Picea glauca

Pinaceae -- Pine family

    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.

     AK  ME  MI  MN  MT  NH  NY  SD  VT  WI
     WY  AB  BC  LB  MB  NB  NF  NS  NT  ON
     PE  PQ  SK  YT

White spruce has a transcontinental distribution.  It grows from
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
[45].

More info on this topic.

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 has 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 (149). In Alaska, it reaches the Bering Sea at Norton Bay and  the Gulf of Alaska at Cook Inlet. In British Columbia, it comes within 100  km (60 mi) of the Pacific Ocean in the Skeena Valley where it overlaps  with Sitka spruce (Picea sitchensis), and from there it extends  south through British Columbia, and east through Alberta and Manitoba to  Lake Winnipeg and south and east through northern Minnesota and Wisconsin,  central Michigan, northeastern New York, and Maine. The contiguous  distribution shown extending south in the Rocky Mountains into Montana  actually may be outliers similar to those found further south in Montana,  in the Black Hills in Wyoming and South Dakota (approximately latitude 44°  N.), and at Cypress Hills in Saskatchewan (149).

    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.

Picea glauca (Moench) Voss:
China (Asia)
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Trees to 30m; trunk to 1m diam.; crown broadly conic to spirelike. Bark gray-brown. Branches slightly drooping; twigs not pendent, rather slender, pinkish brown, glabrous. Buds orange-brown, 3--6mm, apex rounded. Leaves (0.8--)1.5--2(--2.5)cm, 4-angled in cross section, rigid, blue-green, bearing stomates on all surfaces, apex sharp-pointed. Seed cones 2.5--6(--8)cm; scales fan-shaped, broadest near rounded apex, 10--16 ´ 9--13mm, flexuous, margin at apex ± entire, apex extending 0.5--3mm beyond seed-wing impression. 2 n =24.

More info for the term: tree

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

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

Tree, Evergreen, Monoecious, Habit erect, Trees without or rarely having knees, Tree with bark rough or scaly, Young shoots 3-dimensional, Buds resinous, Buds not resinous, Leaves needle-like, Leaves alternate, Needle-like leaf margins entire (use magnification), Leaf apex acute, Leaves < 5 cm long, Leaves < 10 cm long, Leaves blue-green, Needle-like leaves 4-angled, Needle-like leaves not twisted, Needle-like leaf habit erect, Needle-like leaf habit drooping, Needle-like leaves per fascicle mostly 1, Needle-like leaf sheath early deciduous, Needle-like leaf sheath persistent, Twigs glabrous, Twigs viscid, Twigs not viscid, Twigs with peg-like projections or large fascicles after needles fall, Berry-like cones orange, Woody seed cones < 5 cm long, Woody seed cones > 5 cm long, Bracts of seed cone included, Seeds brown, Seeds winged, Seeds unequally winged, Seed wings prominent, Seed wings equal to or broader than body.

Pinus glauca Moench, Verz. Ausländ. Bäume, 73. 1785; Abies canadensis Miller; Picea alba (Aiton) Link; P. alba var. albertiana (S.Brown) Beissner; P. albertiana S.Brown; P. canadensis (Miller) Britton, Sterns, & Poggenburg; P. canadensis var. glauca (Moench) Sudworth; P. glauca var. albertiana (S.Brown) Sargent; P. glauca var. densata Bailey; P. glauca var. porsildii Raup; Pinus alba Aiton

More info for the terms: bog, climax, shrubs, tree

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

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

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

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

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

More info for the term: climax

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 [41].
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
[22].  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 [33]. 

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
     Region, Interior
     Cedar-Hemlock Zone    general veg. eas     Haeussler & others 1985
    Prince Rupert Forest
     Region, Subboreal
     Spruce Zone           general veg. eas     Pojar & others 1984

PQ: Gaspe Peninsula        forest veg. cts      Zoladeski 1988
ON                         forest eas           Jones & others 1983

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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
    16  Aspen
    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
    38  Tamarack
    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
   217  Aspen
   218  Lodgepole pine
   251  White spruce - aspen
   252  Paper birch
   253  Black spruce - white spruce
   254  Black spruce - paper birch

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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

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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
   FRES20  Douglas-fir
   FRES23  Fir - spruce
   FRES28  Western hardwoods

White spruce grows on a wide variety of soils of glacial, lacustrine,  marine, or alluvial origin. Substrata represent the geological eras from  Precambrian to Cenozoic and a great variety of rock formations, including  granites, gneisses, sedimentaries, slates, schists, shales, and  conglomerates (134,158). Some bedrocks are acidic, such as granites, and  others are basic dolomites and limestones.

