Recent divergence in the contributions of tropical and boreal forests to the terrestrial carbon sink

Abstract

Anthropogenic land use and land cover changes (LULCC) have a large impact on the global terrestrial carbon sink, but this effect is not well characterized according to biogeographical region. Here, using state-of-the-art Earth observation data and a dynamic global vegetation model, we estimate the impact of LULCC on the contribution of biomes to the terrestrial carbon sink between 1992 and 2015.   Tropical and boreal forests contributed equally, with the largest share of the mean global terrestrial carbon sink. CO 2 fertilization was found to be the main driver increasing the terrestrial carbon sink from 1992 to 2015, but the net effect of all drivers (CO 2 fertilization and nitrogen deposition, LULCC and meteorological forcing) caused a reduction and an increase, respectively, in the terrestrial carbon sink for tropical and boreal forests. These diverging trends were not observed when applying a conventional LULCC dataset, but were also evident in satellite passive microwave estimates of aboveground biomass. These datasets thereby converge on the conclusion that LULCC have had a greater impact on tropical forests than previously estimated, causing an increase and decrease of the contributions of boreal and tropical forests, respectively, to the growing terrestrial carbon sink.

A physiology‐based Earth observation model indicates stagnation in the global gross primary production during recent decades

“…GPP trends quantified by Earth observation‐based models are generally smaller than those simulated by dynamic global vegetation models, and this difference has been attributed to the absence of CO 2 fertilization effects in the observation‐based approaches (Anav et al., 2015; Kolby Smith et al., 2015; Piao et al., 2020). Many studies have indicated increased CO 2 uptake under elevated CO 2 (Gifford, 2004; Schimel et al., 2015; Tagesson et al., 2020). On the other hand, analyses of biomass increment in CO 2 enrichment experiments and tree rings in forests indicate that the fertilization effect disappears at large spatial scales, due to the overriding effects of other constraints, such as extreme weather events, nutrients and SWC (Hararuk et al., 2019; Terrer et al., 2019).…”

“…Human population growth and increased food and fibre consumption have increased the use of global primary production (Krausmann et al., 2017), with severe consequences for services and functions of global ecosystems (Rockström et al., 2009; Steffen et al., 2015). An improved understanding of spatial and temporal dynamics in regional and global GPP is additionally essential to better understand, quantify and forecast the effects of current and future climate change (Tagesson et al., 2020), also in relation to design of climate change mitigation policies and in the early detection of ecosystem change (IPBES, 2018).…”

Quantification of Moss-Associated Cyanobacteria Using Phycocyanin Pigment Extraction

“…Indeed, it has been predicted that the average annual temperature in the boreal forest will increase by 2°C by 2050 (Price et al, 2013). This will cause the extension of the growth season length (Ouranos, 2015) and, combined with CO 2 increase, will impact boreal forest primary productivity, C cycle, and N demand (Lloyd and Bunn, 2007;Sigurdsson et al, 2013;Tagesson et al, 2020). Evaluating how these environmental changes will affect moss-associated nitrogen fixing bacteria is essential to help better predict the response of the boreal forest to global change.…”

Xylem Anatomical Variability in White Spruce at Treeline Is Largely Driven by Spatial Clustering

“…Boreal forests are ecologically and commercially valuable ecosystems that make up almost a third of the global forest cover (Apps et al, 1993;Hansen et al, 2003). They act as a sink for global atmospheric carbon dioxide (Arneth et al, 2010;Tagesson et al, 2020) but are heavily influenced by humaninduced and natural cover loss (Hansen et al, 2010). According to climate projections, boreal forests will face exceptional changes in climatic conditions within the 21st century (Soja et al, 2007;IPCC, 2013;Charney et al, 2016), threatening ecosystem functions (Gauthier et al, 2015).…”