The seasonal phenomenon, known as Summer Branch Drop (SBD), happens most often among black oaks in Yosemite, according to a safety notice the park posted on its official social media accounts this week. Limbs can fall without wind or another clear warning, the Yosemite National Park social media account warned.
Branches affected by SBD typically snap 3 to 12 feet from the trunk, while wind-damaged limbs usually break where a branch meets the trunk.
"The branches that break are usually long and horizontal, as opposed to upright, frequently extending to or beyond the average tree canopy,” the park said.
“There is no way to know exactly when Summer Branch Drop is going to occur, but there are a few things you can do to prevent injury,” the park advised.
Park visitors are advised to not to sit, picnic, or pitch tents beneath black oak branches on hot days. It also recommends avoiding leaving infants, older adults, or anyone who cannot move quickly under large oak trees.
A loud cracking sound overhead can signal that a branch is about to fall.
"Quickly run away from the tree itself," the park said. Park officials also recommend steering clear of trees that have already lost branches, which helps keep visitors safe and allows staff to monitor and maintain tree health. Anyone who sees a tree or branch fall should report it to the nearest ranger.
Hikers are also advised to carry fluids and electrolytes and schedule strenuous activity during cooler parts of the day.
Lin was struck by a branch in a giant sequoia grove and died from blunt-force injuries. She was pronounced dead at the scene.