Commitments made at COP26 in Glasgow shine a spotlight on how changes in global tree cover are defined, monitored and accounted for. Signed by 141 countries, the Glasgow Leaders’ Declaration on Forests and Land Use1 commits signatories to collectively “halt and reverse forest loss and land degradation by 2030 while delivering sustainable development”. This declaration recognizes that land use and land management are responsible for an estimated 23% of global anthropogenic greenhouse gas emissions and that any plausible scenario to limit global warming to 1.5 °C by 2100 must maintain and expand tree cover2. It also recognizes that sustainable land use requires transformative international-to-local action covering relevant global production and consumption systems while simultaneously empowering smallholders, Indigenous peoples and local communities2. However, timely and effective monitoring of such transformative actions requires improved, open and shared data and new collective modes of ownership for forest information.