- Dutch researcher and tree expert Hans ter Steege is the founder of the Amazon Tree Diversity Network, which brings together hundreds of scientists studying the rainforest to map and understand the region’s biodiversity.
- Ter Steege says the rainforest is in danger of collapse: If the deforestation in Brazil’s Pará state continues at the rate of the year 2000, he warns, “then our models show there will be hardly anything left by 2050.”
- Large trees are dying faster in the Amazon, he said, as they face a greater evaporation demand, which they can no longer meet with the water they extract from the soil, as there are more droughts and less rainfall.
- If the forest collapses, Brazil’s aerial water supply system — and its agriculture — will collapse, Ter Steege says.
Having lived in Guyana for more than a decade, Dutch botanist Hans ter Steege spends his time these days mostly on home soil. Yet his heart and mind very much remain among the trees of the tropics, which he considers his “personal pet plants.”
A professor of community ecology of tropical trees at Utrecht University and senior scientist in the Understanding Evolution Group at the Naturalis Biodiversity Center in Leiden, Ter Steege is the founder of the Amazon Tree Diversity Network, which brings together hundreds of scientists studying the rainforest in an attempt to map and better understand the region’s biodiversity.
In 2013, the network wrote headlines when it concluded that the Amazon is home to an estimated 16,000 plant species, of which about one-third remain unknown to humankind. In line with the golden rule of biodiversity, which states that rare species are common and common species are rare, half of all the trees in the Amazon consist of just 227 species.
According to Ter Steege, research shows that, due to the change in climatic conditions, trees in the Amazon are currently dying at a faster rate than they can regenerate. Yet he says he’s hopeful for the future. “I maintain that a region as big as the Amazon, of which up to half is under some form of environmental protection, is a very good start.”
Mongabay spoke with Hans ter Steege by video call on Sept. 20. The following interview has been edited for length and clarity.
Mongabay: How would you explain the concept of community ecology of tropical trees to a layperson?
Hans ter Steege: Community ecology looks at how systems of numerous tree species are intertwined. We study individual species to try to understand how ecological systems work. Across the Amazon Rainforest, we have a network of 2,054 research posts with a total of 5,122 species. From each species, we document such features as wood density, leaf nutrients, type of fruits, type of roots, connections with soil organisms, etc., to learn more about how individual species make up an ecosystem. What species appear together and why? Are there any basic rules or principles for that? And what does it mean for variables such as biomass or productivity?
Mongabay: Could we compare trees making up a forest to people making up society?
Hans ter Steege: Not individually, but in our case, you could compare a collective of trees to a village. We usually work with 1 hectare [2.5 acres], which consists of some 570 trees. So we study the features of these 570 individuals to see how the “village” works. For example, if a community is more diverse, if it has more trees with different features, it may prove more productive or more resilient against stress.
Mongabay: You are the founding father of the Amazon Tree Diversity Network, which connects more than 200 scientists working across the rainforest. How did that come about?
Hans ter Steege: It was originally founded to write a collective academic paper in response to an article comparing the composition of forests along the Amazon and Mississippi rivers. I did not agree with some of the claims it made and came up with the idea to ask my fellow ecologists and botanists to report what the most dominant species were in the parts of the rainforest where they were working.
But it soon became bigger than that, as it resulted in the 2013 paper “Hyperdominance in the Amazonian tree flora” for Science. This put the Amazon Tree Diversity Network on the map, as we showed that the Amazon Rainforest is home to some 16,000 species, of which 227 hyperdominant species make up half of all trees.
Mongabay: I was stunned when I first read that …
Hans ter Steege: So were we, to be honest. We all know that one of the golden rules of biodiversity is that rare species are common and common species are rare. But 227 out of 16,000 species making up half of all the trees on a 6-million-square-kilometer [2.3-million-square-mile] surface? We’d never expected that.
Mongabay: How many of the 16,000 species are currently known to science?
Hans ter Steege: Of the 16,000 species, some 10,000 to 11,000 are known to science, thanks in no small part to the explorers and collectors who have been working in the Amazon since the 18th century.
Mongabay: Can you give a few examples of the most dominant species?
Hans ter Steege: Six or seven from the 10 most dominant species are palm trees, including Mauritia flexuosa [Moriche palm or buriti], with its large fruits, and the açaí palm [Euterpe oleracea]. The most common tree [Eschweilera coriacea] is related to the Brazil nut tree [Bertholletia excelsa], although there is some debate among botanists if the tree’s regional varieties should be considered separate species. But for now, it is regarded as one species, of which you find specimens from Guyana all the way to Ecuador.
Mongabay: How did this hyperdominance come about? Is it just a matter of adapting better in terms of Darwin’s survival of the fittest?
Hans ter Steege: If you use a mathematical model, in which all species are equal and have an equal chance to die or create offspring and survive, then you come to a ratio in which common species are rare and rare species are common. However, we found that some 50 species are more common than what would be logical according to the model.
Mongabay: What do you think of the notion that part of the rainforest is man-made?
Hans ter Steege: When Michael Heckenberger in 2009 published his work on the human settlements he found in the Upper Xingu [“Lost cities of the Amazon”], many anthropologists claimed that the Amazon was essentially one big garden. I think that’s a bit exaggerated. We are talking about a huge territory. Even considering that a much larger number of people were living in the region before Columbus, that would mean an awful lot of planting trees.
