Abstract
Wildfires are becoming increasingly frequent and devastating in many tropical forests. Although seasonally dry tropical forests (SDTF) are among the most fire-threatened ecosystems, their long-term response to frequent wildfires remains largely unknown. This study is among the first to investigate the resilience in response to fire of the Chiquitano SDTF in Bolivia, a large ecoregion that has seen an unprecedented increase in fire intensity and frequency in recent years. We used remote sensing data to assess at a large regional and temporal scale (two decades) how fire frequency and environmental factors determine the resilience of the vegetation to fire disturbance. Resilience was measured as the resistance to fire damage and post-fire recovery. Both parameters were monitored for forested areas that burned once (F1), twice (F2), and three times (F3) between 2000 and 2010 and compared to unburned forests. Resistance and recovery were analyzed using time series of the Normalized Burn Ratio (NBR) index derived from Landsat satellite imagery, and climatic, topographic, and a human development-related variable used to evaluate their influence on resilience. The overall resilience was lowest in forests that burned twice and was higher in forests that burned three times, indicating a possible transition state in fire resilience, probably because forests become increasingly adapted during recurrent fires. Climatic variables, particularly rainfall, were most influential in determining resilience. Our results indicate that the Chiquitano dry forest is relatively resilient to recurring fires, has the capacity to recover and adapt, and that climatic differences are the main determinants of the spatial variation observed in resilience. Nevertheless, further research is needed to understand the effect of the higher frequency and intensity of fires expected in the future due to climate change and land use change, which may pose a greater threat to forest resilience.
Highlights
In recent years, the large and devastating fires burning the highly biodiverse forests of central South America have made international headlines (Bertrand, 2020)
Of the different major South American biomes, dry tropical forests, which are characterized by a distinct dry period, have seen an unprecedented increase in fire occurrence (Di Bella et al, 2006; Pennington et al, 2009), with some areas hit by fires multiple times within the last decades
The recovery time Rt was longer for F1 and F2 than it was for F3
Summary
The large and devastating fires burning the highly biodiverse forests of central South America have made international headlines (Bertrand, 2020). Forest fires have become increasingly common in the Chiquitanía region of Bolivia (Devisscher et al, 2016a), where approximately 17 million ha of forest burned between 2005 and 2019 (Anívarro et al, 2019) This region is home to the Chiquitano seasonally dry tropical forest (SDTF), the largest intact SDTF block in the Neotropics (Pennington et al, 2004). Much recent work on the effects of fire in the Chiquitanía has been done by Devisscher et al (2016a,b, 2019), who have found shifts in species composition and functional traits with increasing fire frequency that suggest that the Chiquitanía may irreversibly transition into a more fire-adapted state as fires occur more frequently (Devisscher et al, 2016b) Their field work mainly focused on transition zones within the Chiquitanía, and it remains unknown whether these changes would be similar across the region.
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