Growth variation of white oak subjected to historic levels of fluctuating air pollution

Growth of white oak (Quercus alba L.) trees was examined, using tree-ring a nalysis, at three sites near a small, remote coal-fired power plant in cent ral Pennsylvania, USA. Forests immediately adjacent to the power plant have been subjected to power plant emissions since the power plant initiated op eration in 1954. However, localized, ground-level fumigations have been gra dually reduced over the years due to a series of construction projects resu lting in increased stack heights. Comparisons of growth were made among the white oaks growing at the three close-in sites, as well to the growth of w hite oak at three control sites located 10-50 km from the power plant, duri ng periods of differing stack heights. White oak exhibited reduced growth a t two of the close-in sites during the time period when historical ground-l evel air pollution exposures were assumed to be greatest due to low stack h eights. White oak growth at the third close-in site was not substantially r educed during this time period. In 1976, taller stacks were implemented at the power plant to reduce local, ground-level concentrations of air polluta nts. The recovery of tree growth at the two close-in affected sites, and in creased synchronous growth responses from 1976-85 among all three close-in sites, indicates that implementation of taller stacks in 1976 reduced groun d-level pollutant levels to such dosages that growth was not impaired at an y site. Also, growth rates after 1976 were comparable to the growth rates o f the white oaks growing on the control sites. A possible interacting facto r was a severe drought that occurred in the mid-1960s in central Pennsylvan ia. (C) 1999 Elsevier Science Ltd. All rights reserved.