomass (143). Sixty-seven percent of the fine-root production in a mixed spruce-fir stand in British Columbia was in the forest floor and A horizon; the average depth of these horizons was 8.3 cm (3.3 in) (86). Mycorrhizae are an important component of the fine roots (143) of most conifer species (89), but only a few of the fungi that form mycorrhizae have been found on white spruce.
Root grafting appears to be fairly common in white spruce. In one study, about 27 percent of the trees had root grafts with other trees (140,149).
Life History and Behavior
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 . Nienstadt and
Teich  reported that most seeds are shed within about 5 weeks after
cones open; however,, Zasada and others  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.
In the far north, the density of trees originating from layering may reach 1830/ha (740/acre) and generally is inversely related to site quality. Layering is most common in stands in which trees are open grown and the lower branches touch the ground. The branch roots when it is covered by moss, litter, or soil and organic material. The time required for an individual to become independent of the ortet (parent) is not known, but 30- to 50-year-old ramets are no longer connected with the ortet (26).
Air layering on a 6-year-old tree has been successful; early May is the best time for preparing the air layers. Juvenile white spruce can be readily propagated by rooted cuttings (54,55). Rooting ability varies greatly from tree to tree, but it is too low for practical use by the time most trees are 10 to 15 years old. Older trees can be grafted. Results are best in the winter (February, March) in the greenhouse, with forced rootstock in pots and dormant scions, but fall grafting is possible. Late winter-early spring grafting in the field also is possible but should be done before bud swelling becomes pronounced (107).
Prechilling or stratification at 2° to 4° C (36° to 39° F) is recommended for testing seed lots and for improving germination capacity, energy, and survival in the nursery of spring-sown seed. Stratification is not always a prerequisite for complete germination, however (27,47,171,172,193). Germination is epigeal (155).
The period of germination under field conditions is mid-May through early August. With adequate water, seeds germinate as soon as soil surface temperatures are warm enough. Generally, germination (natural seedfall or artificial seeding in fall) is 75 to 100 percent complete by early July. Some white spruce seeds are able to withstand several wetting and drying cycles without losing their viability (63,70,168,189). Germination of spring-sown seeds begins somewhat later than in fall-sown seeds but is complete in 3 to 4 weeks (24,34). Adverse conditions offset germination and may delay it to the following year. Germinants developing after the middle of July have a lower survival probability than those originating in early summer (18,49,62,67,193).
White spruce is capable of reproducing under mature stands of spruce and early succession tree species; however, the response is highly variable and density and percent stocking are low (89,170). In Saskatchewan, for example, advanced regeneration was not present in 88 percent of the stands studied, and one-half of the remaining stands had less than 1,240 seedlings per hectare (500/acre) (84). On upland sites in interior Alaska, advanced regeneration ranged from 1 to 25 percent stocking and density from 120 to 640 stems per hectare (50 to 260/acre) (70).
Regeneration under established stands, whether spruce or other species, occurs on a variety of seedbeds and commonly on rotted logs (25,164,168). Feathermosses (e.g., Hylocomium spp., Pleurozium spp.) and associated organic layers are the most common seedbed surfaces in mature stands (92). Where the L- and F-layers are greater than from 5 to 8 cm (2 to 3 in), they greatly restrict regeneration. This is particularly true in drier western regions. Although this limitation is most often attributed to low water retention, it may be chemical inhibition (allelopathy) caused by some forest floor components, particularly lichens (42). In mature stands, exposed mineral soil after windthrow and floods are the best seedbeds (29,70,165). They can have stocking levels approaching 100 percent.
The average number of seeds required to produce a seedling on recently exposed mineral soil ranges from 5 to 30 (30,36,50,69,193). The seed requirement increases with each year after exposure of the soil because of increasing plant competition and litter accumulation (95). Receptivity of organic seedbeds is generally believed to be extremely low; seed-per-seedling ratios of 500 to 1,000 seeds or more are commonly reported in harvested areas (36,70). These surfaces vary considerably, however, and their receptivity for germination and seedling establishment depend on the amount of solar radiation at the surface, type of organic substrate, degree of disturbance to the organic layers, weather conditions at the time of germination, amount of seed rain, and other biotic and abiotic factors. In undisturbed stands, seedlings are frequently found on organic matter, particularly rotted wood (32,170,187). Germination and seedling establishment, although not as efficient as on mineral soil in terms of seed-to-seedling ratios, are common on organic substrates after harvest in both clearcuts and shelterwoods (124,178).
A key for identifying the seedlings of North American spruce species is available (95).
Optimum conditions for seedling growth have been delineated for container production of planting stock in greenhouses. The most suitable temperature conditions are alternating day/night levels as opposed to a constant temperature regime. At 400 lumens/m² (37.2 lumens/ft², or footcandles) light intensity, a 25°/20° C (77°/68° F) day/night regime is recommended for white spruce (13,122,154). Temperature and light intensity effects interact: at low intensities, about 40 lumens/m² (3.7 lumens/ft²), a 28°/13° C (82°/55° F) day/night regime is favorable (11). A short photoperiod (14 hours or less) causes growth cessation, while a photoperiod extended with low light intensities to 16 hours or more brings about continuous (free) growth. Little is gained by using more than 16 hours low light intensity supplement once the seedlings are in the free growth mode. Long photoperiods using high light intensities of from 10,000 to 20,000 lumens/m² (930 to 1,860 lumens/ft²) increase dry matter production. Increasing the light period from 15 to 24 hours may double the dry matter growth (13,122).
Seedling growth can be closely controlled by manipulating the environment. Short photoperiods induce dormancy and permit the formation of needle primordia. Primordia formation requires from 8 to 10 weeks and must be followed by 6 weeks of chilling at 2° C (36° F) (100,109,123). Prompt bud breaking occurs if the seedlings then are exposed to 16-hour photoperiods at the 25°/20° C (77°/68° F) temperature regime. Freedom from environmental stress (for example, lack of moisture) is essential for maintaining free growth (99, 100). It must be kept in mind that free growth is a juvenile characteristic. According to Logan (99), it is lost when seedlings are 5 to 10 years old, but our observations suggest that it would be extremely rare in seedlings older than 5 years.
At the end of the first growing season, natural regeneration may be from 10 to 20 mm (0.4 to 0.8 in) tall. Root length is from 20 to 100 mm (0.8 to 4.0 in), depending on site and seedbed type. The stem is unbranched; the taproot normally develops lateral roots that may be from 30 to 50 mm (1 to 2 in) long (34,62,72,89,193).
Natural regeneration usually does not exceed from 30 to 50 cm (12 to 20 in) in average height after 4 to 6 years. The number of branches increases significantly during this period. Lateral root length may be as much as 100 cm (39 in), but rooting depth may not increase significantly. Shoot dry weight (including foliage) increases from 0.2 to 5 g (3.09 to 77.16 grains) and root dry weight from 0.06 to 1 g (0.92 to 15.43 grains) between ages 2 and 6 (37,70,72,89,165, 168,190). The length of time required to reach breast height under open conditions ranges from 10 to 20 years depending on site; under stand conditions, growth to this height may take 40 or more years (61).
Growth is greatest at full light intensity (9,98). Reducing light intensity to 50 percent of full light reduced height growth by 25 percent, shoot weight by 50 percent, and rooting depth by 40 percent in 10-year-old seedlings; at 15 percent of full light, no spruce survived (37). Control of competing herbaceous vegetation has resulted in 38 and 92 percent increases in growth 3 years after planting (150).
White spruce is sensitive to transplanting shock. Check-the prolonged period of minimal growth-is considered by some forest managers to be a problem serious enough to disqualify white spruce as a plantation species. The cause of check, though not fully understood, is thought to be nutrient stress resulting from the root's inability to develop in the planting zone. Check is difficult to predict and prevent (141,147), but seedling quality is a factor, and any treatment that will improve early root growth is undoubtedly beneficial (7,9).
Seed Production and Dissemination
A mixture of gibberellins, GA4/7, has been found to substantially increase female flowering in white spruce (15,121). Treatment of elongating shoots was effective, but application to dormant shoots was not (16). Fertilization with ammonium nitrate has also been successful in promoting flowering (68).
Both the initiation and pattern of seed dispersal depend on the weather. Cool, wet, or snowy weather delays the onset of dispersal and causes cones to close after dispersal has begun. Cones reopen during dry weather. A small number of seeds are usually dispersed in August, but most of the seeds fall in September (30,167,186,192,193). Early- and late-falling seeds have a lower viability than seeds falling during the peak period (167). Cones can remain on the tree from 1 to 2 years after the majority of seeds are dispersed. Cone opening and seed dispersal pattern can vary among trees in the same stand (186).
