Chances are that you've never heard the phrase "incidental tree." That's because I'm pretty sure that I created the phrase?
To me, an "incidental tree" is one that started as a small seedling that popped up behind a garage or among shrubs in a hedge row. As the seedling grew into a five to ten foot-tall sapling, at right, the property owner thought, "I'll get around to taking that thing down one of these days."
A few more years pass and maybe the property is sold. The new owners say, "wow, I'm glad we've got that tree growing behind the garage because it makes our backyard so much more private," at left.
All of a sudden, forty years have passed and that seedling has grown into a fifty foot-tall tree that would cost several thousand dollars to remove because it's tight up against the back wall of the garage, below right, its canopy arches over three or four properties, and it will have to be taken down and carried off the property one piece at a time because it's impossible to get a bucket truck anywhere near it!
So, there it grows, and grows, and grows some more - until large parts of it finally start coming down every few years during thunderstorms and/or under the weight of heavy snow.
In our one hundred year-old neighborhood, this scenario plays out to one extent or another during every single storm - or even, sometimes, during perfectly calm, sunny, summer afternoons.
This, in fact, was precisely the case just a couple of years ago when a forty foot-long limb of a neighbor's incidental tree cracked and pulled his phone line to the ground as it came down in slow motion over the course of ten minutes while I sat and watched it from my front porch!
If you have such a tree behind your garage, at left, or along your property line, and there's a "target" nearby (building, utility line, deck, busy street, parked cars, etc.), I strongly urge you to contact a certified arborist immediately to have evaluated it for any of potential problems described at right.