Rainforests Could Turn Into Savannas as Climate Warms, New Study Warns

Ranchland in the Cerrado tropical savanna of Brazil.

BYMalavika VyawahareMongabayPUBLISHEDApril 12, 2021SHAREShare via FacebookShare via TwitterShare via Email

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This story originally appeared in Mongabay and is republished here as part of Covering Climate Now, a global journalism collaboration strengthening coverage of the climate story.

As the planet warms, it isn’t just humans who are feeling the heat — trees are too. Rising temperatures are disrupting a primary engine of life on Earth: photosynthesis.

A recent study from Brazil adds to fears that climate change is altering the face of the planet. Literally. Tropical forests could look more and more like deciduous forests or savannas in the future, according to the research based in Brazil’s Cerrado biome. This ecoregion abjacent to the Amazon Rainforest is where savanna, grasslands and forests mingle.

The paper, published in Environmental Research Letters in March, focused on four trees species found in both the Amazonian tropical forests and savanna land: Qualea parviflora, known as pauterra in Portuguese; Pseudobombax longiflorum, or the Brazilian shaving-brush tree; Hymenaea stigonocarpa (jatobá do Cerrado); and Vatairea macrocarpa, also known as angelim.

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“The article extends present knowledge of heat tolerance to tropical species in particularly hot regions, testing species not tested before,” said Gotthard Heinrich Krause, professor of plant physiology at Heinrich Heine University Düsseldorf, Germany.

Krause, who was not involved with the study, noted that the paper underlines how “increased number of extreme heatwaves, often combined with drought stress,” compound the heat stress faced by trees.

The maximum temperatures in the Cerrado region and neighboring forests can reach 45° Celsius (113° Fahrenheit). The area has warmed perceptibly in recent decades, and heat waves that regularly sweep the region are becoming hotter and dryer.

How much a leaf warms depends on how much solar radiation it absorbs and what it loses through conduction and as long-wave radiation. Leaves facing the harsh tropical sun heat up faster than the ambient air around them.

Igor Araújo installing thermal boxes on trees to measure the temperature of leaves.

Prolonged exposure to heat can induce damage to leaf tissue, compromising photosynthetic efficiency and, consequently, trees’ fitness,” said Igor Araújo, first author of the new paper and an ecologist at the Mato Grosso State University, Brazil.

The disproportionate warming in the Cerrado belt is driven not just by global temperature rise, but also by local deforestation and fragmentation of wooded areas. As pastureland and cropland have eaten away into forests, their cooling effect is becoming muted.

Trees cool themselves and areas around them by transpiring water through the stomata dotting their leaf surfaces. This process, along with evaporation, is also why forested areas induce rainfall. “One single adult tree in the Amazon can transpire up to 1000 L [264 gallons] of water per day, functioning as a natural air conditioner of the environment. This process is called biotic pump, which is reduced by deforestation,” Araújo said.

When faced with scorching heat and dry spells, the pores on leaves clamp shut to conserve water. “This will reduce or prevent transpirational cooling of leaves, causing substantial increases of leaf temperature above air temperature,” Krause said.

The study estimated, for the first time, what temperatures leaves can tolerate. To do this, the authors calculated the temperature at which a critical component of the photosystem breaks down and the temperatures that leaves are experiencing. The difference between the two levels is called the thermal safety margin (Tsm).

Krause said he expected that the temperature at which scientists observe permanent damage to leaf tissue to be higher than what the researchers estimate. This would mean a wider safety net, but it still would not be enough to protect most species considered in the research, given the current pace of warming.

Such a hostile environment is dangerous for leaves and trees. The tree is not shedding leaves as part of a seasonal cycle but rather because they are not performing their function of harnessing energy.

The authors found that in some species, the maximum leaf temperatures are already exceeding this threshold. But if average temperatures rise by even 2.5°C (4.5°F), this will be true for most tree species, they estimate. With a 5°C (9°F) rise, all tree species studied will suffer from leaf burn.

It’s not just tree health that declines; other scientists have shown that heat stress also affects carbon dioxide uptake by trees. According to Krause, there is a reduction in the CO2 absorbed by plants even at temperatures lower than those that short-circuit photosynthesis. “Such reduction will contribute to the reduction in carbon sink of the tropical forest,” he said.

At the moment, savanna species adapted to higher temperatures are doing better than the rainforest species. “Our results thus indicate expected shifts in deciduousness in the future and thus a trend towards savanna vegetation replacing forests in the regions in Southern Amazonia characterized by large patches of deforestation,” the authors write.

What is happening at the Amazon-Cerrado boundary may be a precursor for feverish tropical forests across the world. Unlike humans, these forests won’t have air conditioners or sunscreens to protect them.


