ENSO Wildfires Impact Amazonian Floodplains in Complex Ways

Samenvatting

Amazonian floodplains are the most extensive and biodiverse riverine habitat on Earth. They currently face unprecedented fire regimes as climate change increases the frequency and intensity of drought. While it is clear that fire impacts on floodplain ecology can be severe, fire regimes and their effect on forest ecosystems have yet to be fully examined across the considerable spatial and ecological heterogeneity of Amazonian floodplains. We used the MODIS burned area product to map fire occurrence across Amazonian floodplain forests. Next, we assessed forest recovery after burning using NDVI values from LandSat images. We specifically focused on differences in wildfire dynamics and forest recovery after burning across floodplains associated with the three main river types in the Amazon basin (black-, clear-, and white-water rivers). We found that the occurrence of forest fires in floodplains is strongly associated with ENSO events and increases as land-use intensity increases, dry seasons get longer, soils become sandier, and the synchrony between flooding and precipitation patterns increases. Postfire forest recovery is slower, and reburning risk is higher, on nutrient-poor floodplains of black-water rivers, compared to the nutrient-richer floodplains of white- and clear-water rivers. Moreover, forest recovery is significantly slower in regions flooded for prolonged periods, regardless of river type. Our results call for urgent prevention and monitoring of floodplain forest fires across the Amazon basin, with particular attention to black-water floodplains, to prevent large-scale vegetation shifts and cascading ecosystem changes on biodiversity and ecosystem services provided by floodplain forests.