Having suffered damage to 45.6% of its original vegetation, the biome is becoming warmer, drier, and more prone to large fires.
Rain forming over the Cerrado area of the Jalapão State Park
Fabio Colombini
The Cerrado (wooded savanna), the second largest biome in Brazil and one of the richest in plant and animal diversity, is under threat. The rapid elimination of native vegetation—which this century has occurred at a rate of 0.5% of its area per year, twice as fast as observed in the Amazon—and subsequent conversion of the lands into vast pastures and soy, corn, cotton, and sugarcane farms are changing the ecosystem’s ecology and climate in ways that may be irreversible in some regions. In the dry months, the Cerrado is now up to 4 degrees Celsius (°C) warmer than it was in the 1960s, as well as drier. In some places, it has also been suffering from longer, more intense, and more frequent fires than in previous decades.
These changes, which are now being reflected in systematic measurements and field observations taken by Brazilian researchers, could have significant impacts on fauna and flora in the Cerrado, leading to local extinctions. They could also reduce water availability, negatively affecting the 20 million people who live in the biome and the agribusinesses that have thrived there in recent decades. “The Cerrado is already suffering the consequences of the changes taking place on a local, regional, and global scale,” says Mercedes Bustamante, an ecologist from the University of Brasília (UnB) who specializes in the conservation and sustainable use of this ecosystem.
Over the past 36 years, the Cerrado has lost almost 20% of what was left of its original vegetation. Between 1985 and 2020, roughly 26.5 million hectares of the biome’s three main types of native formation (grassland, savanna, and forest) gave way to new areas for cattle farming and mass production of commodities, according to the most recent report by the Annual Mapping Project for Land Use and Cover in Brazil (MapBiomas), released in September this year. The area of grassland, savanna, and forest lost in this period is almost equivalent to the size of Ecuador and is larger than the area of 120 other countries.
Covering an area of two million square kilometers (km2), corresponding to a quarter of Brazil’s territory, the Cerrado originally occupied the entire central region of the country, from the south of Piauí and Maranhão in the Northeast to the north of Paraná in the South. Today, however, only 54.4% of this area remains covered by native vegetation—and a much smaller proportion (around 20%) is unaltered. With 45.6% of its area now converted into farmland, pasture, roads, hydroelectric plants, and cities, the Cerrado is the second most altered Brazilian biome by human action, second only to the Atlantic Forest, which has lost almost 90% of its original territory.
Some of the effects of this radical transformation of the landscape and land use are increasingly evident: the Cerrado is becoming hotter, drier, and consequently, more prone to devastating fires. Recent studies by research teams from around the country have provided evidence of warmer, drier conditions and a rising number of major fires.
In an article published in the journal Global Change Biology in May, Gabriel Hofmann, a geographer currently studying his second doctorate at the Federal University of Rio Grande do Sul (UFRGS), calculated the temperature increase in the Cerrado over the last 60 years. Together with colleagues from the Brazilian National Institute for Space Research (INPE), the National Museum at the Federal University of Rio de Janeiro (UFRJ), and the Oswaldo Cruz Foundation (FIOCRUZ), Hoffmann evaluated temperature and humidity data collected between 1961 and 2019 by 45 weather stations across the biome and compared them with satellite measurements. They concluded that the average temperature in the Cerrado during the dry season rose by 2.2–4 °C and the relative humidity dropped by 15%.
One possible explanation for the drier conditions is the conversion of native vegetation into farmland and pastures. A team led by Edson Wendland, an engineer from the University of São Paulo (USP), São Carlos, who specializes in water resources, conducted experiments in an area of Cerrado in Itirapina, São Paulo State, and found that in one year, an area with shrubs and trees typical of the savanna ecosystem releases 30% more moisture into the atmosphere than other areas of the same size covered by sugarcane or pasture. “Replacing large vegetation with plants of smaller stature alters water circulation in the different environmental compartments. More water penetrates the soil and reaches the water table, leaving the air drier because of less plant transpiration. We still don’t know if this effect is local or if it can impact the entire ecosystem,” says Wendland.
