&#160;The GEO-TREES initiative: high-accuracy ground data for satellite-derived biomass mapping
Authors: Dion Iris , Chave Jerome , Davies Stuart , Duque Alvaro , Phillips Oliver , Piponiot-laroche Camille , Schwantes Marimon Beatriz , Scipal Klaus , Zo Bi Irie Casimir 
Published: March 2024

Verifiable and consistent measurement of forest carbon stocks and fluxes are necessary and they require to know where the biomass carbon is whether the vital functions of forests are changing, and what their future holds. Space agencies have made enormous investments in Earth Observation missions to map forest biomass across continents to support climate science and carbon markets. But satellites alone cannot produce accurate carbon maps&#8211;all maps vitally rely on field data collected by people and instruments to train their models and validate their products. To ensure satellites are producing reliable maps, it is needed frequently-acquired, high-quality field data. Furthermore, the challenge of acquiring ground biomass measurements is also one of environmental and social justice. The forests for which reference data are most needed, and the people depending on these forests, already suffer the worst impacts of climate change. Those in-country partners with unique forest expertise are key players in the fight against climate chaos, yet they are among the most disadvantaged globally. It follows that they need sustained support not only to collect data but to grow, train, and develop their own group's capacities. The GEO-TREES initiative proposes to fill this critical gap by building the world's first ground-based, standardized, open-access, equitably developed, reference forest biomass validation system to ensure that satellite observations accurately represent real forest carbon stocks, today and in the future. GEO-TREES is an ambitious world-wide network. It aims to establish at least 100 high-intensity forest biomass reference sites, to represent the main environmental and anthropogenic dimensions over which forests occur globally, and achieve greater sampling intensity in the critical tropics with an additional 210 lower-cost highly-distributed sites. Standing at the nexus of ecology and remote sensing, GEO-TREES builds on four principles: 1. Partnerships &amp; engagement: To generate high-quality ground measurements, GEO-TREES partners with ecological and botanical specialists around the world. Partners are fully engaged and involved in every step of building the reference system. Without strong representation and fair funding of partners, particularly from the Global South, science capacity cannot be advanced, and the long-term sustainability of the GEO-TREES system would not be possible. 2. Innovative technologies: Ground measurement involves four integrated sets of measurements: forest inventory plots, airborne laser scanning, terrestrial laser scanning, and climate monitoring. GEO-TREES is based on established recommendations of the Committee on Earth Observation Satellites for validating biomass observations (https://lpvs.gsfc.nasa.gov/AGB/AGB_home.html), and will improve them based on new advances when necessary. 3. Long-term commitment: Forests are alive. Forest carbon stores change, sometimes rapidly, through space and time. Maintaining current, accurate estimates of carbon and biomass stocks requires continued long-term measurements. Long-term measurements also ensure the continued engagement and participation of partners throughout the system. 4. Open-access data: GEO-TREES is committed to equitably produced and openly shared global forest biomass reference measurements. High-quality, high-resolution maps of the world&#8217;s forests developed through the Earth Observation missions in partnership with GEO-TREES will be made open to all.