Average weight per seed varies from 1.1 to 3.2 mg (0.02 to 0.05 grains) (64,193), and there are approximately 500,000 seeds per kilogram (226,000/lb) (155). From 8,000 to 12,000 cones may be produced by individual trees in good years. This corresponds to approximately 35 liters (1 bushel) or about 250,000 seeds (64). Yields in the far north are less (184). Cone production in mature spruce stands occurs primarily in dominant and codominant trees with sporadic and low production in intermediate and suppressed trees (167).
The total number of seeds per cone varies significantly among trees and regions-from 32 to 130 have been reported (87,167,192). Seeds produced on the apical and basal scales are not viable; therefore, the number of viable seeds per cone is much lower-from 12 to 34 and from 22 to 61 full seeds per cone for open and control pollinations, respectively (87).
Seed dispersal as measured by seed trapping varies with seed year and from day to day. In Manitoba, the maximum annual total seedfall was 1400/m² (130/ft²) , and 59 percent were filled. The seed rain exceeded 290/m² (26.9/ft²) in 5 of the 10 years, and 40 to 71 percent of these were filled; for 3 years it was less than 10/m² (0.9/ft²), and of these 2 to 36 percent were filled (167). In Alaska, maximum total seed rain in one stand over a 13-year period was 4,000 seeds/m² (371.7/ft²). Seed rain exceeded 1,000 seeds/m² (92.9/ft²) in 3 years and was between 400 and 500 seeds/m² (37.1 and 46.4/ft²) in 2 other years. In the remaining years, seed rain was less than 100/m² (9.3/ft²) (184).
White spruce is primarily wind-dispersed, and the time in flight and distance of flight for individual seeds was variable and depended on conditions at the time of dispersal (191). The quantity of seed reaching a given area drops precipitously with distance from the seed source. At 50, 100, 200, and 300 m (162.5, 325.0, 650.0, 975.0 ft), seed rain may be as low as 7, 4, 0. 1, and 0. 1 percent of that in the stand. The actual percentage of seeds reaching various distances may vary among sites within a local area and among geographical areas (30,186).
White spruce seed collection is expensive, but cost can be reduced by robbing the cone-caches of red squirrels. The viability of seed from cached cones does not vary between the time squirrels begin to cache cones in quantity and the time the last cones are cached (164). Viability drops to near zero, however, after 1 to 2 years of storage in a cone cache.
White spruce rapidly regenerates the crown after topping, thereby restoring the seed-bearing capacity. In fact, topping may temporarily increase cone production (112). Therefore, it is possible to reduce seed collection costs more than three times by collecting from downed tops (138).
Flowering and Fruiting
Cone-crop potential can be predicted in several ways. An early indication of a potential crop can be abnormally hot, dry weather at the time of bud differentiation, particularly if the current and preceding cone crops have been poor. Estimates of cone crop potential can be made by counting female reproductive buds in fall or winter. Differentiating male and female buds from vegetative buds is difficult, but the external morphology of the buds, and their distribution within the crown, enables the practiced observer to make the distinction (35). Female buds are concentrated in the top whorls. On 17-year-old grafts, the most productive was the 4th whorl from the top, and the productive zone averaged 6.4 whorls (112). In light crop years, the, highest cone concentration is closer to the top than in intermediate or heavy crop years. Male buds generally are located in the middle to lower crown (38).
In the spring, renewed cell division and growth begin before the first evidence of bud elongation. In British Columbia, this is 6 weeks before pollination at low elevations and 8 weeks before pollination at high elevations (119). Meiosis takes place during this period about 3 weeks before maximum pollen shedding. Female receptivity coincides with pollen shedding and usually lasts from 3 to 5 days in May, June, or July depending on geographic location and climate. The southern areas definitely have earlier dispersal than northern areas; however, peak dispersal at latitude 48-50° and 65° N. can occur on the same calendar date (106,108,149,193). Pollination is delayed up to 5 weeks at higher elevations (119,193). The latest pollen dispersal occurs near elevational and latitudinal treeline.'
The time of pollen shedding and female receptivity is undoubtedly temperature dependent and may vary as much as 4 weeks from year to year (44). Pollen dispersal shows a marked diurnal pattern dependent on temperature, humidity, and wind (193).
The period of peak pollination and female receptivity is a critical stage in seed production and is easily disrupted by adverse weather such as rain and frost (102,106,181). Such events can seriously reduce a promising seed crop.
Before pollen dispersal, male flowers are red and succulent; water can be squeezed from the conelet in a substantial drop. Moisture content (percentage of dry weight) was 500 to 600 percent greater than dry weight before pollen dispersal began and dropped precipitously as the male flower dried and pollen was dispersed. Just before shedding, the males are approximately 10 to 12 mm (0.4 to 0.5 in) long. Then the color changes from red to yellow and the conelet is almost dry when squeezed. This is the ideal time for collecting pollen. After the pollen is shed, the structure turns brown and soon falls.
At maximum receptivity, females are erect, 20 to 25 mm (0.8 to 1.0 in) long, and vary in color from green to deep red. Within an individual tree, the color is uniform. When receptive, the scales are widely separated, but they close shortly after pollination and the cones begin to turn down and gradually dull in color. Turning down takes from 2 to 4 weeks and occurs when the cone is growing most rapidly.
Fertilization occurs from 3 to 4 weeks after pollination (103,119,128). Full size and maximum cone water content and fresh weight are attained in late June or early July. The final cone size may vary considerably from year to year (193); it is determined by the weather the previous season, weather during cone expansion, and heredity.
The primary period of embryo growth occurs after cones attain maximum size. Cotyledons appear in middle to late July and embryo development is completed in early to late August (103,119,128,188). Seed development can vary as much as 3 weeks from year to year (33), and cotyledon initiation may differ from 1 to 3 weeks between high and low sites. Embryos have matured on the same date at both high and low elevations (119); however, there can be large differences among elevations in time of seed maturation (188).
The maturation process evidently continues after embryos attain physical and anatomical maturity (33,177,183). Cone dry weight generally increases during this period. Weather is critical to the production of high quality seed. In high elevation and high latitude populations, immature seed with poorly developed embryos are produced during cold growing seasons (183,193). In general, seed quality is highest in years of heavy seed production and lowest in years of low seed production. Cones ripen in August or September from 2 to 3 months after pollen shedding (21,167,177,183).
Cone opening coincides with moisture contents of from 45 to 70 percent and specific gravities of from 0.6 to 0.8 (21,177,193). Cone firmness, seed coat color, seed brittleness, and various flotation tests are indicators of cone and seed maturity (141). Cone color can also be used; but because female cone color can be red, pink, or green (153), no standardized cone color changes are associated with maturity. Most authorities agree on the importance of observing cones closely during the last stages of maturity so that the optimum collection period is not missed.
White spruce seeds can be collected from 2 to 4 weeks before they ripen and seed quality improved by storing under cool (4° to 10° C (40° to 50° F)), ventilated conditions. Collection date and method of cone handling affect prechilling required for germination and early seedling growth. No specifics have been recommended for the best cone handling procedures (33,177,183).
Growth and Yield
The formation of the following year's buds in British Columbia (lat. 54° to 55° N.) begins in late April or early May with the initiation of the first bud scales. Needles for the next growing season are initiated in August and September after the period of shoot elongation. On productive forest sites, visible signs of shoot growth (flushing) are first observed in early May or early June (108), 6 to 7.5 weeks after the first cell divisions signal the end of dormancy. Up to 6 weeks delay in flushing may result from a 500-m (1,640-ft) increase in elevation (120). Growth of the leader and upper branches occurs over a slightly longer period than growth of lower branches (46).
The time of flushing is primarily temperature dependent and therefore varies with the weather. The number of degree days accumulated at the time of flushing may vary from year to year, however, indicating that more than air temperature controls the initiation of the annual shoot-growth cycle (8). Within a stand, there can also be as much as a 3-week difference among individual trees (111,116). The period of shoot elongation is short. In northern Wisconsin, the period from flushing until the terminal leader had completed 95 percent of total elongation ranged from 26 to 41 days among individual trees. This is much shorter than the 6- to 11-week period reported by others (108,149) but agrees closely with data from central British Columbia (120). In interior Alaska (lat. 64° N.), 85 to 90 percent of terminal shoot growth was completed by June 14 and 100 percent by June 28 (70). The cessation of shoot growth is more dependent on photoperiod than on temperature (120).
Cambial activity in Alaska (lat. 64° N.) and Massachusetts (lat. 42° N.) has been compared. The period of cambial activity is about half as long and the rate of cell division twice as great in Alaska as in Massachusetts (56). Wood production (mitotic activity) was observed to begin after 11 degree days (6° C (43° F) threshold) in Alaska (early May) and Massachusetts (late April). Eighty percent of the tracheids were produced in 45 and 95 days in Alaska and Massachusetts, respectively. Variation of the same magnitude depending on site and year has been reported within a small region in Ontario (46).
