litter fall and carbon exchange under extreme climate variability in secondary Dry Dipterocarp Forest (DDF). The aim of the study is to better understand the litter fall timing and its relationship to carbon exchange, and their response to climate variability during El Niño events. II. MATERIALS AND METHODS A. Site Description The study site was located in King Mongkut’s University of Technology Thonburi, Ratchaburi campus, Rang Bour, Chombueng district, Ratchaburi province, western Thailand (Latitude: 13º35´ 13.3´´ N, Longitude: 99º30´ 3.9´´ E, elevation of 118 m). Total area covers 90 ha. The average tree height was 6-7 m. The dominant species are in the Dipterocarpaceae such as Dipterocarpus obtusifolius, D. tuberculatus, Shorea obtusa and S. siamensis. Previously, this forest had been exploited by nearby communities for timber, charcoal or other products. Since 2005, this forest has been conserved and trees could be regenerating as a secondary forest. B. Climate conditions The air temperature and rainfall were measured by Vaisalasenser (Vaisala Inc. Model HMP45C) and tipping bucket rain gauge (model TE525, Cambell Scientific, Inc.). These were connected with data logger (CR1000, Cambell Scientific, Inc.). Soil temperature was measured at a depth of 5 cm with two averaging soil thermocouple probes (TCAV, Campbell Scientific, Inc., USA). Soil moisture was measured at the same level with two averaging Soil Water Content Reflectometers (CS615, Campbell Scientific, Inc.). The moisture sensor was converted from volumetric water content to percent water-filled pore space (%WFPS) by equation; %WFPS = (SWC/BD)/(1-(BD/PD)) where SWC is the soil water content, BD is the bulk density (1.42 g cm-3) and PD is the particle density (2.68 g cm-3) 16. Statistical analysis was performed with R 3.1.2 Software, t-test was used to compare climate condition and its effects to phenology between normal and El Niño years. C. Litter fall collection and carbon content Long-term monthly litter fall production was collected by thirteen litter traps with size of 1 m-2 during 2009-April 2016. The litter was dried at 80oC and weighed. The data in dry season (November to April of the following year) was extracted to calculate normalized litter fall by using the ratios between monthly litter falls to total litter fall in dry season. Statistical data analysis was performed with R 3.1.2 Software. Tukey’s HSD test was performed to identify significant differences of litter fall in each month. The carbon stock was calculated by multiplying the 0.50 conversion factors to biomass of litter fall 17. D. Carbon exchange measurement Carbon exchanges above forest canopy were measured at 10 m by using eddy covariance technique. The CO2 was estimated by an open- path infrared CO2/H2O analyzer (LI-7500, LI-COR, Lincoln, USA). Wind velocity and the speed of sound were measured with three- dimensional sonic anemometer-thermometer (CSAT3, Cambell Scientific, Inc.). Data processing in quality control and half-hourly average of NEE were analyzed by using EddyPro software. Then, the outlier with the range outside of mean 1.96 standard deviations was excluded in post-processing 18. The monthly pattern of gross primary production (GPP) and ecosystem respiration (RE) was calculated by using biometric terms as Proceedings of the International Conference on Climate Change, Biodiversity and Ecosystem Services for the 305 Sustainable Development Goals (SDGs): Policy and Practice 27-29 June 2016, Cha-am, Phetchaburi, Thailand
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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