Why do limbs suddenly break off of trees?

Q: I live on a lot that is heavy with trees, Lately, I have had the large tops of two trees and the heavy limb of a very old oak suddenly break off. Do you have any suggestions on why this happened and how to prevent it? 

A: Art Morris, board-certified master arborist, says it may be a matter of physics. Most of these sudden limb drop cases involve landscape trees. We can infer that portions of the tree receive more sun than they would in a forest, resulting in longer branches and more dense canopy concentrated at the ends. From a physics standpoint, this growth pattern can create a longer lever than the tree is adapted to. Many of the abrupt limb breaks happen some distance out from the trunk, which is where the maximum load on a lever occurs. The offending trees are usually sweet gums, tulip poplars, pecans and the occasional water oak. It’s possible that pruning to reduce limb length or thin the density of the canopy could reduce the risk.