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Key message: A flexible stem respiration chamber was developed and successfully employed in a feasibility study in a tropical forest. We present a flexible chamber to measure the CO2 efflux from tree bark. The easy-to-use chamber is made of stainless steel and is clamped around an individual tree stem section; it uses a portable gas analyzer to retrieve the stem respiration value. Using the individual data points in combination with data from a forest inventory, the data can, in principle, be up-scaled to achieve the stand-scale stem respiration. We performed a feasibility study in a young forest plantation in tropical southern Taiwan, which yielded robust and meaningful results. [ABSTRACT FROM AUTHOR]

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]

Afforestation sequesters carbon from atmosphere and thus is a primary strategy for mitigating global warming. To further the development and management of future plantations, this study examined the monthly CO2 assimilation of four young broadleaf tree species to select the best performer. From December 2010 to December 2011, data were collected from a plantation in southern Taiwan, which experiences a typical tropical monsoon climate. Monthly measurements of diurnal gas exchange revealed that Melia azedarach maintained a high net photosynthesis rate during the dry season, whereas Swietenia macrophylla exhibited a low net photosynthesis rate and stomatal conductance in both the dry and wet seasons. Annual CO2 assimilation occurred primarily during summer and autumn for all species. We measured leaf area indices and generated analytical models involving light response curves to calculate canopy-level, net assimilation rate. M. azedarach, S. macrophylla, Cassia fistula, and Pterocarpus indicus assimilated 38.15, 9.65, 32.19, and 19.14 kilograms tree-1 yr-1 of CO2 at the canopy level and 52.65, 10.33, 46.35, and 22.59 megagrams ha-1 yr-1 at the stand level, respectively. Based on our results, we recommend M. azedarach and C. fistula as the most appropriate plantation tree species for increasing carbon assimilation in monsoon climates. [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]

Background: The environmental stresses caused by climate change have become more severe in recent decades, affecting tree growth and physiology. Tropical forests have great potential for global carbon sequestration. However, they suffer from heavy rainfall and prolonged dry periods due to climate change. Swietenia macrophylla King and Melia azedarach L. are economically valuable trees that are widely planted in southern Taiwan. Plantations are exposed to either prolonged dry periods or heavy rainfall within the seasons of tropical monsoon areas. Photo-physiological comparisons may provide information that can improve management of S. macrophylla and M. azedarach plantations in tropical regions. Results: Both species exhibited a midday depression in leaf photosynthesis regardless of the season. The net photosynthetic rate ( P ), stomatal conductance ( g ), and transpiration rate ( E) in the dry season all significantly decreased in both tree species. In addition, M. azedarach used water more efficiently than did S. macrophylla during the dry season, but S. macrophylla had higher P compared with that in M. azedarach during the wet season. Temperature and vapor pressure deficit influenced P variation in S. macrophylla and M. azedarach, respectively. Our data suggested that the P and g of M. azedarach, but not of S. macrophylla, were linearly correlated during the dry season. The reduction of the leaf area was more sever in M. azedarach than in S. macrophylla, thus preventing water loss more efficiently. Conclusions: M. azedarach adapted to drought by reducing total leaf area and maintaining higher P , g , E, and WUE compared with those measured in S. macrophylla during the dry season. M. azedarach is more drought adaptation and more suitable for both humid and semi-humid areas than S. macrophylla, whereas the latter should be limited to more humid areas. [ABSTRACT FROM AUTHOR]

