Seasonal Growth of Pine Tree Rings: Comparison of Direct Observations and Simulation

Abstract

Repetitive observations (direct measurements) of seasonal kinetics of xylogenesis and simulations (proxy data) with tree growth models are the two main approaches available to assess tree-ring growth and development. Both have drawbacks: short cover period for observations; limited accuracy of simulations depending on input data for models. We proposed an implementation of both approaches on the same trees to find ways for compensation. Cell numbers at subsequent xylogenesis stages were observed for Pinus sylvestris L. over five seasons in moisture-deficient habitats of Southern Siberia. The Vaganov–Shashkin model was parameterized for species and soil-landscape conditions to fit local tree-ring width chronologies (R = 0.56–0.73). Seasonal kinetics variables were then compared among themselves and with the simulated environmentally driven growth rate. The number of cells in the cambial and cell enlargement zone closely followed the curve of the 15-day moving average of the simulated growth rate (R = 0.56–0.87 at one site and R = 0.78–0.89 after shifting rate curve forward by 17–20 days at another site). The maximum number of cambium cells, which occurred within three weeks of the summer solstice, was found to be positively related with the number of tracheids in the complete tree ring (R2 = 0.12–0.75 for individual seasons and 0.49 for total dataset), making it a promising short-term forecast variable for tree radial growth and productivity.