The extreme heat and drought can cause some rarely seen phenomenon. Dennis Patton, our Horticulture Agent in Johnson County has had several reports of apparently sound branches breaking out of what appeared to be a healthy trees (primarily oaks) recently. There was an article written by Richard Harris, the author of a standard Arboriculture text that describes this phenomenon. His observations are summarized below.
This type of damage has been reported on both landscape and forest trees. The landscape trees were found in irrigated and unirrigated situations.
These limbs can be huge; up to 3 feet in diameter. Most often the break occurs 3 to 12 feet from where the branch attaches though at times the branch may break at the attachment. Though breaks do occur in decayed wood, often the broken branch shows no sign of weakness or decay. No firm explanation of a cause has been established though buildup of pressure within the branch has been noted. In some cases, the branch seems to explode and then drop. The reason for this pressure buildup is unclear though several ideas have been put forth.
Certain species are more susceptible to this condition including oaks, poplars, cottonwood, willows, ash, sycamore and Japanese Pagodatree. You will find more detail in Richard Harris’ article at http://artistictreeworks.com/harris.html
Be cautious around these trees during hot, calm weather. Hopefully, the cooler weather we had last week will reduce the changes of this happening. (Ward Upham)
