Effect of Soil Type On Soil Water Content and Carbon Cycle In Different Type of Tropical Forests Using Process Based Model In Thailand, Southeast Asia.

More reliable estimates of carbon (C) stock within forest ecosystems and C emission induced by deforestation are urgently needed to mitigate the effects of emissions on climate change. A process-based terrestrial biogeochemical model (VISIT model: Vegetation Integrative SImulator for Trace gases) evaluates the atmosphere–ecosystem exchange and internal dynamics of C at a daily time step. In this study, the model was applied to tropical primary forests of three types in Thailand: seasonal dry evergreen forest (DEF), seasonal dry deciduous forest (DEF) and seasonal dry mixed forest (MDF). The VISIT model was improved on the estimation of soil water content to change from a bucket model to Darcy’s law, and carbon budgets were estimated at three forests. The unsaturated hydraulic conductivity was calculated by saturated hydraulic conductivity at each soil types and water field pore space, which was calculated by solid ratio of soil and soil water content.

     Soil water content has changed by introducing Darcy's law. Especially, VISIT model was able to estimate the different soil types forest in same area (e.g. DEF and DDF). Comparing to the result of bucket model in DEF, soil carbon content in Darcy’s law was significantly increased, because higher soil water content decrease litter and humus decomposition in VISIT model. In the experiment simulation, soil water content was different due to soil character, especially soil water content decreased with increase of solid ratio. Our results suggested that difference of soil water content affected carbon stock and budget in tropical forest ecosystem (e.g. total biomass, soil organic carbon and soil respiration). However, more data gathered in tropical regions using various methods are needed to validate and improve the VISIT model simulations.