In 2013, a study was published, Hyperdominance in the Amazonian Tree Flora, whose lead author was Dutch tropical forest ecologist Hans ter Steege of the Naturalis Biodiversity Center in Leiden. This study showed that the Amazon basin is home to more than sixteen thousand tree species, but of these sixteen thousand, only two hundred and twenty-seven are hyperdominant or dominant, “a much smaller number than anyone had expected,” according to Hans ter Steege at the time. In numbers, this means that only two hundred and twenty-seven species, or 1.4 percent of all tree species in the Amazon, make up half of the estimated nearly four hundred billion trees that live there. Many of the dominant tree species are also found in large numbers in only a few areas.
Examples of hyperdominant or dominant species include the palm species Euterpe precatoria, the most common tree species in the entire Amazon region and a relative of the açaí palm, whose berries are becoming increasingly popular around the world; the rubber tree; the Brazil nut tree; the walking palm (cashapona or walking palm); and the ungurahui tree. According to Brazilian Eliane Gomes Alves, a researcher in the ATTO* team at the Max Planck Institute for Biogeochemistry in Jena, Germany, the hyperdominance of certain tree species is no coincidence. One reason, she explained to me in the fall of 2021, is that they were domesticated by ancient indigenous peoples.
Tall Tower (Photo © Jorge Saturno MPI-C)
*ATTO, better known as the Amazonian Tall Tower Observatory, is a three-hundred-and-twenty-five-meter research tower that juts out of the rainforest like a needle, one hundred and fifty kilometers northeast of Manaus. It is an “atmospheric laboratory” built to understand how the Amazon rainforest affects climate change and, conversely, how climate change affects the health of the Amazon rainforest. In Manaus, the data from ATTO go to the National Institute for Amazonian Research INPA, and in Germany they are analyzed by the Max Planck Institute for Biogeochemistry in Jena and the Max Planck Institute for Chemistry in Mainz.
Eliane Alves: “A recent study showed that up to 84 percent of hyperdominant trees are useful to humans. This means, among other things, that indigenous peoples and traditional communities have made a significant contribution to the conservation of these species and have also helped to increase their abundance. And that it is important to work with the dominant species because they are likely to have a greater impact on the climate due to their carbon storage and are therefore an important key to combating climate change.”
Eliane Alves’ colleague Santiago Botia, ATTO researcher in Jena for the greenhouse gases CO₂ and CH₄, or carbon dioxide and methane, said the same thing. He explained: “Carbon dioxide is strongly associated with vegetation. Previous findings, recently confirmed, have shown that good vegetation management is crucial in this regard and is often associated with life in indigenous areas and national parks. As much as 58 percent of above-ground carbon is stored in these areas. These places are therefore essential for keeping carbon in the forest, preventing deforestation and storing large amounts of carbon. The Amazon’s carbon balance therefore also has a human component.”
This brings us back to the beginning of this biodiversity and carbon dioxide story, to the ecological interactions between organisms that are highly biodiverse and thus contribute to ecosystem services. In the area where ATTO is located, a number of hyperdominant tree species are very abundant. Measurements of gas emissions, the scents of these species, showed that there is a seasonal change and that the emission of these gases increases as the dry season approaches.
Eliane Alves: “After the article by Hans ter Steege, among others, in 2013, several other studies were launched to understand how these hyperdominant trees could affect the atmosphere in terms of CO₂ absorption and gas emissions. And two years later, there was a paper that said that 15 percent of the carbon stored in trees in the Amazon was stored in hyperdominant species. So we started thinking that these trees might be important for the compound emissions that I work with. Compound emissions are trace gases emitted by plants that are usually released for ecological interactions, such as attracting pollinators. But once they have fulfilled that role, they end up in the atmosphere and become involved in subsequent processes that affect climate, particularly atmospheric chemistry and physics.”
So what does that mean?
Eliane Alves: “I want to study what kind of compounds some of these hyperdominant species can emit and how they vary over the seasons, because temperature stimulates some of these compounds. We selected two hyperdominant species that we found at the ATTO site, distributed in different forest types. One species, found in only three different conditions, was studied over three seasons, during the dry-wet transition, during the wet season, and during the dry season. We found that during the dry season, the composition of the emission mixture changes, and the trees need compounds that are more stimulated by high temperatures. These compounds are more reactive in the atmosphere and very efficient in producing particles for cloud formation. The fact that they are emitted more during the dry season suggests that with global warming we may have more of these kinds of interactions and that these processes will change the atmosphere. Another message is that the same species can have different types of emissions depending on the type of forest they live in. This brings us to the principle that biodiversity has multiple levels and that we need to look at it very broadly.”
More emissions into the atmosphere. More efficient cloud formation. How will this affect the weather, the climate?
Eliane Alves: “This is a difficult question because globally, cloud formation actually requires two things: an aerosol particle and water vapor to condense on that particle. Cloud formation requires a balance between the two. If there are a lot of particles and not too much water vapor, there will be no cloud formation. The water vapor will then condense on many different particles, and they will not clump together; no clouds will form. But if there is a lot of water vapor and not enough particles, that is not good either. At the same time, there are still many uncertainties in the models because there has not been enough research, such as observations, and we would need some laboratory experiments to better understand this process. We think that if there are more emissions and therefore more particles, and there is enough water, this will stimulate cloud formation. But because of deforestation, there will be less water in the atmosphere. So this is a feedback that we do not really understand yet, because there are overlapping things like the loss from deforestation and the increase in temperature. So it is very likely that there will be less water in the atmosphere. And water is the main ingredient in cloud formation.”
