On a Saturday in October, Adalberto Val, a biologist from the Brazilian National Institute of Amazonian Research (INPA) who specializes in fish, visited the Manaus municipal market, a neoclassical building in the city center. At the fish stalls, everything seemed normal, but he soon realized that something was wrong. “Fishers and traders told me that the quantity had decreased and the price for consumers had thus gone up,” he reported.
A decline in the supply of fish, a staple food in the region, is just one of the visible consequences of the intense droughts of recent years—2024 was one of the driest years in history, directly affecting around 700,000 people in the states of Amazonas, Acre, Roraima, Amapá, Rondônia, and Pará. Rivers hundreds of meters wide, such as the Solimões and the Tapajós, became mere streams running through sandbanks. On the banks were thousands or even millions of dead fish. There are no precise figures. “We cannot even list all the locations or intensities at which mortality occurred,” says Val.
Higher temperatures, which have fueled droughts in recent years (and in other parts of the country, more frequent forest fires), have less visible effects. As detailed by the INPA group in an article published in Animal Reproduction Science in March 2024, the sperm of tambaqui (Colossoma macropomum) lose mobility and speed in warmer waters and suffer more deformations, reducing egg fertilization rates and therefore negatively impacting species reproduction.
While the populations of some fish species have been able to recover, revived by the rains that returned at the end of the year, the effects of climate extremes, especially for larger species with lower fertility rates, such as the pirarucu (Arapaima gigas), can last for two or three years. Based on similar situations in previous years, several recent studies indicate that populations of not only fish, but also other animals and plants that grow back in the drought-hit forests, will probably be smaller and less diverse than before the episodes of extreme weather.
“We don’t normally associate fires with rivers, but fish are seriously harmed by them,” says Val. According to him, air-breathing fish species that come to the surface when they need air, such as the pirarucu, the South American lungfish (Lepidosiren paradoxa), and the electric eel (Electrophorus electricus), can end up breathing in toxic fumes, which can even be fatal. Furthermore, the biologist adds, the ash created by burning vegetation increases the alkalinity of the water, affecting other species.
Frequent burning of native vegetation can lead to the selection of species that are more resistant to high temperatures. In an experiment at INPA, biologist Derek Campos found that representatives of the characidae family are highly sensitive to heat and die when the temperature exceeds 32 degrees Celsius (oC). The characidae family includes species widely consumed in the Amazon region, such as the tambaqui and the jaraqui (Semaprochilodus spp.). According to this study, described in the Journal of Thermal Biology in February 2018, a small species called the angelfish (Pterophyllum spp.), now highly sought after as an ornamental species, was capable of resisting temperatures of up to 39 oC.
Controlled fire at Sempre-Vivas National Park, in the municipality of Diamantina, Minas Gerais, July 2023Gudryan Baronio / USP
“Apocalyptic landscape”
At the end of his PhD at the Federal University of Rio Grande do Sul, biologist Ismael Verrastro Brack joined a group of almost 20 people who assessed the impact of wildfires that destroyed more than 90% of the 108,000 hectares (ha) of the Sesc Pantanal reserve in Barão de Melgaço, Mato Grosso, between September and November 2020.
“In two open locations there were dozens of dead animals,” he says. Carcasses of tapirs (Tapirus terrestris), peccaries (Tayassu pecari), gray brockets (Mazama gouazoubira), Azara’s agoutis (Dasyprocta azarae), Azara’s capuchin monkeys (Sapajus cay), cougars (Puma concolor), and other animals were scattered among the burnt vegetation. “Everything was ash, like an apocalyptic landscape,” says the biologist. The intense destruction occurred in an atypical year that was very dry and was influenced by the El Niño climate phenomenon, resulting in enormous wildfires, much larger than commonly occur in both the Pantanal and the Cerrado.
Working in collaboration with Sesc employees, the researchers found hundreds of carcasses of medium and large animals. According to calculations described in a November article in Journal of Applied Ecology, approximately 50,000 mammals likely died in the reserve alone between January and October 2020.
A team led by veterinarian Walfrido Moraes Tomas of EMBRAPA Pantanal in Corumbá, Mato Grosso do Sul, also did field studies looking for dead animals along 114,000 km straight lines called transects. The team’s findings, described in Scientific Reports in December 2021, estimated that 17 million vertebrates died in wildfires across the Pantanal in 2020.
“These populations could recover within a few years if there were no more fires,” says Brack. The problem, he adds, is that the fires have reoccurred in subsequent years (see Pesquisa FAPESP issue nº 342). In 2024, the area affected by fire was 150% larger than the previous year, according to MapBiomas. The animals that survive tend to be left with less food and water and greater difficulty finding mates during breeding seasons.
Fires also modify the structure of the forest, according to a 2019–2020 experiment conducted in the Tapajós-Arapiuns Sustainable-Use Reserve in the Santarém region of Pará. Researchers from the Federal University of Pará (UFPA) evaluated 3,620 trees and palms of 326 species in 16 areas, classified into three categories: unburned old forest, burned once (in 2015), or burned twice (in 2015 and 2017). The 2015 fires in the sustainable-use reserve, triggered by a period of severe drought associated with the 2015 El Niño, which persisted until 2016, destroyed 1 million hectares (ha); in 2017, fires fueled by another period of intense drought, the ongoing impacts of the El Niño, and the flammability of wood that had been dried out the previous year added hundreds of thousands of ha to the areas already affected.
