Fires in the South American Chaco, from dry forests to wetlands: response to climate depends on land cover

Abstract

Abstract Background: Wildfires represent an important element in the biogeophysical cycles of various ecosystems across the globe and are particularly related to land transformation in tropical and subtropical regions. In this study we analyzed the links between fires, land use and meteorological variables in the South American Chaco (1.1 million km²), a global deforestation hotspot and fire prone region that has been highly neglected by environmental sciences so far.Results: Separating our analysis along the region’s marked precipitation gradient between the Wet Chaco (27%) and the Dry Chaco (73%), we combined satellite burnt area and land cover data together with meteorological products to study the fire patterns and drivers in the period 2001–2019. We found that the Dry Chaco has a unimodal fire seasonality (winter-spring) while the Wet Chaco has a bimodal seasonality (summer-autumn and winter-spring). While most of the burnt area was found in the Wet Chaco (113,859 km²; 55% of the entire burnt area), the Dry Chaco showed the largest fraction of forest loss (93,261 km²; 88% of the entire forest loss). For the whole Chaco, 26% of the forest loss was associated to burnt area detections, and this value changes among regions and countries, with Argentina standing as the country with both the largest absolute and fire-related forest loss (51,409 km² of total forest loss; ~40% fire-related). Land cover emerged as the principal factor behind fires, as it controls the effect of meteorological variability on fire exposure and the vulnerability of a region to fire ignition and expansion. While wet areas covered with herbaceous vegetation showed negative correlations with precipitation, some dry regions below 800 mm/year and mostly covered by shrublands, showed positive correlations with precipitation. These results reveal the two different roles of precipitation in a) the production of biomass fuel, and b) its subsequent availability for combustion.Conclusions: As fires and deforestation continue to expand in the South American Chaco while the evolving climate change increases the length of dry season and the frequency of extreme heat, there is an urgent need to conduct further studies in the area paying particular attention to the role and drivers of human fire ignition, combining environmental sciences with social sciences. Such research will help policy makers take action to preserve and protect the remaining forests and wetlands of the Chaco region.