Siberian carbon sink reduced by forest disturbances

Abstract

Siberian forests are generally thought to have acted as an important carbon sink over recent decades, but exposure to severe droughts and fire disturbances may have impacted their carbon dynamics. Limited available forest inventories mean the carbon balance remains uncertain.Here we analyse annual live and dead above-ground carbon changes derived from low-frequency passive microwave observations from 2010 to 2019. We find that during this period, the carbon balance of Siberian forests was close to neutral, with the forests acting as a small carbon sink of +0.02 +0.01 +0.03 PgC yr −1 . Carbon storage in dead wood increased, but this was largely offset by a decrease in live biomass. Substantial losses of live above-ground carbon are attributed to fire and drought, such as the widespread fires in northern Siberia in 2012 and extreme drought in eastern Siberia in 2015. These live above-ground carbon losses contrast with 'greening' trends seen in leaf area index over the same period, a decoupling explained by faster post-disturbance recovery of leaf area than live above-ground carbon. Our study highlights the vulnerability of large forest carbon stores in Siberia to climate-induced disturbances, challenging the persistence of the carbon sink in this region of the globe.

An increasing Arctic-boreal CO2sink offset by wildfires and source regions

“…Larger RMSE and MAE values indicate larger errors, and positive MBE values indicate overestimation. The predictive performance of our models was good or high, ranging from 0.55 to 0.78 for R 2 and 19.4 to 37.3 g C m -2 month -1 for RMSE, but was occasionally limited (Supplementary Fig. 1-3), mostly due to 1) our model not being able to identify landscape heterogeneity with nearby sites showing large differences in CO 2 fluxes (e.g., a forest and wetland site), and 2) our model not capturing inter-annual variability at individual sites, both of which are likely attributed to the coarse, uncertain, and missing predictors characterizing such conditions (e.g., soil moisture, disturbances).…”

“…Using machine learning models that had a high predictive performance (up to two times higher cross-validated R 2 compared to earlier efforts 5,9 ), we find that from 2001-2020 circumpolar tundra was on average CO 2 neutral without accounting for fire emissions (in-situ NEE: -4 ± 44 g C m -2 yr -1 ; upscaled NEE: 7 ± 3 g C m -2 yr -1 ; upscaled budget 45 ± 53 Tg C yr -1 ; mean ± standard deviation; Table 1). In contrast, the boreal was a strong sink (in-situ NEE: -41 ± 82 g C m -2 yr -1 ; upscaled NEE: -43 ± 7 g C m -2 yr -1 ; upscaled budget -593 ± 101 Tg C yr -1 ).…”

Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems

“…This was unexpected, because these are also areas that have low flux data coverage (Table 3). The largest variability in mean NEE was found in western Siberia where the ISIMIP and inversion models showed a much stronger (>25 g C m −2 yr −1 ) average sink than the other approaches; recent remote sensing analyses show a decreasing sink strength in Siberia driven by disturbance (Fan et al., 2023). While part of this disagreement is simply due to the high overall fluxes in this forest‐dominated region, new measurements and process‐level understanding of disturbance effects in this domain are critical to resolving this issue.…”

Russia in a changing climate

“…Siberia, like Europe and North America, experienced massive heatwaves in 3 of 4 years since 2020. Even prior to these extreme events, droughts and fire have been disturbing the carbon balance of Siberian forests, challenging the region's persistence as a carbon sink (Fan et al, 2023). The southern and eastern “bread basket” territories of European Russia, historically prone to severe summer droughts, are projected to experience further decreases in precipitation (Cook et al, 2020; Dronin & Kirilenko, 2011).…”