One tree that topples, pulling up its root mass and exposing the mineral-rich soil to the sun, will start a pocket of new forest in the midst of the old. In the Kluane area, spruce bark beetles are helping regenerate older forests, Olson says. Hidden in the pores of the beetles' wings are fungi spores that rub off and enter the tree's circulation system. A healthy tree can usually fight off the fungi, Olson says, but in weakened trees the fungi block the flow of nutrients up the trunk and the tree dies. The process is different from regeneration by fire, Olson says.
Fire sets the clock of the entire forest back to an early stage, and creates a single-age forest.
Attack by insect or disease removes only the older or more stressed trees, opening up pockets of new growth. The result is a multi-age forest, with all the phases of the forest life cycle represented.