Reductions in tree-ring widths of white pine following ozone exposure at Acadia National Park, Maine, USA

Polluted air masses from the industrialized northeastern corridor of the United States flow through Acadia National Park, Maine, U.S.A. The polluted air masses create elevated ozone episodes throughout the growing season, causing visible foliar damage to some native plant species. This study used dendroclimatic techniques to investigate the possibility that elevated ozone levels adversely affected white pine (Pinus strobus L.) radial growth rates. Tree-ring cores were extracted from white pine trees in eight separate stands within the park. Tree-ring indices were then regressed with ozone variables to model the effects of elevated ozone levels on tree growth under field conditions. Models from seven of the eight stands documented negative associations between tree-ring indices and ozone levels that were stronger than any associations between tree-ring indices and climate. The modeled growth-ozone associations exhibited stand-level variations, suggesting that site characteristics affect tree responses to ozone pollution.