Tropical forests did not recover from the strong 2015–2016 El Niño event

Abstract

Severe drought and extreme heat associated with the 2015–2016 El Niño event have led to large carbon emissions from the tropical vegetation to the atmosphere. With the return to normal climatic conditions in 2017, tropical forest aboveground carbon (AGC) stocks are expected to partly recover due to increased productivity, but the intensity and spatial distribution of this recovery are unknown. We used low-frequency microwave satellite data (L-VOD) to feature precise monitoring of AGC changes and show that the AGC recovery of tropical ecosystems was slow and that by the end of 2017, AGC had not reached predrought levels of 2014. From 2014 to 2017, tropical AGC stocks decreased by 1.31.21.5 Pg C due to persistent AGC losses in Africa (−0.9−1.1−0.8 Pg C) and America (−0.5−0.6−0.4 Pg C). Pantropically, drylands recovered their carbon stocks to pre–El Niño levels, but African and American humid forests did not, suggesting carryover effects from enhanced forest mortality.

Global Monitoring of the Vegetation Dynamics from the Vegetation Optical Depth (VOD): A Review

“…Over a given pixel, it is very likely the value of M gmax , which mainly depends on the vegetation type is relatively constant from year to year. This assumption can be confirmed by results in intact forest regions and non-affected by severe drought/mortality events, showing that VOD present a clear annual cycle with minimum values during the dry season and that it recovers each year to the same value during the wet season [150,169].…”

“…The recovery after the 2015-2016 El Niño is quite slow. If AGC in tropical dryland areas exhibit similar values in 2017 than before the 2015-2016 El Niño event, carbon stocks of African and American humid forests did not recover yet due to an enhanced mortality during this episode of extreme drought [169]. Combining information from multispectral MODIS reflectance to identify and map forest areas and SMOS-IC L-VOD, a recent study showed that standing AGC stocks increased by 0.11 ± 0.05 Pg.C yr −1 over 2002-2017 in southern China as a consequence of land use policies.…”

Identifying areas at risk of drought‐induced tree mortality across South‐Eastern Australia

“…turnover of plant tissues, instantaneous recovery, etc), including drought‐induced mortality. Recovery after drought is not likely to be instantaneous (Saatchi et al., 2013; Wigneron et al., 2020), as commonly assumed by models, implying that surface energy partitioning feedback on atmospheric processes may be in gross error and may be particularly important in future projections.…”

Carbon benefits from Forest Transitions promoting biomass expansions and thickening

“…Monitoring carbon gains in soils is even harder. Remote sensing may not resolve the incremental changes from in the steady accrual of terrestrial carbon, although recent advancement of the research methods show certain promise (Fan et al., 2019; Wigneron et al., 2020). Subtle net gains of carbon at stand level are best observed empirically using the FLUXNET system (Baldocchi et al, 2001) which detects CO 2 exchange at the stand level but provides an insufficient basis for global extrapolations.…”