Soil respiration in response to year-to-year variations in rainfall in a tropical seasonal forest in northern Thailand

In a tropical deciduous forest in northern Thailand, an area affected by the Asian monsoon, we made soil respiration measurements for 4years to determine their inter-annual variability. We also made continuous measurements of soil moisture, soil temperature, and soil CO₂ concentration. Annual soil respiration rates were estimated using two methods: multiple regression analysis and Fick's first law of diffusion. During the study period, between June 2000 and December 2004, the annual rainfall and the length of the wet period showed considerable year-to-year variation, differing by 1162-1435mmyear^-1 falling over 146-189days, respectively. In response to the inter-annual variability in rainfall, annual soil respiration rates estimated by the two models also showed large inter-annual variations for the 4years (coefficient of variation=14-17%). The range in the inter-annual variation for soil respiration was comparable with values for net ecosystem exchange reported in other Southeast Asian tropical forests. Historical rainfall records at this site showed further large inter-annual variations that occurred in times other than in the study period, suggesting that long-term monitoring would be required for a better understanding of the C balance at this site.