White Spruce

Issue: 
May-June 2007

THIS SPECIES FOCUS HAS BEEN INSPIRED by the heavy, heavy cone set on our conifers in general, and on white spruce at the tree line around Churchill, Manitoba – in particular in 2006. White spruce, like jack pine and balsam poplar (tackled in my previous columns; visit the Fact Sheets link on www.isaontario.com) is a Canadian tree. It ranges from Newfoundland into Alaska, with incursions into Maine, New York and across the southern Great Lakes’ watersheds. As a tree typical of the boreal forest, it shares its range with black spruce (Picea mariana). It is naturally absent from Carolinian forests of southern Ontario.

Biology Basics & Distribution
White spruce, with its elegant, spire-like growth in favourable places, has a paler, smoother bark than does black spruce. Its needles are straight and stiff, about 15 to 22 mm long and, although pointed, are not sharply tipped. They are green to bluish green, and when broken or crushed give off a pungent scent that has given rise to another common name, “skunk spruce.” It is the waxy surface of the 4-angled needles that give rise to the name glauca, which means shiny, or lustrous

White spruce grows in many conditions, even invading abandoned farmlands in the east, giving the origin of yet another common name for this tree, “pasture spruce.” Because it is part of the natural assemblage of plants of the boreal forest, it succumbs to forest fires. Its thin bark provides no fire-resistance, but its wind dispersed seeds blow into places usually already colonized by aspen, birch and balsam poplar, where they germinate after overwintering under the snow, establish and overtop the other trees and re-establish themselves. Like most plants of the boreal forest, it has shallow roots, and is susceptible to blow-down. However, on the floodplains of northern rivers, the trees can become exceptionally large with layerings of adventitious roots that grow from the bole as sediment is deposited when the rivers flood. These may become exposed as the river erodes the alluvial deposits in later years.

With its great capacity to grow under widely different conditions, it has huge variability in growth form. At the tree line, white spruce grows very slowly and often takes on typical, short (less than a metre, yet producing cones) krummholz form, pruned by wind-driven ice, snow, soil and sand – especially at the top of the snow layer. In exposed sites in Newfoundland, such as the coastal Avalon and Great Northern Peninsulas, the trees are generally short with tapered boles that are characteristically conical. On sheltered floodplains and valleys, they may grow to heights of 40 metres and have diameters (DBH) of 1 metre and more. The oldest white spruce on record, from the Yukon territory, is dated at 668 years.

Although white spruce can produce cones when young, they do not really start to seed until they are about 30 years-old. The cones vary in colour from green through to deep purple.

Genetic Diversity and Pests
The diversity of growth form is also reflected in the genetic diversity in the species. One of the recognizable varieties is Porsild’s spruce (P. glauca var. porsildii) that grows in the Yukon Territory and northern Alberta. It shares characteristics with balsam fir (Abies balsamea) in having resin blisters on its smooth bark. In the west, where it co-occurs with Engelmann (P. engelmannii) and Sitka (P. sitchensis), hybrids with intermediate characteristics are frequent. Arboricultural varieties are available for ornamental plantings, with “Alberta spruce,” a fine-textured, conical dwarf, and “Black Hills spruce” (Picea glauca densata) are two that are well used, the latter for shelter belts.

As tough as white spruce may be, it has its enemies. Needle and stem rusts, root diseases, trunk rots, mistletoe, bark beetles, wood-boring insects, weevils, spruce budworm (which seems to prefer balsam fir), and yellow-headed spruce sawfly all attack the trees. Squirrels and cone infesting insects (e.g. especially spruce cone maggot, fir cone worm, and spruce seed moth) can cause major losses of seeds.

A Wood of Many Uses
White spruce has been of immense value. Nowadays, it is mostly harvested for pulp and paper, but its overall utility was recognized extensively by people of the First Nations, Métis, and early settlers from Europe. The wood was used for canoe frames, canoe paddles, and of course buildings. The saplings were bent into snowshoe frames and bows. Heated gum is a glue and traditionally was and is used to fasten skins onto bows and arrowheads onto shafts. It was used as a sealant and waterproofing in canoe building. Decayed wood could be made into a yellow dye, provided material for tanning hides, and in powdered form was used for baby care. Spruce bark made roofing, flooring and canoe hulls, cooking pots and trays for harvesting berries. The long and stringy roots are pliable enough to use for lacings in canoe building and basketry.

The trees also provided food. Young male catkins can be eaten raw or cooked as a flavouring. When roasted, immature female cones have a centre that is sweet and syrupy. The inner bark can be dried, ground into a powder and used to thicken soups or added to grains when making bread or bannock. Young shoot tips can be made into a Vitamin C rich and refreshing tea. The trunk yields chewing gum and spruce oil, distilled from the leaves and twigs, is used in the food industry to flavour chewing gum, ice cream, soft drinks and sweets.

White spruce has many uses in traditional herbal medicine. The inner bark and young shoots can be chewed, made into a tea, or used in steam bathing for treatment of tuberculosis, influenza, coughs, colds and rheumatism. The inner bark can be placed on sores and wounds where its antiseptic properties promote healing. The gum has similar properties and can also be used to aid digestion and as a laxative. The cones, made into an infusion, have been used for treating urinary difficulties. Even today, people make both alcoholic and non-alcoholic “spruce beers” using the young shoots. Captain Cook is reported to have used spruce beer on his long voyages to counteract scurvy.

Burning spruce needles on a camp fire has been advocated to repel biting flies. The Koyukon people of Alaska have a tradition that sleeping beneath a white spruce offered protection from malevolent spirits.

The wood is straight-grained, resilient, light and soft, but not strong. It is valued as a timber tree for lumber and pulp and paper. The wood transmits vibrations well so it is useful in making musical instruments such as guitars, violins, piano sounding boards and so on. Spruce wood is also made into specialty items such as canoe paddles and oars, cabinets, boxes and food containers Although spruce is used to make plywood, the famous aeroplane “The Spruce Goose” was made not from spruce-based plywood, but from birch plywood.

White spruce is one of the dominant trees of the moose-spruce biome. Nevertheless, white spruce is not that palatable to moose and deer. Snowshoe hares sometimes feed on saplings and seedlings, but it is the cones and seeds that are eaten extensively by small mammals such as mice, voles, shrews and chipmunks. In the spring, red squirrels clip twigs and feed on vegetative and reproductive buds, especially during years when the cone crop is poor. The seeds are their favoured food, preferred over those of black spruce, and are nutritionally rich enough to sustain the squirrels over winter. Even though the seeds are mostly wind dispersed, they are moved about by squirrels and may germinate in their seed caches. Spruce grouse subsist entirely on spruce needles during winter. Many small birds, such as chickadees, nuthatches, crossbills and pine siskin feed on the seeds from the open cones or on the ground.

Manitoba chose well for its provincial tree. Resilience, strength and utility are all represented. Its prevalence on the Manitoba landscape is important to wildlife and the people. The white spruce is a tree to watch. Will it move north with global warming? My guess is “yes” – and probably quite rapidly once it starts to march. ©

— Peter Kevan, University of Guelph and Helen Murphy, University of Windsor. Photo from: Trees of Ontario, Lone Pine Publishing, 2001.

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.