Altered forest composition and soil properties of historic charcoal hearths in southeastern Pennsylvania

Abstract

This study related age structure and composition of forests in southeastern Pennsylvania to edaphic properties caused by the activities of a local charcoal iron furnace from the late 18th to the late 19th century. Forests surrounding charcoal hearths were harvested on 20- to 30-year rotations to supply wood for charcoal production in earthmound kilns. Charcoal hearths were created by a recurring cycle of disturbance, including the removal of established vegetation, intense heat, and the deposition of charcoal. Thirty-eight hearths of Hopewell Furnace National Historic Site were examined to describe differences in vegetation relative to surrounding forests that have developed since the cessation of charcoal production in 1883. Hearth forests were significantly younger than surrounding forests, with lower tree density and basal area, decreased sapling and shrub abundance, and higher herbaceous cover. Compositional differences on charcoal hearths included decreased importance of several Quercus species and ericaceous shrubs and increased importance of Liriodendrontulipifera L. Results of this study indicated that the initial effect of charcoal production was the prevention of stump sprouting and a delay in recolonization following disturbance due to extreme soil physical and chemical properties. Failure of hearth seedlings to recruit into larger size classes, age–diameter relationships of Liriodendrontulipifera L. trees, and the failure of calcifuge species to reestablish similar cover on charcoal hearths suggested that unfavorable properties of charcoal soils continue to negatively affect long-term productivity. Relative to nonhearth soils, large, significant differences in soil pH, cation exchange capacity, base saturation, and exchangeable Ca, Mg, and K indicated that continuing inhibition of woody plants on charcoal hearths may be related to alterations in soil chemistry that have persisted for 110 years.