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農学部 農学部門森林環境持続性科学領域 附属次世代農学教育研究センター |
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特別助教 |
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小柳 賢太 (コヤナギ ケンタ)
KOYANAGI Kenta
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学位 【 表示 ／ 非表示 】
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PhD in Mountain Environment and Agriculture （ 2026年3月 ボルツァーノ自由大学 ）
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M.Sc. Agriculture and Forestry （ 2019年12月 東フィンランド大学 ）
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M.Sc. Forest Sciences （ 2019年8月 フライブルク大学 ）
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学士（農学） （ 2017年3月 東京農工大学 ）
論文 【 表示 ／ 非表示 】
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Koyanagi K., Andreoli A., Nordio G., Gaudron H., Pöppl R., Comiti F.
Journal of Hydrology Regional Studies 66 2026年8月
掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Hydrology Regional Studies
Study Region: We developed a new experimental nested catchment in the Eggen-Ega River basin, Eastern Italian Alps, comprising four 27 m2 hillslope plots and three watersheds draining 2.34, 42.4, and 166 km2. Study Focus: We aimed to understand scale-dependent magnitude and controls of turbid stormflow transfer across the Alpine catchments. We monitored runoff volume and turbidity at four spatial scales and assessed their dependence on the characteristics of 23–41 rainfall events between April and October 2024. New Hydrological Insights for the Region: Storm runoff coefficients exhibited a negative power-law scaling with drainage area (exponent: −1/10), suggesting stronger scale-dependent runoff fluctuations at finer scales, critically limiting the representativeness of small-scale, single-point stream gauging in the region. On the contrary, the mean runoff coefficients at 42.4 and 166 km2 were both 0.01, suggesting sufficient region-specific drainage sizes to average out the uniqueness of monitoring locations and timing. While rainfall intensity and saturation (event depth and duration) exerted primary controls on event-scale sediment delivery from 27 m2 plots to a 2.34 km2 headwater, turbidity in the larger 42.4 km2 catchment was more variable and less sensitive to rainfall predictors, likely due to sediment routing beyond the timescale of individual storm events. Our novel nested catchment approach highlights scale-dependent observations of turbid stormflow, calling for extended monitoring of nested catchments across the Alpine regions.
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Koyanagi K., Andreoli A., Nordio G., Pitscheider F., Tomelleri E., Comiti F.
Journal of Hydrology 656 2025年8月
掲載種別：研究論文（学術雑誌） 出版者・発行元：Journal of Hydrology
Extensively disturbed catchments undergo heterogeneous vegetation recovery trajectories due to complex disturbance-intervention interactions. Windstorms are one of the major disturbance agents in intensively managed mountain forests of the European Alps; however, little is known about how post-windthrow runoff and erosion processes change in time and space due to limited empirical studies covering multiple disturbances and interventions. Between vegetation periods 2021–2023, we monitored water and sediment fluxes from four 4.5-m-wide × 6.0-m-long plots in a headwater catchment of the Eastern Italian Alps, characterized by deadwood (salvaged/unsalvaged), time since windthrows (3–5 and 21–23 years), and regeneration (natural/artificial). Our monitoring data suggested unsalvaged deadwood has a minimal effect on storm runoff generation for 3–5 years after disturbances, whereas legacy deadwood seemed to offer better soil protection during erosive storms (maximum 5-min intensity > 40.2 mm h<sup>−1</sup>). Recently disturbed plots presented slightly yet significantly 1–2 % higher mean runoff coefficient after prolonged dry periods (30–45 days), implying the importance of disturbance history in better accounting for current hydrological responses. Saplings and trees artificially regenerated after windthrows marginally facilitated quicker runoff transfer, seemingly due to scale-dependent preferential flow pathways (microrelief and litter). Our continuous monitoring efforts underscore the critical need to recognize upstream vegetation recovery trajectories to advance our understanding of catchment-scale responses to major forest disturbances.
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Torresani M., Montagnani L., Rocchini D., Moudrý V., Andreoli A., Wellstein C., Koyanagi K., Ros L.D., Bacaro G., Perrone M., Salvatori C., Menegaldo I., Guatelli E., Tognetti R.
