Hollow tree detection.

Last November, a woman in my parent's town was killed when a "healthy" tree fell on her as she was on her jogging path. Found out the tree had been hollowed out by, I assume, bugs. Being new to recreational tree climbing, this certainly brought me some concern. Is this a valid concern or do I have a better chance of getting hit by lightening? I check for signs of damage, but maybe you can't always tell. I've wondered about a "density" tool of some sort.

Rap on it with your knuckles?

I have never climbed a tree, however any hollow trees that I have found in my forays have had really wild acoustical properties.

A simple method is to hit the base of a tree with a stick or mallet. Don't hit it so hard that you damage bark. With a little practice you can define a hollow ring to the sound. I personally use a Resistograph tool which is a sophisticated instrument (and expensive) to tell me exactly what is under the bark. I am a certified arborist and hazard detection is one of my skills. But beating a tree is a valid first line tool for detecting hollow trees.

As a tree surgeon, I have encountered a number of trees that when hollow have also let out alot of WATER, when I've been doing work in these trees. So sometimes when climbing, if I come to a rotten spot, where I can put my arm in the hole, etc...I feel for whatever,spongewood,squirrel nest, hidey hole...and if I feel water, I try to measure with what ever(polesaw handle, long tree branch...) to find the bottom and then drop down and drill a tap hole to drain out the cavity...if I don't have a drill and the tree is big, I sometimes use my little husky and just bore in with the saw...I've gotten totally wet(on video) when I was taken down this big oak and got over 20 secs of water gushing out, the saw wouldn't cut cause of wet clutch, and ooohhh that smell, we guessed about 100 gals or more....