Land use and land cover changes determine the spatial relationship between fire and deforestation in the Brazilian Amazon

An increased frequency of droughts is predicted for the Amazon rainforest in the 21st century, which, combined with deforestation, could exacerbate fire occurrence in the region. There is ample evidence of the association between fire use and deforestation in the land use and land cover change (LULCC) processes occurring in the Amazon region, but there are no studies on the actual spatial structuring and spatial association between these events. The present study evaluates the existence of such relationships through the use of remotely sensed data and spatial analysis techniques for an active deforestation frontier covering portions of the states of Rondônia and Mato Grosso in the Brazilian Amazon. A map of burn scars for the year 2005 was produced using a Linear Spectral Mixture Model (LSMM) transformation of Landsat Thematic Mapper (TM) images, with subsequent unsupervised classification and manual editing. Annual and aggregated maps of deforested areas up to 2005, produced by the Brazilian Amazon Deforestation Estimation Project (PRODES), were also used. The amount of burn scar occurrences inside both recent (2002–2005) and old (prior to 2002) deforested areas was then determined, and the spatial structure of both variables was assessed using Mantel tests for multiple aggregation scales. A partial Mantel test was also used to test the spatial correlation between burn scars and deforested areas, accounting for the existence of spatial structure. The results show that there is a significant spatial association between recent deforestation and the occurrence of fires. In addition, we identified a large amount of burned areas (∼55%) within older deforested areas. These results highlight the following: 1) the direct role of fire in the land use and land cover change processes in the Brazilian Amazon, and 2) that fire also widely affects previously degraded vegetation, with significant implications for current estimates of forest fire-associated atmospheric carbon emission in the Amazon region.

► Spatial association was observed between recent deforestation and burn scars.
► 1/3 of the area deforested in the previous three years was burned in 2005.
► However, 55% of the burning occurred in areas deforested before 2002.
► Results indicate some dissociation between fire and forest removal.
► Burning in degraded areas could affect carbon emission calculations.