Culture affects growth; thinned, fertilized stands begin growing about 2 weeks earlier (late May versus early June) and have greater growth during the grand period. Termination of growth is not influenced by thinning (157).
Individual white spruce trees more than 30 m (100 ft) tall and from 60 to 90 cm (24 to 36 in) d.b.h. are found on good sites throughout the range. The tallest trees reported are more than 55 m (180 ft) and from 90 to 120 cm (36 to 48 in) d.b.h. (106,149).
Maximum individual tree age appears to occur on stress sites at latitudinal or elevational treeline rather than on good sites where trees attain maximum size. A partially rotted 16.5 cm (6.5 in) tree growing on the Mackenzie River Delta (above lat. 67° N.) had a 589-year ring sequence, and trees nearly 1,000 years old occur above the Arctic Circle (51). On good sites, trees 100 to 250 years old are common, and the oldest trees (250 to 300 years) are frequently found in areas protected from fire, such as islands, and in relatively wet upland situations (83,185).
Normal yield tables and harmonized site-index (base 100 years) curves provide estimates of growth and productivity for unmanaged stands in Alaska and western Canada. In Alaska, Farr (41) reported site indices at age 100 years from 15.2 m (50 ft) to 32.3 m (106 ft). Growth, yield, and selected stand characteristics for well-stocked white spruce stands in Alaska are summarized in table 2.
Table 2- Growth, yield, and selected stand characteristics for well-stocked white spruce stands in Alaska (adapted from 41)
Site index (base age 100)
volume Mean annual increment (M.A.I.)¹
Culmination of M.A.I. m trees/ha m²/ha m³/ha m³/ha yr 14.9 1,324 22.5 78.1 0.8 150 24.4 1,122 33.1 227.2 2.2 100 30.5 959 40.0 351.3 3.6 80 ft trees/acre ft²/acre ft³/acre ft³/acre yr 49 536 98 1,117 12 150 80 454 144 3,245 31 100 100 388 174 5,018 51 80 ¹Trees larger than 11 cm (4.5 in) in d.b.h. The lowest recorded mean annual increment (0.5 m³/ha or 7 ft³/acre) comes from the Mackenzie River Delta-the northernmost area of white spruce in North America.
Site indices ranging from 15.2 to 27.4 m (50 to 90 ft) (base 70-year stump age) have been reported for the Mixedwood region of Alberta (82), and in the Mixedwood section of Saskatchewan, growth and yield were reported for poor (site index 17.1 m or 56 ft), average (site index 21.9 m or 72 ft), and good (site index 26.8 m or 88 ft) sites (84). The Saskatchewan data are summarized in table 3.
Table 3- Growth and yield of white spruce in a mixed-wood section of Saskatchewan (adapted from 84) Site index (base age 70 at stump)
volume Mean annual increment (M.A. I.)¹
Culmination of M.A.I. m trees/ha m²/ha m³/ha m³/ha yr 17.1 1,063 25.7 179.1 2.0 80 22.9 976 35.8 276.4 3.2 70 26.8 815 45.9 373.8 4.3 70 ft trees/acre ft²/acre ft³/acre ft³/acre yr 56 430 112 2,500 28 80 72 395 156 3,950 45 70 88 330 200 5,340 62 70 ¹Trees larger than 9 cm (3.6 in) in d.b.h. Mean annual increments of 6.3 to 7.0 m³/ha (90 to 100 ft³/acre) have been attained on the best loam soils, and the highest site index 36.6 m (120 ft) is for British Columbia white spruce (61). Site indices for the Lake States (14) are somewhat higher than the best in Saskatchewan (84), but below the best sites in British Columbia.
Biomass production in white spruce is not well documented. In the Yukon Flats Region, AK, a 165-year-old stand with a density of about 975 trees per hectare (394/acre), 63 percent less than 20 cm (8 in) in d.b.h., had a standing crop of 12.61 kg/m² (2.58 lb/ft²). It was 97 percent spruce and 3 percent alder and willow. A 124-year-old stand (maximum tree age) with a density of about 3,460 trees per hectare (1,400/acre), 97 percent less than 10 cm (4 in) in d.b.h., had a standing crop of 4.68 k g/m² (0.96 lb/ft²). It was 91 percent spruce and 9 percent alder and willow. Of a total biomass of 57.13 k g/m² (11.70 lb/ft²), 44 percent was overstory, 34 percent forest floor, and 22 percent roots in a 165-year-old interior Alaska stand (194). Within-tree biomass distribution in two approximately 40-year-old trees (total biomass 25 kg or 55 lb) was foliage, 31 percent; branches, 31 percent; and stem, 38 percent. Proportionally, stem biomass was much higher (59 percent) in a 95-year-old tree with a total weight of 454 kg (1,000 lb) above ground; 21 percent was foliage and 18 percent branches (80). Total biomass in an unthinned white spruce plantation in Ontario has been measured at 13.89 kg/m² (2.84 lb/ft²); 19 percent was in roots, 9 percent foliage, and the remaining 72 percent was in the branches and main stem (142).
Natural stands of white spruce can respond well to cultural practices. Released 71-year-old trees in Maine had a mean annual increase (10-year period) in circumference of 1 cm (0.4 in) compared to 0.6 cm (0.2 in) for control trees (45). Basal area increment in 70-year-old Alaskan spruce for a 5-year period was increased 330 percent by thinning and fertilization, 220 percent by thinning, and 160 percent by fertilization (157). Even old white spruce can respond to release.
The ability to respond is related to type of release and degree of damage sustained during release (66). In Manitoba, diameter increment of spruce of all size classes (ages 10 to 60 years) was doubled by removing competing aspen (138). Spruce having their crowns in contact or immediately below those of aspen can be expected to double their height growth following release. The combined effect of increased diameter increment and height growth can increase spruce volume production by 60 percent.
In unmanaged plantations, the onset of density-dependent mortality is determined by site quality and initial spacing. Yield tables for unmanaged white spruce plantations in Ontario (143) indicate that mortality at age 20 years will have occurred at 6,730 trees per hectare (2,722 trees/acre) at site index 15.2 m (50 ft) (base age 50 years). At site index 24.4 m (80 ft), mortality will have occurred at densities of 2,990 trees per hectare (1,210/acre) or more by age 20. At 1,080 trees per hectare (436/acre), predicted mortality begins between 30 and 35 years for site index 24.4 m (80 ft) and 40 and 45 years for site index 21.3 m (70 ft). Total volume production in unthinned plantations in Ontario (table 4) is higher than the production in natural stands in Saskatchewan.
Table 4- Volume of white spruce in unthinned plantations in Ontario (adapted from 121) Site index at base age 50 years Planting density Plantation age 15.2 m or 50 ft 24.4 m or 80 ft trees/ha yr m³/ha 6,714 20 43.3 124.8 50 275.8 513.0 2,197 20 26.8 86.6 50 212.5 461.7 1,077 20 19.0 66.3 50 172.8 430.5 trees/acre yr ft³/acre 2,717 20 619 1,783 50 3,940 7,329 889 20 383 1,237 50 3,036 6,596 436 20 271 947 50 2,469 6,150 White spruce stands should be maintained at basal areas from 23.0 to 32.1 m²/ha (100 to 140 ft²/acre) to provide maximum volume growth and good individual tree development; below these levels, individual tree increment and resistance to some pests are greatly increased, but total volume production is reduced. For the sites studied, maximum mean annual increment occurred at about age 55 in unmanaged plantations; at this age, 10 percent of total volume is lost from competition (5,9,140,142).
Molecular Biology and Genetics
Variation in monoterpenes, DNA content, and taxonomic characteristics suggest two major populations-one in the East, east of longitude 95° W., and another in the West. Further subdivision of these populations must await new research (117). Two high-yielding provenances have been identified. In the East, a source centered around Beachburg and Douglas in the Ottawa River Valley about 97 km (60 mi) northwest of Ottawa has proven superior in the Lake States, New England, and southern portions of the range in eastern Canada (96). In the West, the Birch Island provenance (lat. 51° 37' N., long. 119° 51' W., elev. 425 m (1,400 ft)) has been exceptional. In coastal nurseries, it will grow as fast as Sitka spruce.
Provisional seed zones have been summarized for Canada (141) and are being developed for Alaska. In the Lake States, general zones have been developed, and superior and also inferior seed sources identified (113,135). Tentative seed transfer rules have been suggested for British Columbia. They limit altitudinal movement to 150 m (500 ft) and suggest that high-elevation spruce provenances from southern latitudes can be moved 2 to 3 degrees of latitude. They also warn that a transfer north of more than 3 degrees will probably result in a detrimental silvicultural effect in southern provenances from low elevations (131). Analysis of enzyme patterns is providing new information on population structure that can be used for improving and refining seed management practices for reforestation (2,17,20).
