Presentation Information
[ACG68-P14]Dynamic Environmental Controlling Factors on Water and Carbon Flux in Northern Mongolian Forests under Decadal-Scale Hydroclimatic Variability
*Ayumi Kotani1, Mamoru Ishikawa2, Tetsuya Hiyama3, Shin Miyazaki4, Baatarbileg Nachin5, Dashtseren Avirmed6 (1.Graduate School of Bioagricultural Sciences, Nagoya University, 2.Faculty of Environmental Earth Science, Hokkaido University, 3.Institute for Space-Earth Environmental Research, Nagoya University, 4.Sonic Corporation, 5.National University of Mongolia, 6.Institute of Geography and Geoecology, Mongolian Academy of Sciences)
Keywords:
Boreal forest,ecosystem response,eddy covariance,water and carbon cycles
Forests in northern Mongolia, located at the southern margin of the Eurasian boreal forest and permafrost distribution, form a vegetation ecotone that is highly sensitive to climate change. Larix sibirica, the dominant species in this region, is suggested to possess a higher carbon sequestration potential than L. cajanderi at higher latitudes; however, it is simultaneously vulnerable to drought and heat stress. Over the past few decades, a discrepancy has emerged between "greening," as observed in broad-scale satellite data, and "growth decline," as indicated by tree-ring analyses, leaving a significant gap in understanding climate response mechanisms across different spatiotemporal scales.
In this study, we compared tower-based flux observations at the Udleg Forest Research Station over two distinct periods (2010–2012 and 2023–2025) to examine how varying hydroclimate conditions alter the environmental factors controlling forest fluxes. According to hydroclimatic data (ERA5-Land) and satellite-derived land surface indices from 2000 to 2025, the region experienced a persistent drying trend until the mid-2010s, characterized by declining evapotranspiration ET and aridity indices regardless of precipitation fluctuations. However, since the late 2010s, both precipitation and ET have increased. Following this shift, with a lag of several years, both the Land Surface Water Index (LSWI) and the Normalized Difference Vegetation Index (NDVI) showed significant upward trends, indicating a lagged vegetation response.
Multivariate regression analysis of tower observation revealed a dynamic shift in the primary drivers of ecosystem fluxes between the two periods. During the dry phase of 2010–2012, soil water content was the primary driver of summer ET variability (standardized regression coefficient (β≃1.0). In contrast, during the wet phase of 2023–2025, the influence of soil water diminished, and soil temperature and solar radiation emerged as the dominant factors. Regarding CO2 flux, the contribution of leaf area index increased significantly during 2023–2025 (β>1.0), suggesting that, under sufficient water conditions, enhanced photosynthetic responsiveness associated with phenological dynamics directly drives flux variability. These findings demonstrate that environmental controls on forest ET and CO2 fluxes are state-dependent, shifting dynamically within decadal-scale hydroclimatic cycles.
In this study, we compared tower-based flux observations at the Udleg Forest Research Station over two distinct periods (2010–2012 and 2023–2025) to examine how varying hydroclimate conditions alter the environmental factors controlling forest fluxes. According to hydroclimatic data (ERA5-Land) and satellite-derived land surface indices from 2000 to 2025, the region experienced a persistent drying trend until the mid-2010s, characterized by declining evapotranspiration ET and aridity indices regardless of precipitation fluctuations. However, since the late 2010s, both precipitation and ET have increased. Following this shift, with a lag of several years, both the Land Surface Water Index (LSWI) and the Normalized Difference Vegetation Index (NDVI) showed significant upward trends, indicating a lagged vegetation response.
Multivariate regression analysis of tower observation revealed a dynamic shift in the primary drivers of ecosystem fluxes between the two periods. During the dry phase of 2010–2012, soil water content was the primary driver of summer ET variability (standardized regression coefficient (β≃1.0). In contrast, during the wet phase of 2023–2025, the influence of soil water diminished, and soil temperature and solar radiation emerged as the dominant factors. Regarding CO2 flux, the contribution of leaf area index increased significantly during 2023–2025 (β>1.0), suggesting that, under sufficient water conditions, enhanced photosynthetic responsiveness associated with phenological dynamics directly drives flux variability. These findings demonstrate that environmental controls on forest ET and CO2 fluxes are state-dependent, shifting dynamically within decadal-scale hydroclimatic cycles.