Northern red oak growth response to climate and industrial air pollution in Western Pennsylvania
This article is part of a larger document. View the larger document here.Abstract
Northern red oak (Quercus rubra L.) radial growth response over time and space was examined along an inferred air pollution gradient on Laurel Ridge, a northeast - southwest anticlinal ridge, in relation to local and historically varying air pollutant emissions from coal-burning power generation and iron production within the greater Johnstown area (Conemaugh Gap) in west-central Pennsylvania. The specific objectives were to determine the effects, if any, of industrial air pollution (primarily sulfur dioxide) on: (1) the relationship of tree growth and climate, (2) tree growth as measured by basal area increment and, (3) the separate growth responses that may be related to long-term air pollution from Johnstown industry and more recent coal-burning power generation. On the east side of Conemaugh Gap, the city of Johnstown has been a major iron production center from the 1920’s until 1977. Two power generating stations on the west side of Conemaugh Gap began operation in 1950 and 1970, respectively. We collected pairs of tree cores from at least 20 canopy northern red oaks in 11 mostly ridge top stands ranging from 11 km downwind to 34 km upwind of Conemaugh Gap. Indexed tree-ring chronologies for each stand were derived by standard dendrochronological techniques, and these chronologies were modeled with temperature and precipitation variables by stepwise multiple regression. The resulting growth-climate models indicated that growth of northern red oaks on Laurel Ridge most consistently and positively responded to July precipitation of the growth year, and warmer than normal summer temperatures in the preceding year. In general, upwind control stands showed the strongest relationship with climate, while growth in stands nearer to and downwind of Conemaugh Gap exhibited weaker or virtually no relationship with climate. The spatial patterns of basal area growth rates generally mimicked those of the growth-climate models; an increasing growth rate was evident with distance away from Conemaugh Gap. We conclude that growth of canopy northern red oaks on the upper slopes of Laurel Ridge near to, and downwind of, Conemaugh Gap exhibited anomalous long-term low growth rates and climatic decoupling. The most likely cause of this growth anomaly is historical industrial emissions from Johnstown, with little or no indication of an additional growth impact when the power generating stations went on-line. Whether red oak growth and climatic sensitivity recover in the Conemaugh Gap area as a result of improving air quality is under investigation.