I. INTRODUCTION Ecosystem services are part of the 2030 Agenda for Sustainable Development and Sustainable Development Goals (SDGs) especially SDG 15 (managing sustainable forest, combating desertification, halting land degradation and biodiversity loss) 1. An important ecosystem service is absorbing CO2 from atmosphere into forests by photosynthesis process as a CO2 sink. However, forests also release CO2 to atmosphere by plant and soil respiration processes as a CO2 source. Soil respiration (Rs) or soil CO2 emission which produces CO2 by soil organisms and underground parts of plants in forests is an important component of ecosystem respiration (Re). Moreover, the amount of this CO2 exchange is important in our understanding response of forest during climate variability such as the effects of heavy rainfall events and extended dry periods. Dynamically, soil CO2 emissions occur during both non-steady state (with disturbances) and steady state (without disturbances) 2, and understanding the emissions during both states is crucial to help us quantify soil respiration. The fast response of CO2 emission to these environmental changes and disturbances could be causes of uncertainty associated with CO2 emission quantification 3-9. Therefore, enhancing accuracy in assessment of soil CO2 emission in forest is desired in order to improve our understanding of forest carbon exchange, its source-sink capacity and its responses to climate change/variability. Although, most of researchers in the past had used chamber method (conventional method) because it is economical and easy-to-use, some conventional methods could not detect phenomena of soil respiration responses during such disturbances. On the other hand, soil gradient method using CO2 sensor as a newly established technique could improve the accuracy of the CO2 quantification together with capturing its responses to disturbance including variability in climate 8-9.The sensor method was found to yield a very close result to that obtained by chamber measurements 4-5, 8. A good correlation between the two techniques was also reported 6. Therefore, this study aims to measure soil CO2 by the newly established method using CO2 profile gradient (continuously and frequently recorded every 15 seconds and averaged every 15 minutes) and to study variations in soil CO2 effluxes in a dry dipterocarp forest and a mixed deciduous forest. The monitoring using the soil CO2 probes also enabled us to clearly see the behaviors of soil CO2 emission during climate variability. II. MATERIALS AND METHODS A. Site Description The study sites were located in a dry dipterocarp forest and a mixed deciduous forest. These are among the two of the AsiaFlux network’s sites in Thailand. Both sites are tropical monsoon forest. The first study site was known as DFR site (a Dry Dipterocarp Forest Flux Ratchaburi), King Mongkut’s University of Technology Thonburi (KMUTT), Ratchaburi Campus, Rang Bour, Chombueng, Ratchaburi, western Thailand (Latitude: 13º 35’ 13.3” N, Longitude: 99º 30’ 3.9” E).Another site was MKL site (Mae Klong Watershed Research Station), Thong PhaPhoom, Kanchanaburi, western Thailand (Latitude: 14º 34’ 34.6” N, Longitude: 98º 50’ 38.0” E). The DFR site had been kept as the dry dipterocarp forest for approximately 50 years but communities have exploited for timber and charcoal raw material harvests. As a result, most of trees in this forest were regenerated and ages of the trees were 6-7 years (measurement in 2011). The DFR site was situated at 118 m elevation. The vegetation type was a dry dipterocarp forest and the dominant species were Dipterocarpus intricate, 152 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
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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