Fragmentation-driven divergent trends in burned area in Amazonia and Cerrado

The two major Brazilian biomes, the Amazonia and the Cerrado (savanna), are
increasingly exposed to fires. The Amazonian Forest is a fire sensitive ecosystem where
fires are a typically rare disturbance while the Cerrado is naturally fire-dependent. Human
activities, such as landscape fragmentation and land-use management, have modified
the fire regime of the Cerrado and introduced fire into the Amazonian Forest. There
is limited understanding of the role of landscape fragmentation on fire occurrence
in the Amazonia and Cerrado biomes. Due to differences in vegetation structure,
composition, and land use characteristics in each biome, we hypothesize that the
emerging burned area (BA) patterns will result from biome-specific fire responses to
fragmentation. The aim of this study was to test the general relationship between
BA, landscape fragmentation, and agricultural land in the Amazonia and the Cerrado
biomes. To estimate the trends and status of landscape fragmentation a Forest Area
Density (FAD) index was calculated based on the MapBiomas land cover dataset
for both biomes between 2002 and 2018. BA fraction was analyzed within native
vegetation against the FAD and agricultural land fraction. Our results showed an
increase in landscape fragmentation across 16% of Amazonia and 15% of Cerrado. We
identified an opposite relationship between BA fraction, and landscape fragmentation
and agricultural fraction contrasting the two biomes. For Amazonia, both landscape
fragmentation and agricultural fraction increased BA fraction due to an increase of
human ignition activities. For the Cerrado, on the other hand, an increase in landscape
fragmentation and agricultural fraction caused a decrease in BA fraction within the native
vegetation. For both biomes, we found that during drought years BA increases whilst
the divergent trends driven by fragmentation in the two contrasting global biomes is
maintained. This understanding will be critical to informing the representation of fire
dynamics in fire-enable Dynamic Global Vegetation Models and Earth System Models
for climate projection and future ecosystem service provision.