Black Spruce

Somehow black spruce trees seem like the jackasses of the northern forests--sort of ungainly looking, ugly little beasts that somehow can survive under conditions prohibitive to the taller and more elegant birches and white spruce. But, like donkeys, black spruce have their likable and interesting qualities.

Black spruce are the climax trees on cold, poorly drained soils in Alaska and Yukon. They rarely exceed 45 feet (15 meters) in height or 9 inches (23 centimeters) in diameter. In a typical stand, the diameter of most trees is less than 5 inches, and growth is very slow. Half the trees in a 30-year-old stand may be less that 2 inches in diameter.

Since black spruce do better than other trees on cold, wet soils, it follows that there tends to be an association between black spruce forests and permafrost. While this association is true, it is also true that the fortunes of black spruce forests are closely linked to the occurrence of forest fires.

When a fire strikes a black spruce forest, it usually is hot enough to kill most of the trees but not all of the seeds. Black spruce, unlike some other trees, tend to produce seed annually or nearly annually. They start bearing cones at about age 15. Once black spruce seed cones mature, they may remain on the tree for several years. So regardless of when a fire strikes, mature seeds are available, and many are tough enough to survive the fire.

If there are repeated, but not too-frequent, fires on dry upland areas where white rather than black spruce tend to be the climax trees, the black spruce will encroach upon those areas. This takeover occurs because black spruce reseed more quickly that do the white spruce.

If there are too many fires, neither the black or the white spruce will survive. Nearly permanent grasslands develop on drier ground while bogs and shrub thickets take over in wetter areas.