Hybrids between provenances have been tested on a small scale with promising preliminary results (179). Constructing seed orchards of mixed provenances or of selected alien trees and selection from the local provenance could be an inexpensive approach to increasing yields.
Individual Tree Differences Genetic variation at the individual tree or family level has implications of silvicultural importance. Large differences exist among families representing individual trees within a stand. For example, in a study representing six families from each of seven stands located over a 3550 km² (1,370 mi²) area in the Ottawa River Valley, no differences could be demonstrated. The best of all the families was 28 percent taller than the family mean height (28). This indicates that substantial genetic improvement can be achieved through mass selection and low-cost tree improvement programs.
The general feasibility of phenotypic selection in white spruce has been demonstrated (74). Seed trees, therefore, should be selected for rapid growth and other desirable characteristics; in even-aged stands on uniform sites, this approach may lead to limited improvement. Similarly, the slower growing, poorer trees should consistently be removed in thinning.
Juvenile selections made in the nursery based on height growth maintain superior growth until age 22 and their phenotypic growth superiority probably reflects genetic superiority (111). Silvicultural implications are that extra large seedlings should never be culled merely because "they are too large for the planting machine." On the contrary, they should be given extra care to assure survival and immediate resumption of growth without "check." Furthermore, propagules of such juvenile selections used in intensively managed plantations may lead to immediate yield improvement (115).
Selfing results in serious losses in vigor and lowered survival. Height growth reduction as great as 33 percent has been reported (180). Not much is known about natural selfing in white spruce, but relatedness between individuals within a stand has been demonstrated; it manifests itself in terms of reduced seedset and slower early growth (19). These relations have several implications: (a) culling small plants in the nursery is desirable because it may eliminate genetically inferior inbred seedlings; (b) collecting seed from isolated trees is undesirable because they are likely to produce a high proportion of empty seeds and weak seedlings; and (c) collecting seed in stands likely to represent progeny of one or a few parent trees, as in old field stands, may lead to a degree of inbreeding.
Races and Hybrids No races of white spruce are recognized, but four varieties have been named: Picea glauca, Picea glauca var. albertiana, Picea glauca var. densata, and Picea glauca var. porsildii. It seems unnecessary to distinguish varieties, however (23,96).
White and Engelmann spruce are sympatric over large areas in British Columbia, Montana, and Wyoming. White spruce predominates at lower elevations (up to 1520 m or 5,000 ft), and Engelmann spruce predominates at higher elevations (over 1830 m or 6,000 ft). The intervening slopes support a swarm of hybrids between the two species; these hybrids are the type that gave rise to the so-called variety albertiana.
Sitka and white spruce overlap in northwestern British Columbia and areas in Alaska. The hybrid Picea x lutzi Little occurs where the species are sympatric. The population in Skeena Valley has been studied in some detail. It represents a gradual transition from Sitka to white spruce, a hybrid swarm resulting from introgressive hybridization (20,130).
Natural hybrids between black and white spruce are rare along the southern edge of the species' range, undoubtedly because female receptivity of the two species is asynchronous. A single occurrence from Minnesota has been described (97) and its hybrid origin definitely established (129). To the north, they are more common; intermediate types occur north of latitude 57° N. along the Alaskan highway in British Columbia (130). The hybrids have also been found along the treeline in the forest tundra (93).
Many artificial hybrids have been produced (75,117); a few show some promise, but none has achieved commercial importance.
Barcode data: Picea glauca
Statistics of barcoding coverage: Picea glauca
Public Records: 23
Specimens with Barcodes: 28
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
- 1998Lower Risk/least concern (LR/lc)
National NatureServe Conservation Status
Rounded National Status Rank: N5 - Secure
Rounded National Status Rank: N5 - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Please consult the PLANTS Web site and your State Department of Natural Resources for this plant’s current status, such as, state noxious status and wetland indicator values.
Regeneration following timber harvest: Natural regeneration of white
spruce following timber harvest is unreliable . Spruce seedlings
are, therefore, commonly planted following timber harvest. For adequate
natural regeneration mineral soil seedbeds are required. Mechanical
treatments or broadcast burning may be used to expose mineral soils.
Following timber harvest in Alaska, white spruce seedling density was 10
times greater, frequency 2 times greater, and cover 4 times greater on
scalped versus unscalped surfaces . White spruce seedlings die when
shrub competition becomes severe .
Pests and diseases: The most common insect pests and diseases of white
spruce include needle and stem rusts, root diseases, trunk rots,
mistletoe (Arceuthobium pusillum), bark beetles, wood-boring insects,
weevils, the spruce budworm, and the yellowheaded spruce sawfly, all of
which have been discussed in detail [45,53].
Cultivars, improved and selected materials (and area of origin)
These plant materials are readily available from commercial sources. The cultivar ‘Conica’ (dwarf Alberta spruce, or dwarf white spruce) “is probably the best-known and most widely sold dwarf conifer in the United States (Dirr 1997).”
Contact your local Natural Resources Conservation Service (formerly Soil Conservation Service) office for more information. Look in the phone book under ”United States Government.” The Natural Resources Conservation Service will be listed under the subheading “Department of Agriculture.”
White spruce trees from very young to 200 or more years may show good growth after release resulting from natural causes or silvicultural treatment.
Mature forests with white spruce are easily destroyed because of their high susceptibility to fire. The probability of elimination of this species increases with latitude because good seed years become infrequent and seed quality poorer. At relatively short fire intervals (less than 40-50 years), the source of white spruce seed can be eliminated.
Delivery of seeds to seedbeds for germination may limit regeneration. Squirrels may harvest as much as 90 percent of the cone crop in Alaska. Seed predation by insects and small mammals such as deer mice, red-backed and meadow voles, chipmunks, and shrews also can result in significant seed loss.
Slow initial root growth makes young seedlings and transplants particularly susceptible to frost heaving. The severity of damage generally is greatest on fine-textured and wet soils where water is adequate for ice crystal formation in the surface soil. Defoliation by the spruce budworm and the western spruce budworm can cause mortality if defoliation continues for 2 or more years.
Relevance to Humans and Ecosystems
Uses: Beverage (non-alcoholic), Other food, Folk medicine, Building materials/timber, Gum/resin/latex
Comments: Menomini- tea from inner bark used for internal troubles. Inner bark partly boiled and used as a poultice for wounds, cuts, or swelling. Cree-chewed small spruce cones to relieve sore throats Fort Nelson Slave-bark used to build small canoes. Athabaskans-small paddles made from wood. Gum used for caulking spruce bark canoe. Saplings used to 'rim' canoes. Root used for sewing canoe and for decorative stitching on birch bark baskets. Young twigs and leaves used for tea. Fort Nelson Slave-spruce gum chewed. Kutchin-fiber from under bark eaten in spring. Gum chewed. Spruce beer made from new shoots. Boughs used for mats and beds.
Value for rehabilitation of disturbed sites
overburden. In Alberta, it is considered one of the best conifers for
this purpose . White spruce x Engelmann spruce hybrids have been
observed naturally invading coal mine spoils at high elevations in
west-central Alberta . White spruce has also naturally invaded coal
mine overburden in south-central Alaska. At this location, the
overburden had a clay content of 42 to 44 percent, and was redeposited
on the mined area and graded back to the original contour . On
anthracite strip mine spoils, however, survival of planted white spruce
seedlings was poor to adequate after 5 years .
Results of direct seeding of white spruce onto logged-over areas and
abandoned farmland has been variable . The fact that it naturally
invades mine spoils indicates, however, that direct seeding may be
useful on some disturbed sites. White spruce seed remains viable for up
to 10 years when stored in sealed containers in a cool, dry environment
. The seed requires moist, cool stratification for 60 to 90 days to
break dormancy . Seed from Alberta is an exception, and requires no
Two-year-old or older white spruce nursery stock has been planted in
disturbed areas with relatively good success. Bareroot stock is
recommended for harsh subalpine sites in Alberta where frost heaving may
occur . It is not recommended for planting on steep slopes subject
to erosion. In northeastern Alberta, overwinter survival of
container-grown and transplanted white spruce seedlings was satisfactory
on amended oil sand tailings .
White spruce can be readily propagated by rooted cuttings . Methods
for collecting, processing, storing, and planting white spruce seed have
been described .
