SENSITIVITY OF 4 HARDWOOD SPECIES TO AMBIENT OZONE IN NORTH CENTRAL PENNSYLVANIA

Studies were performed to determine the injury and growth response of four native tree species to ambient ozone on ridgetop sites of the Allegheny Plateau of north central Pennsylvania. Open top chambers were established at each of three sites located in Clear Creek State Park, Jefferson County (41-degrees-9'39"N, 79-degrees-02'35"W), Elliott State Park, Clearfield County (41-degrees-07'02"N, 78-degrees-31'40"W), and Tiadaghton, Lycoming County (41-degrees-0'05"N, 77-degrees-26'57"W). Seedlings of black cherry (Prunus serotina Ehrh.), yellow-poplar (Liriodendron tulipifera L.), red oak (Quercus rubra L.), and red maple (Acer rubrum L.) were exposed to ambient air or to charcoal-filtered air containing approximately 95, 60, or 40% of ambient ozone in randomized, complete blocks in 1988 and 1989. Black cherry seedlings were also exposed in 1990. Ozone was greatest in 1988 at ali sites, and total ozone during the 3-year study was greatest at the westernmost sites (Clear Creek and Elliott). Foliar stipple injury of black cherry and yellow-poplar were correlated positively (p < 0.0001) with ozone within and among sites throughout the study. Premature leaf abscission of both species was significantly (p < 0.005) greater with higher ozone levels at the Elliott site in 1988 and 1989. Ozone stipple was not observed on red maple and red oak seedlings. Ambient ozone did not significantly decrease height, basal diameter, or leaf surface area of any species. Possible explanations for temporal and spatial ozone variation and subsequent plant response are discussed.