Visitors to Yosemite National Park are being warned about a seasonal tree hazard that can occur without warning during hot summer weather. Summer branch drop can cause seemingly healthy tree limbs to suddenly fall, creating a serious risk for people spending time beneath large oak trees.
What Is Summer Branch Drop
Summer branch drop is a seasonal phenomenon that occurs most frequently among black oak trees in and around Yosemite. The hazard is most common during hot, calm afternoons when there is little or no wind.
Unlike branches that break during windy conditions, summer branch drop typically occurs along the length of a limb rather than where the branch connects to the trunk. Breaks often happen between three and 12 feet from the trunk.
The affected limbs are generally long and horizontal. Some extend to or beyond the normal canopy of the tree. While certain fallen branches show signs of wounds or decay, many appear healthy before breaking.
Older and less vigorous trees appear to be more susceptible to summer branch drop. Trees that have already lost a limb through the phenomenon may also be more likely to lose another.
Yosemite Warns Visitors To Stay Alert
There is no reliable way to predict exactly when a branch will fall, making awareness especially important for visitors. Yosemite National Park recommends that people avoid sitting or camping directly beneath the branches of black oak trees on hot days.
The park also advises against leaving people who cannot quickly move away, including infants and elderly visitors, directly underneath large oak trees.
If someone hears a loud cracking sound overhead, the park recommends immediately moving away from the tree.
Visitors Asked To Report Fallen Trees
Yosemite officials are also encouraging visitors to stay away from trees that have already experienced branch failures. Avoiding affected trees can reduce the risk of another incident while also allowing park staff to monitor tree health.
Anyone who sees a tree or large branch fall is asked to report it to the nearest park ranger.