Abstract
Fire has become an increasingly important disturbance event in south-western Amazonia. We conducted the first assessment of the ecological impacts of these wildfires in 2008, sampling forest structure and biodiversity along twelve 500 m transects in the Chico Mendes Extractive Reserve, Acre, Brazil. Six transects were placed in unburned forests and six were in forests that burned during a series of forest fires that occurred from August to October 2005. Normalized Burn Ratio (NBR) calculations, based on Landsat reflectance data, indicate that all transects were similar prior to the fires. We sampled understorey and canopy vegetation, birds using both mist nets and point counts, coprophagous dung beetles and the leaf-litter ant fauna. Fire had limited influence upon either faunal or floral species richness or community structure responses, and stems <10 cm DBH were the only group to show highly significant (p = 0.001) community turnover in burned forests. Mean aboveground live biomass was statistically indistinguishable in the unburned and burned plots, although there was a significant increase in the total abundance of dead stems in burned plots. Comparisons with previous studies suggest that wildfires had much less effect upon forest structure and biodiversity in these south-western Amazonian forests than in central and eastern Amazonia, where most fire research has been undertaken to date. We discuss potential reasons for the apparent greater resilience of our study plots to wildfire, examining the role of fire intensity, bamboo dominance, background rates of disturbance, landscape and soil conditions.
Highlights
Understorey wildfires in humid tropical forests have increased in frequency and prevalence over the last three decades, mainly due to their interaction between fire-dependent agricultural practices and extreme drought events [1,2,3,4]
Much less is known about the responses of south western Amazonian forests to fire disturbance, a large extent of forest was recently affected by severe drought events that occurred in 2005 [14] and 2010 [15]
Tree mortality was higher across all stem size classes in plots in the central Amazon than in southwestern Amazonia, and these differences were highly significant in the 10–19.9 cm size class (Figure 3)
Summary
Understorey wildfires in humid tropical forests have increased in frequency and prevalence over the last three decades, mainly due to their interaction between fire-dependent agricultural practices and extreme drought events [1,2,3,4]. Much less is known about the responses of south western Amazonian forests to fire disturbance, a large extent of forest was recently affected by severe drought events that occurred in 2005 [14] and 2010 [15]. These droughts are related to higher North Atlantic sea-surface temperatures [14], and are distinct from the El Nino associated droughts affecting the northern and eastern Amazon [16]. Conservative estimates suggest that c. 2,800 km of forest burned in the state of Acre in 2005 [17]
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