Modeling the recent drought and thinning impacts on energy, water and carbon fluxes in a boreal forest.

Globally, boreal forests act as important carbon sinks, however, drought and forest management could substantially alter the sink strength, though the controlling mechanisms of drought and management remain unclear. In this study, we combined the detailed process-based CoupModel with multiple measurements to study the impacts of recent drought and forest thinning on a boreal forest during 2018-2021. CoupModel after calibration showed high ability to represent the dynamics of long-term net ecosystem exchange and its responses to environmental changes. The model simulation showed that the canopy temperature exacerbated the dominant role in regulating the boreal forest growth during the 2018 extreme drought year with slight increase in the annual mean net carbon uptake by 76.65 g C/m²/yr compared to 2017. The posterior model simulations ensemble suggested that thinning of trees in 2019-2020 caused the boreal forest in 2020 to be a sink to slight source ([-229.95, 94.90] g C/m²/yr, 90 % confidence interval), while the observations depicted a small source (69.35 g C/m²/yr). Moreover, rapid recovery of the boreal forest to a carbon sink was found in 2021, though remaining smaller than the carbon sink in 2017. Overall, the negative impacts from drought and harvest (2018-2021) were found to have offset the positive impacts from climate by 8 % - 92 %, on the net carbon uptake. This study highlights the resilience of boreal forests as carbon sink and provides new insights into the boreal forests' responses to both climate change and management.