Unveiling the diversity of regional burning patterns at the Brazilian savanna

Fire is an integral and predictable component of ecological functioning and dynamics in fire-prone biomes. However, the relationships and potential feedback between fire and its drivers are complex, as they depend on the temporal and spatial scales adopted when analyzing the fire regime. A remote sensing approach allows the characterization of fire regimes with larger spatial coverage and temporal homogeneity, especially where fire records are rare, as in the Brazilian savannas (Cerrado). The Cerrado is a mosaic of soil types and topographic settings, with varying regional climate patterns, resulting in a variety of fire resistant/sensitivity vegetation types, and recent disturbances, mostly due to increasing economic and agricultural development, along with changes in climate, are disrupting its natural fire patterns. Most studies characterizing fire activity in Cerrado are either performed at the biome-level or focus on very specific locations with results then extrapolated over the whole biome, which may mask important regional patterns. Here, we aim to characterize the regional fire patterns into the Cerrado’s 19 ecoregions, previously defined based on biophysical parameters which do not include fire. 

We use burned area (BA), fire radiative power and individual fire scar data based on MODIS products (respectively, MCD64A1, MCD14ML and Global Fire Atlas) to evaluate inter and intra annual cycles, spatial anomalies and trends of BA, fire intensity and fire size (small fires: <1000ha, medium: 1000-5000ha and large fires: >5000ha) in each ecoregion from 2001 to 2019. 

Our results show a marked north-south BA gradient, with higher annual BA contributions from the northern ecoregions. These ecoregions are mainly located in the latest agricultural frontier, MATOPIBA, where there are more vegetation remnants that are under high anthropogenic pressure due to recent economic development. Conversely, ecoregions showing low BA are highly fragmented and  have been historically deforested for longer periods. Most fires are of low intensity and higher intensity fires occur towards the end of the dry season period (June to October). Moreover, there are considerable differences in extremely intense events, especially in the eastern ecoregions. We also found that temporal and spatial patterns are highly variable, depending on fire scars size. Infrequent medium and large scars account for most of BA compared to common very small and small scars. Overall, fire seasonality varies substantially depending on fire size class: larger scars occur over a 2-month period within the dry season, whereas the remaining classes are increasingly scattered along the year. BA is increasing and fire intensity decreasing over MATOPIBA’s ecoregions, while in southern ecoregions, is the opposite, with a decreasing over BA and an increase of fire intensity. Smaller scars are overall decreasing, whereas medium and larger scars show positive trends over central and northern ecoregions. 

This study highlights the importance of understanding the diversity of fire dynamics in Cerrado to better inform and prepare refined-scale fire management strategies in light of current regional ecosystem disturbances and future climate change. 

The study was funded by CNPQ (grant 441971/2018-0) and P. S. Silva is supported by FCT (grant SFRH/BD/146646/2019).