Responses of Plant Biomass in the Brazilian Savanna to Frequent Fires

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.

Implementation of Fire Policies in Brazil: An Assessment of Fire Dynamics in Brazilian Savanna

“…To have a resilient relationship between fire and pyrophytic vegetation, a period of recovery from fire is necessary since each fire overlapping in the same area can increase the damage and mortality of shrub and tree strata, change the plant physiognomy, and delay the passage of specimens to the reproductive stage [67,68].…”

Experimental burns in an open savanna: Greater fuel loads result in hotter fires

“…In Cerrado, fire suppression has serious implications as it can lead to severe wildfires (in which large areas are burned, e.g., >500 km 2 ) due to fuel load accumulation (Fidelis et al 2018;Barradas & Ribeiro 2021) and, in the long-term, to biodiversity loss and woody encroachment (Abreu et al 2017), eventually causing grasslands and savannas to be replaced by forest vegetation (Pinheiro & Durigan 2009;Stevens et al 2017;Rosan et al 2019). Conversely, frequent fires can negatively affect tree and shrub biomass recovery (Gomes et al 2020a), favor the invasion of exotic grass species (Gorgone-Barbosa et al 2016), and increase carbon emissions (Gomes et al 2020b). Thus, both extremes can be detrimental for the conservation of Cerrado ecosystems, stressing the need for a consistent national fire management policy (Durigan & Ratter 2016).…”

Phytotoxicity and allelopathic potential of extracts from rhizomes and leaves of Arundo donax, an invasive grass in neotropical savannas

“…Its establishment may result in losses of composition, structure, and functioning of native plant and animal communities and of ecosystem processes, which can often not be recovered (Bell, 1997;Coffman et al, 2010;Maceda-Veiga et al, 2016). This is especially critical in the Cerrado of Central Brazil, a complex of seasonal savannas and a hotspot of highly threatened biodiversity (Gomes et al, 2020). The propagation of A. donax in the Cerrado is favoured by the characteristics of its phytophysiognomies, with the dominance of open, herbaceous vegetation with scattered trees and shrubs, which is undergoing fast rates of degradation by human activities and increasingly frequent fires (Myers et al, 2000;Gomes et al, 2020).…”

“…This is especially critical in the Cerrado of Central Brazil, a complex of seasonal savannas and a hotspot of highly threatened biodiversity (Gomes et al, 2020). The propagation of A. donax in the Cerrado is favoured by the characteristics of its phytophysiognomies, with the dominance of open, herbaceous vegetation with scattered trees and shrubs, which is undergoing fast rates of degradation by human activities and increasingly frequent fires (Myers et al, 2000;Gomes et al, 2020). Colonization by this species increases fuel loads as well as fire frequency and intensity.…”