Are deciduous broad leaved trees increasing in hemiboreal forests? Utilization of data of multiple sites, long-term, and tree-rings

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K05682
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 40010:Forest science-related
• Research Institution: The University of Tokyo
• Principal Investigator: Suzuki Satoshi 東京大学, 大学院農学生命科学研究科(農学部), 助教 (20633001)
• Co-Investigator(Kenkyū-buntansha): 香川 聡 国立研究開発法人森林研究・整備機構, 森林総合研究所, 主任研究員 等 (40353635)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 針広混交林 / 気候変動 / 年輪安定同位体比 / 潜在的水利用効率

Outline of Final Research Achievements

It has been reported in the various regions of the northern hemisphere that in the boreal forests where evergreen coniferous trees (hereafter referred to as conifers) and deciduous broadleaf trees coexist, the relative dominance of conifers is decreasing while that of deciduous broadleaf trees is increasing. This study analyzed multi-site data from Hokkaido and long-term data from the University of Tokyo Hokkaido Forest, revealing that in conifer-broadleaf mixed forests in central Hokkaido and the Sea of Japan of northern Hokkaido, the proportion of deciduous broadleaf trees is increasing. Furthermore, analysis of tree rings showed that, while the growth rate of conifers has been continuously decreasing since 1950, the growth rate of deciduous broadleaf trees did not show significant changes until around 2000. This difference was found to potentially correspond to changes in the intrinsic water use efficiency estimated from the carbon stable isotope ratios in the tree rings.

Free Research Field

森林生態学

Academic Significance and Societal Importance of the Research Achievements

本研究は、現在各地で報告されている北方性針広混交林における落葉広葉樹の増加が、1970-1990年代に進行した気候の乾燥化と関係している可能性を、年輪の安定同位体比を用いて初めて示すことができた。北海道の天然林の木材生産においては、天然林の針葉樹資源を安定的に保つことが必要不可欠であり、本研究の成果は針葉樹資源の保全のために有益な情報を提供する。特に針葉樹資源を保全すべき地域の特定や保全の方法についての基礎情報となる。今後、針葉樹資源の保全のためには、天然林において落葉広葉樹を積極的に利用するなど、針葉樹の成長や更新を促す森林管理によって、針葉樹割合を一定以上に保つことが必要である。