Sensitivity of tropical woodland savannas to El Niño droughts

Abstract. The 2015–2016 El Niño event led to one of the most intense and hottest droughts for many tropical forests, profoundly impacting forest productivity. However, we know little about how this event affected the Cerrado, the largest savanna in South America. Here we report 5 years of productivity of the dominant vegetation types in Cerrado, savanna (cerrado) and transitional forest-savanna (cerradão), continuously tracked before, during, and after the El Niño. We carried out intensive monitoring between 2014 and 2019 of the productivity of key vegetation components (stems, leaves, roots). Before the El Niño total productivity was ~25 % higher in the cerradão compared to the cerrado. However, cerradão productivity declined strongly by 29 % during the El Niño event. The most impacted component was stem productivity, reducing by 58 %. By contrast, cerrado productivity varied little over the years, and while the most affected component was fine roots, declining by 38 % during the event, fine root productivity recovered soon after the El Niño. The two vegetation types also showed contrasting patterns in the allocation of productivity to canopy, wood, and fine-root production. Our findings demonstrate that cerradão can show low resistance and resilience to climatic disturbances due to the slow recovery of productivity. This suggests that the transitional Amazon-Cerrado ecosystems between South America’s largest biomes may be particularly vulnerable to drought enhanced by climate change.