Tall Tower measurements (© Jošt Lavrič / MPI-BGC)
Salad Bowls
So far we have talked about trees, animals and fungi. But let’s not forget the presence of microorganisms, which are very abundant in the soil. They are very diverse; they absorb and emit gases.
Eliane Alves: “We have now started a study at ATTO for which we have built soil chambers. We use bowls, ordinary, everyday salad bowls, which are connected to gas sensors to measure what is emitted and what is absorbed. We hope to have the results soon.
“There are different types of forests, from wetlands to highlands. There are organisms in the soil that exchange gases and particles with the above-ground environment. And these exchanges are visible and measured on the ATTO towers. We correlate the tower measurements with satellite observations to get a regional scale. Understanding how these processes work can help us understand larger processes in atmospheric chemistry and physics that affect climate, which in turn is affected by forests. With ATTO, we are trying to unravel the dynamics of this cycle.”
Alarming Numbers
As noted above, when most people think of the Amazon and the climate, they think first and foremost of the forest as a store of carbon dioxide. Recent data (updated to November 18, 2021) from the authoritative World Resources Institute (WRI) in Washington, D.C., in the United States shows grim numbers about the Amazon as a carbon sink. According to WRI, the forests sequester 7.6 billion tons of CO₂ annually. The Amazon Basin accounts for 1.2 billion tons of CO₂ sequestration, but is responsible for 1.1 billion tons of CO₂ emissions. This is a net flux of 100 million tons of CO₂. Comparing this to the figures for the Congo Basin, WRI reports 1.1 billion tons of CO₂ sequestration against 530 million tons of CO₂ emissions, or a net flux of 610 million tons of CO₂. The situation in Southeast Asia, home to the world’s third largest tropical forest, is nothing short of alarming. Over the past twenty years, Southeast Asia’s forests have collectively become a net source of carbon emissions due to plantation logging, uncontrolled fires, and peatland drainage. By the numbers: 1.1 billion tons of CO₂ sequestered versus 1.6 billion tons of CO₂ emitted results in a positive release of 490 million tons of CO₂ into the atmosphere.
The situation in the Amazon is also deteriorating rapidly, with irreversible tipping points looming. I present the WRI figures to Eliane Alves.
Eliane Alves: “There was an article in Nature this year, Amazonia as a carbon source linked to deforestation and climate change, with Luciana Gatti (a scientist at the Brazilian National Institute for Space Research INPE – CCE) as lead author, for which her group tracked atmospheric CO₂ concentrations at four points across the basin. They found that near the deforestation arc, the Amazon is no longer a carbon sink, but a source of CO₂. If you look at the western part of the basin, the Amazon is still a carbon sink because there is less deforestation. But if you take the average of the whole basin, the size of the carbon sink for the whole basin decreases because there are regions that emit more CO₂. Carlos Nobre, a researcher in Brazil, says that we will reach the tipping point of the Amazon Basin completely at 25 percent deforestation of the Amazon. We are now at almost 20 percent. According to his group’s research, once we reach 25 percent, there is no going back. The complication is that deforestation is not just a current problem. I mean, when you take the tree out, you lose the carbon that was stored in it. But what happens after that is just as catastrophic, because you leave a lot of residue and debris that decomposes and emits CO2. Also, if you change the soil and create an edge between forested and deforested areas, you trigger a process called the “edge effect”. Temperatures are higher in these marginal areas, leading to a decrease in vegetation and making the forest more vulnerable to fire and drought. So it is a process with immediate and long-term effects, more than just the removal of the forest itself. Therefore, a deforestation rate of 25 percent will create a large amount of edge areas that are likely to lead to degradation of the remaining forest.”
The journal Nature wrote in July 2021: Southeast Amazonia is no longer a carbon sink.
The Vulnerable Amazon
There is much talk in the media and elsewhere about the Amazon as a carbon sink, its importance. There is much talk in the media and elsewhere about the rich biodiversity of the Amazon, its importance. But it is the combination of the two that really shows how complex the life cycle is in The Wondrous World of the Amazon, to borrow the title of the Disney book from my childhood.
But this complexity also makes it very vulnerable, don’t you think, I ask my conversation partner in Manaus.
She thinks for a long time.
“That’s a good question. I think that deforestation makes us lose complexity, and the loss of complexity makes the forest more vulnerable. If an area is deforested and then left alone, new forest will grow, a regeneration process will take place. Secondary forests will emerge and they will be less complex. They will have fewer species and be more vulnerable to climate change in general. But there is more. Flying rivers, for example, are mostly about the contribution of forests. These rivers that flow through the atmosphere to central and southern South America are fed by a combination of thousands and thousands of species, with the evaporation rate of trees varying from species to species. So if we reduce the complexity, if we reduce the number of trees in terms of species, we make those areas more vulnerable because not every tree is equally strong and evaporates the same amount of water. And that process will eventually stop the flying rivers.”
For more and up-to-date information on the relationship between the Amazon and the climate, see https://banzeiro.greenarkpress.com/ (Dutch) or https://banzeiro.substack.com/ (English).
