Susceptibilidade ao fogo de florestas de igapó de águas pretas no Parque Nacional do Jaú, Amazônia Central

Abstract

Black-water floodplain forests (igapó), despite seasonally inundated, are susceptible to fire. Studies indicate that wildfires associated to extreme weather events cause degradation of this ecosystem, but the impact of fire along the flood gradient in igapós has not been investigated. Fire history of black-water inundation forests of the Jaú National Park (Central Amazonia) and on the edges of this Protected Area (buffer zone of 8 km) was reconstructed from 1982/83 to 2016/17 by satellite imagery. The fires were classified according to the size of the affected area and were spatially and temporally evaluated in relation to El Niño events. We investigated the variations of fine fuel (dry biomass of litter and fine roots), the photosynthetic active radiation and the soil texture along the flood gradient of igapós of the Jaú River, and the interaction of these parameters. The spatial evaluation indicated that there is a local pattern of fire occurrence in the investigated area, which is related to the proximity of settlements in this region, suggesting that the anthropic factor may be the main source of ignition. Fires associated with ENSO events (El Niño Southern Oscillation) accounted for 92% of the total area burned during the study period and fires in the classes of larger burned area (>100 ha) were detected mainly in ENSO years, especially during the severe 2015/16 event. The results suggest that the reduction of precipitation in the dry season and the low water level triggered by El Niño events are fundamental to intensify the occurrence of fires and burn larger areas. The greater volume of litter and light reaching the soil of igapó forests in low and medium topographies indicate that these classes are more susceptible to fire. We concluded that the El Niño effects combined with the anthropic interference are elements that intensify the vulnerability of black-water igapó forests to wildfire and there is an urgent need to develop plans and actions to mitigate the impacts of severe hydroclimatic events on the oligotrophic and vulnerable igapó floodplains.