Tracking the impacts of El Niño drought and fire in human-modified Amazonian forests

Abstract

With humanity facing an unprecedented climate crisis, the conservation of tropical forests has never been so important – their vast terrestrial carbon stocks can be turned into emissions by climatic and human disturbances. However, the duration of these effects is poorly understood, and it is unclear whether impacts are amplified in forests with a history of previous human disturbance. Here, we focus on the Amazonian epicenter of the 2015–16 El Niño, a region that encompasses 1.2% of the Brazilian Amazon. We quantify, at high temporal resolution, the impacts of an extreme El Niño (EN) drought and extensive forest fires on plant mortality and carbon loss in undisturbed and human-modified forests. Mortality remained higher than pre-El Niño levels for 36 mo in EN-drought–affected forests and for 30 mo in EN-fire–affected forests. In EN-fire–affected forests, human disturbance significantly increased plant mortality. Our investigation of the ecological and physiological predictors of tree mortality showed that trees with lower wood density, bark thickness and leaf nitrogen content, as well as those that experienced greater fire intensity, were more vulnerable. Across the region, the 2015–16 El Niño led to the death of an estimated 2.5 ± 0.3 billion stems, resulting in emissions of 495 ± 94 Tg CO2. Three years after the El Niño, plant growth and recruitment had offset only 37% of emissions. Our results show that limiting forest disturbance will not only help maintain carbon stocks, but will also maximize the resistance of Amazonian forests if fires do occur.*

Ten new insights in climate science 2021: a horizon scan

“…Tipping processes are afflicted with high uncertainties (in terms of likelihood or timing, or both), but also associated with large potential impacts on societies and biosphere integrity (e.g. Berenguer et al, 2021;Gatti et al, 2021;Golledge et al, 2019;IPCC, 2021, Chapter 12;Ritchie et al, 2020;Sun et al, 2020). Therefore, they can be classified as high-impact, high uncertainty risks (Lenton et al, 2019).…”

“…Events such as the 2015/2016 El Niño caused an extreme and prolonged drought, which fuelled extensive and damaging fires. This has been putting some regions of the Amazon under such pressure that plant mortality rates remained elevated for 2-3 years after the eventparticularly where forests had already been modified by human activities (Berenguer et al, 2021). The southeastern part of the Amazon basin has turned into a net source of carbon to the atmosphere, not even taking the effect of fires into account (Gatti et al, 2021).…”

Participatory Mapping for Strengthening Environmental Governance on Socio-Ecological Impacts of Infrastructure in the Amazon: Lessons to Improve Tools and Strategies

“…There are various challenges and threats affecting this region, which is recognized for its significant importance for the conservation of Amazonian socio-biodiversity [54]. Among these challenges and threats are the uncontrolled encroachment at the agricultural frontier, illegal logging [55] and mining, forest fires [56], land tenure insecurity and land grabbing [57], low government presence and services [58] and major infrastructure projects, such as the paving of half of the 2.687 km of Federal and State Highways (BR-319, BR-230 and BR-364) and the Santo Antônio and Jirau hydroelectric dams, among others [50].…”

Fires Drive Long-Term Environmental Degradation in the Amazon Basin

“…Recently, advances in remote sensing have made it possible to quantify and monitor environmental degradation [1,14] caused by climate change [46], fires [47], changes in gross primary production (GPP) [48], and C supply [14]. Using the wide availability of products generated by remote orbital sensors, it is possible to study degradation in large areas, such as the Amazon Basin, over a relatively long span of time.…”