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

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.

Assessing the growth and climate sensitivity of secondary forests in highly deforested Amazonian landscapes

“…), and only around twice that recorded in Amazonia’s primary forests. Although this rate of carbon accumulation is comparable to recent continental‐scale estimates of biomass recovery in older (20–80 yr old) tropical secondary rainforests in the Americas (Requena Suarez et al ; Fig. ), this similarity masks one important difference: our long‐term plots had a much lower lifetime recovery rate than the same continent‐scale estimates (Fig.…”

“…It seems likely that the increase in landscape‐scale restoration will also increase secondary forest permanence, moving beyond the current situation where secondary forests are often cleared again within 5–20 yr (Aguiar et al , Reid et al ). Although our current understanding of younger forests is good (Poorter et al , , , Martínez‐Ramos et al , Villa et al , Rozendaal et al ), and the nonlinear response of forest recovery over time is well established (Poorter et al , Ferreira et al , Lennox et al , Requena Suarez et al , Rozendaal et al ), there is far too much variation in the relationship to use young forests to predict recovery rates in older forests accurately. Moreover, the relative recovery rates of carbon and biodiversity are unclear.…”

Elevation and latitude drives structure and tree species composition in Andean forests: Results from a large-scale plot network

“…The majority of the plots are located in mature forests but the AFN also includes several older secondary forests plots, i.e. > 30 years old [50] as a result of human activities and the associated land use changes [19,51,52,53]. Censuses of plots were conducted between 2002 and 2017 (mean year of census = 2010.5±0.26) with the exception of one plot censused in 1988.…”

Secondary forests offset less than 10% of deforestation‐mediated carbon emissions in the Brazilian Amazon

“…While the carbon balance of undisturbed forests has been well studied (Brienen et al, 2015;Hubau et al, 2020;Pan et al, 2011;Saatchi et al, 2011), estimates of the rate of carbon sequestration in secondary forests remain highly variable (Elias et al, 2019;Grace et al, 2014;Pan et al, 2011;Saatchi et al, 2011). Requena Suarez et al (2019) have made huge advances in refining our understanding of secondary forest carbon accumulation. However, there are uncertainties associated with applying their rates universally in order to produce large-scale estimates.…”