## 6 Pan-Tropical AGB Mapping
### Concepts, Approaches, Coping Capacities and Limitations  
Several international organizations are working together under the umbrella of UN programs, as well as independently, to improve mapping, monitoring, validation and reporting of net forest and carbon loss across the globe. The Global Forest Observations Initiative (GFOI) was established by Group on Earth Observations (GEOs) in 2011, provides satellite-based forest measurements as well as field-based methodologies for the production of globally consistent reports and reliable findingson forest cover change, forest use and greenhouse gas (GHG) emission and removals accounting for REDD+ activities [178]. According to the IPCC's guidelines, forest carbon stock assessment can be categorized into three Tiers ranging from the simple global/ecological zone level emission factor (Tier 1) to country-specific forest inventories (Tier 2) and high precision plot level carbon dynamics models [178; 179]. The Global Observation of Forest Cover and Land Dynamics (GOFC-GOLD) which is an ad-hoc REDD working group of international experts, facilitates scientific communities, national space agencies and remote sensing analysts to maintain standards while using Earth Observation (EO) datasets [180]. REDD+ has had significant progress during the last decade. REDD+ helps developing countries to become part of their program to reduce carbon emission and enhance forest sinks. The UNFCC report published regularly to update nations about the latest development in the understanding of MRV for REDD+ activities [167]. The United Nations Strategic Plan for Forests (UNSPF) 2030, UN forum on the forest, set six global objectives for forests to be achieved by 2030, including intent to reverse forest loss, improvements in forest-dependent people livelihood by enhancing forest-based benefits, the sustainability of forest management to increase the area of protected forest, mobilization of financial resources for forest management, governing framework for forest management and enhance cooperation, coordination and synergies [181]. The FRAs coordinated by FAO publishes recent trends in forest studies and updates of technical terms after every five years to maintain consistency. The FRA 2020 [6] adapted internal forest policy such as Agenda 2030 for Sustainable Development, the UNSPF-2030 and the Paris agreement. Their working paper improves the understanding, definitions and terminologies for forest resources; assessments and countries are advised to strictly follow its guidelines. The recent report by FAO in 2019 [167] provided a technical assessment of carbon stock of thirty-nine countries. Out of these, eight countries reported more than 8 billion tons of carbon emissions reduction mostly by Brazil. Reports from six countries, which submitted the Forest Reference Emission Levels (FREL) and REDD+ reports, indicate uncertainties in the estimation of forest emission. Based on these reports, a major source of the uncertainties was the assumption of total carbon loss from the AGB, below-ground biomass (BGB), litter (I) and deadwood (DW) carbon pools due to deforestation. They did not consider the removal of carbon from subsequent vegetation growth and post-deforestation land use. Only Cambodia, Chile, Ghana, Indonesia, Lao People's Democratic Republic, and Vietnam submitted the reports with the use of remote sensing and field inventories [167]. Despite positive advancement in global effort in providing guidelines and giving incentive to countries to implement reforestation strategies, recent studies suggest that many uncertainties occur in the estimation of AGB and the detection of the total forest land. More emphasis should be given to capacity building programs, such as FAO and REDD+, to enhance capacities of developing countries to maintain and streamline national forest monitoring efforts which require continuous positive corrections and adjustment in their mapping and reporting mechanisms [182].