Fire as a recurrent event in tropical forests of the eastern Amazon: Effects on forest structure, biomass, and species composition

The effects of fire on forest structure and composition were studied in a s everely fire-impacted landscape in the eastern Amazon. Extensive sampling o f area forests was used to compare structure and compositional differences between burned and unburned forest stands. Burned forests were extremely heterogeneous, with substantial variation in forest structure and fire damage recorded over distances of <50 m. Unburned forest patches occurred within burned areas, but accounted for only six pe rcent of the sample area. Canopy cover, living biomass, and living adult st em densities decreased with increasing fire intensity/frequency, and were a s low as 10-30 percent of unburned forest values. Even light burns removed >70 percent of the sapling and vine populations. Pioneer abundance increase d dramatically with burn intensity, with pioneers dominating the understory in severely damaged areas. Species richness was inversely related to burn severity, but no clear pattern of species selection was observed. Fire appears to be a cyclical event in the study region: <30 percent of the burned forest sample had been subjected to only one burn. Based on estimat ed solar radiation intensities, burning substantially increases fire suscep tibility of forests. At least 50 percent of the total area of all burned fo rests is predicted to become flammable within Ib rainless days, as opposed to only 4 percent of the unburned forest. In heavily burned forest subjecte d to recurrent fires, 95 percent of the area is predicted to become flammab le in <9 rain-free days. As a recurrent disturbance phenomenon, fire shows unparalleled potential to impoverish and alter the forests of the eastern A mazon.