Climate affects wood formation with consequences for the functioning and survival of trees. Since tree-rings tissues (i.e., earlywood and latewood) are formed at different time in the season, the impact of climate change might differently affect their functions. In this study, we combine quantitative tracheid anatomy with the Vaganov-Shashkin growth model (VS-model) to investigate how summer drought affected the annual ring structure of Pinus sylvestris L. from a forest-steppe zone in Southern Siberia. In particular, we used climate-growth relationships over a 50-year period to identify the timing of climatic signal of early-, transition-, and late-wood tracheid's diameters (D_EW, D_TW and D_LW). Corresponding daily growth rates (Gr) obtained by the VS-model were applied to calculate the changes in the width of the relative tree-ring sectors considering different levels of aridity.
Results indicate that tracheid size is sensitive to drought with temporal shifts among the climatic signal of D_EW (in May), D_TW (June) and D_LW (July). A comparison of modeled daily-growth rate cumulated over the climatic window of each ring sector and grouped by years with different level of aridity, indicated that a release of summer drought mostly affected the widths of the transition (+28.1%) and (+48.6%) latewood sectors, thus matching observations performed on the same cores.
These results suggest that current changes in climate seasonality, as occurring in the selected area, are positively impacting both the hydraulic efficiency (by increasing the diameter of the earlywood cells) and the latewood width of the wood produced in the area.