White spruce provides good wildlife cover. It may be particularly
important as winter shelter [45,52], especially to caribou which use it
for protection from strong winter winds .
squirrels which can survive the winter on a diet consisting entirely of
white spruce seeds. In Alaska, white spruce seeds averaged 6,615 cal/g
Data from a nutritional study of white spruce needles collected in the
winter on the Kenai Peninsula, Alaska, are presented below :
(percent chemical composition and caloric content)
protein 5.5 - 8.1 6.32
fat 2.8 - 4.1 3.34
crude fiber 21.0 - 25.9 23.5
ash 2.6 - 4.4 3.27
nitrogen free extract 61.4 - 65.0 63.51
Kilogram calories/100 g 486 - 506 494.8
Importance to Livestock and Wildlife
Browse: Livestock and wild ungulates rarely eat white spruce. Snowshoe
hares sometimes feed heavily on white spruce saplings and seedlings. On
a cut-over site in northern Alberta, 40 percent of 2- and 3-year-old
white spruce seedlings were browsed by hares . In Alaska, white
spruce needles, bark, and twigs comprise a major portion of the snowshoe
hare's winter diet. During this time of the year, snow covers many
other foods, leaving only trees and shrubs above snowline available for
hares to browse . Mice and voles eat spruce seedlings . Red
squirrels clip twigs and feed on vegetative and reproductive buds in the
spring . Consumption of leaders and the ends of upper branches by
red squirrels tends to be greatest during poor cone crop years. Spruce
grouse feed entirely on spruce needles during winter .
Seed: Numerous seed-eating birds and mammals feed on white spruce seed.
White spruce seed is a primary food of red squirrels . White spruce
habitats are favored by red squirrels because of the highly palatable
seeds; squirrel density is much greater in white spruce stands than
black spruce stands . Red squirrels are so dependent on this food
source that population density is directly related to the periodicity of
good seed crops . Mice, voles, shrews, and chipmunks consume large
quantities of white spruce seeds off the ground . Chickadees,
nuthatches, crossbills, and the pine siskin extract seeds from open
spruce cones and eat seeds off the ground .
Wood Products Value
White spruce wood is light, straight-grained, and resilient. It is an
important commercial tree harvested primarily for pulpwood and lumber
for general construction . Logs are used extensively for cabin
construction . It has also been used for specialty items such as
sounding boards, paddles and oars, cabinets, boxes, and food containers
Other uses and values
White spruce was important to native peoples of interior Alaska .
Poles were used to construct dwellings, and bark was used as roofing
material. Thin, straight, pliable roots were used as rope. Pitch,
watery sap, and extracts from boiled needles were used for various
medicinal purposes. Boughs were used for bedding, and rotten wood for
smoking moose hides [34,45]].
moose, elk, white-tailed deer, and mule deer, but it may be moderately
palatable to bighorn sheep [11,21]. Red squirrels prefer white spruce
seed over black spruce seed .
Historically, white spruce provided shelter and fuel for both Indians and white settlers of the northern forest. White spruce was the most important species utilized by natives of interior Alaska (105). The wood was used for fuel, but other parts of the tree also had a purpose; bark was used to cover summer dwellings, roots for lashing birchbark baskets and canoes, and boughs for bedding. Spruce pitch (resin) and extracts from boiled needles were used for medicinal purposes (163).
White spruce stands are a source of cover and food for some species of game. Moose and hares frequent these forests but seldom eat white spruce, whereas red squirrels and spruce grouse live in these forests and also consume parts of the tree. Prey species (furbearers) such as marten, wolverine, lynx, wolves, and others utilize these forests.
White spruce forests have significant value in maintaining soil stability and watershed values and for recreation. White spruce can be planted as an ornamental and is used in shelterbelts.
The wood of white spruce is used primarily for pulpwood and lumber for various construction, prefab houses, mobile homes, furniture, boxes and crates, and pallets. It also is used for house logs, musical instruments, and paddles. Because of its wide geographic range and abundance, it is (de facto) highly significant for food and cover of many wildlife species, for soil stability, watershed value, and recreation. It was historically important for food, shelter, medicine, fuel, and other uses by American Indians. White spruce is the provincial tree of Manitoba and the state tree of South Dakota. White spruce is much used in some areas for Christmas trees and is a good ornamental and shade tree.
Picea glauca (white spruce) is a species of spruce native to the northern temperate and boreal forests in North America, from central Alaska to as far east as the Avalon Peninsula in Newfoundland, and south to northern Montana, Minnesota, Wisconsin, Michigan, northwestern Pennsylvania, upstate New York, Vermont, New Hampshire, and Maine; there is also an isolated population in the Black Hills of South Dakota and Wyoming. It is also known as Canadian spruce, skunk spruce, cat spruce, Black Hills spruce, western white spruce, Alberta white spruce, and Porsild spruce.
The white spruce is a large coniferous evergreen tree which grows normally to 15 to 30 metres (49 to 98 ft) tall, but can grow up to 40 metres (130 ft) tall with a trunk diameter of up to 1 metre (3.3 ft). The bark is thin and scaly, flaking off in small circular plates 5 to 10 centimetres (2.0 to 3.9 in) across. The crown is narrow - conic in young trees, becoming cylindric in older trees. The shoots are pale buff-brown, glabrous (hairless) in the east of the range, but often pubescent in the west, and with prominent pulvini. The leaves are needle-like, 12 to 20 millimetres (0.47 to 0.79 in) long, rhombic in cross-section, glaucous blue-green above with several thin lines of stomata, and blue-white below with two broad bands of stomata.
The cones are pendulous, slender, cylindrical, 3 to 7 centimetres (1.2 to 2.8 in) long and 1.5 centimetres (0.59 in) wide when closed, opening to 2.5 centimetres (0.98 in) broad. They have thin, flexible scales 15 millimetres (0.59 in) long, with a smoothly rounded margin. They are green or reddish, maturing to pale brown 4 to 8 months after pollination. The seeds are black, 2 to 3 millimetres (0.079 to 0.118 in) long, with a slender, 5 to 8 millimetres (0.20 to 0.31 in) long pale brown wing.
The root system of white spruce is highly variable and adaptable (Wagg 1964, 1967), responding to a variety of edaphic factors, especially soil moisture, soil fertility, and mechanical impedance. On soils that limit rooting depth, the root system is plate-like, but it is a common misconception to assume that white spruce is genetically constrained to develop plate-like root systems irrespective of soil conditions (Sutton 1969). In the nursery, or naturally in the forest, white spruce usually develops several long “running” roots just below the ground surface (Mullin 1957).
Seeds are small (2.5 mm to 5.0 mm long), oblong, and acute at the base. Determinations of the average number of sound seeds per white spruce cone have ranged from 32 to 130 (Waldron 1965, Zasada and Viereck 1970).
Each seed is clasped by a thin wing 2 to 4 times as long as the seed. Seed and wing are appressed to the cone scale. Embryo and megagametophyte are soft and translucent at first; later the endosperm becomes firm and milky white, while the embryo becomes cream-colored or light yellow. At maturity, the testa darkens rapidly from light brown to dark brown or black (Crossley 1953). Mature seed “snaps in two” when cut by a sharp knife on a firm surface (Crossley 1953).
White spruce cones reach their maximum size after 800 growing degree days (GDD). Cone moisture content decreases gradually after about 1000 GDD (Cram and Worden 1957)
Cone colour also can be used to help determine the degree of maturation, but cones may be red, pink or green (Teich 1970). Collection and storage dates and conditions influence germination requirements and early seedling growth (Zasada 1973, Edwards 1977, Winston and Haddon 1981).
A bushel (35 L) of cones, which may contain 6500 to 8000 cones, yields 6 to 20 ounces (170g to 567 g) of clean seed (USDA Forest Service 1948).
Seed dispersal begins after cone scales reflex with cone maturation in the late summer or early fall of the year of formation. Cones open at moisture contents of 45% to 70% and specific gravities of 0.6 to 0.8 (Cram and Worden 1957, Zasada 1973, Winston and Haddon 1981). Weather affects both the initiation and pattern of seed dispersal (Nienstaedt and Zasada 1990), but cone opening and the pattern of seed dispersal can vary among trees in the same stand (Zasada 1986). Even after dispersal has begun, cold, damp weather will cause cone scales to close; they will reopen during dry weather. Most seed falls early rather than late, but dispersal may continue through fall and winter (Zasada 1986), even into the next growing season (Rowe 1953). Seed dispersal occurs mainly in late summer or early fall (Waldron 1965).
White spruce seed is initially dispersed through the air by wind. Both the initiation and pattern of seed dispersal depend on the weather (Nienstaedt and Zasada 1990), but these can vary among trees in the same stand (Zasada 1986). Small amounts of white spruce seed are normally dispersed beyond 100 m from the seed source, but exceptionally seeds have been found more than 300-400 m from the nearest seed source (Zasada 1986).
White spruce can live for several hundred years. Ages of 200 to 300 years are commonly attained throughout much of the range, and Dallimore and Jackson (1961) estimated the normal lifespan of white spruce at 250 to 300 years.
