Friday, December 5, 2008

If a trees falls in the forest..

If a tree falls in the forest and no one is there to hear it, does it make a sound? I won’t get into that philosophical question but I recently spent a few days in a forest and had time to make some observations that made me think about tree mortality.

At Penn State Extension, we frequently get questions about why a particular tree has died or is dying. Sometimes we can attribute an insect or disease pathogen to the problem. However, almost all tree mortality is a complex situation involving environmental stresses as well as destructive organisms. Many people want a simple answer (and solution) about tree death but usually the story is more complex and does not have a simple diagnosis or treatment.
What struck me as I sat in the woods and observed trees was that there were a lot of dead and dying trees around me. Walk into any woods and look around. You’ll see the same thing…more or less. I don’t think this is unusual. It’s natural. Sure, there is explanation for most of it. I know that insect defoliation was involved in the death of some of the trees I was seeing. I know that competition for light was thinning out others. I could see lots of fungal pathogens. One species always seems to die at a relatively young age without apparent cause.

What does this mean? For me, it puts tree mortality in perspective. No one likes it when trees die and when important trees die, or die suddenly without explanation, we look for answers. Sometimes the diagnosis appears straight forward. For instance, hemlock wooly adelgid is the primary cause of hemlock mortality in the woods I was sitting in. And in this case, I think I was witnessing not only individual trees dying but perhaps the demise of our state tree as a species in Pennsylvania. More often, trees fail and exhibit a range of symptoms that lead to educated guesses about the cause. Most of the time that’s as far as our knowledge goes.
The suburban trees that we pamper and tend to in landscapes are subject all of the stresses as their wild forest relatives. It’s sad, but part of Nature’s way when they die.

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