PNNL

Abstract

Tropical forests have been a permanent feature of the Amazon basin for at least 55 million years, yet climate change and land use impacts threaten the forest’s future over the next century1. Understory fires in Amazon forests reflect the combined influence of human ignitions and drought. Fires are common at the land use frontier, with significant impacts on forest structure, composition, and biodiversity2–4. Away from the land use frontier, scarce fire ignitions and high moisture levels preclude significant burning, yet projections of climate change and land use may render these regions fire prone. Here, we use a fire model specifically parameterized for Amazon understory fires to simulate the combined influence of anthropogenic activities and climate change on future fire regimes. In a scenario of low mitigation efforts, understory fires increase in frequency and duration, burning 4-28 times more forest by 2080-2100 than during 1990-2010. In contrast, a scenario of active climate mitigation and forest conservation successfully constrains fire activity to 0.9-5.4 times contemporary burned area. Importantly, if climate mitigation fails, forest conservation alone is very effective under low to moderate 1 climate change, but does little to reduce fire activity under the most severe climate projections. These model results underscore the potential for a fire-driven transformation of Amazon forests without substantial mitigation.