Abstract
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.
Highlights
Brazil contains a diverse range of biomes across different climate and soil gradients, ranging from Amazonia and Atlantic rainforest to tropical dry forest, savannas, and natural grasslands to wetlands
Our study demonstrates that in Amazonia, landscape fragmentation increases the burned area (BA) fraction within native vegetation fragments and that this pattern is opposite in the Cerrado, where a higher degree of landscape fragmentation leads to a decrease in BA within the remaining intact fragments
We found a positive trend in landscape fragmentation between 2002 and 2018 in about 16% of the Amazonia and the carbon losses due to this process is currently not being accounted in the national greenhouse gas inventories (NGHGI)
Summary
Brazil contains a diverse range of biomes across different climate and soil gradients, ranging from Amazonia and Atlantic rainforest to tropical dry forest, savannas, and natural grasslands to wetlands. The two largest biomes of Brazil, Amazonia, and Cerrado (Savanna), occupy together approximately 73% of the total country area, each biome with 49 and 24%, respectively These two major biomes have attracted attention because of their vast area and their important contribution for key ecosystem services, notably the role of intact vegetation to the natural carbon (C) sink (Malhi et al, 2006; Pan et al, 2011; Gloor et al, 2012; Poulter et al, 2014), biodiversity (Morandi et al, 2018) and agricultural production. Both biomes are subjected to fires with different degree of occurrence, shaping their vegetation composition through time (Pivello, 2011). There are no studies showing the relationship between fragmentation and fire dynamics for the Cerrado biome and whether or not the relationship is common across major global biomes, such as Cerrado (savanna) and Amazonia (tropical forest), as typically assumed by global fire models
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