MSU researcher poses the question – what is the future of the Amazon forest?

Assistant Professor Scott Stark in the Department of Forestry at Michigan State University is tackling a worldwide environmental concern: what’s happening in the Amazon?

Photo of a tree burned in large-scale fires that occurred during a major Amazon forest drought in 2015/2016. This tree had been on the border of a savanna-to-forest transition zone in Alter do Chão, Santarém, Pará, Brazil.
A tree burned in large-scale fires that occurred during a major Amazon forest drought in 2015/2016. This tree had been on the border of a savanna-to-forest transition zone in Alter do Chão, Santarém, Pará, Brazil.

EAST LANSING, Mich. – Tropical ecosystems in the Amazon are threatened by deforestation, fire and drought. Over time, these disturbances may end up permanently changing forests into savanna-like areas, which could have devastating long-term effects globally.

Scott Stark, Assistant Professor in Michigan State University’s Department of Forestry, recently published “Reframing tropical savannization: linking changes in canopy structure to energy balance alterations that impact climate” with a Brazilian and international team of scientists that discusses these topics in Ecosphere. (DOI:10.1002/ecs2.3231)

Stark also contributed to a letter on smoke pollution featured in Science magazine entitled “Smoke pollution’s impacts in Amazonia.” (DOI: 10.1126/science.abd5942)

“You can either have forest or savanna in the same climate and rainfall regions. The main thing that keeps these distinctively different from one another is fire. Savannas exist when there is periodic fire.” said Stark. “To reduce global warming, it is better to have tropical forests stay forests rather than turn into tropical savannas.”

As climate changes, Stark wants to determine if a tropical forest will stay a dense forest or turn into an open savanna. He is studying the factors that decide whether tropical forests will be converted into savanna in the long run. This question has a history in forest ecology, but the need to combat climate change by preserving forests makes it much more important now to predict precisely these transitions of forest to savanna.

The problem, Stark said, is what ecologists call “disturbance.”

“Disturbances include droughts, which get worse from climate change. Droughts and other disturbances kill trees, and you certainly expect that will help give the forest a nudge towards turning into a savanna,” he said.

Other disturbances are directly caused by humans, like partial “selective” logging, or clear cutting the forest and then later leaving it fallow to natural vegetation. Fires set to manage cleared land also can burn into nearby Amazon forests during the dry season and cause disturbances.

“Fire in old-growth Amazon forests is kind of shocking,” said Stark. “These are rainforests with no real history of natural fire, and so you can imagine that some trees are likely to die after having their trunks damaged by fire. We don’t really know what the consequence of this is for the future of the forest because of all of these new pressures now faced by the forest.”

After a disturbance, the forests might be resilient and recover back to the original rainforest, or it might stay open and become a savanna with lower value for fighting climate change.

“We need to know how the different types of disturbances and different possible climate change conditions that affect these odds to know if we will have forest or savanna in the future, and that’s a tough problem,” said Stark.

“A good place to start is better understanding how different types of disturbance change the local conditions. If things get hotter and drier after trees die and the canopy opens up that means that fire is more likely to come back and tree growth gets a lot harder and more trees might die if there is a drought” said Stark. “There are not many studies in the tropics that measure these specific changes from disturbance.”

Stark and his team, including international collaborators, were able to conduct rapid assessments by using a portable lidar system and setting up temporary towers reaching above the canopy in disturbed forests. They obtained a small data set that helped understand how different histories of forest disturbance changed these local conditions.

The results showed interesting contrasts that help frame tropical forest changes in a more general framework between forest and savanna.

One location compared undisturbed rainforest with rainforest impacted by fire and a natural savanna. This is a particularly valuable study location—Alter do Chão, Pará, Brazil—because it offers a contrast of natural forest and savanna in the center of the Amazon rainforest, where droughts and fires may be converting more forest to savanna. During the exceptional fire season of 2019, the Alter do Chão savanna and forest mosaic was heavily impacted by fire; Stark and collaborators in Brazil at the Federal University of Western Pará (UFOPA) are beginning to document the damage and future forest change.

Another location where Stark's team rapidly assessed a forest change gradient was hundreds of miles west in a famous ecological research area in Manaus Brazil, called the Biological Dynamics of Forest Fragments Project. This area included mature rainforest, a forest that was 25 years old and growing back from previous clear cutting, and a nearby open savanna-like area where past clearing was maintained by the yearly application of fire by ranchers.

Despite the big differences in the disturbances that created the forest gradients in these locations, the impacts of changing forests on local temperature and related factors that impact the atmosphere—called heat fluxes—were very similar.

“This gives us hope that if we know the exact change in the forest canopy we can predict what that means for the local conditions in the canopy” said Stark. “This is great because now we have technology based on aircraft and satellites, specifically lidar remote sensing, that can rapidly tell us what the exact three-dimensional characteristics of forests are.”

Stark said, “soon we’ll have a first generation of digital three-dimensional maps of the whole Amazon forest, so we might be able to really study in detail how canopy disturbances change forest conditions and then how these conditions decide whether the impacted forest stays forest or becomes a savanna. This would be a big advance.” 

The danger of fire in the Amazon is currently posing additional threats to human life. With current conditions including huge increases in deforestation in the last two years and the likelihood of drought in the western Amazon, there is an increasing potential for a dramatic fire season stretching towards the end of the year. Already between January and August 2020 there were 54,559 fires detected by Brazil’s National Institute for Space Research (INPE), and the number of fires in the Amazon in this time window are the worst in a decade, reflecting expanding deforestation. Concern now looms over rising smoke pollution from these fires and its significant negative impact on human health.

The Amazon has one of the highest infection rates of COVID-19 in the world, and many Amazon residents do not have access to quality medical treatment or personal protective equipment. Concerns for those affected by COVID-19 are high, as smoke inhalation has severe effects, inflaming your lungs and airway, causing them to swell and block oxygen. This could prove life threatening to those already affected by a dangerous respiratory virus.

Analyzing the current climate and rapid changes happening in the Amazon, “savannization” and the fire trap are paramount to understanding the future of the Amazon, the safety of its native people and the future of the global environment.

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