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 central Alaska all through the east, across western and southern/central Canada to the Avalon Peninsula in Newfoundland, Quebec, Ontario 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, Black Hills spruce, western white spruce, Alberta white spruce, and Porsild spruce.
Description
The white spruce is a large evergreen conifer which normally grows to tall, but can grow up to tall with a trunk diameter of up to . The bark is thin and scaly, flaking off in small circular plates across. The crown is narrowconical in young trees, becoming cylindrical 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, long, 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.
Common causes of empty seed are lack of pollination, abortion of the ovule, and insect damage.
The average weight per individual seed varies from .
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.
Cone colour also can be used to help determine the degree of maturation, but cones may be red, pink or green. Collection and storage dates and conditions influence germination requirements and early seedling growth.
, which may contain 6,500 to 8,000 cones, yields 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. Seed dispersal occurs mainly in late summer or early fall. 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
thumb|Trunk; bark is scaly or flaky and grey-brown.
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 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
thumb|upright=.8|Dwarf Alberta white spruce in [[Los Angeles County Arboretum and Botanic Garden]]
Several geographical varieties have been described, but are not accepted as distinct by all authors. These comprise, from east to west: On the west coast of Hudson Bay, it extends to Seal River, about 59°N, "from which the northward limit runs apparently almost directly north-west to near the mouth of the Mackenzie River, or about latitude 68°". Collins and Sumner reported finding white spruce within 13 km of the Arctic coast in the Firth Valley, Yukon, at about 69°30′ N, 139°30′ W. It reaches within 100 km of the Pacific Ocean in the Skeena Valley, overlapping with the range of Sitka spruce (Picea sitchensis), and almost reaching the Arctic Ocean at latitude 69° N in the District of Mackenzie, with white spruce up to 15 m high occurring on some of the islands in the Delta near Inuvik. The wide variety of ecological conditions in which 4 Quebec conifers, including white spruce, are able to establish themselves, was noted by Lafond, but white spruce was more exacting than black spruce. In the United States, the range of white spruce extends into Maine, Vermont, New Hampshire, New York, Michigan, Wisconsin, Minnesota, and Alaska, where it reaches the Bering Strait in 66°44′ N" at Norton Bay and the Gulf of Alaska at Cook Inlet. and southeastern Alberta, northwestern Montana,
White spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie River delta. It grows between sea level and an elevation of . Its northern distribution roughly correlates to the location of the tree line, which includes an isothermic value of for mean temperature in July, as well as the position of the Arctic front; cumulative summer degree days, mean net radiation, and the amount of light intensities also figure. White spruce is generally found in regions where the growing season exceeds 60 days annually. By itself, or with black spruce and tamarack (Larix laricina), white spruce forms the northern boundary of tree-form growth. White spruce up to 15 m in height occur at 69°N on islands in the Mackenzie Delta near Inuvik in the Northwest Territories. Hustich (1966) depicted Picea spp. as forming the northernmost limit of tree growth in North America.
The arctic or northern timberline in North America forms a broad transition zone from Labrador to northern Alaska. In Labrador, white spruce is not abundant and constitutes less than 5% of the forest, with a range that coincides very closely with that of black spruce but extending slightly further north.
The range of white spruce extends westwards from Newfoundland and Labrador, and along the northern limit of trees to Hudson Bay, Northwest Territories, Yukon, and into northwestern Alaska. Spruce characteristically occurs in fingers of tree-form forest, extending far down the northern rivers and as scattered clumps of dwarfed "bush" spruce on intervening lands. In Manitoba, Scoggan found white spruce in the northern edge of continuous forest in central Canada at Ennadai Lake, about 60°45′ N, 101°'W, just north of the northwest corner of Manitoba. Bryson et al.] in 1896". Collins and Sumner
The southern limit of distribution of white spruce is more complex. From east of the main range of coastal mountains in British Columbia, the southern continuous limit of white spruce is the forest/prairie interface through Alberta, Saskatchewan, Manitoba, the northern parts of Minnesota and Wisconsin, central Michigan, northeastern New York, and Maine. excluded New York and states further west, they included Massachusetts as far south as Amherst and Northampton, "probably the southern limit of the species" in that area. Nisbet gave the range of white spruce as extending to "Carolina", but he did not recognize red spruce as a species and presumably included it with white spruce.
Towards the southern parts of its range, white spruce encounters increasingly effective ecological competition from hardwoods, some of which may reinforce their growth-rate or sprouting competitiveness with allelopathic depredation of coniferous regeneration. Further southward extension of the distribution is inhibited by white spruce's cold requirement.
As an exotic species
As an exotic, white spruce is widespread but uncommon. It was introduced into England and parts of continental Europe in or soon after the year 1700, into Denmark about 1790, and into Tasmania and Ceylon shortly before 1932.
