Radial growth-climate relationships of white ash (Fraxinus americana L. Oleaceae) in the eastern United States

This study characterized associations between climate variables and radial growth of white ash (Fraxinus americana L.) at 12 sites along a longitudinal climate gradient in the eastern USA. Growth responses of this species to climate stresses have not been well documented, and this study sought to improve understanding of how climate change might affect white ash. Total annual ring-width data were obtained for trees at all sites, and data for earlywood and latewood width were obtained at six sites. Pearson's correlation coefficients were computed among radial growth indices and temperature, precipitation, and Palmer drought severity index (PDSI). Total ring width was positively correlated with precipitation and PDSI and negatively correlated with temperature during the months of May to July, when most radial growth occurs. These spatially replicated correlations indicate that white ash growth is most strongly influenced by drought stress in the first half of the growing season. Correlations between climate variables and latewood width were the same as for total ring width; latewood width explained 98% of the variation in total ring width. Earlywood width exhibited less interannual variation than latewood width did and was weakly correlated with climate variables for months before leaf-out was complete but not after. These correlations were consistent with the ecology and carbon allocation patterns of other tree species with ring-porous wood anatomy. The effect of climate change on white ash growth will depend on how changes in the balance between increasing temperature and precipitation alter the frequency and intensity of early growing-season droughts.