As described in Environmental Research Letters last October, the volume of forest (the biomass) above ground decreased by 44% in once-burned forest areas and by 71% in twice-burned forest. There was also a 50% reduction in species diversity in areas that had experienced two fires, after which small, fast-growing pioneer species less susceptible to fire predominated.
In the Cerrado (a wooded savanna biome), constant natural fires have led to the selection of trees with thicker bark, capable of withstanding high temperatures. However, faced with highly frequent fires, some species may become smaller or even die. “The trees are not very resistant to fires that occur as frequently as once or twice a year—there is no time for young individuals to develop thick bark,” says Vânia Regina Pivello, a biologist from the University of São Paulo (USP). In an article published in Fire Ecology in April 2011, she warned about the damage to diversity being caused by intensifying forest fires in the Amazon, highlighting the contrast with the Cerrado, where many plants, especially ground cover, benefit from periodic fires.
It is not just trees that diminish in size as a result of frequent fires. Several everlasting species (Comanthera spp.), some of which are already at risk of extinction, return smaller and grow more slowly when subjected to annual fires, according to experiments carried out at Sempre-Vivas National Park, Minas Gerais, by USP biologist Gudryan Baronio.
It was a good place to evaluate the effects of forest fires because craftspeople who make products from everlasting flowers use controlled burns in the region to stimulate plant growth. With the support of the team from the park, the researchers studied two areas, each with eight plots (four burned for the experiment and four unburned), at the beginning and end of the dry season, in May and September 2019 respectively.
The objective, as described in an article published in the scientific journal Flora in November, was to verify not only the immediate effects of fire on plants, but also the impact of the time of year. Late fires that occur at the end of the dry season tend to be naturally more intense than early fires that occur at the beginning of the dry season, when the vegetation and soil still retain some moisture.
“After two years, the herbaceous vegetation that was affected by early fires had recovered almost completely, but plants affected by late fires had only partially recovered,” says Baronio. “For both, however, the height of the plants that regrew was on average four centimeters (cm) lower than in the control group.” Depending on the species, adult everlasting plants are typically 8 to 24 inches (20 to 60 cm) tall.
The research is part of a project led by Pivello that is funded by the Brazilian National Council for Scientific and Technological Development (CNPq) and has resulted in recommendations for flower collectors. “Burning every year is out of the question, as there is no time for the rupestrian vegetation to recover,” she says. “We need to rethink when, where, and how to use controlled fire—which is an important strategy for traditional vegetation management and park managers—so as to reduce combustible material and prevent forest fires, which are difficult to control.”
The story above was published with the title “Less life in the forest” in issue 347 of january/2025.
Projects
1. How does fire management affect interactions between plants, pollinators, and ants in rupestrian grasslands? (nº 21/09247-5); Grant Mechanism Postdoctoral Fellowship in Brazil; Supervisor Vânia Regina Pivello (USP); Beneficiary Gudryan Jackson Baronio; Investment R$269,092.13.
2. Reproductive success of plants and their responses to fire: The role of pollen deposition (nº 23/04378-0); Grant Mechanism Postdoctoral Fellowship Abroad; Supervisor Vânia Regina Pivello (USP); Beneficiary Gudryan Jackson Baronio; Investment R$378,467.44.
Artigos científicos
BARONIO, G. J. et al. Vegetation dynamics after fire in the Brazilian campo rupestre: Effects on native plant communities and flower harvesting. Flora. vol. 320, 152611. nov. 2024.
BRACK, I. V. et al. Spatial modelling and estimation of mammals’ mortalities by Pantanal 2020 megafires. Journal of Applied Ecology. vol. 61, no. 11. nov. 2024.
CAMPOS, J. F. et al. The influence of lifestyle and swimming behavior on metabolic rate and thermal tolerance of twelve Amazon forest stream fish species. Journal of Thermal Biology. vol. 72, pp. 148–54. feb. 2018.
CASTRO, J. da S. et al. In vivo exposure to high temperature compromises quality of the sperm in Colossoma macropomum. Animal Reproduction Science. vol. 262, 107412. mar. 2024.
PEREIRA, C. A. et al. Recurrent wildfires alter forest structure and community composition of terra firme Amazonian forests. Environmental Research Letters. vol. 19, no. 11. oct. 8, 2024.
PIVELLO, V. R. The use of fire in the Cerrado and Amazonian rainforests of Brazil: Past and present. Fire Ecology. vol. 7, pp. 24–39. apr. 1, 2011.
TOMAS, W. M. et al. Distance sampling surveys reveal 17 million vertebrates directly killed by the 2020’s wildfires in the Pantanal, Brazil. Scientific Reports. vol. 11, 23547. dec. 16, 2021.