In the six decades analyzed by Hofmann and his colleagues, there were significant changes to the landscape and land use in much of the Cerrado. “Deforestation, which initially took place in small areas to extract charcoal or establish pastures for subsistence cattle farming, gave way to the felling of extensive stretches of native vegetation to make room for large pastures and monoculture,” recalls the geographer.
During this period, the greatest increase was to the maximum temperature recorded in the early afternoon, although the minimum, measured at night, also increased significantly. The warming was most evident in October, in the transition between the end of the dry season and the beginning of the rainy season. At temperatures of around 33 °C, October 2019 was 4 degrees warmer on average than the same month in 1961. At night, the average temperature was approximately 22 °C, up to 2.8 degrees higher than 60 years prior. Projections made by the group suggest that the phenomenon is likely to worsen, with temperatures in both the day and night rising by another 2 degrees by 2050.
The warming observed in the Cerrado is well above the 0.2 °C increase per decade forecast for the southern hemisphere a few years ago by the Intergovernmental Panel on Climate Change (IPCC). According to the study authors, the process follows a pattern that suggests it is caused by changes in land cover and use. The pattern is marked by greater temperature increases in the daytime (maximum) than in the night (minimum).
In the last 60 years, the average temperature of the Cerrado has risen by 2.2–4 °C in the dry season and the relative humidity has decreased by 15%
To understand how the researchers concluded that climate change is not the primary factor, it must be remembered that the planet’s ecosystems consume much of the light energy they receive from the Sun through photosynthesis and evapotranspiration. During the day, solar radiation crosses the atmosphere almost without heating it and bathes the vegetation. A significant proportion of this energy (25%) is used by plants to synthesize carbohydrates (glucose) via photosynthesis, with large volumes of water vapor released into the atmosphere via evapotranspiration. When native vegetation is replaced by crops that leave the land bare or covered with straw for part of the year (usually in the dry season), the energy previously used in photosynthesis and evapotranspiration goes straight to the soil, which heats up more during day and increases the air temperature near the ground. “If the phenomenon were caused exclusively by climate change and the increased amount of greenhouse gases in the atmosphere, you would expect to see a greater rise in night-time temperatures,” explains Hofmann. These gases trap the heat stored near the Earth’s surface during the day and released into the atmosphere in the evening, reducing cooling overnight.
The authors also noted that during the period analyzed, the formation of dew became less common. Caused by the condensation of water vapor in the air when it makes contact with a cooler surface, dew serves as a water source—especially in dry months—for plants with short roots or those that grow on rocks (for example, those of the genus Vellozia) or other plants (bromeliads, orchids, and lianas). Dew on vegetation and the ground is also important for insects and other small animals that generally stay in one place.
“Many plants in the Cerrado seem to depend on dew. If it continues to become less likely to occur, the effect could be disastrous for some flora,” says Rafael Oliveira, a botanist from the University of Campinas (UNICAMP) who is investigating the influence of fire and water availability on certain formations in the biome. The impact of dew reduction, according to Hofmann, could affect biodiversity at different scales. “It can harm individual growth and reproduction, eliminate certain populations, and alter the ecological relationship between different species,” says the UFRGS researcher.
In parallel with the increasing temperatures and decreasing humidity, the Cerrado is also facing changes in relation to wildfires. In the last two decades, small fires have decreased in number and frequency while larger, stronger fires have increased. Based on satellite data, a group led by Renata Libonati, a meteorologist at UFRJ, evaluated the frequency, intensity, duration, seasonality, and size of fires in the Cerrado between 2001 and 2019, superimposing the information over a map of the 19 regions with distinct ecological characteristics (ecoregions) into which the biome is divided.
Two-thirds of the area burned each year is located in just five of the 19 ecoregions, the researchers describe in an article published in the Journal of Environmental Management in October. The largest, most intense and frequent fires occur in the northern half of the Cerrado, which is home to almost 90% of the biome’s remaining native vegetation and has suffered the most from agricultural expansion since the mid-1980s.
