Responses of Plant Biomass in the Brazilian Savanna to Frequent Fires

Letícia Gomes,Mercedes M C Bustamante,Lucas Rodrigues,Britaldo Soares-Filho,Heloisa Sinátora Miranda,Ubirajara Oliveira

doi:10.3389/ffgc.2020.507710

Letícia Gomes, Mercedes M C Bustamante + Show 4 more

Open Access

https://doi.org/10.3389/ffgc.2020.507710

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Abstract

Fire has been a natural feature of the ecosystem for million years. Still, currently fire regimes have been increasingly altered by human activities and climate change, causing economic losses, air pollution, and environmental damage. In Brazil, savannas (locally known as the Cerrado) occupy almost 25% of the area of the country and contain 70% of the concentrated burned area. Fire frequency is related to the use of biannual fire in agricultural practices, aiming at cleaning cattle pastures, which act as ignition sources for the surrounding natural vegetation. Here, we present an ecological model to demonstrate how biennial fire affects plant biomass and carbon release from fine fuel in the Cerrado. The BEFIRE model (Behavior and Effect of Fire) is the first quantitative model to simulate the relationships between fire frequency, plant biomass, and fire-associated emissions based on the synthesis of knowledge about fire behavior and the effects on ecosystems compiled from experimental burnings in the Cerrado. Our model uses microclimate variables and vegetation structure (the amount of the aboveground biomass of trees, shrubs, herbs, and grasses) as inputs, and generates outputs related to the fire behavior (fire spread rate, fire intensity, and heat released) and the fire effects on the dynamic of plant biomass and post-fire carbon emissions. The BEFIRE model predicts that biennial fires allow for the recovery of the biomass of herbs and grasses, due to its fast growth. However, this fire interval does not allow for the recovery of the biomass of shrubs and trees. These growth limitations alter the co-existence of trees/shrubs and herbs/grasses and prevent the uptake of the total amount of emitted carbon from the combustion of fine fuel. Based on the model results, we proposed some recommendations for fire management in this threatened biome.

Highlights

Fire is a historical and frequent event that plays a key role in the processes and functions of global ecosystems, influencing the dynamics of vegetation, biogeochemical cycles, and climate (Beerling and Osborne, 2006; Pausas and Bond, 2020)
The biennial fire regime is associated with ecological impacts, such as the reduction of tree biomass (Garda, 2018; da Silva Rios et al, 2018; Montenegro, 2019), species diversity (Silva, 1999; Ribeiro et al, 2012; da Silva Rios and Sousa-Silva, 2017), and the uptake of carbon emitted by fire (Sato, 2003; Sato et al, 2010)
Tree biomass recovers more rapidly after one fire event (1F) than other vegetation strata, as tree individuals are generally more protected from fire damage, because of higher height, trunk diameter, and bark thickness (Hoffmann et al, 2003; Souchie et al, 2017)

Summary

Introduction

Fire is a historical and frequent event that plays a key role in the processes and functions of global ecosystems, influencing the dynamics of vegetation, biogeochemical cycles, and climate (Beerling and Osborne, 2006; Pausas and Bond, 2020). A high frequency of fire events occurred in the northern portion of the biome (Santana et al, 2020), where the remaining native vegetation grows (Sano et al, 2010) This high frequency is mainly related to the use of fire as a management tool in agricultural practices like cleaning converted areas and stimulating the resprout of pastures (Mistry, 1998; Miranda et al, 2002). These practices use fire biennially and are important sources of ignition for the spread of fire in the surrounding native vegetation (Medeiros and Fiedler, 2003; França et al, 2007; Dias and Miranda, 2010), especially during the dry season (August– September) when the vegetation is more flammable (Miranda et al, 2010). The biennial fire regime is associated with ecological impacts, such as the reduction of tree biomass (Garda, 2018; da Silva Rios et al, 2018; Montenegro, 2019), species diversity (Silva, 1999; Ribeiro et al, 2012; da Silva Rios and Sousa-Silva, 2017), and the uptake of carbon emitted by fire (Sato, 2003; Sato et al, 2010)

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