Abstract
Abstract. More reliable estimates of the 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) was applied to tropical primary forests of two types (a seasonal dry forest in Thailand and a rainforest in Malaysia) and one agro-forest (an oil palm plantation in Malaysia) to estimate the C budget of tropical ecosystems in Southeast Asia, including the impacts of land-use conversion. The observed aboveground biomass in the seasonal dry tropical forest in Thailand (226.3 t C ha−1) and the rainforest in Malaysia (201.5 t C ha−1) indicate that tropical forests of Southeast Asia are among the most C-abundant ecosystems in the world. The model simulation results in rainforests were consistent with field data, except for the NEP, however, the VISIT model tended to underestimate C budget and stock in the seasonal dry tropical forest. The gross primary production (GPP) based on field observations ranged from 32.0 to 39.6 t C ha−1 yr−1 in the two primary forests, whereas the model slightly underestimated GPP (26.5–34.5 t C ha−1 yr−1). The VISIT model appropriately captured the impacts of disturbances such as deforestation and land-use conversions on the C budget. Results of sensitivity analysis showed that the proportion of remaining residual debris was a key parameter determining the soil C budget after the deforestation event. According to the model simulation, the total C stock (total biomass and soil C) of the oil palm plantation was about 35% of the rainforest's C stock at 30 yr following initiation of the plantation. However, there were few field data of C budget and stock, especially in oil palm plantation. The C budget of each ecosystem must be evaluated over the long term using both the model simulations and observations to understand the effects of climate and land-use conversion on C budgets in tropical forest ecosystems.
Highlights
More detailed estimations of the carbon (C) stocks within forest ecosystems and of C emissions induced by deforestation are important environmental research goals
Because the ecophysiological parameters used in the model simulations were set at the same values at the two forests (Table 1), the difference in their C budgets were mainly attributable to the differences in air temperatures, precipitation and site-specific soil parameters
The aboveground biomass estimated by the Vegetation Integrative SImulator for Trace gases (VISIT) model was about 71 % of the field measurement in dry evergreen forest (DEF)
Summary
More detailed estimations of the carbon (C) stocks within forest ecosystems and of C emissions induced by deforestation are important environmental research goals. To evaluate the annual C emission from land-use change, several models considered the different decay rates of harvested forest products based on the method of Houghton et al (1983). Cramer et al (2004) reported that C emission due to land-use change had a great uncertainty in Southeast Asia; Houghton (1999) estimated the value as 1.08 Gt C yr−1, whereas the estimate of Cramer et al (2004) was 0.30–0.49 Gt C yr−1.
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