Climatically-driven variability in annual growth of diffuse-porous tree species in the subtaiga of southeast Western Siberia

Amidst regional climate changes as a consequence of global fluctuations, research focusing on the impact of these changes on the growth of forest-forming species is increasingly relevant. In Russia, forests are a crucial renewable natural resource, playing a leading role in the economy and holding national ecological, economic, and social significance. Trees in temperate zones annually accumulate wood during the growing season, forming annual layers (growth rings). The dynamics of trees' annual growth is largely determined by the weather conditions of a particular year. Dendrochronological analysis, which aims to identify the response of different tree species to climatic events, especially anomalies, is used for their assessment. This article examines the influence of hydrothermal factors on the growth of forest-forming small-leaved species (birch, aspen) in the subtaiga landscapes of Southeast Western Siberia, against the backdrop of regional climate peculiarities. The research area is the basin of the Basandayka River, on the outskirts of Tomsk, where trees were cut down at two key sites. The age of the sampled trees was 9-10 years (15 samples). For analysis, 6 tree cuts of comparable age were used, as their planting years were known: -for birch, 10 years (2008-2017), and for aspen, 9 years (2009-2017). Meteorological data (temperature and precipitation) of average daily data from the VNIIGMI-MCD database for the period 2008-2017 at the Tomsk weather station served as the basis for studying regional climate changes and their impact on the growth of birch and aspen. Climate changes were analysed according to calendar dates and natural seasons. The boundaries and structure of natural seasons were established using a complex-genetic method applied to studying the seasonal rhythms of the climate. The study revealed trends in the annual growth of the tree species examined, as well as the indicators of thermal regime and moisture at monthly, annual, and seasonal levels. Leading climatic indicators that determine both favourable and unfavourable conditions for the development of small-leaved species and their response to climate change were identified. Our research indicated that the dominant importance of each climatic indicator for tree growth in the subtaiga is mainly due to the phase of the vegetative period and the natural season of the year, as other geographical growth conditions are identical. An increase in the duration of the vegetative part of the annual cycle, combined with a decrease in the duration of the cold-snowy part and an increase in cold season temperatures, can be viewed as regional climatic changes positively affecting the growing conditions of birch. It was also found that the most significant climatic response in this small-leaved species is associated with summer temperatures, while for aspen, it is with winter temperatures. Aspen shows a high positive correlation with precipitation during the phases of 'late summer' and 'early autumn' (August-September), and a significant negative dependency on central summer precipitation. Thus, the ongoing regional climate changes towards warming and increased moisture, overall, positively influence the growth conditions of small-leaved species." Contribution of the authors: the authors contributed equally to this article. The authors declare no conflicts of interests.

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