Not seeing the carbon for the trees? Why area-based targets for establishing new woodlands can limit or underplay their climate change mitigation benefits

•Emission reduction outcomes for area-based afforestation targets are uncertain•A new spatial analysis method was implemented to reduce this uncertainty•Afforestation of higher carbon soils with low timber yields can result in net carbon losses•Net emissions depend on how policies shape the mix and location of woodland types•C storage targets for new afforestation would put a floor under emission outcomes