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

Presettlement forests were dominated by Quercus alba. In a relatively undisturbed remnant of this forest type on a mesic site this old-growth stand is now dominated by Fagus grandifolia, Acer rubrum and Liriodendron tulipifera, representing 62% of the importance value total. Oaks (Q. alba, Q. rubra, Q. velutina) totalled only 18% of the importance value total. The overstory mainly comprised L. tulipifera, F. grandifolia, Q. alba and Nyssa sylvatica. Acer rubrum and Prunus serotina were the most abundant seedlings, and few saplings of any species were present. Over 90% of all trees were <120yr old, including many F. grandifolia, L. tulipifera, A. rubrum and A. saccharum, but few oaks. Logging of several trees in the 1930-1940s apparently accelerated the speed of obtaining dominance for these mixed mesophytic species. On average, the oldest oaks exhibited slow radial growth of <0.75mm/yr. Many understory trees had average radial growth of >1.5-2.0mm/yr and exhibited a release in growth associated with logging in the 1930-1940s. This forest represents an advanced stage of oak replacement by mixed mesophytic species, a process that seems inevitable in many eastern US forests. -from Authors