13C isotopic fingerprint of Pinus pinaster Ait. and Pinus sylvestris L. wood related to the quality of standing tree mass in forests from NW Spain

Abstract

Pine forest plantations of P. pinaster Ait. and P. sylvestris L. located in Galicia, NW Spain, were selected to study the 13C/12C isotopic fingerprint in wood core samples in order to find possible relationships between the ¿13C at natural abundance levels and the quality of the standing tree mass. For each pine species, 24 forests growing on acidic soils were studied: half developed over granite and half over schists. Two dominant trees from each plot, corresponding to all possible combinations of forest stands with high or low site index and with adults or young trees, were drilled at the basal part of trunks using a Pressler¿s drill to obtain tree ring samples. The C isotopic composition of the litter and the soil organic matter from different soil depths were also determined and statistically significant correlations between these values and the 13C content of the wood were observed. Despite internal variations due to the influence of site index, tree age and parent material, the isotopic fingerprint of P. pinaster wood (mean value ¿13C = - 26.2¿ ± 0.8) significantly differed (P<0.001) from that of P. sylvestris (mean value ¿13C = - 24.6¿ ± 0.7). Relationships between the quality of the stand and the C isotopic composition of the wood were observed, high quality stands having trees more 13C depleted as compared with low quality ones. A high correlation between wood ¿13C and site index values for P. pinaster stands (r = - 0.667, P<0.001) was found, this correlation being even clearer when only P. pinaster growing over schist (r = - 0.833, P<0.001) are considered. Again, the correlation between the site index and the wood ¿13C of young P. pinaster trees was higher when plots over granite or schists are separately considered. A similar fact occurs for adult P. sylvestris trees from schists stands, high quality specimens being 13C depleted as compared with low quality ones. On the other hand, 13C natural abundance of wood from P. sylvestris trees seems to be also strongly influenced by the underlying parent material, young trees from granite stands having a statistically higher 13C isotopic composition (P<0.05) than young trees from schists stands.