If a Forest Canopy Dies, Does It Matter?

“If a tree falls in the forest, and no one is around to hear it, does it make a sound?” It’s a classic debate, with many answers. Yes, of course, a tree falling makes a great sound.  But let’s suppose the out-of-earshot tree falls more slowly, succumbing to a creeping infestation that takes it and all its cousins. What sound does it make then? Will we hear it in time to do anything about it? What difference will it make if we don't?