Role of forest regrowth in global carbon sink dynamics

By T. Pugh, M. Lindeskog, Benjamin Smith, B. Poulter, Almut Arneth, V. Haverd, L. Calle. Proceedings of the National Academy of Sciences of the United States of America, 2019

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Significance Regrowth of forests following past disturbances is expected to be an important driver behind the large uptake of anthropogenic CO2 emissions by the terrestrial biosphere. Yet estimates of the size of this uptake vary widely. We combined independent observation-based and model-based sources of disturbance history information to calculate the carbon sink in regrowth forests. On-going carbon uptake due to forest demography is large, but much smaller than previous influential estimates have suggested. Contrary to previous findings, these latest data sources indicate that the sink is predominantly in mid-high latitude, rather than tropical, forests. The remaining uptake potential in forest biomass under current disturbance rates is equivalent to 7 years of emissions from fossil fuel burning at 2016 levels. Although the existence of a large carbon sink in terrestrial ecosystems is well-established, the drivers of this sink remain uncertain. It has been suggested that perturbations to forest demography caused by past land-use change, management, and natural disturbances may be causing a large component of current carbon uptake. Here we use a global compilation of forest age observations, combined with a terrestrial biosphere model with explicit modeling of forest regrowth, to partition the global forest carbon sink between old-growth and regrowth stands over the period 1981–2010. For 2001–2010 we find a carbon sink of 0.85 (0.66–0.96) Pg year−1 located in intact old-growth forest, primarily in the moist tropics and boreal Siberia, and 1.30 (1.03–1.96) Pg year−1 located in stands regrowing after past disturbance. Approaching half of the sink in regrowth stands would have occurred from demographic changes alone, in the absence of other environmental changes. These age-constrained results show consistency with those simulated using an ensemble of demographically-enabled terrestrial biosphere models following an independent reconstruction of historical land use and management. We estimate that forests will accumulate an additional 69 (44–131) Pg C in live biomass from changes in demography alone if natural disturbances, wood harvest, and reforestation continue at rates comparable to those during 1981–2010. Our results confirm that it is not possible to understand the current global terrestrial carbon sink without accounting for the sizeable sink due to forest demography. They also imply that a large portion of the current terrestrial carbon sink is strictly transient in nature.

Subfields: Agronomy and Crop Science, Environmental Engineering, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/abfb4a39bfe9a9db120d32282cd21770e417a752

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Citations in the corpus

Getting the message right on nature‐based solutions to climate change (2021, unknown): “Constraints on land area and tree growth dynamics limit the amount of carbon that can ultimately be removed by tree planting or forest regrowth (Pugh et al., 2019 Standard for NbS to ensure the quality of offset projects (IUCN, 2020).”
Climate-driven risks to the climate mitigation potential of forests (2020, background): “5 Pg CO2e year −1 over 2000–2007, where CO2e denotes CO2 equivalents (2, 3)].”
Pervasive shifts in forest dynamics in a changing world (2020, background): “1A and 2), they are threatened by other disturbances that have shifted landscapes from old to young growth–dominated stands (14), such as wildfire (29), windthrow (30), and biotic outbreaks (31).”
Fostering natural forest regeneration on former agricultural land through economic and policy interventions (2020, background): “Carbon sinks in regenerating forests are located mostly in deciduous broadleaf and evergreen coniferous forests in temperate zones, whereasmost of world’s remaining old-growth forest stands are in the moist tropics and boreal Siberia (Pugh et al 2019).”