    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).

White spruce has been described as a, "plastic" species  because of its ability to repopulate areas at the end of glaciation. It  grows under highly variable conditions, including extreme climates and  soils.

    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.

Muskegs, bogs, and river banks to montane slopes; 0--1000m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Maine, Mich., Minn., Mont., N.H., N.Y., S.Dak., Vt., Wis., Wyo.

Systems

• Terrestrial

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.

Foodplant / parasite
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

Eastern Forest- The forest cover type White Spruce (Society of  American Foresters Type 107) (40) is found in either pure stands or mixed  stands in which white spruce is the major component. Associated species  include black spruce, paper birch (Betula papyrifera), quaking  aspen (Populus tremuloides), red spruce (Picea rubens), and  balsam fir (Abies balsamea). Yellow birch (B. alleghaniensis)  and sugar maple (Acer saccharum) are sometimes included in the  community mix.

    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 
16 Aspen 
18 Paper Birch 
38 Tamarack

    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 
217 Aspen 
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.

Throughout the range of white spruce, fire has  been an important, sometimes dominant factor in forest dynamics  (25,136,162). Mature forests are easily destroyed because of their high  susceptibility to fire. Under certain circumstances, in unmanaged forests  white spruce may be eliminated; the probability increases with latitude  because seed years are infrequent and seed quality poor in some years in  the north (136,183). During early- and mid-succession, white spruce is   more susceptible to fire than aspen, birch, black spruce, and lodgepole  pine (182).

    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.

More info for the term: fuel

Broadcast burning can be used for fuel reduction and site preparation
following logging of white spruce [68].  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 [5].

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. 

More info for the terms: density, fire use, frequency, prescribed fire, tree, wildfire

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) [31].  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 [66].

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 [16] 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 [74] 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.

Following fire, white spruce reestablishes via wind-dispersed seeds from
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.

More info for the terms: fire intensity, severity, tree, wildfire

Viereck and Schandelmeier [61] 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 [24].  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 [31].

Following a late May-early June wildfire in Interior Alaska, Zasada
[66] 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.

More info for the terms: duff, litter

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 [41].  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
[55].  Cones are not necessarily destroyed by summer fires, but immature
seeds will not ripen on fire-killed trees.

More info for the terms: fire frequency, frequency

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 [41].  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 [66].  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 [1].

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
[45].  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 [32].  Fire frequency in white spruce forest
types is generally between 60 and 200 years [45].  In Alaska, Foote [24]
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
old.

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
exposed [24].

More info on this topic.

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 [56].  White
spruce seedlings establish under these seral hardwoods, develop and grow
slowly, and eventually replace them.  White spruce-aspen, white
spruce-birch, and white spruce-balsam poplar are common mid-successional
communities that, with the continued absence of fire, will gradually be
replaced by essentially pure stands of white spruce.  Foote [24]
outlined six postfire successional stages for sites capable of
supporting climax white spruce stands in interior Alaska:

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

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

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

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

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

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

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

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

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

More info for the terms: codominant, layering, litter, natural, tree

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

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

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

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

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

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

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

More info on this topic.

More info for the terms: phanerophyte, therophyte

   Undisturbed State:  Phanerophyte (mesophanerophyte)
   Burned or Clipped State:  Therophyte

More info for the term: tree

Tree

   off-site colonizer; seed carried by wind; postfire years 1 and 2

White spruce is intermediate in  tolerance to shade. It is equally or less tolerant to shade than black or  red spruce, hemlock (Tsuga spp.), balsam and alpine fir, sugar  maple, and beech (Fagus spp.). It is more tolerant than aspen,  paper birch, and lodgepole pine.

    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.

