Assessing the environmental sustainability of the billion trees afforestation project through life cycle assessment

Afforestation is increasingly promoted as a nature-based solution for climate change mitigation, yet large-scale projects are seldom assessed for environmental sustainability. This study presents the first comprehensive Life Cycle Assessment (LCA) of the Billion Trees Afforestation Project (BTAP) in Pakistan, aiming to quantify environmental impacts and identify major hotspots. The assessment included land preparation, nursery operations, seedling transport, plantation, and initial watering using a spatially explicit inventory. Seedling production showed the highest burdens for toxicity and climate change, notably in aquatic toxicity (marine 90.2 and freshwater 0.031 kg 1,4-dB eq.), human toxicity (0.052 kg 1,4-dB eq.), and global warming potential (GWP) (0.139 kg CO₂ eq.). Fertilizers are the dominant contributors accounting for 52-59 % of human toxicity and GWP as well as 34 % of aquatic toxicity. Diesel emerges as second largest contributor, especially for watering operations (8-35 %). The results highlight opportunities to reduce impacts through organic soil amendments, lower agrochemical use, and efficient irrigation. More broadly, the study emphasizes the need to harmonize LCA methodologies for afforestation to improve comparability and policy relevance. While projects like BTAP deliver critical ecosystem services such as carbon sequestration, erosion control, and flood regulation, they also entail notable trade-offs. Embedding LCA into planning and policy can guide more sustainable afforestation strategies and strengthen their role in climate change mitigation.