Nisbet The age of the belt was not recorded, but adjoining 66-year-old stands may have been of the same vintage.
White spruce has also been used as a minor plantation species in England and Scotland. In Scotland, at Corrour, Inverness-shire, Sir John Stirling Maxwell in 1907 began using white spruce in his pioneering plantations at high elevations on deep peat. However, plantations in Britain have generally been unsatisfactory, mainly because of damage by spring frosts after mild weather had induced flushing earlier in the season. However, the species is held in high regard in the Belgian peat region, where it grows better than other spruces.
Ecology
thumb|upright=1.3|Growing in the [[riparian zone amid treeless bogs]]
White spruce is a climax canopy tree in the boreal forests of Canada and Alaska. It generally occurs on well-drained soils in alluvial and riparian zones, although it also occurs in soils of glacial and lacustrine origin. In the far north, the total depth of the moss and underlying humus is normally between , although it tends to be shallower when hardwoods are present in the stand. The seeds are eaten by small mammals like the American red squirrel and birds such as chickadee, nuthatch, and pine siskin. The wide range of textures accommodated includes clays, even those that are massive when wet and columnar when dry, sand flats, and coarse soils. Its occurrence on some organic soils is not characteristic, except perhaps on shallow mesic organic soils in Saskatchewan and in association with black spruce on organic soils in central Yukon. White spruce makes good growth on well-drained lacustrine soils in Alberta Mixedwoods, on moderately-well-drained clay loams in Saskatchewan, and on melanized loams and clays (with sparse litter and a dark-coloured organically-enriched mineral horizon) in the Algoma district of Ontario.
On dry, deep, outwash deposits in northern Ontario, both white spruce and aspen grow slowly. But, broadly, white spruce is able to tolerate considerable droughtiness of sites that are fertile, and no fertile site is too moist unless soil moisture is stagnant. Soil fertility holds the key not just to white spruce growth but to the distribution of the species. At least moderate fertility is needed for good growth, but white spruce occurs on many sites where nutrient deficiencies depress its growth more than that of black spruce, red spruce, Norway spruce, and the pines generally. Minimum soil-fertility standards recommended for white spruce sufficient to produce 126 to 157 m<sup>3</sup>/ha of wood at 40 years are much higher than for pine species commonly planted in the Lake States (Wilde 1966): 3.5% organic matter, 12.0 meq/100 g exchange capacity, 0.12% total N, 44.8 kg/ha available P, 145.7 kg/ha available K, 3.00 meq/100 g exchangeable Ca, and 0.70 meq/100 g exchangeable Mg.
thumb|upright|Mossy forest floor under white spruce
Forest floors under stands dominated by white spruce respond in ways that vary with site conditions, including the disturbance history of the site. Acidity of the mineral soil sampled at an average depth of 17 cm in 13 white spruce stands on abandoned farmland in Ontario increased by 1.2 pH units over a period of 46 years.
A considerable range of soil pH is tolerated by white spruce. rooting depth in those soils was at least 81 cm. An abundant calcium supply is common to most white spruce locations in New York state. High-lime ecotypes may exist, and in Canada Forest Section B8 the presence of balsam poplar and white spruce on some of the moulded moraines and clays seems to be correlated with the considerable lime content of these materials, while calcareous soils are favourable sites for northern outliers of white spruce. The thickness of the moss–organic layer commonly exceeds 25 cm in the far north and may approach twice that figure. The mosses compete for nutrients and have a major influence on soil temperatures in the rooting zone. Permafrost development in parts of Alaska, Yukon, and the Northwest Territories is facilitated by the insulative organic layer (Viereck 1970a, b, Gill 1975, Van Cleve and Yarie 1986).
Cold hardiness
thumb|left|Young tree with light snowcover
White spruce is extremely hardy to low temperatures, provided the plant is in a state of winter dormancy. Throughout the greater part of its range, white spruce routinely survives and is undamaged by winter temperatures of , and even lower temperatures occur in parts of the range.
Especially important in determining the response of white spruce to low temperatures is the physiological state of the various tissues, notably the degree of "hardening" or dormancy. A natural progression of hardening and dehardening occurs in concert with the seasons. While different tissues vary in ability to tolerate exposure to stressful temperatures, white spruce, as with woody plants in general, has necessarily developed sufficient winter hardiness in its various tissues to enable them to survive the minimum temperatures experienced in the distribution range.
White spruce is subject to severe damage from spring frosts. Newly flushed shoots of white spruce are very sensitive to spring frost. This sensitivity is a major constraint affecting young trees planted without overstorey nurses in boreal climates.
