Text by Mariana Dairel
Savannas are characterized by open physiognomies dominated by a rich and diverse herbaceous layer. One can picture very well by imagining Simba from The Lion King, running through the large open landscape with scattered shrubs and trees. These landscapes are representations of the African savannas, one of these grassy biomes that we have around the globe. In Brazil, we have systems like the African savannas, which we know as Cerrado.
But, why to talk about Cerrado and fire? The Cerrado evolved in the presence of fire, being resilient to it, and thus, after this disturbance, the vegetation community has a high capacity to regenerate. There are still many misconceptions and lack of knowledge about fire and it is necessary to demystify fire as the villain. To demonstrate one of the positive effects of fire, and I say in some cases even essential, in the Cerrado, MSc. Mariana Dairel and Dr. Alessandra Fidelis developed a study recently published in Seed Science Research.
After disturbance events, the vegetation community can regenerate by resprouting, or from seeds. Fire is a frequent disturbance in the Cerrado which consumes the aboveground biomass, which in turn increases the amount of bare soil, resulting in changes in the microclimate such as alterations in temperature fluctuation at the soil surface. Also, the passage of the flames influences directly the seeds due to the exposure to high temperatures. Thus, the objective of this study was to evaluate the effects of fire (direct and indirect) on the germination of seeds of native grasses.
Therefore, seeds of 10 representative native grass species were collected in different areas (Estação Ecológica de Itirapina – Southeastern Brazil, and Reserva Natural Serra do Tomabador - Central Brazil) and two experiments were carried out, aiming to mimic the passage of fire: daily temperature fluctuation (DTF) and heat shocks (HS). For daily temperature fluctuation, a germination experiment was set up in which seeds were exposed to a temperature fluctuation curve (19 ° -55 °C), evaluating the indirect effect of fire on seed germination. The heat shock evaluated the direct effects of fire on seed, by exposing seeds to different temperatures and time of exposure: 100 °C for 1 minute, 100 °C for 3 minutes, and 200 °C for 1 minute. After that, seeds were put to germinate. There was also a control treatment, in which the seeds were not submitted to any previous treatment before.
What was the result? Are these seeds resistant to fire? Germination of most species submitted to daily temperature fluctuation was not affected, and those species with seeds with dormancy had their germination increased. Positive point! Germination was increased with the indirect effects of fire in species with dormancy. When seeds were exposed to high temperatures, some species proved to have resistant seeds, and even when subjected to temperatures of 200 °C they were able to germinate. Now an interesting case: a species showed higher germination percentage after being subjected to temperatures of 200 °C. So interesting! It is a species that has physiological dormancy and it needs an extra factor to break this dormancy, allowing the germination and establishment in the system. In this case, the fire showed to be really important.
Now I return to the initial question: is fire always a synonym of destruction? In Brazil, the remaining fragments of Cerrado are in Protected Areas that still adopt the zero-fire policy, which directly compromises the conservation of these open physiognomies. Currently, much has been discussed about the use of fire as a management tool, aiming conservation and restoration of the Cerrado. As this study showed, fire is not always a villain, and for Cerrado species, it could also be the “good guy”, helping to maintain important ecological processes.
If you want to know more check these out: Dairel M, Fidelis A (2020). How does fire affect germination of grasses in the Cerrado? Seed Science Research 1–9. https://doi.org/10.1017/S0960258520000094
Projects:
Fire-adapted seed traits in Cerrado species (FAPESP 2019/09903-0)
How fire season affects Cerrado vegetation? (FAPESP JP 2015/06743-0)
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