Canopy Carbon Balance of the Sakaerat Dry Evergreen and the Maeklong Mixed Deciduous Forests

Abstract

A study on canopy carbon balance, undertaken at the Sakaerat dry evergreen forest, Nakhon Ratchasima province, and the Maeklong mixed deciduous forest, Kanchanaburi province, aimed to determine gross canopy photosynthesis and compare the canopy carbon balance of the two contrasting forests. Diurnal courses of the leaf photosynthesis were simulated by modeling photosynthesis with related physiological parameters and climatic data inputs. The gross canopy photosynthesis and respiration of the two forests were then simulated through the relationship between diurnal courses of leaf photosynthesis and leaf area index. The canopy carbon balance of the two forests was also analyzed and compared.

Diurnal courses of simulated leaf photosynthesis varied daily and seasonally with changes in environmental factors. Leaf photosynthesis of all species studied was generally high in the wet season and decreased considerably in the dry season due to seasonal water limitations. The simulated values of leaf photosynthesis of all species in various seasons appeared to be more than 75% correlated with the observed ones. The monthly gross photosynthesis production of the two forests, simulated from a direct and diffuse light model, reflected seasonal changes in leaf physiological characteristics and climatic factors. The Sakaerat dry evergreen forest not only sequestered considerably greater CO₂, indicated by gross primary production (GPP), but also released larger amounts of CO₂ to the atmosphere through autotrophic respiration compared to the Maeklong mixed deciduous forest. Nevertheless, the findings suggest that the former had higher net primary production (NPP), indicating its greater potential for canopy CO₂ uptake.

Keywords: canopy photosynthesis, gross primary production, net primary production, dry evergreen forest, mixed deciduous forest