Dead or Alive?

Spring 2007


Ahh, spring! Buzzing bees, blossoming flowers, warm weather, and dead trees. What? Dead trees? Yes, dead trees. Every spring the green forest landscape is pock marked with brown and red tree crowns, indicating dead trees. Quite possibly those trees have been dead for awhile and we just didn’t know it. Let me explain.

First, let’s examine how common forest pests work in our area. Bark beetles are responsible for killing a substantial number of Inland Northwest trees every year. Bark beetles burrow under the bark during the summer to raise their brood.In a heavily infested tree, bark beetles will girdle and kill the inner bark, thereby causing the tree to die because the flow of food between the crown and roots is stanched.

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But bark beetles usually don’t work alone. Hitchhiking along with the bark beetles is a fungus.In pines, this pathogen is known as the “blue stain” fungus. This fungus effectively clogs wood pores and shuts down the tree’s ability to transfer life-sustaining water and minerals into the crown from the roots. Trees quickly succumb to the one-two punch of having their food supply choked off by bark beetles and their water pipes clogged with blue stain fungus.

But here’s the surprise;even though the tree is virtually dead following these insect and fungus attacks during the summer, it oftentimes will not turn brown until the following spring. This is because after the attack, the tree is fairly dormant andbrown foliage does not develop until moisture exits the needles the following spring. Thus, many trees appear to die in the spring, but actually were killed the previous year.

Thankfully for the savvy observer, there are early indicators of at-risk trees. For example, many tree species create globs of pitch on their bark in an attempt to fight off bark beetles, or boring dust (fine sawdust) may be noticeable within bark crevices. Unfortunately, these signs are not foolproof, so the definitive diagnosis remains the “dead-as-a-door-nail” appearance of brown needles.
— M. Wolcott

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