GFI/BCCR Seminar: Modeling oil palm monoculture and its associated impacts on land-atmosphere carbon, water and energy fluxes in Indonesia

Yuanchao Fan (University of Göttingen, Germany):

Modeling oil palm monoculture and its associated impacts on land-atmosphere carbon, water and energy fluxes in Indonesia

Abstract
In Southeast Asia, the rapid expansion of oil palm monocultures and the concurrent destruction of rainforests and peatlands have been in the spotlight for their prominent roles in greenhouse gas emission. A thorough  quantification of the carbon balance of oil palm plantations and the long-term and large-scale forest – oil palm replacement effects is necessary for understanding the climatic impacts of tropical land use change.

This study presents a comprehensive analysis of the carbon dynamics and water and energy exchanges of oil palm plantations throughout developmental stages (from planting to rotation) with a land surface modeling approach. A new modeling scheme for palm species has been developed within the Community Land Model framework (named CLM-Palm). CLM-Palm incorporates the agricultural model capacity for simulating growth and yield of palms with unique phenology and allocation functions and a suit of new parameterizations on biogeophysics (e.g. radiative transfer and evapotranspiration (ET)) and on biogeochemistry (e.g. carbon and nitrogen dynamics, fertilization effects).

Validated with available field data, the simulation shows clear distinctions between young and mature oil palm plantations and old-growth rainforest in carbon fluxes (e.g. GPP, NEE) and biophysical properties (e.g. ET, surface albedo and temperature). A transient simulation spanning two rotation periods (each 25 years) showed that long-term oil palm cultivation is only able to restore about a half of the original total carbon storage capacity of the forested site before clear-cut. More than 50% of the net primary production by the oil palm plantation is not retained on the site but instead exported as oil products which are soon reverted to CO2. Soil carbon stocks decline slowly and gradually due to the limited litter return in the managed plantation. Conversion of rainforest to oil palm plantation also has potential warming effects on the land surface at the site scale.