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ABSTRACTIn this study, we evaluate the relationships between the standing stock, field-measured LAI, and NDVI from remotely sensed images and in situ measurements at plantation forests in the subtropics–tropics region of southern Taiwan. The purpose is to facilitate assessing the biomass of reforestation sites in large areas applying the possible stock-LAI-NDVI relationships analyzed in this study. 15–16 years old forest in one square kilometer area with 14 tree species was tested at different spatial scales. In addition, we also assess the relationship of plots with pure tree species for the effect mixed tree species. By long-term monitoring, intensive measurement for 5 years and analysis at different spatial scales, the results show the correlation coefficient of stock-LAI is not significant while that of stock-NDVI is 0.5639, 0.7230 and 0.9283 as the spatial scale enlarges. Negative stock-LAI correlations found for three tree species but all the stock-NDVI correlations for six specific tree species are positive. If the multi-regression is applied, the correlation coefficient of stock-LAI-NDVI is higher than that of the stock-LAI and stock-NDVI, which reaches to the 0.6470, 0.7680 and 0.9995 at the plot, block and site level, respectively; the correlation coefficients of six specific tree species are also larger at the plot level.

Afforestation is considered a major tool for climate change mitigation with high potential particularly in the tropics. In this study we analyzed CO2fluxes of an afforested former sugar cane plantation in southern Taiwan, as this forest had been planted with the goal of sequestering CO2to 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 CO2fluxes 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−2year−1and −322 g C m−2year−1, respectively. Between 2011 and 2014, the yearly increment in AGB increased with a mean increment of 509 ± 181 (SD) g C m−2year−1. We observed high seasonal difference in CO2fluxes particularly in ER and GPP, and conclude that high winter precipitation enhances CO2uptake. Furthermore, frequent typhoons reduced the CO2uptake and increment in AGB, such as in 2016, when a very strong typhoon passed the forest. 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 CO2uptake 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. 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 A young, heterogeneous forest planted on a former sugar cane plantation is a carbon dioxide sink 8 and 14 years after planting The forest shows high seasonal differences in carbon dioxide fluxes. In 2016, high precipitation during the dry season enhanced the carbon dioxide uptake Frequent impact of tropical cyclones (typhoons) reduce carbon dioxide uptake and increment in above‐ground biomass at this forest site