Aboveground forest biomass varies across continents, ecological zones and successional stages: refined IPCC default values for tropical and subtropical forests

Danaë M A Rozendaal ,Lourens Poorter ,Valerio Avitabile ,Ted R Feldpausch ,Justin Kassi N’dja ,Andrés Espejo ,Eliakimu Zahabu ,Luca Birigazzi ,Esteban Álvarez-Dávila ,Emilio Vilanova ,Maria M H Wang ,Benjamin Barca ,Dos Santos Silayo ,Véronique De Sy ,Oliver L Phillips ,João M B Carreiras ,Beatriz Schwantes Marimon ,Eric Konan ,Alexandra Morel ,Maurizio Santoro ,Javier G P Gamarra ,Alejandro Araujo‐Murakami ,Plínio Sist ,Mathieu Decuyper ,Daniela Requena Suárez ,Eurídice N Honorio Coronado ,Roberto Cazzolla Gatti ,Martin J P Sullivan ,Anny Estelle N’guessan ,Lan Qie ,Roel Brienen ,Bronson W Griscom ,Nancy L Harris ,Kristina J Anderson‐Teixeira ,Ben Devries ,Ervan Rutishauser ,Abel Monteagudo ,Bruno Hérault ,Anssi Pekkarinen ,Bonaventure Sonké ,Sarah Carter ,Susan C Cook‐Patton ,Sara M Leavitt ,Constant Yves Adou Yao ,Anne Branthomme ,Jeremy A Lindsell ,Simon L Lewis ,Casey M Ryan ,Edward T A Mitchard ,Julian C Fox ,J W Ferry Slik ,Timothy R Baker ,Frans Bongers ,Gaia Vaglio Laurin ,Inge Jonckheere ,Luzmila Arroyo ,Martin Herold

doi:10.1088/1748-9326/ac45b3

Abstract

For monitoring and reporting forest carbon stocks and fluxes, many countries in the tropics and subtropics rely on default values of forest aboveground biomass (AGB) from the Intergovernmental Panel on Climate Change (IPCC) guidelines for National Greenhouse Gas (GHG) Inventories. Default IPCC forest AGB values originated from 2006, and are relatively crude estimates of average values per continent and ecological zone. The 2006 default values were based on limited plot data available at the time, methods for their derivation were not fully clear, and no distinction between successional stages was made. As part of the 2019 Refinement to the 2006 IPCC Guidelines for GHG Inventories, we updated the default AGB values for tropical and subtropical forests based on AGB data from >25 000 plots in natural forests and a global AGB map where no plot data were available. We calculated refined AGB default values per continent, ecological zone, and successional stage, and provided a measure of uncertainty. AGB in tropical and subtropical forests varies by an order of magnitude across continents, ecological zones, and successional stage. Our refined default values generally reflect the climatic gradients in the tropics, with more AGB in wetter areas. AGB is generally higher in old-growth than in secondary forests, and higher in older secondary (regrowth >20 years old and degraded/logged forests) than in young secondary forests (⩽20 years old). While refined default values for tropical old-growth forest are largely similar to the previous 2006 default values, the new default values are 4.0–7.7-fold lower for young secondary forests. Thus, the refined values will strongly alter estimated carbon stocks and fluxes, and emphasize the critical importance of old-growth forest conservation. We provide a reproducible approach to facilitate future refinements and encourage targeted efforts to establish permanent plots in areas with data gaps.

Highlights

Tropical forests contain two-thirds of the total global terrestrial biomass (Pan et al 2013), but these forests and their carbon stocks are rapidly disappearing due to land use conversion (FAO)
aboveground biomass (AGB) in tropical forests varied by an order of magnitude across continents, ecological zones, and successional stages based on the included plots
For subtropical forests in Africa and the Americas across all successional stages, refined default values were highest for dry forests, unexpectedly, followed by humid forests and steppe based on the AGB map

Summary

Introduction

Tropical forests contain two-thirds of the total global terrestrial biomass (Pan et al 2013), but these forests and their carbon stocks are rapidly disappearing due to land use conversion (FAO). Countries in the tropics and subtropics can benefit from reducing emissions from deforestation and forest degradation and forest enhancements (REDD+) programs by maintaining and increasing their forest carbon stocks, but are required to monitor forest carbon stocks and fluxes, following Intergovernmental Panel on Climate Change (IPCC) good practice guidance for National Greenhouse Gas (GHG) accounting (IPCC 2006, 2019). The availability of recent NFI data, or publicly available forest plot data in general, is limited in the tropics (Romijn et al 2015, Liang and Gamarra 2020), IPCC default values are, in absence of more detailed data, widely used for carbon pool reporting, technical assessments (e.g. UNFCCC reviews), global assessments (e.g. FAO forest resources assessment) and by researchers (e.g. Achard et al 2014). In 2015, 84 out of 99 tropical countries were still reporting forest carbon pools at the tier 1 level (Romijn et al 2015)

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