Role of forest regrowth in global carbon sink dynamics

Abstract

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−1located in intact old-growth forest, primarily in the moist tropics and boreal Siberia, and 1.30 (1.03–1.96) Pg year−1located 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.

Sources of Uncertainty in Regional and Global Terrestrial CO2 Exchange Estimates

“…DGVMs tend to simulate a slower increase in CO uptake than reported by inversions in several regions and globally. The weak negative trend in is consistent with studies showing that DGVMs may underestimate the response of vegetation to the effect of CO fertilization (Fernndez‐Martnez et al, ; Thomas et al, ), or the effect of N deposition in Asia (Liu et al, ), or forest regrowth (Pugh et al, ). The positive values for the trend in EU, KAJ, and SEAS indicate that DGVMs show a stronger long‐term increase in the land sink compared to inversions.…”

Fostering natural forest regeneration on former agricultural land through economic and policy interventions

“…Compared to subtropical and temperate zones, natural regeneration on former agricultural land in the tropics tends to be a more recent phenomenon, where net forest loss is still occurring (Song et al 2018). Tropical secondary forests are younger (mean of 18 year) compared to temperate deciduous forests (mean of 52 year) and coniferous evergreen forests (mean of 72 year) (Pugh et al 2019). In Latin America, cases of forest gain through natural regeneration from 2001 to 2014 fell into five main clusters that reflect topographic features and related aspects of agro-ecological marginality, climate change, rural population decline, and increased urbanization (Nanni et al 2019).…”

“…Naturally regenerating forests on former agricultural land can provide solutions for conservation of biodiversity, mitigation of, and adaptation to, climate change, and multiple ecosystem goods and services (Houghton et al 2015, Locatelli et al 2015, Wilson et al 2017, Jones et al 2019, Matos et al 2019, Pugh et al 2019. Similar benefits can be provided by active forest restoration (e.g.…”

Modeling and empirical validation of long‐term carbon sequestration in forests (France, 1850–2015)

“…At the same time, while wood was the main fuel in France until the 1870s (Smil, 2017), providing energy for heating and cooking in French homes, the switch from wood to coal certainly relieved pressure on wood extraction and may have been the prime reason of the observed transition of forest biomass density (Figure 4). Therefore, another relevant factor to explain the divergence between the CRAFT and bookkeeping models is the effect of forest age structure, controlled by the expansion of forest area and variation in harvest rates, which affects the growth rate of forest stand density (He, Chen, Pan, Birdsey, & Kattge, 2012;Noormets et al, 2015;Pan, Birdsey, Phillips, & Jackson, 2013;Pretzsch et al, 2014;Pugh et al, 2019;Vilén et al, 2012). This effect of age structure can be accounted by both the CRAFT and static CRAFT approaches thanks to the nonlinear relationship between NPP and standing biomass.…”