Why Healthy Oaks Drop Branches

Heard it about 11 p.m.: Slow cracking and then a whoosh and thump. This is the third time in 14 years so I know what it is, and outdoors with a flashlight--stepping very carefully in case any copperheads are out lounging on the gravel like before--see that one of the twin oaks, tall and very old but thriving, has dropped a huge live branch, blocking the lane but causing no damage. I text the handymen and they chainsaw it up the next morning.

Before they arrived I had a good look at it and wondered why well-leafed oak branches drop and found an excellent online article by Heather Hacking (a fine name for a reporter interested in botany) who interviewed arborist Scot Wineland:

"Trees draw up a tremendous amount of water during the day and release the moisture through their leaves. The process is known as evapotranspiration.

If you tied a plastic bag around a potted plant, the bag would become cloudy as moisture is released to the air. If the tree hasn't had a chance to shed some of that moisture, the "phenomenal weight" of the water can bust a limb.

Sometimes a tree will have an ever-so-slight defect, or a crack. Perhaps woodpeckers or squirrels damaged the limb in a way that leads to a larger crack over time and later decay.

When the limb gets too heavy with water, that crack can lead to a break. There can literally be buckets of water that flows from where the limb breaks, the arborist said."

See the entire article here. It's from the Chico, California Enterprise-Record. Maples and other trees have limb drop, too.

I didn't see any water in the morning, nor any black ants at the core of the fallen branch, but that doesn't mean they weren't there, because my eye is untrained. I am relieved the 25-foot branch didn't fall on anyone or anything.