open access

https://doi.org/10.14943/doctoral.k16523

https://hdl.handle.net/2115/95110

空間明示的個体ベース動的全球植生モデルを用いた気候変動下における非構造性炭水化物の生産が森林構造に与える影響の将来予測

英語

2025-03-25

Hokkaido University

ⅳ，130p

Forest dynamics need to be considered when estimating the global carbon budget. The alteration of forest structure and function under a changing climate and expanding human activity could lead to a reduction of forest canopy cover and a spread of lower-biomass ecosystems in warm and dry regions. A non-structural carbohydrate (NSC) acts as a storage buffer between carbon supplied by assimilation and carbon consumed by respiration, reproduction, and pests. Estimation of NSC concentrations in a tree is very important for accurate projection of future forest dynamics. I developed a new NSC module for incorporation into a spatially explicit individual-based dynamic global vegetation model (SEIB-DGVM) to validate the simulated NSC dynamics with observations. NSC pools were simulated in three plant organs: leaves, trunk, and roots. The seasonal dynamics of the NSCs varied among plant species, and the sizes of the NSC pools inferred from observations differed between the boreal, temperate, and tropical climates. The NSC models were therefore validated for each of the three climatic regions at both point and global scales to assess the performance of the models. The modeled NSCs showed good agreement in seasonality with the observed NSCs at four sites – Canada (boreal), Austria and Switzerland (temperate), and Panama (tropical) – and in mean values for three climate zones derived from the global NSC dataset. I compared forest composition and biome type percentages in Asia, Europe, and North America under SSP scenarios between the new and previous models. In the new model, taller trees accumulate more NSCs, which slows their growth, resulting in lower mean tree height and DBH. Unlike the previous model, where taller trees dominated, the new model allows shorter trees to outcompete taller ones, creating a broader range of tree sizes, including more near-zero values. The new model also incorporates a carbon starvation mortality process. When carbon starvation is "switched on," tree density decreases, favoring taller tree growth while shortening tree lifespans due to increased vulnerability of shorter trees. The SEIB-DGVM-NSC improves simulations of vegetation distribution, GPP, and forest composition caused by the changes in NSC dynamics at global scales. This research advances understanding of NSC dynamics and their role in the terrestrial carbon cycle, particularly under climate change

2025-03-25

甲第16523号

博士(食資源学)

(主査) 教授 加藤 知道, 教授 高橋 昌志, 准教授 高須賀 太一

国際食資源学院（国際食資源学専攻）

博士論文

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