Afforestation is an effective solution for restoring forest ecosystems and mitigating climate change in the tropics. In this study, we analyzed the soil respiration (Rs) at four afforested sites with different tree species exposed to a monsoon climate with frequent typhoon occurrences in southern Taiwan. The aim of this study is to examine (1) the distinct seasonal variation that strongly affects the Rs among four tree species at afforested sites, (2) the patterns of Rs that differ among the four species at the afforested sites, and (3) the influence of typhoons on forest structure and consequently the degree of Rs. The annual mean Rs among the four tree species at the afforested sites in the pretyphoon disturbance year was approximately 7.65 t C ha−1, with the post-typhoon year having an annual mean Rs of approximately 9.13 t C ha−1. Our results clearly show Rs variations in the four tree species at the young afforested sites under the influence of typhoon disturbances. The high seasonal variations in Rs were controlled by soil temperature and soil moisture. The different tree species also led to variations in litterfall production and consequently influenced Rs variation. Forest structures, such as aboveground biomass and consequently the degree of Rs, were disturbed by severe typhoon impacts in 2016, resulting in high aboveground biomass with tree height losses and litterfall accumulation. Furthermore, Rs increased immediately after litterfall input to the soil, and the addition effect of litter and the soil C release occurred throughout the year after typhoon disturbances. Our results contribute to understanding impact of typhoon disturbances on the degree of Rs at tropical afforested sites. [ABSTRACT FROM AUTHOR]

As anthropogenic greenhouse gas emissions intensify global climate change, plantations have become an important tool to mitigate atmospheric CO2. Our aim in this study was to estimate carbon assimilation and clarify the impact of environmental factors on the photosynthesis of Zelkova serrata (Thunb.) Makino, an important plantation species that is extensively planted in low altitude regions of East Asia. We measured monthly gas exchange parameters and leaf area index to estimate carbon assimilation. The results showed that gas exchange was significantly affected by vapor pressure deficit and temperature, especially in the dry season, and both photosynthetic rate and carbon assimilation decreased. Lower daytime assimilation and higher nighttime respiration during the dry season, which caused a 43% decrease in carbon assimilation in Z. serrata plantations. Z. serrata exhibited lower photosynthetic rate and lower carbon assimilation following planting in a tropical monsoon climate area. Therefore, the effects of extreme weather such as high temperature and vapor pressure deficit on Z. serrata forest carbon budget could be stronger in the future. Leaf area showed seasonal variation, and severe defoliation was caused by a typhoon in the summer. The annual carbon assimilation was estimated at 3.50 Mg C ha−1 year−1 in the study area. [ABSTRACT FROM AUTHOR]

Soil respiration represents the second largest carbon flux, next to photosynthesis of the terrestrial biosphere, and thus plays a dual role in regional and global carbon cycles. However, soil respiration in Asian monsoon forests with high rainfall has rarely been studied. In this study, we continuously measured soil respiration using a 12-channel automated chamber system in a 61-year-old Japanese cedar forest in central Taiwan with annual rainfall greater than 2500 mm. A 4-year (2011–2014) continuous half-hourly dataset was used to quantify the influences of soil temperature and moisture, especially rainfall events, on both total soil respiration (Rs) and heterotrophic respiration (Rh). The annual mean Rs was approximately 10.8 t C ha−1 (ranging from 10.7 to 10.9) t C ha−1, with Rh contributing approximately 74.6% (ranging from 71.7% to 80.2%). Large seasonal variations in both Rs and Rh were primarily controlled by soil temperature. Over 45.8% of total annual rainfall amounts were provided by strong rainfall events (over 50 mm), and over 40% of rainfall events occurred during summers between 2012 and 2014. These strong rainfall events caused rainwater to enter soil pores and cover the soil surface, which resulted in limited soil microorganism activity and, consequently, restricted CO2 production. The mean Q10 values were 2.38 (ranging from 1.77 to 2.65) and 2.02 (ranging from 1.71 to 2.34) for Rs and Rh, respectively. The Q10 values in this study, which were lower than in global forest ecosystems, may imply that the interannual Rs values observed in this study that were caused by high rainfall were less temperature-dependent than the Rs levels in global forest ecosystems. Both Rs and Rh were negatively correlated with soil moisture, which indicated that the soil moisture levels in the studied forest were usually under saturated conditions. These results also provide the lack of data for respiration in the Asian monsoon region under high-rainfall conditions. [ABSTRACT FROM AUTHOR]