After a fire, shrubs blossom in Chapada dos Veadeiros: the herbs Bulbostylis paradoxa…Rafael Oliveira / Unicamp
The most affected areas are the north of Mato Grosso and west of Maranhão, in a transition zone between the Cerrado and the Amazon that has been significantly altered by humans and is known as the Arc of Deforestation, as well as in the ecoregions located in Matopiba, covering the state of Tocantins and parts of Maranhão, Piauí, and Bahia. “The southern region of the Cerrado features agricultural areas that have been well established since last century and the remaining native vegetation is highly fragmented, making large fires less likely to occur,” explains Libonati.
The risk of fires in Matopiba could still get worse. Encompassing 337 municipalities in over 73 million hectares (almost a third of the Cerrado), this region is important to domestic soy, corn, and cotton production. Over the past three decades, its climate has undergone major changes, with a potential impact on agriculture and native vegetation.
Analyses recently submitted for publication in a scientific journal by a team led by climatologist José Marengo confirm the trends observed by the UFRGS group and indicate that Matopiba is 1.2 °C warmer today than it was in 1981. According to the group’s projections, the temperature there will continue to increase at a rate of 0.45 °C per decade for the rest of this century. The average number of consecutive dry days also increased and the rainy season now begins a month later than in the past.
“These changes seem to be the result of a combination of the effects of global warming and land use changes in the region,” says Marengo, research coordinator at the Brazilian Center for Natural Disasters Monitoring (CEMADEN) run by the Ministry of Science, Technology, and Innovations (MCTI) and coordinator-general of the National Institute of Science and Technology (INCT) for Climate Change, funded by FAPESP. “The delayed arrival of the rain alters river supply and increases the risk of fires,” says the climatologist.
This is not the only threat to agriculture in Matopiba. Marcia Zilli, an environmental engineer currently on a postdoctoral fellowship at Oxford University, UK, recently used a computer model to assess how 18 Brazilian agricultural crops, five forestry products, and seven livestock products will be affected until 2050. The model takes into account the competition for land between agriculture, the restoration of native vegetation, and the production of renewable energy for both an optimistic climate change scenario (with a temperature increase of 1.7 °C by the middle of the century) and a pessimistic one (2 °C). Described in an article publiched in the journal Science of the Total Environment in 2020, the results indicate that in both situations, soybean and corn production would decrease in Brazil, especially in Matopiba, due to unfavorable climate conditions. As a result, some farms would move to the south and southeast of the country.
Like the savannas of Africa and Australia, the Cerrado is an environment naturally shaped by fire. Many of the 12,699 plant species in the biome have fire-resistant characteristics—seeds that only germinate after being burned, trunks covered with a thick layer of cork, and fruits with tough skins—which emerged around 4 million years ago, at the same time as many grasses, which are highly flammable in the dry season. There is evidence that fires have naturally been occurring in the planet’s savannas for millions of years. In the 1990s, scientists studied fragments of coal trapped in deep layers of sediment and concluded that fires were a frequent occurrence in the Cerrado 12,000 years ago. There are also signs that human groups living in the biome used fire to alter the landscape at least 4,000 years ago.
“Many plant species in the Cerrado benefit from fire. They produce more flowers and seeds after a fire,” says Giselda Durigan, a forestry engineer and researcher at the São Paulo Institute for Environmental Research (IPA), who has been studying Cerrado management and restoration strategies for nearly three decades. Under her guidance, biologist Natashi Pilon compared the flower and seed production of 47 plant species from two areas of the Cerrado—one that experienced fires six months earlier and the other that had not. According to the results, published in Plant Ecology & Diversity in 2018, 63% of the plant specimens bloomed in the burnt regions, compared to 19% in the area not affected by fire. “Fire induced flowers to bloom in 79% of the species studied, including 20 that only produced flowers after burning,” says Durigan.
