What would happen if the Amazon forest dry? This experience of several decades has answers
Caxiuana National Forest, Brazil – A few steps under the dense Amazon canopy, the forest opens suddenly. The fallen balls are rotten, the trees become sparse and the temperature increases in places that sunlight knocks on the ground. This is what 24 years of severe drought looks like in the largest tropical forest in the world.
But this degraded forest plot, the size of a football field, is a scientific experience. Launched in 2000 by Brazilian and British scientists, Esecaflor – Abbreviation of “Forest Drought Study Project” in Portuguese – has decided to simulate a future in which the evolution of the climate could exhaust the Amazon of precipitation. It is the oldest project of the genre in the world, and has become a source of dozens of academic articles in fields ranging from meteorology to ecology and physiology.
Understanding how drought can affect the Amazon, an area twice the size of India which is transformed into several South American nations, has implications far beyond the region. The tropical forest stores a massive quantity of carbon dioxide, a greenhouse gas which is the main engine of climate change. According to a studyThe Amazon stores the equivalent of two years of world carbon emissions, which mainly come from the combustion of coal, oil and gasoline. When the trees are cut, or wither and die from drought, they release the carbon in the atmosphere they stored, which accelerates global warming.
To imitate the stress of drought, the project, located in the Caxiuana National ForestAssessed approximately 6,000 rectangular transparent plastic panels on one hectare (2.5 acres), diverting around 50% of forestry grounds. They were placed 1 meter above the ground (3.3 feet) on the sides 4 meters (13.1 feet) above the ground in the center. The water has been channeled in the gutters and channeled through trenches dug around the perimeter of the plot.
Next to it, an identical plot was not left to serve as control. In the two areas, instruments were attached to the trees, placed on the ground and buried to measure the humidity of the soil, the air temperature, the growth of the trees, the flow of the sap and the development of the roots, among other data. Two metal towers are above each layout.
In each round, NASA radars measure the amount of water in plants, which helps researchers understand overall forest stress. The data is sent to the spatial agency propulsion laboratory in California, where it is processed.
“The forest initially seemed to be resistant to drought,” said Lucy Rowland, professor of ecology at the University of Exeter.
However, it started to change about 8 years. “We have seen a great drop in biomass, large losses and the mortality of the biggest trees,” said Rowland.
This led to the loss of around 40% of the total weight of the vegetation and carbon stored inside the plot. The main conclusions were detailed in a study Posted in May in the journal Nature Ecology & Evolution. This shows that during the years of loss of vegetation, the tropical forest has gone from a carbon well, that is to say a carbon dioxide rider, to a carbon transmitter, before finally stabilizing.
There was good news: the drought of several decades did not transform the tropical forest into a savannah, or a large grassy plain, as predicted by previous studies based on models.
In November, most of the 6,000 transparent plastic covers were removed, and now scientists observe how the forest changes. There is currently no end date for the project.
“The forest has already adapted. Now we want to understand what will happen next,” said Meteorologist João de Athaydes, vice-coordinator of Esecaflor, professor at the Federal University of Para and co-author of The Nature Study. “The idea is to see if the forest can regenerate and return to the reference base from the start of the project.”
During a visit in April, Athaydes guided journalists from Associated Press through the site, which had many researchers. The region was so distant that most of the researchers had endured a boat trip from a day in the city of Belem, which will host the next annual United Nations climate talks later this year. During the days in the field, scientists remained at the scientific base of Ferreira Penna from the Emilio Goeldi museum, a few hundred meters (meters) of the plots.
Four teams were at work. We collected soil samples to measure the growth of the roots in the upper layer. Another has gathered the weather data and followed the temperature and soil humidity. A third was measured the humidity of the vegetation and the flow of sap. The FOURT focused on the physiology of plants.
“We know very little how drought influences the soil processes,” said ecologist Rachel Selman, researcher at the University of Edinburgh and one of the co-authors of Nature study, during a break.
The Simulation of Dryer of Esecaflor establishes parallels with the last two years, when a large part of the Amazonian forest, under the influence of El Nino and the impact of climate change, endured its most serious drought periods ever recorded. The devastating consequences varied from the deaths of dozens of river dolphins due to warming and decline in large forest fires in old areas.
Rowland explained that the recent El Nino had brought intense short -term impacts to the Amazon, not only by reduced precipitation but also with temperature and steam pressure deficit, a measurement of dry air. On the other hand, ESECAFLOR's experience focused only on manipulation of soil humidity to study the effects of long -term changes in precipitation.
“But in both cases, we see a loss of the forest's ability to absorb carbon,” she said. “Instead, carbon is released in the atmosphere, as well as the loss of forest coverage.”
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