D. obtusifolius, D. tuberculatus, Shorea obtuse and S. siamensis 10. The canopy was about 5-7 m height (measurement in 2009). Soil texture was a loamy sand soil 11. The MKL site was in mixed deciduous forest which was mature forests (age was about 37 years in year 2015). It was situated at 231 m elevation. The vegetation type was tropical seasonal deciduous forest (mixed deciduous forest) and the dominant species were Shorea siamensis, Vitex peduncularis, Xylia xylocarpus. The canopy was about 30 m height (measurement in 2008). Soil texture was a sandy clay loam soil 12-13. B. Soil CO2 measurement by sensor method Soi l CO2 c o n c e n t r a t i o n s wer e continuously measured by the soil CO2 sensors (GMP343, Vaisala Inc., Finland), which were horizontally buried along soil profiles at depths of 5 cm and 20 cm. The sensors scanned for concentration determination every second, recorded every 15 seconds and averaged every 15 minutes. These sensors were connected with a transmitter, a data logger and a computer for data records. In this study, three replications were made. The measurements at DFR site were commenced on the 1st to the 181st day of the year in 2011 for 181 days and MKL site were commenced on the 121st day in 2014 to the 120th day in 2015 for 365 days. In order to impartially compare, the results in two forests were determined at the same months during January to June for 181 days. C. Measurements of Environmental parameters Air temperature was measured by Vaisala sensors (HMP45C, Vaisala Inc., Finland). At the depths of 5 cm, soil temperature and soil moisture were continuously measured every 15 seconds and averaged every 15 minutes by custom-built thermocouple sensors and water content reflectometers (CS615, Campbell Scientific, Inc., USA), respectively. The water content reflectometers started to collect the data at the same time as with CO2 sensors. D. Determination of the Soil Respirations (Rs) and Ecosystem Respirations (Re ) Soil CO2 emissions were calculated using data on the soil CO2 concentrations (μmol mol-1 or μmol m-3) together with environmental factors. We followed the steps of the calculations from Tang et al 5. The main equation of the soil CO2 effluxes (F, μmol m-2 s-1) was determined as shown in the following Equation (1). (1) where F is soil CO2 efflux (μmol m-2 s-1), Ds is CO2 diffusion coefficient (m2 s-1), dC/dz is the vertical soil CO2 gradient, C is CO2 concentration (μmol m-3) and z is depth (m). Moreover we determined fores t ecosystem respiration (Re) in dry dipterocarp forest at DFR site from eddy covariance night time flux at the same period with their soil respiration which was 5.88 kg CO2 m-2 y-1. Forest ecosystem respiration (Re) in mixed deciduous forest at MKL site which had been determined by 14 was 9.44 kg CO2 m-2 y-1. E. Data Analysis T-Test at significance level of 0.05 was applied to compare soil CO2 effluxes between a mixed deciduous forest and a dry dipterocarp forest. Percentage of CV (coefficient of variation) was applied to study variations of the soil CO2 effluxes. Linear Regression Analysis was applied to study relationships between the soil CO2 efflux with their soil temperature and moisture. III. RESULTS AND DISCUSSIONS A. Soil CO2 Concentration Measured by Soil CO2 Probes in the Forests Soil CO2 concentrations were measured by burying of CO2 probes in soil profiles at Proceedings of the International Conference on Climate Change, Biodiversity and Ecosystem Services for the 153 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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