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

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 Nino, a region that encompasses 1.2% of the Brazilian Amazon. We quantify, at high temporal resolution, the impacts of an extreme El Nino (EN) drought and extensive forest fires on plant mortality and carbon loss in undisturbed and human-modified forests. Mortality remained higher than pre-El Nino 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 Nino 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 Nino, 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.*

Automated summary

The study focuses on the impact of the 2015-16 El Nino event on the Amazonian forests, revealing that extreme El Nino drought and fires resulted in plant mortality and significant carbon loss, with human disturbance exacerbating these effects. Findings suggest that limiting forest disturbance can help maintain carbon stocks and enhance the resistance of Amazonian forests to fires.