Spruce decay classes

Decay class one boles usually have no decay, fine twigs remaining, and complete bark coverage. The sapwood and heartwood are clear or slightly blue stained. Moss is absent.

Decay class two boles are slightly decayed with most of the bark present and most of fine twigs still remaining. The sapwood is rotted, but the heartwood is mostly sound.

Decay class three boles are moderately decayed with some bark and most of the branches present. Where the bark is gone, some sloughing of the outer wood is apparent. The sapwood and heartwood show strong signs of decay. But the bole still can support itself.

Decay class four boles can no longer support themselves. Frequently, all the bark is gone. The sapwood is often absent, and the deep red-brown heartwood crumbles into chunks upon handling. Some branches and branch stubs are present.

Decay class five boles are detected only by their moss or grass outline on the forest floor. The cross section of the bole is no longer round but elliptical, and the bark is completely absent. The wood resembles red powder with little discernible structure or sign of rings. Long lasting branch stubs can be used for spruce identification on this stage of decay.

Decay class descriptions after Graham and Cromack, 1982.

Questions? Email Dr. Mark Harmon at

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