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Afforestation is considered a major tool for climate change mitigation with high potential particularly in the tropics. In this study we analyzed CO2 fluxes of an afforested former sugar cane plantation in southern Taiwan, as this forest had been planted with the goal of sequestering CO2 to help mitigate climate change. The plantation is exposed to a monsoon climate with dry but warm winter seasons, heavy precipitation during the summers and experiences a rather high frequency of typhoons (0.7 per year). The aim of this study is to quantify the net ecosystem exchange (NEE), ecosystem respiration (ER), gross primary production (GPP) and increment in above‐ground biomass (AGB) at the site. Specifically, we aim to analyze the influence of the distinct wet and dry seasonality and the frequent typhoon impact on these fluxes. We estimated the CO2 fluxes for two years using the eddy covariance approach. In 2010 and 2016 the forest sequestered carbon from the atmosphere with a NEE of −116 g C m−2 year−1 and −322 g C m−2 year−1, respectively. Between 2011 and 2014, the yearly increment in AGB increased with a mean increment of 509 ± 181 (SD) g C m−2 year−1. We observed high seasonal difference in CO2 fluxes particularly in ER and GPP, and conclude that high winter precipitation enhances CO2 uptake. Furthermore, frequent typhoons reduced the CO2 uptake and increment in AGB, such as in 2016, when a very strong typhoon passed the forest. Plain Language Summary: Afforestation is a key tool against climate change because a growing forest sequesters CO2, an important greenhouse gas. The scope of this study was to develop a deeper understanding of CO2 uptake through afforestation and the respective driving mechanisms. We estimated the yearly carbon uptake of an afforested former sugar cane plantation in tropical southern Taiwan for the years 2010 and 2016. We found that the carbon uptake increased between 2010 and 2016 and that carbon fluxes show huge differences between the dry winter and the wet summer seasons. Additionally, we found that more precipitation in winter 2016 caused a higher uptake in spring 2016, as compared to spring 2010. We discovered that the frequent typhoon occurrence (0.7 per year) had a huge impact on the forest. Climate change will likely lead to more intense cyclones (such as typhoons) worldwide and changes in regional precipitation patterns. Overall, afforestation is a tool to mitigate climate change, and, against this background, our results provide meaningful insights into the development of a newly planted forest in a region that frequently experiences typhoons and has a pronounced seasonal climate. Key Points: A young, heterogeneous forest planted on a former sugar cane plantation is a carbon dioxide sink 8 and 14 years after plantingThe forest shows high seasonal differences in carbon dioxide fluxes. In 2016, high precipitation during the dry season enhanced the carbon dioxide uptakeFrequent impact of tropical cyclones (typhoons) reduce carbon dioxide uptake and increment in above‐ground biomass at this forest site [ABSTRACT FROM AUTHOR]

Tropical, temperate, and boreal forests are the subject of various eddy covariance studies, but less is known about the subtropical region. As there are large areas of subtropical forests in the East Asian monsoon region with possibly high carbon uptake, we used three years (2011–2013) of eddy covariance data to estimate the carbon balance of a subtropical mountain forest in Taiwan. Two techniques of flux partitioning are applied to evaluate ecosystem respiration, thoroughly evaluate the validity of the estimated fluxes, and arrive at an estimate of the yearly net ecosystem exchange (NEE). We found that advection is a strong player at our site. Further, when used alone, the nighttime flux correction with the so-called u∗ method (u∗ = friction velocity) cannot avoid underestimating the nighttime respiration. By using a two-technique method employing both nighttime and daytime parameterizations for flux corrections, we arrive at an estimate of the three-year mean NEE of −561 (±standard deviation 114) g·C·m−2·yr−1. The corrected flux estimate represents a rather large uptake of CO2 for this mountain cloud forest, but the value is in good agreement with the few existing comparable estimates for other subtropical forests. [ABSTRACT FROM AUTHOR]