Picea glauca, the white spruce, is a species of spruce native to the northern temperate and boreal forests in Canada and United States, North America.
Picea glauca is native from west-central Alaska and east across western, southern/central and eastern Canada to the Avalon Peninsula in Newfoundland, and south to Montana, North Dakota, Minnesota, Wisconsin, Michigan, Upstate New York and Vermont, along with the mountainous and immediate coastal portions of New Hampshire and Maine, where temperatures are just barely cool and moist enough to support it. There is also an isolated population in the Black Hills of South Dakota and Wyoming. It is also known as Canadian spruce, skunk spruce, cat spruce, and in its varieties, Black Hills spruce, western white spruce, Alberta white spruce, and Porsild spruce.
Description White spruce is a medium-sized evergreen conifer which typically grows to tall, with a trunk diameter of up to . Citations of much greater heights, to 40–50 m, refer to the taller-growing tree previously treated as the western variety albertiana, but now treated separately as the hybrid Picea × albertiana. The bark is thin and scaly, flaking off in small circular plates across. The crown is narrow conical in young trees, becoming columnar with a conical top in older trees. The shoots are pale buff-brown, glabrous in the east of the range, but often pubescent in the west, and with prominent pulvini. The leaves are needle-like, mostly long, occasionally to or exceptionally even , rhombic in cross-section, glaucous blue-green above (hence glauca), with several thin lines of stomata, and blue-white below with two broad bands of stomata.
The cones are pendulous, slender, cylindrical, long and 1.5 cm wide when closed, opening to 2.5 cm broad. They have thin, flexible scales 15 mm long with a smoothly rounded margin. They are green or reddish, maturing to pale brown 4 to 8 months after pollination. The seeds are black, 2 to 3 mm long, with a slender, tan wing 5 to 8 mm long.
Seeds
The seeds are small, long, oblong, and acute at the base. Determinations of the average number of sound seeds per white spruce cone have ranged from 32 to 130.Zasada, J.C.; Viereck, L.A. 1970. White spruce cone and seed production in interior Alaska, 1957–68. USDA, For. Serv., Pacific NW For. Range Exp. Sta., Portland OR, Res. Note PNW-129. 11 p. [Coates et al. 1994]
Common causes of empty seed are lack of pollination, abortion of the ovule, and insect damage.
The average weight per individual seed varies from .Hellum, A.K. 1976. Grading seed by weight in white spruce. USDA, For. Serv., Tree Plant. Notes 27(1):16–17, 23–24. (Cited in Coates et al. 1994).- Zasada, J.C.; Foote, M.J.; Deneke, F.J.; Parkerson, R.H. 1978. Case history of an excellent white spruce cone and seed crop in interior Alaska: cone and seed production, germination and seedling survival. USDA, For. Serv., Pacific NW For. Range Exp. Sta., Portland OR, Gen. Tech. Rep. PNW-65. 53 p.
Each seed is clasped by a thin wing 2 to 4 times as long as the seed. Seed and wing are appressed to the cone scale. Embryo and megagametophyte are soft and translucent at first; later the endosperm becomes firm and milky white, while the embryo becomes cream-coloured or light yellow. At maturity, the testa darkens rapidly from light brown to dark brown or black.Crossley, D.I. 1953. Seed maturity in white spruce. Canada Dep. Resour. and Devel., For. Branch, For. Res. Div., Ottawa ON, Silv. Res. Note 104. 16 p. Mature seeds "snaps in two" when cut by a sharp knife on a firm surface.
White spruce cones reach their maximum size after 800 GDD. Cone moisture content decreases gradually after about 1000 GDD.Cram, W.H.; Worden, H.A. 1957. Maturity of white spruce cones and seed. For. Sci. 3:263–269.
Cone colour also can be used to help determine the degree of maturation, though immature cones may be red, pink or green.Teich, A.H. 1970. Genetic control of female flower colour and random mating in white spruce. Can. Dep. Fish. For., Can. For. Serv., Ottawa ON, Bi-mo. Res. Notes 26:2. Collection and storage dates and conditions influence germination requirements and early seedling growth.Zasada, J.C. 1973. Effect of cone storage method and collection date on Alaskan white spruce (Picea glauca) seed quality. p. 1–10 (paper 19) in Proc. Seed Problems. IUFRO Symp. Seed Processing, Bergen, Norway. Working Party S2.01, Royal Coll. For., Bergen, Norway, Vol. 1. [Coates et al. 1994]Edwards, I.K. 1977. Fertility of transplant fields at the Prince Albert Forest Nursery. Can. Dep. Fish. Environ., Can. For. Serv., Northern For. Res. Centre, Edmonton AB, Inf. Rep. NOR-X-189. 21 p.Winston, D.A.; Haddon, B.D. 1981. Effects of early cone collection and artificial ripening on white spruce and red pine germination. Can. J. For. Res. 11:817–826.
, which may contain 6,500 to 8,000 cones, yields of clean seed.USDA Forest Service. 1948. Woody-plant Seed Manual. USDA, For. Serv., Washington DC, Misc. Publ. 654. 416 p.
