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Understory forest fires threaten the integrity of the forest because they cause the degradation and loss of functions of water recycling, soil renewal and maintenance, and carbon storage. Because the intensification and frequency increase of events as prolonged droughts by the El Niño phenomenon, changes in land use and cover and by selective logging, the incidence of those events in the Amazon is reaching areas of humid forests with insignificant numbers of those occurrences. The objectives of this study were:(i) to estimate the area impacted by understory forest fires and;(ii) to estimate the dead biomass by forest physiognomy as a result of the fire effect. The analyzes were anchored in field data (frequency and mortality of trees by fire), in satellite images in a GIS environment. The total area burned reached 1,861.5 km2, affecting 68.0 x 106 Mg of biomass, of which 15.3 x 106 Mg (22.4%) died. The Dense Ombrophylous Forest (Ds) was the most affected by the fires, as it covers Settlement Projects along the two main access roads of the State. Selective logging, coupled with the inappropriate use of fire and abnormal drought conditions, contributed to the spread of fire in the region. More detailed studies are needed in this wetland of Roraima to assess other impacts of fires (hydrological and social) and the main consequences on the forest structure and ecology of animal and plant species.