Intra-annual variability of wood formation and δ13C in tree-rings at Hyytiala, Finland

Investigation of the relationship between tree-ring stable carbon isotope composition (delta C-13) and environmental variables at the intra-seasonal scale can inform on the understanding of the environmental forcing affecting trees during the active period of radial growth. Recent progress in the measurement techniques for assessing the delta C-13 signature of tree rings at high spatial resolution provides an opportunity to derive tree physiological information at fine temporal scale, within a given year. Three delta C-13 time series of resin-extracted wholewood from tree-rings of Scots pine trees (Pinus sylvestris L.) sampled at Hyytiala (Finland) have been produced by using laser-ablation stable isotope mass spectrometry. These intra-seasonal stable isotope series exhibit a strong common signal (EPS = 0.96) demonstrating the capacity of trees within a stand to preserve a common intra-seasonal response to external controls in a similar manner as found with annual measurements. To estimate when wood cells are active and responsive to environmental information, a Gompertz approach, assessed against microcore data, was adopted to model the timing of wood formation. The addition of a cell lifetime function into environment-growth models may evaluate more completely, the environmental effect on intra-annual tree-ring delta C-13 values and that during the growing season. Statistical analysis of the resulting tree-ring delta C-13 intra-annual signal implies a shift in importance from the influence of the environmental variables through out the growing season. (C) 2016 Elsevier B.V. All rights reserved.