Tree-ring responses to drought across species and contrasting sites in the ridge and valley of Central Pennsylvania

Annual tree-ring variation between 1984 and 1995 was measured in ten hardwood species in central Pennsylvania (USA) to assess differential drought impacts on xeric ridge, dry-mesic barrens, mesic valley, and wet-mesic riparian sites. Each tree species occurred on two or more sites. Four droughts of moderate to severe intensity occurred during the study period. In general, trees on the xeric ridge and wet-mesic riparian sites were more frequently impacted with reductions in the ring width index, whereas trees on the mesic valley and dry-mesic barrens sites had fewer growth reductions. Annual variation in growth was negatively correlated with summer temperature, particularly for species on the riparian site. Six of twenty-three species-by-site combinations had above average growth during one or more of the droughts, while 8 of 23 species-by-site combinations had below average growth the year following drought. The species with the largest decrease in the ringwidth index during drought varied among the sites, and included Acer rubrum in the valley, Prunus serotina in the barrens and riparian sites, and Quercus rubra and Acerrubrum on the ridge. Comparing tree-ring data from this study with leaf gas exchange data from other studies resulted in several inconsistencies in drought responses; therefore, information from both approaches may be needed in accurately assessing species drought tolerance rating.