Slow-growing trees in rigorous climates are also capable of great longevity. White spruce 6 m to 10 m high on the shore of Urquhart Lake, Northwest Territories, were found to be more than 300 years old (Hare and Ritchie 1972),
The bark of mature white spruce is scaly or flaky, gray-brown (Brayshaw 1960) or ash-brown (Harlow and Harrar 1950), but silvery when freshly exposed. Resin blisters are normally lacking, but the Porsild spruce Picea glauca var. porsildii Raup has been credited with having smooth resin-blistered bark (Hosie 1969).
White spruce has a transcontinental range in North America. In Canada, its contiguous distribution encompasses virtually the whole of the Boreal, Subalpine, Montane, Columbia, Great Lakes – St. Lawrence, and Acadian Forest Regions (Rowe 1972), extending into every province and territory (Forestry Branch 1961). On the west coast of Hudson Bay, it extends to Seal River, about 59°N, “from which the northward limit runs apparently almost directly north-west to near the mouth of the Mackenzie River, or about latitude 68°” (Bell 1881). Collins and Sumner (1953) reported finding white spruce within 13 km of the Arctic coast in the Firth valley, Yukon, at about 69°30′ N, 139°30′ W. It reaches within 100 km of the Pacific Ocean in the Skeena Valley, overlapping with the range of Sitka spruce (Picea sitchensis [Bong.] Carr.), and almost reaching the Arctic Ocean at latitude 69° N in the District of Mackenzie, with white spruce up to 15 m high occurring on some of the islands in the Delta near Inuvik (Northwest Territories webpage). The wide variety of ecological conditions in which 4 Quebec conifers, including white spruce, are able to establish themselves, was noted by Lafond (1966), but white spruce was more exacting than black spruce. In the United States, the range of white spruce extends into Maine, Vermont, New Hampshire, New York, Michigan, Wisconsin, Minnesota, and Alaska (Sargent 1922, Harlow and Harrar 1950), where it reaches the Bering Strait in 66°44′ N” at Norton Bay and the Gulf of Alaska at Cook Inlet (Nienstaedt and Zasada 1990).
Southern outliers have been reported in southern Saskatchewan and the Cypress Hills of southwestern Saskatchewan (Scoggan 1957, Nienstaedt and Zasada 1990) and southeastern Alberta (Cypress Hills Alberta Web site), northwestern Montana (Munns 1938, Harlow and Harrar 1950), south-central Montana (Munns 1938), in the Black Hills on the Wyoming–South Dakota boundary (Munns 1938, Fernald 1950), on the Manitoba–North Dakota boundary (Munns 1938), and at Shushan, New York (Cook and Smith 1959).
White spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie River delta. It grows between sea level and an elevation of 1,520 metres (4,990 ft). Its northern distribution roughly correlates to the location of the tree line, which includes an isothermic value of 10 °C (50 °F) for mean temperature in July, as well as the position of the Arctic front; cumulative summer degree days, mean net radiation, and the amount of light intensities also figure. White spruce generally is found in regions where the growing season exceeds 60 days annually.
The southern distribution corresponds to the July isotherm of 18 °C (64 °F) around the Great Lakes; in the Prairie Provinces its limit is north of this isotherm. During the summer solstice, photoperiod values range from 17 hours at its southern limits to 24 hours above the Arctic Circle.
One of the hardiest conifers, white spruce in parts of its range withstands mean daily January temperature of -6.7°C and extreme minimum temperatures as low as -56.5°C; minimum temperatures of -50°C are general throughout much of the range except the southernmost and southeasternmost parts (Fowells 1965). By itself, or with black spruce and tamarack (Larix laricina (Du Roi) K. Koch), white spruce forms the northern boundary of tree-form growth (Sutton 1969). White spruce up to 15 m in height occur at 69°N on islands in the Mackenzie Delta near Inuvik in the Northwest Territories. Hustich (1966) depicted Picea spp. as forming the northernmost limit of tree growth in North America.
The arctic or northern timberline in North America forms a broad transition zone from Labrador to northern Alaska. In Labrador, white spruce is not abundant and constitutes less than 5% of the forest, with a range that coincides very closely with that of black spruce but extending slightly further north (Wilton 1964).
The range of white spruce extends westwards from Newfoundland and Labrador, and along the northern limit of trees to Hudson Bay, Northwest Territories, Yukon, and into northwestern Alaska (Fowells 1965). Although Bell (1881) was emphatic that it “nowhere reaches the Atlantic coast [from which it recedes] further and further in going north”. Across western Canada and Alaska, white spruce occurs further north than black spruce, and, while poplar (Populus), willow, and birch may occur along streams well into the tundra beyond the limits of spruce, the hardwoods are usually no more than scrub (Hustich 1953). Spruce characteristically occurs in fingers of tree-form forest, extending far down the northern rivers and as scattered clumps of dwarfed “bush” spruce on intervening lands (Munns 1938, Halliday and Brown 1943). In Manitoba, Scoggan (1957, citing a 1951 but otherwise unreferenced report by Baldwin) noted that the northernmost collection of white spruce was at latitude 59°48’N, but Bryson et al. (1965) found white spruce in the northern edge of continuous forest in central Canada at Ennadai Lake, about 60°45′ N, 101°’W, just north of the northwest corner of Manitoba. Bryson et al. (1965) noted that the forest retained “the same general characteristics as when it was first described [by Tyrrell (1897)] in 1896”. Collins and Sumner (1953) reported finding white spruce within 13 km of the Arctic coast in the Firth valley, Yukon, at about 69°30′ N, 139°30′ W, and Sargent (1922) noted that white spruce in Alaska “reached Behring Strait in 66°44′ N”.
Climate, especially temperature, is obviously a factor in determining distributions of northern flora. Halliday and Brown (1943) suggested that white spruce’s northern limit corresponds “very closely” with the July mean monthly isotherm of 10°C in Ungava, but that the northern limit west of Hudson Bay was south of that isotherm. Other climatic factors that have been suggested as affecting the northern limit of white spruce include: cumulative summer degree days, position of the Arctic front in July, mean net radiation especially during the growing season, and low light intensities (Nienstaedt and Zasada 1990). Topography, soil conditions, and glaciation may also be important in controlling northern limits of spruce (Drew and Shanks 1965).
The southern limit of distribution of white spruce is more complex. From east of the main range of coastal mountains in British Columbia, the southern continuous limit of white spruce is the forest/prairie interface through Alberta, Saskatchewan, Manitoba, the northern parts of Minnesota and Wisconsin, central Michigan, northeastern New York, and Maine (Fowells 1965). Sargent (1922) and Harlow and Harrar (1950) also included Vermont and New Hampshire; and, while Dame and Brooks (1901) excluded New York and states further west, they included Massachusetts as far south as Amherst and Northampton, “probably the southern limit of the species” in that area. Nisbet (1905) gave the range of white spruce as extending to “Carolina”, but he did not recognize red spruce as a species and presumably included it with white spruce.
Towards the southern parts of its range, white spruce encounters increasingly effective ecological competition from hardwoods, some of which may reinforce their growth-rate/sprouting competitiveness with allelopathic depredation of coniferous regeneration (Tubbs 1976). Further southward extension of the distribution is inhibited by white spruce’s cold requirement.
White spruce as an exotic species
As an exotic, white spruce is widespread but uncommon. It was introduced into England (Hereman 1868) and parts of continental Europe (Nisbet 1905, Jackson 1948) in or soon after the year 1700, into Denmark about 1790 (Sabroe 1954), and into Tasmania and Ceylon shortly before 1932 (Troup 1932).
Nisbet (1905) noted that firmly-rooted white spruce served very well to stabilize windswept edges of woods in Germany. In a narrow belt of mixed Norway and white spruces over an extremely exposed hilltop crest at high elevation in northern England, the Norway spruce were “completely dwarfed” whereas the white spruce had reached heights of between 3 and 4.3 m (Guillebaud et al. 1920). The age of the belt was not recorded, but adjoining 66-year-old stands may have been of the same vintage.
White spruce has also been used as a minor plantation species in England (Selby 1842, Anon. 1879) and Scotland (United Kingdom Forestry Commission 1920). In Scotland, at Corrour, Inverness-shire, Sir John Stirling Maxwell in 1907 began using white spruce in his pioneering plantations at high elevations on deep peat. However, plantations in Britain have generally been unsatisfactory (Edlin 1962), mainly because of damage by spring frosts after mild weather had induced flushing earlier in the season. However, the species is held in high regard in the Belgian peat region, where it grows better than do the other spruces (Fraser 1933).
White spruce is a climax canopy tree in the boreal forests of Canada and Alaska. It generally occurs on well-drained soils in alluvial and riparian zones, although it also occurs in soils of glacial and lacustrine origin. The understory is dominated by feather mosses (Hylocomium splendens and Pleurozium schreberi, Ptilium crista-castrensis, and Dicranum spp.), and occasionally peat moss. In the far north, the total depth of the moss and underlying humus is normally between 25 to 46 centimetres (9.8 to 18.1 in), although it tends to be shallower when hardwoods are present in the stand.
