Dr. H. Dennis P. Ryan is an Arborist and the Program Coordinator of the Arboriculture/Urban Forestry Program at the University of Massachusetts , Amherst . Prior to joining the faculty at the University, Dr. Ryan was Executive Director of Forestry and Horticulture for the Parks Department of the City of New York . In addition to municipal experience, he also worked as a commercial arborist for ten years. Dr. Ryan’s consulting work is in the area of tree and arboricultural accidents and he is Chairperson of the ANSI Z-133 Arboricultural Safety Committee.