Response from driscoll and colleagues

We appreciate Dr. Sharpe's interest in our article (Driscoll et al. 2001). Our intent was to conduct a synthesis of research on acidic deposition in the northeastern United States, focusing on advances since the 1990 Amendments to the Clean Air Act. Through our review of largely peer-reviewed literature, we attempted to reach a consensus on the state of acidic deposition and associated effects in the Northeast. In the section on effects on trees, as in each of the sections, our goal was to present a balanced summary of the current state of the science. This was one of the most challenging sections to prepare, because the effects of acidic deposition on trees have proven to be difficult to quantify. Trees are exposed to multiple stresses whose effects can be direct or indirect, and may not be expressed for years or decades. Nevertheless, we ventured out of the northeastern United States (as Dr. Sharpe noted) to include a discussion of research on relationships between acidic deposition and sugar maple (Acer saccharum), because we felt that this information was scientifically significant and ecologically relevant to the northeastern United States, where sugar maple is a highly valued species.