reported that the litter fall had a significant positive correlation with soil moisture and a significant negative correlation with soil temperature 16. C. Effects of El Niño on Carbon exchange and carbon contents in litter fall The potential carbon uptake in the whole dry season was reduced during El Niño in 2009-2010 and 2015-2016. The GPP were 432.87 and 719.67 g Cm-2 during El Niño and 1,030.80 and 1,021.22 g Cm-2 during the normal years (Table 1). Therefore, the GPP seems to be quite sensitive to El Niño as it Table 1 Summary of carbon contents in litter fall and total carbon exchange during dry season in secondary dry dipterocarp forest year Events Total carbon content in litter fall, gC m-2 Total GPP, gC m-2 Total RE, gC m-2 Total NEE, gC m-2 308 Proceedings of the International Conference on Climate Change, Biodiversity and Ecosystem Services for the Sustainable Development Goals (SDGs): Policy and Practice 27-29 June 2016, Cha-am, Phetchaburi, Thailand Total GPP/RE 2009-2010 El Niño 213.83 432.87 406.53 -26.34 1.06 2010-2011 normal 256.36 1030.80 702.91 -327.89 1.47 2014-2015 normal 282.15 1021.22 629.97 -391.25 1.62 2015-2016 El Niño 299.56 719.67 410.15 -309.53 1.75 decreased drastically during El Niño compared to the normal years. Furthermore, the carbon uptake reduced rapidly during El Niño events and during the peaking time of litter fall. The uptake of carbon was decreased by 600 g Cm-2 in the 1st El Niño and 300 g Cm-2 in the 2nd El Niño compared to the normal years (Fig.3). The RE were also low during El Niño which were 406.53 and 410.15 g Cm-2, compared to 702.91 and 629.97 g Cm-2 during normal years. The total NEE for whole season were -26.34 and -309.53 g Cm-2 during the 1st and 2nd El Niño events, respectively. These were -327.89 and -391.25 g Cm-2 in normal years (Fig.3 and Table 1). Interestingly, the NEE was considerably positive during the El Niño especially during the 1st El Niño. About 1.38- 91.50 g CM-2 month-1 was emitted between January to April (Fig.3). The results of NEE were consistent with the GPP/RE. The GPP/RE of more than 1 indicates that the forest is a net carbon sink 22. During four study periods, GPP/RE had increased continuously between 1.06 and 1.75. It means that this forest is a carbon sink for whole dry season and the potential to be a carbon sink has continuously increased. Comparing GPP/RE in each month shows that this forest was a sink for carbon every month during the normal year (Except on April 2015, GPP/RE was 0.98, this might be because of El Niño impact during the end of period). During El Niño, the GPP/RE was 0.46-0.96 between February to April and March to April in the 1st and 2nd events, respectively. So, that El Niño induced carbon loss was obvious. The low soil moisture due to reduced rainfall had an important role to control the GPP during El Niño events. The soil moisture was quite different between these two events.
Proceedings of International Conference on Climate Change, Biodiversity and Ecosystem Services for the Sustainable Development Goals : Policy and Practice 27-29 June 2016 at the Sirindhorn International Environmental Park, Cha-am, Phetchaburi, Thailand
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