How often should we burn the Cerrado? The effect of fire frequency on Cerrado communities

Author(s)

Cassy Anne dos Santos Rodrigues

• Document type: Master's Dissertation
• Press: Rio Claro. 2020-01-27.
• Institution: Universidade Estadual Paulista (Unesp). Instituto de Biociências. Rio Claro
• Defense date: 2019-11-29
• Advisor: Alessandra Tomaselli Fidelis

Abstract

The Cerrado is formed by grasslands and savannah physiognomies, evolved in the presence of fire and depends on it to maintain its physiognomies and biodiversity. The fire regime influences the plant community assembly, the regeneration and the competitive abilities of the plants. Frequency is one of the factors of the fire regime and changes in it can be detrimental even to fire-adapted plants and communities. Therefore, this study aimed to understand the effects of different fire frequencies in campo sujo of Cerrado communities. For this, vegetation surveys and biomass collection were carried out in areas with different fire histories (excluded from fire, burned annually and biennially), which provided community composition and productivity data. Surveys, including coverage (%) by species, were performed on 10 1x1m subplots per treatment (10 subplots / treatment, 3 treatments, 4 plots / treatment). We also evaluated through propagation rate (m.s-1), firing efficiency (%) and intensity (kW.m-1) among other fire parameters, the effects of different frequencies on fire behavior. Our results showed that species richness of plant communities was higher in areas with annual fire frequency than in excluded areas 6 months after fire and higher for biennials than those excluded 12 months after fire. The diversity index was higher in the annual burn treatment before and 12 months after the burns. Regarding the number of species per functional group, only the forbs presented increase and only in the plots with burns. Moreover, we found differences in the percentage of coverage according to the growth form, only the forbs between the burn treatments and the exclusion fire plots. Regarding the cover, the percentages of dead biomass and bare soil vary among fire histories. The plots with lower burning frequency showed about 7 times more dead biomass coverage than the other treatments. These results suggest that 6 years of fire exclusion begin to cause loss and changes in species cover pattern. Regarding fire behavior, we found for communities with annual burns less dead and total biomass and higher percentages of bare soil than with biennial burns. Regarding the burning parameters, the intensity, flame height, maximum temperatures and residence time were lower in the annual plots. Higher frequency of fire changed vegetation structure and burning parameters responded to these changes. We conclude that the frequency of burning influences fire behavior, affecting the increase of dead biomass. Plant communities under annual burns have not accumulated the same amount of dead biomass as biennial burns, therefore they have higher percentages of bare soil. This combination affects the fire behavior due to a decrease and discontinuity of available fuel load, which makes it difficult to sustain and spread the fire. Thus, we aimed through this study to understand the influence and importance of fire frequency on the dynamics and assembly of Cerrado plant communities, as well as on the behavior of fire. This should contribute to the development of fire management strategies for the conservation of this ecosystem. (AU)

• FAPESP's process: 17/22618-7 - How often should we burn the Cerrado? the effect of fire frequency on Cerrado communities
• Grantee: Cassy Anne dos Santos Rodrigues
• Support Opportunities: Scholarships in Brazil - Master