Agricultural and Forest Meteorology 359 2024年12月
掲載種別：研究論文（学術雑誌） 出版者・発行元：Agricultural and Forest Meteorology
With climate change intensifying, forests globally are becoming more susceptible to extreme weather events, such as windstorms, which account for a significant share of Europe's economic losses. The Vaia windstorm of late autumn 2018, striking Italy's North-East alpine ecosystem, highlighted this vulnerability, toppling over 8.5 million cubic meters of timber and sparking debates on forest management's role in mitigating such disasters. This study aims to evaluate the impact of structural and topographical characteristics on the damage caused by Vaia, using Airborne Light Detection And Ranging (LiDAR) data collected before the storm, in four heavily affected forest areas in the Italian Alps (Carezza in the Province of Bolzano-Bozen, Predazzo, Manghen, and Primiero in the Province of Trento). We analyzed structural metrics like forest height heterogeneity (HH), forest mean height, and density, alongside topographical features such as aspect, slope, and altitude, to discern their influence on the storm's severity. Our results revealed that the most significant difference between affected and unaffected areas is forest mean height that was found higher in areas hit by the storm. Forest density played a lesser but important role, with denser areas experiencing more severe damage, though this was only significant in certain areas. Contrary to common assumptions, our analysis revealed that forest height heterogeneity (HH) did not have a significant effect on damage levels. The findings, consistent with previous research, revealed a significant association between specific aspects, particularly the South-East orientation, which aligned with the predominant wind direction during the Vaia storm, and an increased likelihood of damage. Both structural and topographical factors interact in complex ways to influence the outcome of such extreme events. The study emphasizes the dominant impact of the Vaia windstorm, noting that while managing forest height and density may help, the diverse topography complicates these efforts. Our study explicitly tested the effectiveness of using Airborne LiDAR data to explore forest structural and topographical factors that influenced Vaia storm damage. The achieved results demonstrate that LiDAR serves as a useful tool to field data, offering valuable insights for broader applications in this domain.
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堆砂条件と流木長が不透過型砂防堰堤の流木捕捉効果に与える影響の実験的検討 査読あり
平田 遼, 小柳 賢太, 石井 靖雄
砂防学会誌 77 ( 2 ) 3 - 11 2024年7月
記述言語：日本語 掲載種別：研究論文（学術雑誌） 出版者・発行元：公益社団法人 砂防学会
To investigate the effectiveness of closed-type check dams on retaining driftwood, we conducted a series of wood-laden debris flow flume experiments. In the experiments, we varied (1) the initial sedimentation condition of the check dam and (2) the length of input driftwood, investigating the amount of driftwood retained by the check dam and its temporal change. As a result, we found that the retention mechanism of the driftwood is more strongly governed by the difference in the initial sedimentation condition rather than by the difference in driftwood length. The ratio of retained driftwood to supplied driftwood was generally higher under the empty-dam condition, by which more than half of the driftwood was retained regardless of experiment cases. The ratio was notably higher under the empty-dam condition, with driftwood length longer than the spillway width. Under the filled-dam condition, on the other hand, the ratio showed relatively wider fluctuation among experiment cases, even when the driftwood length was longer than the spillway width. In light of the log behavior behind the check dam under all cases, driftwood was more certainly retained due to the resilient blockage structures formed by driftwood near the check dam spillway. In the case of the empty-dam condition, driftwood at the head of the debris flow that reached the check dam was covered and immobilized by the following sediment. Further efforts should be made to evaluate other factors, e.g., congestion level of log transport that potentially affect the effectiveness of closed-type check dams. Our findings suggest that maintaining the storage capacity of closed-type check dams is essential for utilizing existing structures for mitigating driftwood disasters.
DOI： 10.11475/sabo.77.2_3
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Nordio G., Koyanagi K., Comiti F., Andreoli A.
2024 IEEE International Workshop on Metrology for Agriculture and Forestry Metroagrifor 2024 Proceedings 376 - 381 2024年
掲載種別：研究論文（国際会議プロシーディングス） 出版者・発行元：2024 IEEE International Workshop on Metrology for Agriculture and Forestry Metroagrifor 2024 Proceedings
Windstorm events are the primary natural disturbances in the Italian Alps. The combined effects of climate change and windstorm-induced land cover changes are expected to significantly influence the hydrological and erosional responses of forested watersheds. This study presents preliminary results from both plot-scale monitoring and large-scale modeling conducted in the subalpine catchment of Val d'Ega (BZ). At the plot scale, runoff and erosion were monitored in 4.5m x 6m plots, which were characterized by either natural or artificial regeneration following storm events. Water and sediment yields were measured across 75 rainfall events from 2021 to 2023. Initial results reveal considerable inter-plot variability in runoff and erosion dynamics, with artificially regenerated plots exhibiting higher water and sediment transport rates. Furthermore, the pre-storm soil conditions and microtopography appear to play a significant role in these dynamics. At the larger scale, surface runoff and sediment yield were evaluated using the SWAT model, comparing pre- and post-Vaia windstorm (October 2018) conditions. Four different scenarios, varying in both spatial extent and scale of land use changes, were assessed. Results indicate a 3% to 16% increase in annual surface runoff in scenarios accounting for land cover changes, compared to the 'no-damage' scenario. Consequently, sediment yield increased by up to four times, with the greatest impact observed in subbasins most affected by the Vaia windstorm. These findings highlight the need for further investigation into effective management strategies in response to the evolving post-windstorm hydrological and erosional dynamics.
書籍等出版物 【 表示 ／ 非表示 】
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図説 日本の森林: 森・人・生き物の多様なかかわり
五味 高志, 小柳 賢太（ 担当： 分担執筆 , 範囲: 第3部 森林と人 3 暮らしを守る森）
朝倉書店 2024年9月
著書種別：学術書