Araújo, I., Marimon, B. S., Scalon, M. C., Fauset, S., Marimon Junior, B. H., Tiwari, R., … Gloor, M. U. (2021). Trees at the Amazonia-Cerrado transition are approaching high temperature thresholds. Environmental Research Letters, 16(3), 034047. doi:10.1088/1748-9326/abe3b9

Tiwari, R., Gloor, E., Cruz, W. J., Schwantes Marimon, B., Marimon‐Junior, B. H., Reis, S. M., . . . Galbraith, D. (2020). Photosynthetic quantum efficiency in south‐eastern Amazonian trees may be already affected by climate change. Plant, Cell & Environment. doi:10.1111/pce.13770

We are entering an era of pandemics – it will end only when we protect the rainforest

Peter Daszak

Reducing deforestation and the exploitation of wildlife are the first steps in breaking the chain of disease emergence

Tue 28 Jul 2020 01.00 EDTLast modified on Wed 29 Jul 2020 14.10 EDT


Transportation of timber logs, Amazon rainforest Brazil
 Logging in the Brazilian rainforest. ‘Human activity has created a continuous cycle of viral spillover and spread.’ Photograph: Brazil Photos/LightRocket via Getty Images

In late 2013, in the village of Meliandou in rural Guinea, a group of children playing near a hollow tree disturbed a small colony of bats hiding inside. Scientists think that Emile Ouamouno, who later became the first tragic “index” case in the west African Ebola outbreak, was likely exposed to bat faeces whileplaying near the tree.

Every pandemic starts like this. An innocuous human activity, such as eating wildlife, can spark an outbreak that leads to a pandemic. In the 1920s, when HIV is thought to have emerged in what is now the Democratic Republic of the Congo, scientists believe transmission to humans could have been caused by a bushmeat hunter cutting themselves while butchering a chimpanzee. In 2019, we can speculate that a person from south-west China entered a bat cave near their village to hunt wildlife for sale at the local wet market. Perhaps they later developed a nagging cough that represents the beginning of what we now know as Covid-19.Now, a growing human population, ever-encroaching development and a globalised network of travel and trade have accelerated the pace of pandemic emergence. We’re entering a new pandemic era.Advertisementhttps://6e1601c5dd35a5062108976ebb5bcf12.safeframe.googlesyndication.com/safeframe/1-0-37/html/container.html

Most pandemics begin in the emerging disease hotspots of the world; the edges of forests in regions such as west Africa, the Amazon basin and south-east Asia. Tropical rainforests are home to a rich diversity of wildlife, which in turn carry an array of viruses. We know far more about these animals than we do about the viruses they carry. An estimated 1.7m viruses exist in mammals and birds (the origins of most pandemics), but less than 0.1% have been described. They spread to millions of people each year; though they often don’t cause noticeable symptoms, the sheer volume means that plenty can.

Before humans became an agricultural species, our populations were sparser and less connected. A virus infecting a hunter-gatherer might only reach family members or perhaps a hunting group. But the Anthropocene, our new geological epoch, has changed everything. A great acceleration of human activity has dramatically altered our planet’s landscapes, oceans and atmosphere, transforming as much as half of the world’s tropical forest into agriculture and human settlements.

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About one-third of emerging diseases are the product of these rapid changes in land use, as people are pushed into contact with wildlife they would once have rarely encountered. The viruses that emerge, such as Zika, Ebola and Nipah, include the latest of our foes, Covid-19, transported from the altered rural landscape of China to a city near you.

Human activity has created a continuous cycle of viral spillover and spread. Our current approach is to wait for outbreaks to start, and then design drugs or vaccines to control them. But as we’ve seen with Covid-19, this approach isn’t good enough: while we wait for a vaccine, hundreds of thousands of people have died, and millions have been infected. By the time the US produced sufficient doses to vaccinate against the H1N1 influenza pandemic in 2009, the virus had already infected about a quarter of the people on our planet.

If we are to prevent future pandemics, we will need to reassess our relationship with nature, blocking each step in the chain of disease emergence. This should begin with reducing the rampant consumption that drives deforestation and wildlife exploitation. We’ll also need to remove viral-risk species from wildlife markets, crack down on the illegal wildlife trade and work with communities to find alternatives. We should be putting more pressure on industries that harvest tropical timber and wildlife products, rewarding corporate sustainability and legislating against overconsumption. Consumer-led campaigns against palm oil, for example, have had a ripple effect on sustainability.

