From modeling the kinetics of cell enlargement to building tracheidograms of Larix gmelinii Rupr. (Rupr.) in the permafrost zone in Siberia

Boreal forest ecosystems are a crucial element in the global climate balance. In harsh environments functioning lateral meristems of trees are more regulated by the exogenous (included local climate) than endogenous factors. This information is encoded in the tree-ring structure which can be effectively decomposed by the process-based tree-ring growth simulations. Moreover, the process-based modeling can be used to describe non-linear processes linking climate variables with tree-ring formation. In this study, we applied the Vaganov-Shashkin model to simulate seasonal cell production and cell enlargement of Larix gmelinii Rupr. (Rupr.) growing in the permafrost zone of Central Siberia. We developed a procedure for calculating the radial cell diameter based on specific Gompertz function combined with the “instantaneous tracheidogram” approach to estimate effectively seasonal cell production and timing of cell enlargement under climate control. Simulated cell number and cell size matched well with direct xylogenesis observations. The developed procedure demonstrate strong relationships between seasonal simulated growth rate and measured tracheid radial size (the average correlation is 0.64, p < 0.01). A highly significant correlation (p < 0.01) between simulated and observed cell profiles was obtained for 71% of the growing seasons over the period 1950–2011. The strong exponential relationship (R2 = 0.67) was obtained between the day of the year (DOY) when cambial cell transfers into enlargement zone and simulated time intervals of cell enlargement. Based on the strong exponential relationship it was possible to reproduce the basic pattern of the observed tracheidograms over 1950–2011 with a systematic overestimation of final cell sizes at the beginning of the growing season, which will be possible to eliminate by using more anatomical data (trees) and longer period. The proposed approach of simulating intra-annual cell dynamics (cell production) has a great potential for studying how climate affects tree-ring formation.