Similar Climate, Different Carbon Uptake: Ecophysiological and Phenological Controls on Interannual Variability in Nearby Evergreen and Deciduous Forests of East Asia

Global warming has extended the growing season in temperate forests, and this trend is expected to continue. While changes in forest physiological processes enhance our understanding of carbon uptake and phenology, the mechanisms underlying interannual variability in carbon balance across adjacent different forest types under similar monsoon-influenced climatic conditions, particularly in East Asia, remain unclear. This study aimed to identify the ecophysiological and phenological drivers of net carbon uptake based on eddy covariance flux observations from adjacent temperate forest ecosystems in East Asia, affiliated with the KoFlux and JapanFlux networks: evergreen forests and deciduous forests. The interannual variability of net ecosystem production (NEP) in evergreen needleleaf forests (ENF) was generally dominated by environmental controls, particularly water availability and temperature. In contrast, in deciduous forests—including both deciduous broadleaf and deciduous needleleaf forests (DBF and DNF)—interannual variability of NEP was largely regulated by environmental conditions but consistently modulated by phenology, with the timing and duration of carbon uptake playing an additional and critical role across East Asia. The results of this study are expected to have high applicability as a foundational dataset for future improvements in global carbon budget predictions driven by climate change. Not only do they provide scientific data to support future carbon neutral, but they also reveal the interannual variability characteristics of carbon uptake through the integrated consideration of ecophysiological and phenological factors.