Estimating aboveground net biomass change for tropical and subtropical forests: Refinement of IPCC default rates using forest plot data.

Daniela Requena Suárez ,Lourens Poorter,Ted R Feldpausch,Simon L Lewis,Alejandro Araujo‐Murakami,Luzmila Arroyo,Lan Qie,Bruno Hérault,Martin Herold,Timothy R Baker,Eurídice N Honorio Coronado,Susan C Cook‐Patton,Oliver L Phillips,Bonaventure Sonké,Ervan Rutishauser,Bronson W Griscom,Maria M H Wang,Abel Monteagudo Mendoza,Frans Bongers,Sarah Carter,Sara M Leavitt,Danaë M A Rozendaal,Martin J P Sullivan,Christopher Martius,Nancy L Harris ,Beatriz Schwantes Marimon ,Anny Estelle N’guessan ,Kristina J Anderson‐Teixeira ,Justin Kassi N’dja ,Emilio Vilanova Torre ,Plínio Sist ,Esteban Álvarez-Dávila ,Véronique De Sy ,Roel Brienen

doi:10.1111/gcb.14767

Abstract

As countries advance in greenhouse gas (GHG) accounting for climate change mitigation, consistent estimates of aboveground net biomass change (∆AGB) are needed. Countries with limited forest monitoring capabilities in the tropics and subtropics rely on IPCC 2006 default ∆AGB rates, which are values per ecological zone, per continent. Similarly, research into forest biomass change at a large scale also makes use of these rates. IPCC 2006 default rates come from a handful of studies, provide no uncertainty indications and do not distinguish between older secondary forests and old‐growth forests. As part of the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, we incorporate ∆AGB data available from 2006 onwards, comprising 176 chronosequences in secondary forests and 536 permanent plots in old‐growth and managed/logged forests located in 42 countries in Africa, North and South America and Asia. We generated ∆AGB rate estimates for younger secondary forests (≤20 years), older secondary forests (>20 years and up to 100 years) and old‐growth forests, and accounted for uncertainties in our estimates. In tropical rainforests, for which data availability was the highest, our ∆AGB rate estimates ranged from 3.4 (Asia) to 7.6 (Africa) Mg ha−1 year−1 in younger secondary forests, from 2.3 (North and South America) to 3.5 (Africa) Mg ha−1 year−1 in older secondary forests, and 0.7 (Asia) to 1.3 (Africa) Mg ha−1 year−1 in old‐growth forests. We provide a rigorous and traceable refinement of the IPCC 2006 default rates in tropical and subtropical ecological zones, and identify which areas require more research on ∆AGB. In this respect, this study should be considered as an important step towards quantifying the role of tropical and subtropical forests as carbon sinks with higher accuracy; our new rates can be used for large‐scale GHG accounting by governmental bodies, nongovernmental organizations and in scientific research.

Highlights

Signatory nations of the Paris Agreement agreed to report on green‐ house gas (GHG) emissions and removals for climate change miti‐ gation efforts (UNFCCC, 2015)
As part of the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC, 2019), we pro‐ vide a rigorous refinement of the Tier 1 IPCC 2006 default ∆aboveground live tree biomass (AGB) rates for tropical and subtropical forests by incorporating forest plot data that have become available since the publication of the IPCC 2006 default rates
Our refined rates disaggregate forests >20 years old into older secondary forests and old‐growth for‐ ests, and provide measures of variation to account for their uncer‐ tainty

Summary

| INTRODUCTION

Signatory nations of the Paris Agreement agreed to report on green‐ house gas (GHG) emissions and removals for climate change miti‐ gation efforts (UNFCCC, 2015). Countries with tropical and subtropical forests can benefit from climate change mitigation policies through land restoration initiatives and Reducing Emissions from Deforestation and Forest Degradation (REDD+) schemes as a way to conserve and enhance their forest C sinks These initiatives and schemes require monitoring, reporting. IPCC 2006 Tier 1 forest C pools and sinks in natural forests are characterized in part as aboveground live tree biomass (AGB) and rates of aboveground net biomass change (∆AGB). To provide a thorough characterization of natural forest C sinks, IPCC 2006 de‐ fault ∆AGB rates can be used together with other Tier 1 default val‐ ues—such as AGB, belowground biomass (BGB) to AGB ratios—and loss estimates of AGB by anthropogenic activities. In the interest of facilitating the scientific use and future update of these default rates, we (a) incorporate newly available data on secondary, old‐growth and managed/logged for‐ ests; (b) disaggregate forests over 20 years into older secondary and old‐growth forests; (c) derive ∆AGB rate estimates in a clear, rigor‐ ous and reproducible manner; and (d) identify areas where better ∆AGB data are needed

| MATERIALS AND METHODS

| Data availability

G G GGGG G

| DISCUSSION

Findings

| CONCLUSIONS