After a Quarter Century, What Does the Pennsylvania Regeneration Study Tell Us About the Future of Mixed Oak Forest Under Stress?


William H. McWilliams, James A. Westfall, Patrick H. Brose, Shawn L. Lehman, Todd E. Ristau, Alejandro A. Royo, and Susan L. Stout

Research Foresters (WHM and JAW), USDA Forest Service, Northern Research Station, 11 Campus Blvd, Newtown Square, PA 19073; Research Foresters (PHB and SLS) and Research Ecologists (TER and AAR), USDA Forest Service, Northern Research Station, PO Box 267, Irvine, PA 16329; Section Chief (SLL), Inventory and Monitoring Section, Pennsylvania Department of Conservation and Natural Resources, Bureau of Forestry, 137 Penn Nursery Road, Spring Mills, PA 16875; WHM is corresponding author: to contact, call 610-557-4050 or email at

Abstract – The Pennsylvania Regeneration Study (PRS) was initiated in 1989 to address the need for landscape-level information on regeneration quality and abundance due to concern over the impacts of herbivory and other factors on forest regeneration in Pennsylvania. The PRS is comprised of a suite of Regeneration Indicator (RI) measurements installed on a subset of USDA Forest Service, Northern Research Station (NRS), Forest Inventory and Analysis (FIA) monitoring plots. The approach leverages the RI data with the full complement of NRS-FIA forest inventory variables for a holistic look at mixed-oak forest conditions. Pennsylvania’s mixed oak forests have been under increasing stress as aging stands originating from large-scale disturbances over a hundred years ago are inundated by native and non-native invasive pests and diseases. Currently, only 4-percent of the State’s mixed-oak forest is in young stands less than 20-years of age. Maintaining the role of oaks in new stands is difficult due to lack of fire, herbivory, invasive plants, climate change, and other factors. This paper summarizes current NRS-FIA and PRS results to provide a look at the future of oak forests and likely challenges faced by managers and policymakers. Creating disturbances and conditions that match the phenology of young oak forests will be critical for restoring mixed-oak forests in Pennsylvania and elsewhere. Management prescriptions that provide favorable amounts of light, control herbivory, and eliminate competing vegetation are needed for successful establishment and development of young mixed-oak forests to replace today’s aging ecosystem.