In a recently published paper, a number of scientists, myself included, laid out the economic case for preventing the disease spillover that leads to pandemics by reducing deforestation and the wildlife trade. We estimate that the annual costs of programmes to reduce deforestation and the wildlife trade and build pandemic surveillance in disease hotspots would be $17.7–26.9bn, more than three orders of magnitude smaller than the current estimate cost of Covid-19 economic damages, of $8.1-15.8tn. Our costs include the collateral benefits of carbon sequestration by reducing forest loss. While the coronavirus pandemic has devastated the global economy, our current trajectory could see the cost of future pandemics rocket into the tens of trillions.

As we rebuild our economies after the coronavirus pandemic, rather than returning to the system of unchecked consumption that brought us Covid-19, we have an opportunity to green our economies. Centuries of environmental exploitation have put us in a fragile position on this planet. While some may balk at the costs of avoiding environmental breakdown, or fail to understand the value of preserving a species of butterfly, frog or fish, most of us recognise that Covid-19 has brought death and economic misery on a global scale. Once we accept that human activity is what led to this, we may finally be empowered to escape the pandemic era.

• Peter Daszak is president of EcoHealth Alliance, a non-profit dedicated to analysing and preventing pandemics

Earth Overshoot Day Shows We’re Devouring The Planet’s Resources Much Too Fast

We need 1.7 planets to fulfill our appetite for stuff. And it’s getting worse.

Global Footprint Network, an international nonprofit that calculates how we are managing ― or failing to manage ― the world’s resources, says that in the first seven months of 2018 we devoured a year’s worth of resources, such as water and fibers like cotton, to produce everything from the food on our plates to the clothes we’re wearing and the gas in our cars.

This year sees the earliest Earth Overshoot Day since the 1970s, when humanity’s resource consumption first started to exceed what the planet could renew in a year.


“At the moment, we’re able to live in this ecological debt by using up the Earth’s future resources to operate our economies in the present ― in other words, we’re running a Ponzi scheme with our planet,” Mathis Wackernagel, CEO of Global Footprint Network, told HuffPost. “It might work for now, but as we dig ourselves deeper into debt it will eventually all fall apart.”

Wackernagel said he is certain that humanity will move out of overshoot. “The question,” he said, “is whether we do so by design or by disaster.”

Rampant deforestation, acute freshwater shortagescollapsing fisheries and dramatic biodiversity loss show some of the ways that our overuse of resources is already being felt.

There’s a human cost to all of this, said Michael O’Heaney, executive director of environmental campaign group The Story of Stuff.

“When we don’t live in harmony with the Earth’s ability to sustain itself, people get hurt ― you see ecosystem collapse in places primarily impacting poor people, people in the global south,” O’Heaney said.

Research indicates that while the effects of climate change will be felt everywhere, the poorest nations will be hit hardest.

Yet it’s some of the wealthiest countries that are creating the most ecological debt. If the world’s population lived like the U.S. currently does we would need five planets to sustain consumption levels, according to Global Footprint Network’s data. In contrast, if the world lived like India we would require only 0.7 of a planet to maintain annual resource demands.

Globally, we’re using up nature 1.7 times faster than our planet’s ecosystems can regenerate. In other words, our planet relies on 1.7 planets worth of resources.


“This is not an individual consumer problem,” said O’Heaney. “There’s a systemic problem here ― we have a system that chews up resources, creates products using those resources, spits them out and then makes them so that they’re not durable, makes them so that people throw them away. Take the example of bottled water. We all did fine without water in plastic bottles 25 years ago.”

As corporations have convinced us that we need things like bottled water, governments have been doing an increasingly bad job of protecting our natural resources, O’Heaney said.

Ultimately, he said, the solution lies in transitioning away from the “dinosaur economy” that relies on rampant consumption of resources and is powered by fossil fuels, and instead pushing for economies that use sustainable materials and run on renewables.

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HuffPost’s “This New World” series is funded by Partners for a New Economy and the Kendeda Fund. All content is editorially independent, with no influence or input from the foundations. If you have an idea or tip for the editorial series, send an email to thisnewworld@huffpost.com. 

Brazil abolishes huge Amazon reserve in ‘biggest attack’ in 50 years


To Brazil’s National Congress, the Special House Committee, and President Michel Temer:

We demand that you listen to the appeal of the Brazilian people and stop, once and for all, passing laws, decrees, and any other irresponsible legislative measure to please the interests of powerful parties and politicians. This abuse triggers deforestation and the irreversible destruction of the Amazon rainforest, which is part of the shared heritage of humanity for present and future generations.


Brazilian court blocks abolition of vast Amazon reserve (The Guardian)
https://www.theguardian.com/environment/2017/aug/30/brazilian-court-blocks-abolition-of-vast-amazon-reserveBrazil abolishes huge Amazon reserve in ‘biggest attack’ in 50 years (The Guardian)

Temer pushes Amazon deforestation bill in Brazil (Financial Times)

Activists decry Temer’s Amazon deforestation bill (Al Jazeera)