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 15 to 30 metres (50 to 100 ft) tall, with a trunk diameter of up to 1 m (3 ft 3 in). 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 5 to 10 centimetres (2 to 4 in) 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 8 to 13 mm (1⁄4 to 1⁄2 in) long, occasionally to 20 mm (3⁄4 in) or exceptionally even 25 mm (1 in), 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, 2.5 to 7 cm (1 to 2+3⁄4 in) 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, 2.5 to 5 mm (0.098 to 0.197 in) 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. Common causes of empty seed are lack of pollination, abortion of the ovule, and insect damage. The average weight per individual seed varies from 1.1 to 3.2 mg (0.017 to 0.049 gr). 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. 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. Cone colour also can be used to help determine the degree of maturation, though immature cones may be red, pink or green. Collection and storage dates and conditions influence germination requirements and early seedling growth. 1 imperial bushel (36 L), which may contain 6,500 to 8,000 cones, yields 6 to 20 ounces (170 to 570 g) of clean seed. 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. 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. 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. In the nursery, or naturally in the forest, white spruce usually develops several long 'running' roots just below the ground surface. The structure of the tracheids in the long lateral roots of white spruce varies with soil nitrogen availability.
Stem
White spruce can live for several hundred years, with an estimated average lifespan of 250 to 300 years. Slow-growing trees in rigorous climates are also capable of great longevity. White spruce 6 to 10 m (20 to 33 ft) high on the shore of Urquhart Lake, Northwest Territories, were found to be more than 300 years old.
Bark The bark of mature white spruce is scaly or flaky, grey-brown or ash-brown, but silvery when freshly exposed. Resin blisters are normally lacking, but the Porsild spruce Picea glauca var. porsildii Raup has been credited with having smooth resin-blistered bark. White spruce bark is mostly less than 8 mm and not more than 9.5 mm thick.
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:
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