Seed dispersal begins after cone scales reflex with cone maturation in the late summer or early fall of the year of formation. Cones open at moisture contents of 45% to 70% and specific gravities of 0.6 to 0.8. Weather affects both the initiation and pattern of seed dispersal, but cone opening and the pattern of seed dispersal can vary among trees in the same stand. Even after dispersal has begun, cold, damp weather will cause cone scales to close; they will reopen during dry weather. Most seed falls early rather than late, but dispersal may continue through fall and winter and even into the next growing season.Zasada, J. 1986. Natural regeneration of trees and tall shrubs on forest sites in interior Alaska. p. 44–73 in Van Cleve, K.; Chapin, F.S.; Flanagan, P.W.; Viereck, L.A.; Dyrness, C.T. (Eds.). Forest Ecosystems in the Alaskan Taiga: a Synthesis of Structure and Function. Springer-Verlag New York NY.Rowe, J.S. 1953. Viable seed on white spruce trees in midsummer. Can. Dep. Northern Affairs and National Resources, For. Branch, For. Res. Div., Ottawa ON, Silv. Leafl. 99. 2 p. Seed dispersal occurs mainly in late summer or early fall.
White spruce seed is initially dispersed through the air by wind. Both the initiation and pattern of seed dispersal depend on the weather, but these can vary among trees in the same stand. Small amounts of white spruce seed are normally dispersed beyond 100 m from the seed source, but exceptionally seeds have been found more than 300–400 m from the nearest seed source.
Root system
The root system of white spruce is highly variable and adaptable, responding to a variety of edaphic factors, especially soil moisture, soil fertility, and mechanical impedance.Wagg, J.W.G. 1964. White spruce regeneration on the Peace and Slave River lowlands. Can. Dep. For., For. Res. Branch, Ottawa ON, Publ. 1069. 35 p.Wagg, J.W.B. 1967. Origin and development of white spruce root-forms. Can. Dep. For. Rural Devel., For. Branch, Ottawa ON, Publ. 1192. 45 p. On soils that limit rooting depth, the root system is plate-like, but it is a common misconception to assume that white spruce is genetically constrained to develop plate-like root systems irrespective of soil conditions.Sutton, R.F. 1969. Form and development of conifer root systems. Commonw. For. Bureau, Oxford, U.K., Tech. Communication No. 7. 131 p. In the nursery, or naturally in the forest, white spruce usually develops several long 'running' roots just below the ground surface.Mullin, R.E. 1957. Experiments with root and top pruning of white spruce nursery stock. Ont. Dep. Lands For., Res. Div., Toronto ON, Res. Rep. 36. 31 p.
The structure of the tracheids in the long lateral roots of white spruce varies with soil nitrogen availability.Krasowski, M.J.; Owens, J.N. 1999. Tracheids in white spruce seedling's long lateral roots in response to nitrogen availability. Plant and Soil 217(1/2):215–228.
Stem
White spruce can live for several hundred years, with an estimated average lifespan of 250 to 300 years.Dallimore, W.; Jackson, A.B. 1961. A Handbook of Coniferae including Ginkgoaceae, 3rd (1948) ed. reprinted with corrections. Arnold, London, U.K. 686 p.
Slow-growing trees in rigorous climates are also capable of great longevity. White spruce high on the shore of Urquhart Lake, Northwest Territories, were found to be more than 300 years old.Hare, F.K.; Ritchie, J. 1972. The boreal bioclimates. Geogr. Rev. 62:333–365.
Bark The bark of mature white spruce is scaly or flaky, grey-brown or ash-brown, but silvery when freshly exposed.Brayshaw, T.C. 1960. Key to the native trees of Canada. Canada Dep. For., Bull. 125. 43 p.Harlow, W.M.; Harrar, E.S. 1950. Textbook of Dendrology, 3rd ed. McGraw-Hill, New York NY. 555 p. Resin blisters are normally lacking, but the Porsild spruce Picea glauca var. porsildii Raup has been credited with having smooth resin-blistered bark.Hosie, R.C. 1969. Native Trees of Canada, 7th ed. Can. Dep. Fish. For., Can. For. Serv., Ottawa ON. 380 p.
White spruce bark is mostly less than 8 mm and not more than 9.5 mm thick.Hale, J.D. 1955. Thickness and density of bark. Pulp and Paper Mag. Canada, Dec.:3–7.Chang, Y.P. 1954. Bark structure of North American conifers. USDA, For. Serv., Tech. Bull. 1095. 86 p.
Chemistry Isorhapontin can be found in spruce species such as the white spruce.
P. glauca has three different genomes; a nuclear genome, a mitochondrial genome, and a plastid (i.e. chloroplast) genome. The large (20 Gbp) nuclear genome of P. glauca (genotype WS77111) was published in 2015, and the organellar (plastid and mitochondrial) genomes (genotype PG29) were published in SD Jackman et al. 2015. The plastid genome of P. glauca (genotype WS77111) has also been published.
Varieties Four geographical varieties have been described, but not all are accepted as distinct by all authors. These comprise, from northeast to southwest: Picea glauca var. glauca (typical or eastern white spruce) — Newfoundland west to eastern Alberta, on lowland plains. Picea glauca var. porsildii (Alaska white spruce) — Alaska and Yukon. Often considered a synonym of var. glauca. Picea glauca var. densata (Black Hills white spruce) — the Black Hills in South Dakota. Picea glauca var. albertiana (Alberta white spruce) — the Rocky Mountains in Alberta, British Columbia and northwest Montana. Now considered to be a natural hybrid with the closely related Engelmann spruce (P. engelmannii), as Picea × albertiana
The western populations are distinguished by pubescent shoots. This pubescence may be related to the extensive hybridisation and intergradation with the closely related Engelmann spruce found further south in the Rocky Mountains, with which it forms the nothospecies Picea × albertiana, but pubescence is also present in var. porsildii. White spruce also hybridises readily with the closely related Sitka spruce where they meet in southern Alaska and northwestern British Columbia; this hybrid is known as Picea × lutzii.
Distribution and habitat