Very strong winds are the main cause of death for trees located on the southern edge of the Amazon.
This is the main conclusion of a study carried out by scientists at Unemat (University of the State of Mato Grosso) in partnership with the British universities of Leeds and Oxford.
Thanks to monitoring that has lasted nearly three decades and individually analyzes 15,000 trees from time to time, the group was able to identify the factors behind the death of trees.
The work showed that the main cause of damage, often irreversible, are atypical winds, followed by periods of drought.
“And we know that global warming causes these extreme weather events to become increasingly common, which represents a threat to the forest”, adds biologist Simone Matias Reis, lead author of the article.
Understand below how the study helps to diagnose the current situation and what it reveals about the future of the entire Amazon.
Where does the transition take place?
To carry out this type of investigation, the specialists did not choose the southern edge of the forest, which comprises the states of Mato Grosso and Pará, by chance.
Oliver Phillips, professor of tropical ecology at the University of Leeds, UK, explains that this is a transitional area between the Amazon and the Cerrado.
“Transition areas are naturally more sensitive, so it is already expected that they will be the first to feel the effects of climate change”, he says.
The expert, who also signed the recently published study, draws attention to the fact that this southern edge is one of the driest, hottest and most fragmented regions in all of South America.
“This can give us ideas of what the future of tropical forests will be like, including the Amazon itself”, he adds.
Forest engineer and ecologist Beatriz Schwantes Marimon, who is a professor at Unemat and was also one of the research coordinators, says that the monitoring of large green areas usually uses satellite images, which allow for larger and large-scale analyses.
On the other hand, this work took a different approach. Specialists went out into the field to check the health status of more than 15,000 trees spread across 19 points in the forest — an “ant-like” effort, in the researchers’ own assessment.
“We’ve been doing this routinely for 27 years, but starting in 2008, we started looking at the tree itself, how much of the canopy was broken, if there was a lot of vines, if it was leaning, with holes or other signs of aging,” he said. list.
“I remember where I could find a certain jatobá, a palm tree… And then, when I returned to that place, a wind had knocked everything down”, confesses the researcher.
It was from the compilation of all these observations that the group was able to understand what was causing the death of these native species: the atypical winds and periods of drought.
The study was published in Journal of Ecology on February 22 and had the support of the National Council for Scientific and Technological Development, CNPq.
A slow and painful death
“The data show us that the frequency of strong winds has been increasing in this region”, says Reis.
The most violent gusts are capable of shaking the tree greatly, to the point where the branches break or the root detaches from the earth.
With important parts of the structure broken, part or all of the crown, where the leaves are located, is lost.
Without the leaves, the photosynthesis process ends up compromised, which makes it impossible to “feed” the tree.
Now, if the rupture occurs at the root, the plant has little (or no) contact with the soil and can no longer extract the water and nutrients necessary for its survival.
Reis adds that this is a process that can take a long time.
“When we returned to observe trees that had a broken crown, about 70% of them are dead after two or three years”, calculates the biologist.
A process that feeds back
Marimon points out that the death of natural vegetation is stimulated and facilitated by a number of extra factors.
“We are also experiencing periods of drought more and more often, which makes the trees fragile,” he says.
“Then you don’t even need such a strong wind to cause damage or knock down branches and trunks”, he adds.
According to the expert, it is also necessary to keep in mind that the death of a tree represents a danger to all the others around it: the more the forest is fragmented, the greater the risk of the crowns and branches being exposed to the gusts.
“In these cases, a stronger wind is enough to knock down an entire stretch of forest”, says the ecologist.
How to change this scenario?
According to experts heard by BBC News Brasil, the observations made on the southern edge of the Amazon indicate what could happen to this entire biome in the coming decades.
“If climate change and vegetation loss continues at this rate, this scenario of wind and drought is expected to spread deeper into the heart of the Amazon,” warns Phillips.
“Our work serves, therefore, as a window to glimpse what the future of the entire region could be”, adds Reis.
To prevent this scenario from becoming a reality, the only way out is to stop deforestation and even think of ways to restore vegetation in the most degraded areas, the researchers believe.
“We need a complete moratorium on the destruction of green areas around here, as there are already many places that have been opened and are misused”, proposes Marimon.
“The tree death rate is accelerating and we see that the forest is starting to lose its ability to recover,” adds Phillips.
“And we need to give what’s left of the forest a chance to find balance again”, concludes the researcher.
