The Brazilian savanna at risk because of the combination of disturbances

Recently, the effects of climate change in the Amazon have captured the world’s attention, but the future of the Brazilian savanna is also at risk due to the synergy of climate change, defaunation and fires, reports a study published last May in the journal Ecological Modelling.

The Brazilian savanna is the second most diverse ecosystem in South America in terms of the number of plant species only after the tropical forests of the Amazon and the Atlantic Forest, explains conservation biologist Everton A. Maciel from the University of Campinas and first author of the publication.

And this ecosystem is not only important for its biodiversity. The savanna, a fire-dependent biome found in Africa, Australia and mainly South America, improves air and water quality, and acts as an important carbon sink. Maciel explains that the woody plants of the Brazilian savanna capture between 3 and 37 metric tonnes of carbon per hectare, depending on the type of savanna. This carbon is stored in the long roots that the plants in this ecosystem use to tap into underground water.

Maciel, who studies the effects that humans have on biodiversity and possible ways to mitigate them, says that he chose to work in the Brazilian savanna not only because of its high biological diversity, but because it is an ecosystem that, according to climate change models, will face major changes.

“[The] combination of different factors [rising temperatures, droughts, fire frequency and defaunation] will result in a great loss of biodiversity and ecosystem services,” Maciel says.

The loss will depend on the characteristics specific to the different species making up the savanna. According to the study, deciduous species, or those unable to regrow after a fire or that depend on animals to disperse their seeds, will be the most affected.

For their study, Maciel and nine other researchers from institutions in Brazil and Germany simulated the effects of these disturbances on the plant communities of three distinct areas: the open savanna, with crown cover of 10% or less, the woody savanna, in the heart of the Brazilian Cerrado, where trees of up to 14 metres high live, making up a crown cover of 40–60% and the savanna woodland with trees taller than 15 metres and 70% crown cover.

The researchers estimated the aerial biomass of 135 woody species, both deciduous and evergreen, at 8 sites in the open savanna, woody savanna, and savanna woodland using the FORMIND model. The team of scientists added information collected through bibliographical searches on height and diameter, as well as growth, mortality, fire tolerance, seed dispersal and carbon fixation. They used these data to model the biomass accumulation of woody species under different scenarios: higher temperature, longer dry season, higher frequency of fires and defaunation effects. The simulations were carried out both individually and in combination for a period of 1000 years.

When researchers modeled the effects in combination, species in all three types of savanna had  between  35% and 77% less aerial biomass, with the woody savanna being the most impacted. As if that were not enough, this would cause an increase in greenhouse gas emissions. The researchers also discuss in their article that biomass losses in the woody savanna could be due to the close relationship that woody species and seed-dispersing animals have – animals that would be absent in defaunation scenarios which would lead to an “extinction vortex.”

In terms of mitigating these effects, Maciel says that “the fragmentation in the savanna must stop” and adds that there is no reason to continue logging trees and using these lands for agriculture.

In their article, the researchers recommend managing fire, so they occur every 4 years, as they naturally do. “Fire is important for the savanna,” explains Maciel. “Without fire, diversity is also lost.” To manage fire, says the researcher, it is essential to implement measures that consider the knowledge that indigenous groups in the area have about fire.

Maciel emphasizes that the effects of climate change should be part considered when crafting conservation policies, both inside and outside protected areas and says that raising awareness of the wildlife of the savanna is necessary.

RESEARCH ARTICLE

Everton A. Maciel, Valeria F. Martins, Mateus D. de Paula, Andreas Huth, Frederico A.G. Guilherme, Rico Fischer, André Giles, Reinaldo I. Barbosa, Osmar Cavassan, Fernando R. Martins. Defaunation and changes in climate and fire frequency have synergistic effects on aboveground biomass loss in the brazilian savanna. Ecological Modelling 454. https://doi.org/10.1016/j.ecolmodel.2021.109628.

Mónica Pérez Monterrubio is an English and French translator and interpreter. She currently works towards a diploma in scientific translation.

English translation by Lorena Villanueva Almanza