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 h ardwood species in central Pennsylvania (USA) to assess differential d rought impacts on xeric ridge, dry-mesic barrens, mesic valley, and we t-mesic riparian sites, Each tree species occurred on two or more site s. Four droughts of moderate to severe intensity occurred during the s tudy period. In general, trees on the xeric ridge and wet-mesic ripari an sites were more frequently impacted with reductions in the ring wid th index, whereas trees on the mesic valley and dry-mesic barrens site s had fewer growth reductions. Annual variation in growth was negative ly correlated with summer temperature, particularly for species on the riparian site. Six of twenty-three species-by-site combinations had a bove average growth during one or more of the droughts, while 8 of 23 species-by-site combinations had below average growth the year followi ng drought, The species with the largest decrease in the ring width in dex during drought varied among the sites, and included Acer rubrum in the valley, Prunus serotina in the barrens and riparian sites, and Qu ercus rubra and Acer rubrum on the ridge. Comparing tree-ring data fro m this study with leaf gas exchange data from other studies resulted i n several inconsistencies in drought responses; therefore, information from both approaches may be needed in accurately assessing species dr ought tolerance rating.