Incorporating enhanced rock weathering into sustainable forest management

Enhanced rock weathering (ERW) can be implemented in managed forests that use selective harvesting through trail networks for carbon dioxide removal (CDR) while improving soil health by neutralizing excess acidity and restoring base cations. Wollastonite-rich rock powder (Wo = 28.4 wt% and D₅₀ = 350 μm) was applied using a tractor and spreader from a trail in Haliburton Forest, Ontario, Canada, to evaluate the practicability and challenges of incorporating ERW into silviculture practices. The intended amendment dosage of 5 t/ha aimed to replace soil Ca losses due to historic acidic deposition. Based on trail networks mapped in Haliburton Forest and a spreading width of 12 m, 85 % of the forest area could potentially be amended, assuming no overlapping areas. Spreading of 5 t/ha over the annually harvested area (∼700 ha) has a maximum potential to sequester 1120-1270 t CO₂/yr based on the CDR potential of the amendment (377-427 kg CO₂/t), calculated using its bulk geochemical composition. Assuming the same trail coverage as in Haliburton Forest and a dosage of 5 t/ha wollastonite-rich amendment, managed forests undergoing selection harvest in the United States and Canada have a maximum potential to sequester 4.5-5.1 Mt CO₂/yr. The CDR rate of forest ERW requires field-based monitoring and life-cycle assessments. This application test successfully showed the technical feasibility of incorporating ERW into forest management via trail networks. However, it also demonstrated considerable spatial heterogeneity in dosages (0.8-6.7 t/ha), varying by proximity to trail centers, obstructions such as large trees, and overlapping applications in dense trail networks, which challenges the accuracy and verifiability of carbon credits generated. Selecting monitoring sites near trail centers and away from large obstructions and trail junctions will help ensure dosages are representative of the larger application. Furthermore, we recommend verifying dosages to avoid over- or under-estimating CDR in future forest ERW studies.