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Thai farmers plant eucalyptus trees on their unused farmlands with poor fertility soils to raise their incomes and in response to inducements from the Government. The conversion of unused farmlands to eucalyptus can contribute to climate change mitigation as the growing trees sequester carbon. To estimate the contribution of eucalyptus plantations to climate change mitigation requires not only accounting for the sequestered carbon, but also for the production of charcoal using eucalyptus wood residues from harvesting and from paper refineries. These by-products are the main raw materials used by rural communities in Thailand for charcoal making. This paper estimates the contribution of eucalyptus plantations on unused farmlands in Khon Kaen province in northeast Thailand, accounting for carbon sequestrated by the plantations, greenhouse gas emissions from eucalyptus charcoal production, and net avoided emissions from substituting fossil fuels with charcoal for heating. Carbon sequestration by the plantations was assessed for trees aged 1, 2 and 3 years by summing the aboveground biomass (stems, branches and leaves) and belowground biomass (roots). Three-year old eucalyptus trees are the main supply for the paper refineries. The amount of biomass and carbon stored in the eucalyptus plantations depend on age and productivity. The average carbon stored in 3-year old eucalyptus plantations at the study sites was 0.777 ton/ha. Eucalyptus growers received about 1,689 USD per ha from the harvesting of 3-4 year old eucalyptus plantations. Emissions from eucalyptus charcoal production were estimated by accounting for transportation of wood residues from the farms and refineries to kilns and charcoal processing. Emissions from charcoal production were estimated at 0.37 g CO2eq/MJ, meaning that substituting fossil fuels with eucalyptus charcoal reduces emissions for heat production by 99.5%. The eucalyptus plantation on unused land provided climate benefits and alternative income for local farmers. Based on these findings, the government should consider promoting eucalyptus plantation and eucalyptus charcoal production on unused suitable farmland under its policies on climate change mitigation, energy security and rural development.
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