Carbon benefits from Forest Transitions promoting biomass expansions and thickening

Abstract

The growth of the global terrestrial sink of carbon dioxide has puzzled scientists for decades. We propose that the role of land management practices—from intensive forestry to allowing passive afforestation of abandoned lands—have played a major role in the growth of the terrestrial carbon sink in the decades since the mid twentieth century. The Forest Transition, a historic transition from shrinking to expanding forests, and from sparser to denser forests, has seen an increase of biomass and carbon across large regions of the globe. We propose that the contribution of Forest Transitions to the terrestrial carbon sink has been underestimated. Because forest growth is slow and incremental, changes in the carbon density in forest biomass and soils often elude detection. Measurement technologies that rely on changes in two‐dimensional ground cover can miss changes in forest density. In contrast, changes from abrupt and total losses of biomass in land clearing, forest fires and clear cuts are easy to measure. Land management improves over time providing important present contributions and future potential to climate change mitigation. Appreciating the contributions of Forest Transitions to the sequestering of atmospheric carbon will enable its potential to aid in climate change mitigation.

Altered growth conditions more than reforestation counteracted forest biomass carbon emissions 1990–2020

“…While both harvest rate and burnt area increase globally over the period of observation, the increased forest growth rate that we calculate with CRAFT for both primary and managed forests over 1990–2020 emerges here as the only factor explaining increased biomass density at the global level. This is in line with other research pointing to the relevance of biomass thickening for forest C sequestration 19 . In addition, our finding that the forest growth rate increased annually by 0.19%, 0.21%, and 0.21% from 1990 to 2020, respectively, for primary, managed and total forests of the world is consistent with Kolby Smith et al 20 who find that also net primary production (NPP) increased annually between 0.10 and 0.25% in the period 1982–2011, as well as with other modeling and remote-sensing studies documenting a global greening trend, i.e., vegetation thickening following increased vegetation growth rate 21 , 22 .…”

“…2d ). Possible reasons explaining the negative effect of change in forest growth rate are forest degradation, increasing drought, cloudiness, or insect outbreaks 15 – 19 . Over the period 1990–2020, the strongest harvest impacts are observed in countries with large area of managed forest and high harvest pressure, mostly located in temperate and subtropical areas (CF5; Fig.…”

Critical adjustment of land mitigation pathways for assessing countries’ climate progress

“…1b), which mostly occur in forests. This difference is potentially a consequence of: (1) simplified and/or incomplete representations of land-use change and management in global models 14,17 , which includes the role of forest management in promoting biomass expansions and thickening 18 , and the impact of forest demography 19 , (2) inaccurate and/or incomplete estimation of LULUCF fluxes in NGHGIs 3 , especially in non-forest land uses and in soils, and (3) conceptual inconsistencies between global models and NGHGIs in estimating 'anthropogenic' CO 2 fluxes from land, which mean the estimates are hardly comparable 15 . The impacts of (1) and ( 2) are difficult to quantify, and result in uncertainties that will decrease slowly over time through improvements of both the models and NGHGIs.…”

Applying a science‐based systems perspective to dispel misconceptions about climate effects of forest bioenergy

“…Expectation of increasing biomass demand could stimulate establishment of new forests to secure future wood production, which would provide additional carbon storage, and motivate management changes in existing forests to enhance growth (e.g. improved site preparation, faster growing tree species, fertilization), which could improve the climate outcomes from forests managed for biomass and other products (Favero et al, 2020; Galik & Abt, 2012; Kauppi et al, 2020; Laganière et al, 2017). For example, in Sweden, which was widely deforested in the 1800s, forest expansion together with intensive forest management has doubled the standing volume of forests over the last 100 years, at the same time as annual harvest has increased (Figure 2).…”