COMMUNITY, EDAPHIC, AND HISTORICAL-ANALYSIS OF MIXED OAK FORESTS OF THE RIDGE AND VALLEY PROVINCE IN CENTRAL PENNSYLVANIA

Fifty-nine mixed oak stands in the Ridge and Valley Province of central Pennsylvania were sampled to evaluate the potential for oak replacement by later successional species or oak stability across a diverse landscape. Using species importance, stands were separated into four groups along detrended correspondence analysis axes 1 and 2. Betula lenta L. - Quercus prinus L. - Quercus rubra L. and Q. prinus - Q. rubra groups occurred on sandstone-based Inceptisols and Ultisols on ridges, whereas mixed-Quercus and Quercus alba L. groups were representative of limestone-based Alfisols on valley floors. Quercus species dominated the overstory of all groups; however, the understories mainly comprised shade-adapted Acer rubrum L., Acer pensylvanicum L., and (or) B. lenta on the xeric ridges and A. rubrum and Prunus serotina Ehrh. in the mesic valleys. The presettlement forests consisted of Quercus, Pinus, and Castanea dentata (Marsh.) Borkh. on the ridges and Quercus, Pinus, and Carya in the valleys. Comparisons between presettlement and present-day forests indicate that Pinus strobus L. and C. dentata have declined dramatically, whereas Quercus species have increased. Changes in disturbance patterns following European settlement (e.g., the charcoal iron industry) initially favored Quercus expansion, followed later by increases in Acer, Prunus, and Betula. Under existing conditions where large-scale disturbances from fire or logging are minimal, Quercus species are expected to decline slowly in importance, being replaced by Acer, Prunus, and (or) Betula species regardless of site moisture relations. Thus, mixed oak forests do not appear to represent a prominent edaphic climax in the region, despite the long history of oak domination.