Pasadena Tree Failure Due to 'Summer Limb Drop', Lack of Adequate Root Crown Among Other Things

Last month when a large Mediterranean pine fell in Pasadena, seriously injuring two children, I was interviewed by KNBC as to what could cause trees to fail during the summer. I mentioned several causes, one of which involved water rushing up to the limbs but not being able to escape due to high humidity and low wind-speed reducing the amount of water that is eliminated normally due to transpiration. Apparently Ted Lubushkof, the independent consulting arborist who was hired by the city of Pasadena, cited that as the main cause of the failure. Summer limb drop is quite common, it's just that it rarely occurs at the same time people are underneath the trees.