White spruce grows in soils with pH values of 4.7—7.0, although they have been found in soils as acidic as 4.0 in subalpine fir forests in the Northwest Territories. A presence of calcium in the soil is common to white spruce found in northern New York. White spruce most commonly grows in the soil orders of Alfisols and Inceptisols. Soil properties such as fertility, temperature, and structural stability are partial determinants of the ability of white spruce to grow in the extreme northern latitudes. In the northern limits of its range, white spruce is the climax species along with black spruce; Birch and aspen are the early succession species. Wildfires typically occur every 60 to 200 years, although they have been known to occur as infrequently as every 300 years.
White Spruce will grow in USDA Growing Zones 3-7, but is not adapted to heat and humidity and will perform poorly in a hot climate. The tree attains its greatest longevity and growth potential in Zones 3-4.
White spruce occurs on a wide variety of soils, including soils of glacial, lacustrine, marine, and alluvial origins; overlying basic dolomites, limestones and acidic Precambrian and Devonian granites and gneisses; and Silurian sedimentary schists, shales, slates, and conglomerates (Halliday 1937). The wide range of textures accommodated includes clays (Wilde et al. 1949, 1954; Nienstaedt 1957, Rowe 1972), even those that are massive when wet and columnar when dry (Jameson 1963), and sand flats, and coarse soils (Forest Section L 4d, Rowe 1972). Its occurrence on some organic soils is not characteristic, except perhaps on shallow mesic organic soils in Saskatchewan and in association with black spruce on organic soils in central Yukon (Nienstaedt and Zasada 1990).
Podzolized, brunisolic, luvisolic, gleysolic, and regosolic (immature) soils are typical of those supporting white spruce throughout the range of the species (Nienstaedt 1957). Soils supporting white spruce are most commonly Alfisols or Inceptisols (Nienstaedt and Zasada 1990). In the podzol region of Wisconsin, white spruce occurs on loam podzols, podzolized gley loams, strongly podzolized clays, gley-podzol clays, stream-bottom soils, and wood peat (Wilde et al. 1949). Moist sandy loams also support good growth (Harlow and Harrar 1950). On sandy podzols (Wilde et al. 1949), it is usually a minor species (Nienstaedt and Zasada 1990). Good development occurs on moist alluvium (Seeley, cited by Nienstaedt 1957; Jeffrey 1961, 1964; Lacate et al. 1965; Viereck 1973) on the banks of streams and borders of swamps (Sargent 1898, Kenety 1917, Rowe 1972). White spruce makes good growth on well-drained lacustrine soils in Alberta Mixedwoods (Heger 1971), on moderately-well-drained clay loams in Saskatchewan (Kabzems 1971), and on melanized loams and clays (with sparse litter and a dark-coloured organically-enriched mineral horizon) in the Algoma district of Ontario (Wilde et al. 1954).
White spruce becomes less accommodating of soil with increasing severity of climate. The distribution of white spruce in Labrador seems to depend almost entirely on the character of the soil (Sargent 1898), and between the southwestern shores of Hudson Bay and the northeastern regions of Saskatchewan, white spruce is confined to very local physiographic features, characterized by well-drained or fertile soils (Ritchie 1956).
On dry, deep, outwash deposits in northern Ontario, both white spruce and aspen grow slowly (MacLean 1960). But, broadly, white spruce is able to tolerate considerable droughtiness of sites that are fertile, and no fertile site is too moist unless soil moisture is stagnant (Sutton 1968). Soil fertility holds the key not just to white spruce growth but to the distribution of the species. At least moderate fertility is needed for good growth, but white spruce occurs on many sites where nutrient deficiencies depress its growth more than that of black spruce, red spruce, Norway spruce, and the pines generally (Heiberg and White 1951, Lafond 1954, McLeod 1956, MacArthur 1957, Paine 1960, Swan 1960). Minimum soil-fertility standards recommended for white spruce sufficient to produce 126 to 157 m3/ha of wood at 40 years are much higher than for pine species commonly planted in the Lake States (Wilde 1966): 3.5% organic matter, 12.0 meq/100 g exchange capacity, 0.12% total N, 44.8 kg/ha available P, 145.7 kg/ha available K, 3.00 meq/100 g exchangeable Ca, and 0.70 meq/100 g exchangeable Mg.
Forest floors under stands dominated by white spruce respond in ways that vary with site conditions, including the disturbance history of the site (Nienstaedt and Zasada 1990). Composition, biomass, and mineral soil physical and chemical properties are affected. In Alaska, the accumulation of organic layers (to greater thicknesses in mature stands of spruce than those in hardwood stands on similar sites) leads to decreased soil temperatures, in some cases leading to the development of permafrost (Viereck 1970a, b, Viereck et al. 1983). Acidity of the mineral soil sampled at an average depth of 17 cm in 13 white spruce stands on abandoned farmland in Ontario increased by 1.2 pH units over a period of 46 years (Brand et al. 1986).
A considerable range of soil pH is tolerated by white spruce (Nienstaedt 1957). Thrifty stands of white spruce in Manitoba have developed on soils of pH 7.6 at only 10 cm below the surface, and pH 8.4 at 43 cm below the surface (Stoeckeler 1938, USDA Forest Service 1938); rooting depth in those soils was at least 81 cm. An abundant calcium supply is common to most white spruce locations in New York state (Nienstaedt and Zasada 1990). Chlorosis was observed in young white spruce in heavily-limed nursery soils at about pH 8.3 (Stone, cited by Nienstaedt 1957). Wilde (1966) gave 4.7 to 6.5 as the approximate optimum range of pH for white spruce in Wisconsin, but optimum growth seems possible at pH levels up to 7.0 and perhaps higher (Sutton 1968). Alluvium on the floodplains of northern rivers shows pH levels from 5.0 to 8.2 (Zasada et al. 1977). High-lime ecotypes may exist (Pelletier 1966), and in Canada Forest Section B8 the presence of balsam poplar and white spruce on some of the moulded moraines and clays seems to be correlated with the considerable lime content of these materials (Rowe 1972, Stiell 1976), while calcareous soils are favourable sites for northern outliers of white spruce (Hustich 1953).
Mature stands of white spruce in boreal regions often have well-developed moss layers dominated by feather mosses, e.g., Hylocomium splendens (Hedw.) B.S.G., Pleurozium schreberi (Brid.) Mitt., Ptlium crista-castrensis (Hedw.) De Not., and Dicranum Hedw. spp. rather than Sphagnum Dill. spp. (La Roi and Stringer 1976, Viereck 1987). The thickness of the moss–organic layer commonly exceeds 25 cm in the far north and may approach twice that figure. The mosses compete for nutrients and have a major influence on soil temperatures in the rooting zone. Permafrost development in parts of Alaska, Yukon, and the Northwest Territories is facilitated by the insulative organic layer (Viereck 1970a, b, Gill 1975, Van Cleve and Yarie 1986). The role of windthrow in maintaining diversification of the bryophyte flora in boreal spruce forests has been described by Jonsson et al. (1990) and Jonsson and Dynesius (1993).
White spruce is extremely hardy to low temperatures, provided the plant is in a state of winter dormancy. Throughout the greater part of its range, white spruce routinely survives and is undamaged by winter temperatures of -50°C, and even lower temperatures occur in parts of the range (Fowells 1965, Nienstaedt and Zasada 1990). Boreal Picea are among the few extremely hardy conifers in which the bud primordia are able to survive temperatures down to -70°C (Sakai and Larcher 1987).
Especially important in determining the response of white spruce to low temperatures is the physiological state of the various tissues, notably the degree of “hardening” or dormancy. A natural progression of hardening and dehardening occurs in concert with the seasons (Glerum 1985). While different tissues vary in ability to tolerate exposure to stressful temperatures, white spruce, as with woody plants in general, has necessarily developed sufficient winter hardiness in its various tissues to enable them to survive the minimum temperatures experienced in the distribution range.
White spruce is subject to severe damage from spring frosts. Newly flushed shoots of white spruce are very sensitive to spring frost (Smith 1949, Rowe 1955, McLeod 1964). This sensitivity is a major constraint affecting young trees planted without overstorey nurses in boreal climates (Sutton 1992).
Forest succession in its traditional sense implies two important features that resist direct examination (Solomon et al. 1981). First, classical definitions generally connote directional changes in species composition and community structure through time, yet the time frame needed for documentation of change far exceeds an average lifespan (Solomon et al. 1981). The second feature that defies quantitative description is the end point or climax.
Floodplain deposits in the Northwest Territory, Canada, are important in relation to the development of productive forest types with a component of white spruce (Jeffrey 1964). The most recently exposed surfaces are occupied by sandbar vegetation or riparian shrub willows and alder (Alnus incana); with increasing elevation, the shrubs give way successively to balsam poplar and white spruce forest. In contrast, older floodplains, with predominantly brown wooded soils, typically carry white spruce–trembling aspen mixedwood forest.
