Forward Modeling Reveals Multidecadal Trends in Cambial Kinetics and Phenology at Treeline

Abstract

Significant alterations of cambial activity might be expected due to climate warming, leading to growing season extension and higher growth rates especially in cold-limited forests. However, assessment of climate-change-driven trends in intra-annual wood formation suffers from the lack of direct observations with a timespan exceeding a few years. We used the Vaganov-Shashkin process-based model to: (i) simulate daily resolved numbers of cambial and differentiating cells; and (ii) develop chronologies of the onset and termination of specific phases of cambial phenology during 1961–2017. We also determined the dominant climatic factor limiting cambial activity for each day. To asses intra-annual model validity, we used 8 years of direct xylogenesis monitoring from the treeline region of the Krkonoše Mts. (Czechia). The model exhibits high validity in case of spring phenological phases and a seasonal dynamics of tracheid production, but its precision declines for estimates of autumn phenological phases and growing season duration. The simulations reveal an increasing trend in the number of tracheids produced by cambium each year by 0.42 cells/year. Spring phenological phases (onset of cambial cell growth and tracheid enlargement) show significant shifts toward earlier occurrence in the year (for 0.28–0.34 days/year). In addition, there is a significant increase in simulated growth rates during entire growing season associated with the intra-annual redistribution of the dominant climatic controls over cambial activity. Results suggest that higher growth rates at treeline are driven by (i) temperature-stimulated intensification of spring cambial kinetics, and (ii) decoupling of summer growth rates from the limiting effect of low summer temperature due to higher frequency of climatically optimal days. Our results highlight that the cambial kinetics stimulation by increasing spring and summer temperatures and shifting spring phenology determine the recent growth trends of treeline ecosystems. Redistribution of individual climatic factors controlling cambial activity during the growing season questions the temporal stability of climatic signal of cold forest chronologies under ongoing climate change.

Modeling Climate Impacts on Tree Growth to Assess Tree Vulnerability to Drought During Forest Dieback

“…The VS model (VS-oscilloscope ver.1.362) was used for modeling the Miedes and Orera RWI series of D and ND trees. The VS model is a process-based growth model of intermediate complexity that has been widely applied and validated in conifers (refer, among others, Vaganov et al, 2006 ; Touchan et al, 2012 ; Shishov et al, 2016 ; He et al, 2017 ; Popkova et al, 2018 ; Tychkov et al, 2019 ; Tumajer et al, 2021 ). The model simulates daily Grs focusing on xylogenesis (enlargement, division, and differentiation of tracheids) and considering the data daily values of air temperature, Prec., and radiation as input.…”

Growing faster, longer or both? Modelling plastic response of Juniperus communis growth phenology to climate change

“…In addition to comparing simulated and observed site chronologies, the VS model output can be compared against xylogenesis data to assess the precision of simulated intra-annual growth phenology and kinetics (Buttò et al, 2020;Tumajer et al, 2021). We compared (1940-1980) and verification (1980-2006/2016) periods equalled .50 (.26) and .42 (.20), respectively (Figure 1; Table 1).…”

A Band Model of Cambium Development: Opportunities and Prospects

“…This hypothesis was used as a basis for the Vaganov-Shashkin process-based tree-ring model (VS-model) developed for conifer species [27]. Cell production during the growing season is simulated in accordance with nonlinear responses of tree-ring growth rate to climate forcings (temperature, soil moisture, and solar irradiation) [27,[37][38][39][40][41][42][43]. However, even using multidimensional and multicriteria parameterization of the model [35,39,[44][45][46], the cambial block (kinetic model of cambium) is still very complex to use and a challenge to interpret directly.…”

“…However, even using multidimensional and multicriteria parameterization of the model [35,39,[44][45][46], the cambial block (kinetic model of cambium) is still very complex to use and a challenge to interpret directly. This submodel is based on the kinetic process of complex cambium functioning, i.e., position control of cambial mother cells relative to initial, and their rates of division [27,39,43]. Moreover, the 12 submodel cambial parameters cannot be readily tested using experimental or direct measurements [43].…”

“…This submodel is based on the kinetic process of complex cambium functioning, i.e., position control of cambial mother cells relative to initial, and their rates of division [27,39,43]. Moreover, the 12 submodel cambial parameters cannot be readily tested using experimental or direct measurements [43]. As a result, it was not possible to characterize the entire spectrum of cambium production variability, which can be specific to different years of tree growth, to individual trees with different growth energy, or across various conifer species and habitats [40].…”