Oaks and Other Trees May Naturally Shed Small Branches
From time to time, natural pruning of small branches from oaks and other trees causes alarm to homeowners because they think the tree is dying. This is referred to as branch abscission or cladoptosis. A similar abscission process occurs when deciduous trees shed their leaves each fall.
The link address is: http://txforestservice.tamu.edu/forestry_education/general_foresty/abscission.html