Interrelationships among nutrient cycling, regeneration, and subsequent forest development on floodplains in interior Alaska were addressed by Van Cleve et al. (1980), who pointed out that the various stages in primary succession reflect physical, chemical, and biological controls of ecosystem structure and function. Thus, each successional stage has a species combination in harmony with site quality. Short-circuiting succession by planting a late successional species such as white spruce on an early successional surface may result in markedly reduced growth rates because of nitrogen insufficiency. Without application of substantial amounts of fertilizer, use would have to be made of early successional alder and its site-ameliorating additions of nitrogen.
Neiland and Viereck noted that “the slow establishment and growth of spruce under birch stands [in Alaska] may be partially due to effects of shading and general competition for water and nutrients, but may also be more directly related to the birch itself. Heikinheimo (1915 cited by Lutz 1956), found that birch ash inhibited white spruce seedlings, and Gregory (1966) found that birch litter has a smothering effect on spruce seedlings” (Neiland and Viereck 1977).
On dry upland sites, especially south-facing slopes, the mature vegetation is white spruce, white birch, trembling aspen, or a combination of these species. Succession follows in one of two general patterns. In most cases, aspen and birch develop as a successional stage after fire before reaching the spruce stage. But, occasionally, with optimal site conditions and a source of seed, white spruce will invade with the hardwoods or within a few years thereafter, thereby producing even-aged white spruce stands without an intervening hardwood stage.
Associated forest cover
The White Spruce Cover Type may include other species in small numbers. In Alaska, associates include paper birch, trembling aspen, balsam poplar, and black spruce; in western Canada, additional associates are subalpine fir, balsam fir, Douglas-fir, jack pine, and lodgepole pine (Dyrness 1980). Seral species giving way to white spruce include paper birch, aspen, balsam poplar, jack pine, and lodgepole pine. On certain river bottom sites, however, black spruce may replace white spruce (Viereck 1970a). Earlier successional stages leading to the white spruce climax are the white spruce–paper birch, white spruce–aspen, balsam poplar, jack pine, and lodgepole pine types. The type shows little variation. The forest is generally closed and the trees well formed, other than those close to the timberline. Lesser vegetation in mature stands is dominated by mosses. Vascular plants are typically few, but shrubs and herbs that occur “with a degree of regularity” include: alder, willows, mountain cranberry, red-fruit bearberry, black crowberry, prickly rose, currant, buffaloberry, blueberry species, bunchberry, twinflower, tall lungwort, northern comandra, horsetail, bluejoint grass, sedge species, as well as ground-dwelling mosses and lichens. Several white spruce communities have been identified in interior Alaska: white spruce/feathermoss; white spruce/dwarf birch/feathermoss; white spruce/dwarf birch/sphagnum; white spruce/avens/moss; and white spruce/alder/bluejoint (Viereck 1975, Dyrness 1980).
Of the Eastern Forest Cover Types recognized by the Society of American Foresters (Eyre 1980), only one, White Spruce, names that species in its title. The eastern White Spruce Cover Type, as defined, encompasses white spruce both in pure stands, and in mixed stands “in which white spruce is the major [undefined] component” (Payette 1980).
In most of its range, white spruce occurs more typically in association with trees of other species than in pure stands.
White spruce is an associated species in the following Eastern Forest cover types, by the Society of American Foresters: In the Boreal Forest Region: (1) Jack pine, (5) Balsam fir, (12) Black Spruce, (16) Aspen, (18) Paper birch, and (38) Tamarack. In the Northern Forest Region: (15) Red pine, (21) Eastern white pine, (24) Hemlock-Yellow birch, (25) Sugar maple-Beech-Yellow birch, (27) Sugar maple, (30) Red spruce-yellow birch, (32) Red spruce, (33) Red spruce-Balsam fir, (37) Northern white-cedar, and (39) Black ash-American elm-Red maple (Nienstaedt and Zasada 1990, Eyre 1980).
- Picea glauca var. glauca (Typical or Eastern white spruce). From Newfoundland west to eastern Alberta, on lowland plains.
- Picea glauca var. densata (Black Hills white spruce). The Black Hills in South Dakota.
- Picea glauca var. albertiana (Alberta white spruce). The Rocky Mountains in Alberta, British Columbia and northwest Montana.
- Picea glauca var. porsildii (Alaska white spruce). Alaska and Yukon.
The two western varieties are distinguished by pubescent (downy) shoots, and may be related to extensive hybridisation and/or intergradation with the closely related Engelmann Spruce found further south in the Rocky Mountains. White spruce also hybridises readily with the closely related Sitka Spruce where they meet in southern Alaska; this hybrid is known as Picea × lutzii.
Although sometimes described, e.g., by Switzer (1960), as relatively resistant to attack by insects and disease, white spruce is far from immune to depredation. Important insect pests of white spruce include the spruce budworm (Choristoneura fumiferana [Clemens]), the yellow-headed spruce sawfly (Pikonema alaskensis Rohwer), the European spruce sawfly (Gilpinia hercyniae [Hartig]), and spruce beetle (Dendroctonus rufipennis [Kirby]) (Fowells 1965, Rose and Lindquist 1985, Ives and Wong 1988). As well, other budworms, sawflies, and bark beetles, gall formers, bud midges, leaf miners, aphids, leaf eaters, leaf rollers, loopers, mites, scales, weevils, borers, pitch moths, and spittlebugs cause varying degrees of damage to white spruce (Ives and Wong 1988).
A number of sawflies feed on spruce trees. Among them European spruce sawfly, Yellow-headed spruce sawfly, Green-headed spruce sawfly and the Spruce webspinning sawfly (Rose and Lindquist 1985).
More than a dozen kinds of looper feed on the spruces, fir, and hemlock in eastern Canada. The full-grown larvae of the larvae vary in length from 15 mm to 35 mm. Some feed briefly in the fall and complete their feeding in the spring; others feed mainly in the summer; still others feed mainly in the late summer and fall.
The fall and spring feeding group includes the dash-lined looper (Protoboarmia porcelaria indicataria Walker), the diamond-backed looper (Hypagyrtis piniata Packard), the fringed looper (Campaea perlata Guenée), and the false loopers (Syngrapha species). The summer feeding group includes the false hemlock looper (Nepytia canosaria Walker), occasionally occurring in large numbers and usually in conjunction with the hemlock looper (Lambdina fiscellaria fiscellaria Guenée), the small spruce loopers Eupithecia species, the yellowlined conifer looper (Cladara limitaria Walker), and the saddleback looper (Ectropis crepuscularia Denis and Schiffermüller).
The late summer and fall group includes the common spruce-fir looper (Semiothisa signaria dispuncta Walker) and the similar Semiothisa fissinotata Walker on hemlock, the small spruce loopers Eupithecia species, the spruce looper Caripeta divisata Walker, occasionally abundant, the transversebanded looper (Hydriomena divisaria Walker), and the whitelined looper (Eufidonia notataria Walker).
A dwarf cultivar, P. glauca var. albertiana 'Conica', is a popular garden plant. It has very slender leaves, like those normally found only on one-year-old seedlings, and very slow growth, typically only 2–10 centimetres (0.79–3.94 in) per year. Older specimens commonly 'revert', developing normal adult foliage and starting to grow much faster; this 'reverted' growth must be pruned if the plant is to be kept dwarf.
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Picea glauca (white spruce) is the provincial tree of Manitoba and the state tree (as Black Hills spruce) of South Dakota.
Names and Taxonomy
The currently accepted scientific name of white spruce is Picea glauca
(Moench) Voss . The genus Picea consists of about 30 species of
evergreen trees found in cool, temperate regions of the northern
hemisphere. Seven species of Picea, including white spruce, are native
to North America. White spruce is widely distributed across northern
North America and exhibits considerable geographic variation. However,
Little  thinks it unnecessary to distinguish varieties, although up
to four have been recognized by various other authorities.
Natural hybridization between species of Picea is common. Engelmann
spruce (P. engelmannii) x white spruce hybrids are common where the
ranges of these species overlap. Natural crosses between these species
occur from central British Columbia as far south as eastern Washington
and Yellowstone National Park . Within this area trees at low
elevations closely resemble pure white spruce, while pure Engelmann
spruce tends to dominate at higher elevations. Hybrids between the
species are concentrated on intervening slopes. Sitka spruce (P.
sitchensis) and white spruce are sympatric in northwestern British
Columbia and southwestern Alaska. Hybrids occur in this area of
sympatry, and have been classified as Picea X lutzii Little. Hybrids
between black spruce (P. mariana) and white spruce are relatively rare
western white spruce
Black Hills spruce
Alberta white spruce