Experts say that the Cerrado’s characteristic mosaic of fields, savanna, and forest is influenced by fires. Fires started by lightning at the beginning of the rainy season—the Cerrado region has one of the highest lightning strike rates in the country—seem to be less intense and burn a smaller area, since they are often extinguished by rain. These small fires, which are also sometimes started and controlled by humans, burn dead biomass and help maintain the Cerrado’s characteristic mosaic pattern formed by patches of open vegetation (fields) and savanna (with trees of varying sizes).
The predominance of open landscapes, which represent almost 40% of the Cerrado, actually seems to be essential to the biome’s ability to function as a large water collector. Without larger vegetation, rainwater infiltrates the soil and supplies the water table and rivers. “This is one of the main ecosystem services the Cerrado provides to society,” says Durigan.
…and a field of Paepalanthus chiquitensisRafael Oliveira / Unicamp
Controlled, low-intensity fires also help to prevent larger ones. The protective effect of this landscape management strategy was observed by teams led by Libonati and Isabel Schmidt, a ecologist from UnB. Together with their colleagues, they monitored fire dynamics between 2003 and 2018 in two areas of the state of Tocantins where integrated fire management was implemented in 2015: the Xerente Indigenous Reservation and the Araguaia Indigenous Park. The use of fires at specific times of the year reduced the frequency, scale, and intensity of major fires, according to an article published in the journal Fire in September.
“The Cerrado suffers more from fires than any other biome in Brazil. On average, 6 million hectares—corresponding to 3.3% of its total area—catch fire every year,” says Ane Alencar, a geographer from the Amazon Environmental Research Institute (IPAM) and head of the MapBiomas team that analyzes the Cerrado. According to data published in September, 36% of the biome caught fire at least once in the last 36 years. Of this area, 60% was burned more than once and 15% more than five times in the period.
The problem, as Libonati’s group found, is the change in fire patterns. “What we are seeing is not consistent with natural fires, which occur at the beginning of the rainy season and are smaller and less intense,” says Vânia Pivello, a biologist from USP studying the effects of fire on the Cerrado. “The increased intensity of the fires and the reduced interval between them modify the structure and diversity of the vegetation,” he says. There are also signs that many of these fires are caused by human activity (intentional or accidental). Satellite monitoring by INPE shows that more than 60,000 fires were recorded in the Cerrado in more than half of the years since 1998. Almost 90% of them occurred during the dry period, when there is less lightning.
The lower rainfall and more frequent fires lead to impacts on vegetation that would normally be wetter and thus would not burn, such as riverside forests, which provide shelter to many animals (see the article “Fire on the riverbanks” on the Pesquisa FAPESP website). “Fires in these forests affects fauna much less adapted to fire,” says Reuber Brandão, a zoologist from UnB. “In some regions, this impact of fire is exacerbated by the use of water to irrigate crops,” he says. For over 20 years he has been studying amphibians and reptiles in western Bahia, where the use of water for agriculture has increased dramatically. As a result, the water table has dropped, causing lakes and large swamp areas to dry up and some populations of frogs, lizards, and snakes to disappear.
Projects 1. Transitioning to sustainability and the water-agriculture-energy nexus: exploring an integrative approach with case studies in the Cerrado and Caatinga biomes (nº 17/22269-2); Grant Mechanism Research Program on Global Climate Change; Principal Investigator Jean Pierre Ometto (INPE); Investment R$2,983,408.46. 2. Water availability and contamination risks in outcrop areas of the Guarani Aquifer System (nº 15/03806-1); Grant Mechanism Bioen Program; Principal Investigator Edson Cezar Wendland (USP); Investment R$1,993,093.16. 3. INCT for Climate Change (nº 14/50848-9); Grant Mechanism Research Program on Global Climate Change; Principal Investigator José Antonio Marengo Orsini (CEMADEN); Investment R$4,149,665.28. 4. Effect of prescribed burning and frost on the diversity and structure of the herbaceous-shrub stratus of the Cerrado (nº 16/17888-2); Grant Mechanism Doctoral (PhD) Fellowship; Supervisor Giselda Durigan (IPA); Grant Beneficiary Natashi Aparecida Lima Pilon; Investment R$178,118.16.
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