Tree Connections

At the top of my long driveway through a patch of diverse forest that is at least 130 years old, there was a peculiar episode of mortality not long ago. The deaths involved three large trees that, up until the time their leaves withered and transpiration failed, appeared healthy. They all died within a two month period. The victims were within forty feet of each other,and though trees were of three different species -  a white oak, a mockernut hickory, and a southern red oak. Other than a couple of recent droughty summers that likely stressed the forest to some degree, common causative signs of tree deaths were absent the scene.