Effects of 21 Years of Simulated Acidic Deposition on Tree Growth and Species Composition in an Aggrading Appalachian Hardwood Forest

Abstract

The long-term effects of soil acidification on the development of a young aggrading Appalachian forest were examined after 21 years of continuous treatment. Beginning with a clearcut harvest in 1997, annual ammonium sulfate (N+S) and ammonium sulfate with lime (N+S+LIME) treatments were aerially applied to a developing forest. The lime treatment was designed to counteract the acidification of the nitrogen and sulfur amendments. After 21 years, the N+S and N+S+LIME treatments had little impact on total woody biomass accumulation relative to the control. There were significant differences among species and treatment responses with respect to woody biomass accumulation, however. Biomass of Prunus pensylvanica was about twice as much as any other species in N+S and N+S+LIME treatments but was similar to Liriodendron tulipifera and Betula lenta on control areas. Treatment effects were not significant for average tree diameter or stem density, although both varied among the six tree species with the highest importance values. The importance value of P. pensylvanica decreased by almost half in the last 6 years due to mortality, but this was not associated with either the N+S or N+S+LIME treatments. The dynamic nature of this short-lived tree species is potentially masking any effects of the N+S or N+S+LIME treatments to date. Study Implications: We examined the long-term impact of nitrogen and sulfur additions with and without lime on forest stand development. After 21 years, the forest showed little change in aboveground woody biomass, although the distribution of biomass among species was affected by the treatments. Prunus pensylvanica (pin cherry) accumulated the greatest biomass on N+S and N+S+LIME treatments relative to the untreated areas. However, P. pensylvanica is a short-lived species, and our data show it is declining. It is unclear whether the treatments are having minimal impacts or they are being masked by the early dominance and subsequent mortality of P. pensylvanica.