White spruce

Appearance

The white spruce is a large coniferous evergreen tree which grows normally to 15 to 30 m tall, but can grow up to 40 m tall with a trunk diameter of up to 1 m . The bark is thin and scaly, flaking off in small circular plates 5 to 10 cm across. The crown is narrow – conic in young trees, becoming cylindric 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, 12 to 20 mm long, rhombic in cross-section, glaucous blue-green above with several thin lines of stomata, and blue-white below with two broad bands of stomata.

The cones are pendulous, slender, cylindrical, 3 to 7 cm 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, 5 to 8 mm long pale brown wing.

Naming

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 noted that firmly-rooted white spruce served very well to stabilize windswept edges of woods in Germany. In a narrow belt of mixed Norway and white spruces over an extremely exposed hilltop crest at high elevation in northern England, the Norway spruce were “completely dwarfed” whereas the white spruce had reached heights of between 3 and 4.3 m . 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 do the other spruces .

Distribution

White spruce has a transcontinental range in North America. In Canada, its contiguous distribution encompasses virtually the whole of the Boreal, Subalpine, Montane, Columbia, Great Lakes – St. Lawrence, and Acadian Forest Regions , extending into every province and territory . 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 , 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 .

Southern outliers have been reported in southern Saskatchewan and the Cypress Hills of southwestern Saskatchewan and southeastern Alberta , northwestern Montana , south-central Montana , in the Black Hills on the Wyoming–South Dakota boundary , on the Manitoba–North Dakota boundary , and at Shushan, New York .


White spruce is the northernmost tree species in North America, reaching just north of 69°N latitude in the Mackenzie River delta. It grows between sea level and an elevation of 1,520 m . Its northern distribution roughly correlates to the location of the tree line, which includes an isothermic value of 10 °C for mean temperature in July, as well as the position of the Arctic front; cumulative summer degree days, mean net radiation, and the amount of light intensities also figure. White spruce generally is found in regions where the growing season exceeds 60 days annually.

The southern edge of the zone in which white spruce forms 60% or more of the total stand corresponds more or less to the July isotherm of 18 °C around the Great Lakes; in the Prairie Provinces its limit is north of this isotherm. During the summer solstice, day length values range from 17 hours at its southern limits to 24 hours above the Arctic Circle.

One of the hardiest conifers, white spruce in parts of its range withstands mean daily January temperature of −6.7 °C and extreme minimum temperatures as low as −56.5 °C ; minimum temperatures of −50 °C are general throughout much of the range except the southernmost and southeasternmost parts . By itself, or with black spruce and tamarack , 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 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 . Although Bell was emphatic that it “nowhere reaches the Atlantic coast [from which it recedes] further and further in going north”. Across western Canada and Alaska, white spruce occurs further north than black spruce, and, while poplar , willow, and birch may occur along streams well into the tundra beyond the limits of spruce, the hardwoods are usually no more than scrub . 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 noted that the northernmost collection of white spruce was at latitude 59°48’N, but Bryson et al. 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. noted that the forest retained “the same general characteristics as when it was first described [by Tyrrell ] in 1896”. 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, and Sargent noted that white spruce in Alaska “reached Behring Strait in 66°44′ N”.

Climate, especially temperature, is obviously a factor in determining distributions of northern flora. Halliday and Brown suggested that white spruce’s northern limit corresponds “very closely” with the July mean monthly isotherm of 10 °C in Ungava, but that the northern limit west of Hudson Bay was south of that isotherm. Other climatic factors that have been suggested as affecting the northern limit of white spruce include: cumulative summer degree days, position of the Arctic front in July, mean net radiation especially during the growing season, and low light intensities . Topography, soil conditions, and glaciation may also be important in controlling northern limits of spruce .

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 . Sargent and Harlow and Harrar also included Vermont and New Hampshire; and, while Dame and Brooks 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/sprouting competitiveness with allelopathic depredation of coniferous regeneration . Further southward extension of the distribution is inhibited by white spruce’s cold requirement.

Habitat

White spruce is a climax canopy tree in the boreal forests of Canada and Alaska. It generally occurs on well-drained soils in alluvial and riparian zones, although it also occurs in soils of glacial and lacustrine origin. The understory is dominated by feather mosses , and occasionally peat moss. In the far north, the total depth of the moss and underlying humus is normally between 25 to 46 cm , although it tends to be shallower when hardwoods are present in the stand.

White spruce grows in soils with pH values of 4.7–7.0, although they have been found in soils as acidic as 4.0 in subalpine fir forests in the Northwest Territories. A presence of calcium in the soil is common to white spruce found in northern New York. White spruce most commonly grows in the soil orders of Alfisols and Inceptisols. Soil properties such as fertility, temperature, and structural stability are partial determinants of the ability of white spruce to grow in the extreme northern latitudes. In the northern limits of its range, white spruce is the climax species along with black spruce; birch and aspen are the early succession species.
Wildfires typically occur every 60 to 200 years, although they have been known to occur as infrequently as every 300 years.

White spruce will grow in USDA Growing Zones 3-7, but is not adapted to heat and humidity and will perform poorly in a hot climate. The tree attains its greatest longevity and growth potential in Zones 3-4.

Predators

Outbreaks of spruce beetles have destroyed over 2,300,000 acres of forests in Alaska.

Although sometimes described, e.g., by Switzer , 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 , the yellow-headed spruce sawfly , the European spruce sawfly , the spruce bud moth ','' and spruce beetle . 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 .

A number of sawflies feed on spruce trees. Among them European spruce sawfly, yellow-headed spruce sawfly, green-headed spruce sawfly and the spruce webspinning sawfly .

More than a dozen kinds of looper feed on the spruces, fir, and hemlock in eastern Canada. The full-grown larvae of the larvae vary in length from 15 mm to 35 mm. Some feed briefly in the fall and complete their feeding in the spring; others feed mainly in the summer; still others feed mainly in the late summer and fall.

The fall and spring feeding group includes the dash-lined looper , the diamond-backed looper , the fringed looper , and the false loopers . The summer feeding group includes the false hemlock looper , occasionally occurring in large numbers and usually in conjunction with the hemlock looper , the small spruce loopers ''Eupithecia'' species, the yellowlined conifer looper , and the saddleback looper .

The late summer and fall group includes the common spruce-fir looper and the similar ''Semiothisa fissinotata'' Walker on hemlock, the small spruce loopers ''Eupithecia'' species, the spruce looper ''Caripeta divisata'' Walker, occasionally abundant, the transversebanded looper , and the whitelined looper .

Uses

White spruce is of major economic importance in Canada for its wood, harvested for paper-making and construction. It is also used to a small extent 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.

White spruce is the provincial tree of Manitoba and the state tree of South Dakota.