Tree-ring cellulose δ18O variability in pine and oak and its potential to reconstruct precipitation and relative humidity in central Japan

Oxygen isotope ratios (delta O-18) of tree-ring cellulose in pine (Pinta densiflora) and oak (Quercus serrate and Quercus variabilis) growing in central Japan from 1970 to 2011 share a common inter-annual variance among different cores in a tree, different trees in a species, and different species in a forest. The high mean correlation between the two radii ((r) over bar = 0.738) of individual trees and the mean standard deviation of two measurements for the same year from the two radii of eight trees ((sigma) over bar = 0.361 parts per thousand) reveals the reliability and representativeness of single cores. The significant correlation (r = 0.667, p < 0.01) between pine and oak cellulose delta O-18 suggests that delta O-18 in tree-ring cellulose is controlled by common external factors, and that it is possible to establish a unique delta O-18 chronology using different tree species. The delta O-18 values of tree-ring cellulose in pine and oak trees are negatively correlated with precipitation from June to August (correlation coefficients are -0.679 for pine and -0.583 for oak), which is attributable to the precipitation amount effect, mainly caused by the stagnant rain front (Baiu) in early summer and typhoons in late summer in this region. The delta O-18 values are negatively correlated with relative humidity from April to September for pine (r = -0.632, p < 0.01), and in June and July for oak (r = -0.437, p < 0.01); these correlations probably reflect different lengths of the growing season. Multiple regression analysis reveals that tree-ring delta O-18 values of pine and oak in this region are largely governed by summer precipitation. Relative humidity does not appear to greatly affect tree-ring delta O-18 of oak, in contrast to pine, which may be interpreted in terms of differences in leaf morphology and/or cellulose synthesis processes. Our results indicate that delta O-18 values of tree-ring cellulose can provide a potential crossdating tool, irrespective of the physiological differences between gymnosperms and angiosperms. In central Japan, tree-ring delta O-18 values of both pine and oak can act as reliable proxies of June August precipitation, while pine trees tend to exhibit more potential for reconstruction of relative humidity.