Enhanced BVOC emissions and the corresponding biogeochemical cooling effects controlled by future forestation scenarios in China

China has pledged to achieve carbon neutrality by 2060, with forestation as one of the key mitigation strategies due to its capacity to absorb and store carbon. However, forests can also emit biogenic volatile organic compounds (BVOCs), potentially affecting the climate. Here, we used the Model of Emissions of Gases and Aerosols from Nature (MEGAN) combined with future forestation dataset for China to investigate the changes in BVOC emissions and the potential climatic effects. The forestation dataset is developed based on the policies and tree species suitability, including a maximal carbon stock scenario and a maximal suitability scenario. To estimate BVOC emissions more accurately, we modified MEGAN to incorporate species-specific emission factors. The simulated results under forestation scenarios maximizing either carbon stock or ecological suitability show that BVOC emissions in China will increase by 0.21 and 0.19 Tg/year under Shared Socioeconomic Pathway 1-2.6 (SSP1-2.6), respectively. Forestation contributes more than 30% of the total BVOC emission increase, although the magnitude varies across scenarios. Broadleaf tree species are the dominate BVOC emitters, which are prioritized in southeastern and southwestern China under the maximal biomass scenario, while are selected in northeastern China under the maximal suitability scenario. These differences thus lead to distinct spatial patterns of BVOC emission increases and the associated climatic effects. Using emission-based radiative forcing responses derived from CMIP6, it is found that the increase in BVOC emissions induced by forestation will result in an additional cooling effect, thereby enhancing the biogeochemical cooling of forestation, particularly under the maximal biomass scenario. These findings highlight the necessity of accounting for BVOC emissions when assessing the climate mitigation potential of forestation.