Dynamics of forest fires in the southwestern Amazon

The synergism between climatic change and human action has provided conditions for the occurrence of forest fires in the Amazon. We used annual mapping to reconstruct the history of fire in Brazil's state of Acre to understand the forest-fire regime over a period of 33 years (1984-2016). The burn-scar index (BSI) derived from the fractions of soil and of photosynthetic and non-photosynthetic material was generated by CLASlite© software using Landsat-TM and OLI satellite images. The area of forest-fire scars totaled 525,130 ha in the period analyzed. This total includes forests that fire affected only once (388,350 ha), twice (59,800 ha) and three times (5727 ha). The years 2005 and 2010 represent 90% of the total area of forest fires in Acre, coinciding with severe droughts caused by the anomalous warming of the tropical North Atlantic Ocean. The most heavily impacted portion of Acre was in the eastern part of the state, which has the greatest forest fragmentation, consolidation of agricultural activity and presence of settlement projects. In 2005, the municipalities of Acrelândia, Plácido de Castro and Senador Guiomard accounted for more than 50% of the forest remnants impacted by fire. Of the total extent of forest fires in Acre, 43% occurred in settlement projects administered by the National Institute for Colonization and Agrarian Reform (INCRA) and 16% in conservation units administered by the Ministry of Environment (MMA). The area of forest fires was 36 times greater in the 16 years after 2000, compared to the 16 years before 2000. The frequency of fires increased dramatically from one fire episode roughly every ten years (period from 1984 to 2004), to one fire every five years (period from 2005 to 2016). With the projections of warmer climate and advancing deforestation, the forest fires in Acre will tend be more intense and frequent.