White spruce is frequently characterized as  shallow rooted. This generalization stems, however, from the species'  ability to occupy sites where soil conditions limit rooting depth (148);  depending on soil conditions, competition, and genetics, different forms  of taproots and layered roots do develop (145,166). The adventitious  multilayered root systems that develop on floodplains in response to silt  deposits are particularly noteworthy. Trees from 2 to 132 years old can   grow new roots in this way; the response is probably important for  maintaining tree vigor (77,164).

    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).

More info on this topic.

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

Vegetative reproduction from layering  is common at some latitudinal treeline sites in Canada and Alaska (26,39).  Layering probably is an important means of maintaining the stand when  sexual reproduction is limited or nonexistent because of climatic  limitations.

    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).

White spruce seed shows conditional  dormancy that varies in response to temperature and light conditions and  therefore can be modified by stratification or prechilling. Optimum  germination temperatures are from 10° to 24° C (50° to 75°  F); maximum germination temperature is between 29° and 35° C (84°  and 95° F). Minimum constant temperature is 5° C (41° F),  but most germination ceases below 10° C (50° F). A diurnal  fluctuation in temperature may be favorable (27,47).

    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).

Cones and seeds have been  produced by 4-year-old trees (149). Production "in quantity" on  10- to 15-year-old trees has been reported, but it is usually low in  younger trees and depends on site and season. Seed production in quantity  begins at age 30 or older for most natural stands (44,117). The interval  between good to excellent cone and seed crops varies with site and  geographic location. On good sites, good to excellent years can occur at  2- to 6-year intervals but may be as many as 10 to 12 years apart  (88,167,184,192). Excellent seed years may be related to hot, dry summers  at the time of bud differentiation (112). They are always followed by poor  ones; the alternation can result from carbohydrate and nutrient  deficiencies or the lack of sites in the crown able to produce  reproductive buds (117).

    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).

White spruce is monoecious. Reproductive  buds are differentiated at the time shoot growth ceases, the year before  flowering and seed dispersal (35,118). The process lasts about a week. In  British Columbia, it occurs during the last 2 weeks of July over a wide  range of sites; this suggests that it may occur at about the same time  throughout much of the species' range. Development of reproductive buds  continues for 2 to 2.5 months and coincides with shoot maturation. The   male buds become dormant first (about October 1 at Prince George, BC)  followed by the vegetative and female buds about 2 weeks, later (118).

    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).

In white spruce, strong apical dominance of  the terminal shoot leads to the excurrent growth form. Crown form may  deviate substantially from the idealized conical shape because of  variation in the growth of lateral branches as a result of tree and branch  age, damage, or growing conditions. The most significant deviations occur  near the treeline where marginal growing conditions can result in  shrub-like trees. During the juvenile phase, trees can be kept growing  continuously if all growth factors are within the optimum range. This is  called "free growth." In older trees shoot growth is  determinate; that is, the annual complement of needles is preformed in the  overwintering bud.

    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)   
Stand density 
  Basal  
area    
Total  
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)   
Stand  
density   
Basal 
area 
  Total  
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).

Population Differences    White spruce is highly variable over its range; the variation pattern is  clinal and generally follows the latitudinal and altitudinal gradients. As  an example, southern provenances are the fastest growing and the latest  flushing when tested near the southern edge of the range; Alaskan trees  are dwarfs and are susceptible to spring frost because they flush early.  Soil-related adaptive variation has been demonstrated, and variation in  germination temperature requirements have also been described (117).  Because the species shows such strong adaptive affinity to local  environments, seed collection and seed and seedling distribution must  adhere to seed zoning and seed transfer rules.

    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.

The following is a representative barcode sequence, the centroid of all available sequences for this species.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 23
Specimens with Barcodes: 28
Species With Barcodes: 1

Year Assessed

• Needs updating

Assessor/s

Reviewer/s

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

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.

More info for the terms: competition, cover, density, frequency, natural

Regeneration following timber harvest:  Natural regeneration of white
spruce following timber harvest is unreliable [53].  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 [67].  White spruce seedlings die when
shrub competition becomes severe [17].

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]. 

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.

White spruce trees yield many useful products (105,148). The manufacture  of wood fiber and lumber products is well known and white spruce continues  to be one of the most important commercial species in the boreal forest.  Less well-known uses of white spruce wood are for house logs, musical  instruments, paddles, and various boxes and containers.

    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.

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.

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.