One summer several years ago, I was a witness (and nearly a victim) to summer limb drop.  While weeding under a grove of eucalyptus trees I heard a loud “crack!” I looked up into the tree canopy and saw a branch falling towards me. Like a deer in the headlights, I stood frozen to the spot for a few seconds in disbelief as the branch slowly continued its descent towards me.  Luckily I snapped out of my daze and quickly ran out of the path of the falling limb. The branch landed where I had been standing just a few seconds before. This was my first experience with summer limb drop, also known as summer branch drop.

What is Summer Limb Drop?

Summer limb drop occurs when mature trees drop a limb or a branch during hot weather on a calm summer day. Unfortunately, sometimes these branches fall on cars, houses and even people. The branches in these pictures were small and luckily fell onto a lawn.

Most people are used to seeing broken branches in the gutter or street after a rainstorm. During cool weather, wind causes branches to break off at the point where they are connected. However, in summer branch drop, the limbs tend to break horizontally along the limb about 3-12 feet away from the trunk.

Why Does Summer Limb Drop Happen?

Trees draw up large amounts of water during the day, and release this moisture through their leaves. When a really hot day suddenly cools off, the tree can’t get rid of the moisture quickly enough. The sheer weight of the water weighs the limb down and causes it limb to break. The crazy thing is, tons of water can be seen pouring out of the breaks after it happens.

Usually the limb that drops is one that was already damaged. Unfortunately, the damage may not be visible to most people.  However, correctly training and pruning young trees, and giving trees adequate moisture as they mature, and inspecting trees for decay may help to prevent summer branch drop.

Also, avoid creating areas for people such as play structures or picnic tables under large trees and especially older trees. Tree species that have been known to drop branches include oak, eucalyptus, sycamore, elm, ash, and poplar.

To learn more about the strange phenomena of summer branch drop, visit the USGS.