Faculty Profiles - KOTANI, Ayumi

Presentations -

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Interannual and seasonal change of surface energy balance in temperate mixed forest.:Relationship between energy balance closure and energy fluxes. International conference

Tanaka Takayuki, Kotani Ayumi, Ohta Takeshi

The Japanese Forest Society Congress 2011 THE JAPANESE FORESTRY SOCIETY

Seasonal variability of scalar turbulent transport above forest canopy International conference

Kotani Ayumi, Hamazaki Shunki, Ohta Takeshi

Proceeding of Annual Conference 2012 THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES

Language：Japanese Presentation type：Oral presentation (general)

This study investigates seasonal variation in applicability of the turbulent similarity theory, and similarity or dissimilarity in the scalar transfer characteristics observed over forest canopy in the tropical monsoon, temperate, and boreal region. Deviation from the similarity theory and the small transfer efficiency was observed for CO2 variation at the boreal and temperature variation at the cool-temperate forest. Forests including deciduous trees showed clear seasonal variation in not only scalar flux itself but also its transfer characteristics especially in the case of CO2 variation, while the evergreen forest did not present such seasonal variation.

The causes of deviations from turbulent similarity in the atmospheric boundary layer above forests International conference

HAMAZAKI Shunki, KOTANI Ayumi, OHTA Takeshi

The Japanese Forest Society Congress 2011 THE JAPANESE FORESTRY SOCIETY

Winter Soil Temperature and Growing Season Net COĉ Exchange in Eastern Siberian Larch Forests International coauthorship International conference

A. Kotani, T. Hiyama, T. Nakai, T. C. Maximov

Seventh International Symposium on Arctic Research 2023.3.8

Spatio-temporal variability of vegetation response to climate in the forest-tundra ecotone of northeastern Siberia International conference

Japan Geoscience Union meeting 2022 2022.5.27

Language：Japanese Presentation type：Oral presentation (general)

Northern hemisphere terrestrial greening (positive trends in vegetation productivity) along with amplifying warming has been detected via field measurements and satellite observation over the past 40 years. Meanwhile, in some regions, a slowing or reversing response to warming trends has been reported in the recent decade. Understanding spatial and temporal heterogeneity in vegetation response on climate variability, which depends on differences in plant functional type or regional environment, is critical to studying vegetation dynamics over the northern high latitude under climate change.
This study investigated spatio-temporal variability of vegetation response in the forest-tundra ecotone region of northeastern Siberia to reveal 1) spatial variability in greening/browning trends, 2) regulation factors shift from temperature to water, and 3) perennial accumulated effect of land wetness condition on vegetation activity. We analyzed spatial variation of satellite-derived vegetation index and its correlation to climate variables in the last two decades from 2001 to 2020. Our study area covers the arctic coastal lowland to the mountainous region (over 2000 m) underlying continuous permafrost in northeast Siberia (60–75° N and 110–170° E). Vegetation also shifts from tundra to shrub and taiga along latitude and altitude. The annual maximum of the normalized difference vegetation index (hereafter, NDVImax) was derived from Moderate Resolution Imaging Spectrometer (MOD13A2) data. Climate variables such as thawing index (TI, annual sum of daily air temperature above 0°C), freezing index (FI, similar to TI but below 0°C in a year starting from previous September) and Climate Moisture Index (CMI, difference between annual precipitation and potential evapotranspiration) calculated from climate reanalysis data of ERA5-Land are prepared.
We examined 20-year time series of NDVImax, which were aggregated to 1° grid, by K-means cluster analysis, and divided them into four representative clusters; no clear trend region along the arctic sea, increase trend region east to south part, and the rest two intermediate clusters were scattered over the study area. The correlation of NDVImax and climate variables calculated for each pixel (0.1° resolution) showed heterogeneous spatial distribution. Positive correlation with the TI concentrated in the higher latitude area, while the positive correlation with FI expanded over the entire study area. The area with the significant correlation with FI shifted to the southeast from the first decade (2000-2010) to the latter (2011-2020). Vegetation response to climate is heterogeneous temporally and spatially, but we indicate climate parameters for seasons when vegetation doesn't grow may be important for vegetation. We calculated CMI for a year (from the previous September to the current year August) and two and three years (from two and three autumns ago). A positive correlation of NDVImax and 1-year CMI was mainly found around the northeast part, and its distribution area reduced in the recent decade. Toward the southeast, a positive correlation with perennial CMIs was pronounced rather than with 1-year CMI. This result indicates the possibility that precipitation allowed vegetation to grow after two years via water storage in the upper permafrost.

Forest carbon cycle based on tower flux observation Invited

A Kotani

National Summer Field School "Greenhouse Gases and Climate: Monitoring, Manipulation, Modeling and Management“ 2022.8.15 Institute of Biological Problems of Cryolithozone SB RAS

東シベリアの落葉針葉樹林における冬季温度と植物成長期のCO2収支

小谷亜由美，中井太郎，檜山哲哉

水文・水資源学会研究発表会 2022.9.7

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