Reforestation of tropical rainforests as a negative emissions technology in Malaysia: An environmental and economic sustainability assessment.

Forest carbon sequestration is a promising negative emissions technology as it is relatively simple and inexpensive. Its potential for climate mitigation could be particularly high in tropical rainforests as they can store more carbon at a faster rate. However, the understanding of its sustainability is limited due to the scarcity of studies. Focusing on reforestation, this work is the first to present an extensive environmental and economic assessment of forest CO₂ sequestration in a tropical rainforest country such as Malaysia. Life cycle assessment (LCA) and life cycle costing (LCC) are combined to evaluate the sustainability of reforestation with four tropical tree species: keruing (Dipterocarpus spp.), meranti (Shorea leprosula), rubber (Hevea brasiliensis) and kapok (Ceiba Pentandra). Considering the horizon of 60 years, the system boundaries comprise site infrastructure, land clearing, tree planting and growing, and forest management. The dynamics of greenhouse gas (GHG) and other air emissions are also considered over the period, including carbon sequestration and land use change, nitrous oxide and ethylene emissions. All tree species lead to a net-negative GHG emissions, ranging from -558 to -808 kg CO₂ eq./t CO₂ removed, with kapok having the highest and rubber the lowest sequestration potential. The latter has the highest values in 13 other impact categories considered, while keruing is the best option for 12 impacts. The main environmental hotspot for all species is the forest management stage. The LCC range from -US$17 to US$12/t CO₂ removed. Reforestation on lands available in Malaysia could remove 105.9-473.3 Mt CO₂ over 60 years, or 1.8-7.9 Mt CO₂/yr, equivalent to 7.4-33 % of the agricultural emissions. Rubber and kapok could generate US$640 M and US$8.06 bn in profits over 60 years from latex and fibre, respectively. Therefore, reforestation has a significant potential to help tropical countries, such as Malaysia, achieve net-negative emissions, while at the same time boosting the economy.