More than 60% of tree phytomass is concentrated in stem wood, which is the result of periodic activity of the cambium. Nevertheless, there are few attempts to quantitatively describe cambium dynamics. In this study, we develop a state-of-the-art band model of cambium development, based on the kinetic heterogeneity of the cambial zone and the connectivity of the cell structure. The model describes seasonal cambium development based on an exponential function under climate forcing which can be effectively used to estimate the seasonal cell production for individual trees. It was shown that the model is able to simulate different cell production for fast-, middle- and slow-growing trees under the same climate forcing. Based on actual measurements of cell production for two contrasted trees, the model effectively reconstructed long-term cell production variability (up to 75% of explained variance) of both tree-ring characteristics over the period 1937−2012. The new model significantly simplifies the assessment of seasonal cell production for individual trees of a studied forest stand and allows the entire range of individual absolute variability in the ring formation of any tree in the stand to be quantified, which can lead to a better understanding of the anatomy of xylem formation, a key component of the carbon cycle.

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.

The development of the tree ring is a process occurring under limitations caused by a complex of environmental factors and intrinsic regulatory mechanisms. Its understanding is of interest in many scientific fields, but most quantitative models trying to describe its details meet several issues stemming from the difficulty of its verification. This study attempted to combine several observational and modeling approaches to verify intermediate details of the description of xylogenesis, aiming to restore the tree-ring seasonal growth kinetics on the basis of dendrochronological and wood anatomical data. It was carried out for Scots pine in two semiarid habitats in South Siberia. The Vaganov-Shashkin model was used jointly with tree-ring width chronology and climatic data to model the tree radial growth rate with daily precision. The Band-model was then used to calculate the kinetics of tracheid production from the growth rate and actual final number of cells per radial file in the ring. Seasonal observations of cell population and final measurements of cell sizes were used to fit model parameters and verify the numbers of developing tracheids produced by the Band-model. The patterns of modeled seasonal kinetics for six seasons and two sites were found to repeat the actual drought-derived deviations in tree growth and observations (R² = 0.70–0.84). Further research is required to test other climatic limitations and species-specific ecophysiological mechanisms of growth regulation.