Successional replacement of old-growth white oak by mixed mesophytic hardwoods in southwestern Pennsylvania

Abstract

Presettlement forests in southwestern Pennsylvania were dominated by Quercusalba L. A relatively undisturbed remnant of this forest type on a mesic site was surveyed to investigate the successional status of Q. alba in the region. This old-growth stand is now dominated by Fagusgrandifolia Ehrh., Acerrubrum L., and Liriodendrontulipifera L., representing 62% of the importance value total. Oaks (Q. alba, Q. rubra L., and Q. velutina Lam.) totalled only 18% of the importance value total. The overstory mainly comprised L. tulipifera, F. grandifolia, Q. alba, and Nyssasylvatica Marsh. Acerrubrum and Prunusserotina Ehrh. were the most abundant seedlings, and few saplings of any species were present. The oldest and largest trees were oak, with two Q. alba >300 years. Over 90% of all trees were 1.5–2.0 mm/year and exhibited a release in growth associated with logging in the 1930–1940s. We believe this forest represents a primary example of an advanced stage of oak replacement by mixed mesophytic species, a process that seems inevitable in many eastern forests.