Rotten trunks and thunderstorms do not mix. Photo: Steve Bender

I remember the first time I noticed that tree in our neighborhood. A rotten strip of flaking bark ran straight up one side for 15 to 20 feet. "That tree could snap in half and fall on their house at any second," I grumbled grimly to Mrs. Grumpy. "If it were mine, I'd have it taken down right now."

Well, that tree didn't fall down that day or the next day. In fact, it stood up to storm after storm for another eight months. Then last evening, a garden variety thunderstorm blew through with wind gusts of I guess around 40 MPH. And this is what that tree (above) looks like this morning. At least, it missed the house.

OK, OK, I can hear the umbrage rumbling around in your heads. You're thinking, "Well, if you knew that tree was hazardous, why didn't you warn the homeowner?" For several reasons. I didn't know him. He might have thought it was none of my business. Plus, the trunk was so obviously rotten, he should have spotted it himself. Heartless Grumpy.

emCloser look at the rotten trunk. Photo: Steve Bender/em

What caused the entire side of a seemingly healthy oak to die and rot? My guess is a lightning strike. Usually, when lightning strikes a tree, the tree dies immediately. I've seen huge trees literally blown to bits by a strike. By sometimes, fickle lightning travels down just one side of a tree between cloud and ground. The sap on that side turns to steam. The bark dies and flakes off, exposing a long, sunken scar. This opens up the heartwood of tree -- the source of its structural strength -- to insects and rot. It won't take a tornado, hurricane, or even a severe thunderstorm (winds greater than 58 MPH) to bring it down. Time will.

Trouble Signs To Watch For When some trees fall, there's no way you could have seen it coming. Maybe your shade tree is basically growing on rock, so that all of its roots are near the surface. Maybe your tree looks fine, but most of its biggest roots are rotten. The only way you discover those things is when it comes crashing down.

However, some very clear warning signs tell you that a big tree is hazardous. Here's one.

emShelf or bracket fungus. Photo:

This is shelf (aka bracket) fungus. The plate-like growths are the fruiting bodies of a fungus that lives inside the tree digesting its heartwood. If you see shelf fungus growing from a branch, the branch will eventually break and fall. The same thing will happen to the trunk. The only cure for a tree that looks like the one above is a chainsaw.

Other worrisome signs include a hollow trunk (duh), a tree with healthy branches at the bottom and dead ones at the top, a trunk riddled with insect holes, a large cavity at the base of the tree, dark liquid that oozes from the base of the tree after a rain, and any kind of mushrooms growing from the trunk or roots.

If you see any of these signs, it would behoove you to ask a professional arborist to examine the tree and recommend a course of action. Make sure the outfit is licensed and insured. Should you decide to let the matter go for now, remember this. If an obviously hazardous tree falls on your house, you pay for the damage. If it falls on your neighbor's house, you pay too.