[M-IS01] Environmental, Socio-Economic and Climatic Changes in Northern Eurasia

[MIS01-15] Spring and autumn warming trends since 1960 increase the carbon sink capacity of the Siberian forests

*Alberto Arzac¹、Daniel Díaz de Quijano¹、Alexander V Kirdyanov^1,2、Ivan I Tychkov¹、Oksana V Sergeeva^1,2、Vladimir V Shishov¹、Viktor Ilyn¹、Vladimir V Kukarskih¹、Eugene A Vaganov^1,2 (1.Siberian Federal University、2.V.N. Sukachev Institute of Forest SB RAS)

キーワード：climate change, forest-steppe, taiga, forest-tundra, temperature trends, tree growth

Siberia, the largest northern land mass and permafrost region, plays a critical role in global carbon budgets and climate dynamics. While this vast region has been described to be endangered by high latitude warming in recent decades, experiencing extreme heatwaves, the long-term assessments of spatiotemporal trends affecting regional biomes have been incomplete and unsuited to detail. Here, we analyze the spatiotemporal temperature and precipitation trends over an evenly distributed network of 311 climate stations continuously covering the 1960–2020 period across Siberia, and its relationship with tree growth phenology simulations in three major biomes (i.e., forest-tundra, taiga and forest-steppe) over the same period. Temperature trends revealed substantial warming up to 0.5 ºC/decade throughout much of the cold season (October to June), but a lack of such warming during the mid-summer. Precipitation trends are less significant and spatially heterogeneous. On the other hand, tree growth model simulations carried out on the main conifer forest-forming species (e.g., Larix sibirica, Larix cajanderi, Pinus sylvestris), suggested changes in the timing of the start, ending and length of the growing season linked to spring and late summer warming over the covered period, with a delay of up to forty-six days in the start of the growing season between the forest-steppe and the forest-tundra ecotones. In addition, growing season lengths have been increasing in recent decades due to mid-spring and late-summer warming, with the most significant changes found in the forest-tundra (2.1 days/decade), whereas less significant in the forest-steppe (1.0 days/decade). Nevertheless, generalized additive mixed models suggested that alterations in tree growth phenology only seem to affect tree growth in the forest-tundra and taiga, where earlier growth in spring promotes wider tree rings independently of the length of the growing season. These changes in tree growth and phenology related to climate warming may increase carbon sequestration periods at the forest-tundra and the taiga, influencing the Siberian ecosystem's structure and global carbon dynamics, potentially increasing biomass accumulation and short-term carbon pools across the taiga and forest-tundra and decreasing in the forest-steppe due to summer water shortages. The results presented in the study provided a new view of the spatiotemporal trends over the major Siberian biomes and highlight the relevance of Siberia in the global context of climate and dynamics.

This study was supported by the Ministry of Science and Higher Education of the Russian Federation [FSRZ-2020-0014], the Russian Science Foundation [Grants 18-74-10048P and 22-14-00048]