Influence of topographic aspect, precipitation and drought on radial growth of four major tree species in an Appalachian watershed

This study used dated and measured tree-ring data to examine relationships between radial growth, topographic aspect, and precipitation for four hardwood species, yellow-poplar (Liriodendron tulipifera L.), northern red oak (Quercus rubra L.), chestnut oak (Quercus prinus L.), and red maple (Acer rubum L.), growing on contrasting aspects in north-central West Virginia (39degrees39'43N, 79degrees45'28W). The main objectives of the study were to determine variation in growth between northeast and southwest aspects, examine changes in annual growth related to changes in precipitation and Palmer drought severity index (PDSI), and test for the existence of an interaction between species' growth response to drought and topographic aspect. The study found that all species except northern red oak showed significant differences in growth between the northeast and southwest aspects (P < 0.05). Where significant differences were found, all except chestnut oak exhibited higher growth rates at the northeast aspect. The largest and the least difference in growth between the northeast and southwest aspects were found for yellow-poplar and northern red oak, respectively. Among the four species studied, yellow-poplar showed a sharp decline in growth from the late 1950s to the late 1960s, which was evidently caused by several years of below-average precipitation. The more conservative species, red oak, chestnut oak and red maple, showed a mild response to the drought compared to yellow-poplar which experienced 30-40% less growth relative to its peak growth in the late 1950s. A rapid growth recovery, in the early 1970s, following the decline in the late 1960s was associated with wetter than average conditions of the early 1970s. Analysis of drought effects in 1953, 1966, 1988 and 1991 indicated that most species experienced below-average growth although drought-related growth declines lasted only for a few years and recovery following drought was rapid. Regarding the interaction of aspect and response to drought, yellow-poplar displayed greater response to periodic droughts at the southwest aspect while the oaks showed little evidence of an aspect-related interaction with drought response. The results of this study are logical in terms of the ecological strategies of the species; yellow-poplar is widely known to be site specific and exploitive, whereas oaks and maples are more conservative. (C) 2002 Elsevier Science B.V. All rights reserved.