Forest succession
thumb|upright=1.2|Disturbed roadside blooms with early succession [[fireweed; behind, late-succession Alaskan white spruce forest, Yukon]]
Forest succession in its traditional sense implies two important features that resist direct examination. First, classical definitions generally connote directional changes in species composition and community structure through time, yet the time frame needed for documentation of change far exceeds an average human lifespan. who pointed out that the various stages in primary succession reflect physical, chemical, and biological controls of ecosystem structure and function. Thus, each successional stage has a species combination in harmony with site quality. Short-circuiting succession by planting a late successional species such as white spruce on an early successional surface may result in markedly reduced growth rates because of nitrogen insufficiency. Without application of substantial amounts of fertilizer, use would have to be made of early successional alder and its site-ameliorating additions of nitrogen.
thumb|upright=1.2|left|Old-growth Alaskan white spruce, [[Yukon]]
Neiland and Viereck noted that "the slow establishment and growth of spruce under birch stands [in Alaska] may be partially due to effects of shading and general competition for water and nutrients, but may also be more directly related to the birch itself. Heikinheimo found that birch ash inhibited white spruce seedlings, and Gregory found that birch litter has a smothering effect on spruce seedlings.".
On dry upland sites, especially south-facing slopes, the mature vegetation is white spruce, white birch, trembling aspen, or a combination of these species. Succession follows in one of two general patterns. In most cases, aspen and birch develop as a successional stage after fire before reaching the spruce stage. But, occasionally, with optimal site conditions and a source of seed, white spruce will invade with the hardwoods or within a few years thereafter, thereby producing even-aged white spruce stands without an intervening hardwood stage.
Associated forest cover
thumb|[[Taiga in the Gaspésie, Québec, including other species]]
The White Spruce Cover Type may include other species in small numbers. In Alaska, associates include paper birch, trembling aspen, balsam poplar, and black spruce; in western Canada, additional associates are subalpine fir, balsam fir, Douglas-fir, jack pine, and lodgepole pine. Seral species giving way to white spruce include paper birch, aspen, balsam poplar, jack pine, and lodgepole pine. On certain river bottom sites, however, black spruce may replace white spruce.
In most of its range, white spruce occurs more typically in association with trees of other species than in pure stands.
White spruce is an associated species in the following Eastern Forest cover types, by the Society of American Foresters; in the Boreal Forest Region: (1) jack pine, (5) balsam fir, (12) black spruce, (16) aspen, (18) paper birch, and (38) tamarack; in the Northern Forest Region: (15) red pine, (21) eastern white pine, (24) hemlock-yellow birch, (25) sugar maple-beech-yellow birch, (27) sugar maple, (30) red spruce-yellow birch, (32) red spruce, (33) red spruce-balsam fir, (37) northern white-cedar, and (39) black ash-American elm-red maple.
Predators
thumb|left|upright=1.1|[[Choristoneura fumiferana, the eastern spruce budworm. Adult (silvery) and pupa (dark brown) on a white spruce.]]
Outbreaks of spruce beetles have destroyed over of forests in Alaska.
Although sometimes described as relatively resistant to attack by insects and disease, white spruce is far from immune to depredation. Important insect pests of white spruce include the spruce budworm (Choristoneura fumiferana), the yellow-headed spruce sawfly (Pikonema alaskensis), the European spruce sawfly (Gilpinia hercyniae), the spruce bud moth (Zeiraphera canadensis), As well, other budworms, sawflies, and bark beetles, gall formers, bud midges, leaf miners, aphids, leaf eaters, leaf rollers, loopers, mites, scales, weevils, borers, pitch moths, and spittlebugs cause varying degrees of damage to white spruce.
- Species feeding in autumn and spring include the dash-lined looper (Protoboarmia porcelaria), the diamond-backed looper (Hypagyrtis piniata), the fringed looper (Campaea perlata), and several false loopers (Syngrapha).
- Picea glauca 'Echiniformis'
- Picea glauca var. albertiana 'Alberta Globe'
- Picea glauca var. albertiana 'Conica'
'Conica' is a dwarf conifer with very slender leaves, like those normally found only on one-year-old seedlings, and very slow growth, typically only per year. Older specimens commonly 'revert', developing normal adult foliage and starting to grow much faster; this 'reverted' growth must be pruned if the plant is to be kept dwarf.
Uses
thumb|Black Hills spruce grown as [[bonsai]]
The wood of white spruce is of a lower quality than that of Engelmann spruce, but is stronger. It was used to make shelters and as firewood by Alaska Natives and European settlers in Alaska, where lodgepole pine does not grow. The wood is of major economic importance in Canada, being harvested for paper and construction.
It is also used as a Christmas tree.
The wood is also exported to Japan where, known as "shin-kaya", it is used to make go boards as a substitute for the rare kaya wood. Additionally, Picea glauca var. densata is used for bonsai.
White spruce is the provincial tree of Manitoba and the state tree of South Dakota.
The new growth or tips of white spruce is used in beer making, gin production, flavouring soda, candy making or in pickles and preserves.