(white spruce)Select an option below for more information on this species
Picea glauca (white spruce) is a coniferous tree that can grow to more than 30 m in height in Denali, with basal diameters of up to 70 cm. However, because of our location near the edge of this species' northern range limit, and the high topographic diversity in the park, white spruce trees here are often smaller than 30 m tall, particularly in cold, wet, exposed or high elevation sites.
In outline, white spruce trees usually taper from a wide base to a narrow conical crown, and open-grown individuals often develop a symmetrical and attractive strongly conical shape with branches reaching several meters out from the bole near the ground. White spruce trees growing in dense stands, in contrast, are often asymmetrical with more columnar or irregular silhouettes due to injury or differential growth due to shading by neighbors. Branches of white spruce droop from their point of attachment to the bole, and sometimes have upturned ends near the crown perimeter, as they reach for sunlight.
Picea glauca has stiff, blue-green, four-angled needles with whitish lines on the underside. Needles extend in all directions (like a bottlebrush) from the twigs and each needle is borne on a small peg-like pedicel, which remains once the needle falls, giving fallen twigs a rough texture. Twigs of white spruce are hairless (in contrast to the minutely red-haired twigs of black spruce, Picea mariana). Picea glauca has thin grey bark and nearly white wood.
The cylindrical female cones, which are light brown at maturity, hang downward from branches and are usually positioned toward the branch-tips and clustered near the top of the tree. In contrast, male cones are borne lower in the canopy and wither and fall soon after pollen is distributed in spring. Seed-bearing cones open in late August and September while on the tree and winged seeds fall to the ground after cones open.
Though white spruce is typically large and black spruce (P. mariana) is often dwarfed, these habits can be misleading. The absence of red hairs on young twigs and cylindrical cones borne at branch ends (instead of ovoid cones borne close to the bole) are the best characters to identify white spruce. Hybrids with black spruce are known to occur.
There are many insects that utilize P. glauca, the actions of which can have broad implications for forest structure and function, succession, wildfire dynamics, and nutrient cycling. Probably the most important insect on white spruce is the spruce bark beetle (Dendroctonus rufipennis) which can cause significant mortality, particularly in drought stressed or otherwise weakened trees. Large outbreaks of spruce beetles, probably fueled by warmer temperatures, have killed millions of acres of spruce forest (primarily in south-central Alaska) in the last 30 years, and continue to spread to living trees. Presently spruce beetles exist at low levels in Denali but have not as of yet caused widespread mortality.
Other important insects that feed on P. glauca include (but are not limited to): engraver bark beetles (Ips spp.), spruce coneworm (Dioryctria reniculelloides), spruce budworm, Choristoneura spp), giant conifer aphid (Cinara spp.), and the spruce gall aphids (Adelges spp. and Pineus spp.) (Holsten et al. 2001).
There are numerous important fungal diseases that affect Picea glauca in Alaska. Probably the most noticeable disease is spruce broom rust, caused by the fungus (Chrysomyxa arctostaphyli, which produces the distinctive perennial "witches brooms". Arctostaphylos uva-ursi is the secondary host for this fungus (required to complete its life cycle). Although broom rust doesn't kill the tree, it can weaken it and could serve as an entrance for other decay fungi to infect the tree. Brooms are important nesting sites for wildlife including red and flying squirrels (Holsten et al. 2001). Spruce needle rust (Chrysomyxa ledicola) is a similar fungal disease that affects new needle growth of P. glauca. Labrador tea (Rhododendron groenlandicum and/or R. tomentosum ssp. decumbens) is the secondary host for this fungus. There are various root rot and decay fungi that grow on P. glauca that are important contributors to boreal forest structure, function, succession, and nutrient cycling including, but not limited to: red belt fungus (Fomitopsis pinicola, tomentosus root rot (Inonotus tomentosus), and pini conk (Phellinus pini) (Holsten et al. 2001).
White spruce is a softwood regularly used as lumber, its bark in roofing, and long roots for twine or in baskets. It is the favorite species for cabin logs in interior and northern Alaska, due to its size and usually straight boles. In industrial applications white spruce is also used as pulpwood and cut into lumber for use in construction. Spruce roots are traditionally harvested by interior Natives to make baskets. Tea brewed from the soft growth tips can be consumed for colds or pleasure. The Dena'ina use spruce roots, pitch, bark and tips for a variety of medicinal purposes (Kari 1995). Pitch is used to help heal cuts, and also is converted into a healing salve by mixing with fat (or wax) for use on other types of skin injuries and infections by the Inupiat, Yup'ik and Tlingit (Garibaldi 1999, Jernigan et al. 2015). The pitch is commonly chewed like gum.
Picea glauca occurs naturally only in North America, although it has been planted by people on other continents. White spruce occurs across the full extent of boreal North America, from Newfoundland, Nova Scotia, and Maine in the east across Canada and Alaska to the Noatak Valley and Seward Peninsula in western Alaska including on both sides of the Alaska Range in Denali. In isolated stands, white spruce reaches as far south as Wyoming in the west, and Wisconsin in the Midwest, but it is almost exclusively a tree of the boreal forest region, thus it is also sometimes called 'Canadian Spruce'. In Alaska, P. glauca occurs across the longitudinal extent of the state, from the Yukon border to the west coast, although it known only from south of the Brooks Range. In Alaska white spruce reaches the Arctic slope in the Firth River drainage in Canada It is abundant in productive sites in both interior and south-central Alaska, and is likely the most common tree species in both Denali and Alaska more generally.
Details are shown in the Plots & Charts found at right, depicting recent Denali data.
White spruce is the dominant (and usually the only) tree species occurring in treeline sites in Denali, where it occurs at elevations from 67 m all the way up to 1451 m (which is a small seedling among extensive talus). The mean elevation for this species in our dataset is 596 m, highest for all tree species occurring in the Park. This species prefers upland terrain and alluvium, because sites in these areas tend to be better drained and free of permafrost.
Details are shown in the Plots & Charts found at right. For more on how to interpret these figures, visit Understanding Data Presented.