Last year, we took part in a research project by Brazil’s remote-sensing institute [INPE], which was published by Science. INPE had asked scientists to share any lidar data they had on the Amazon, and they flew over the forest with lidar equipment themselves to look for so-called earthworks, remnants of human occupation.
With a very complicated model, they concluded that there are still some 10,000 to 24,000 earthworks waiting to be discovered. However, they also said that the biggest chance of finding them is in the southwestern part of the Amazon, the region which faces the highest rate of deforestation. In 90% of the Amazon, the chance of finding something is only 1.2%.
So, people have influenced the forest, but not everywhere in an equal manner. In Bolivia, for example, parts of the forests consist of 60% domesticated [plant] species. Most likely a human hand played a role in that. Yet other parts of the rainforest tell a different story.
Having said that, I do believe people have been everywhere in the Amazon. We once traveled to a remote bauxite plateau in the rainforest of Suriname. After being dropped off by plane and a long walk, on which we only met a few hunters and garimpeiros [wildcat miners], we found ourselves in the middle of nowhere. Then we came across a dozen seringueira trees [rubber tree, Hevea brasiliensis], all of which had been carved and tapped for their rubber, even though there was no sign of occupation anywhere near.
Mongabay: While 227 species make up half of all trees in the Amazon, 11,000 species make up only 0.12 percent of all trees. Some 6,000 species consist of less than 1,000 individuals. Could you give an example of a really rare tree?
Hans ter Steege: One day researchers came across a conifer in Rondônia state, which up to that point had not been known to science. So they took the coordinates and decided to come back another day. That turned out to be easier said than done without GPS, but in the end they managed. Today, there are only five specimens known to exist, two of which are found in the garden of the Emilio Goeldi Museum in Belém.
Mongabay: You would not expect a conifer in the rainforest. How did it end up there?
Hans ter Steege: It is arguably a relic from other times. In this case, a lone survivor from the Ice Age some 20,000 years ago. Likewise, you find at times migrants from the savanna in the rainforest. Since the end of the Ice Age, the rainforest has expanded at the expense of the savanna, and here and there you still find a lone survivor.
Mongabay: A few years ago, Bas Haring, a Dutch professor of philosophy at Leiden University, caused quite a stir regarding biodiversity, saying, “We can do with a few species less.” What do you think of that?
Hans ter Steege: Nonsense, of course. I think he posed it as a philosophical question at the time. I don’t think he actually believed what he said. In any case, you will not be able to get a very stable system with, say, six species. Do you need all 16,000 species? Probably not. There has always been a strong dynamism. Some species die. Others take their place. Again, others make a comeback. One hectare of forest is never the same [as another].
If you look at the Permian mass extinction, some 250 million years ago, up to 90% of all life on Earth went extinct. Yet life gradually recovered afterwards. And in the end the diversity of species always increased. Despite several rounds of extinction, biodiversity always increased. So we can do without a few species, but to suggest we could do with, say, six species is a terrible simplification.
Mongabay: Research has shown that more trees are dying in the Amazon. Especially large specimens are suffering. How come?
Hans ter Steege: Because they stick out above the canopy and face a bigger evaporation demand, which they can no longer meet with the water they extract from the soil. The soil is drier, as there is less rainfall. The problem of climate change for trees in the Amazon is not so much the higher temperature. There are many species that have survived previous time periods that were hotter. So heat is not necessarily the problem.
In fact, due to the higher temperatures and higher amount of carbon dioxide in the atmosphere, the forest initially started growing faster. At first, that seemed favorable. Yet what our models are showing now is that trees are dying faster than they are able to regenerate. This is clearly visible in our data. The main problem is that climate change brings less rain and creates drier conditions in the Amazon.
Mongabay: How do you feel when you see the Amazon rivers run dry and swaths of forests being burnt down?
Hans ter Steege: Seeing rivers run dry and thousands of dead fish floating in the water I find extremely painful to watch. It is bad for everyone. For the people, the fish, the forest. Regarding forest fires, when they are illegal, that is of course something that should not happen.
But here I am more nuanced. If you live somewhere with nothing to eat and burning part of the forest is your only option in order to grow something, then that is a different story. I mean, that is something we would do too. What’s more, I’m not in a position to say anything about that, as that’s something we in Europe have always done as well. So I’m less hard on that.
Mongabay: But does it not make a difference if someone burns part of the forest to grow his own food or has a herd of cows grazing? Or plant a field of soy?
Hans ter Steege: Seeing cows in what used to be forest is deplorable. You could still debate soy. The main problem with soy is that we feed it to our cattle, which means you lose 80% of the proteins. That is extremely inefficient. Having said that, it is a landscape of nothing, of course. Those endless green fields with perhaps here and there a Brazil nut tree because they are protected.
I still remember the first time I flew from Guyana, which has relatively little deforestation, to Pará [state in Brazil]. I was shocked. I had to stand on top of a car to see a tiny strip of forest on the horizon. Add to that the image of the meager pastures with a few bony cows and the only thing you can think is, “This must be the end of the world.”
If the deforestation in Pará continues at the rate of the year 2000, then our models show there will be hardly anything left by 2050. It is part of the arc of deforestation. It is a similar story in states like Acre and Rondônia. And comparable to the state of the Atlantic Forest, of which some 12% remains.
On the other hand, there is still hope. If you fly over the Amazon and you see some 85% of the forest still standing, then you think, “I don’t want to make an emergency landing here, ’cause I’ll never make it out alive.”
Mongabay: For 65 million years, the Amazon has not fundamentally changed. Today, due to a combination of drought, deforestation and climate change, the region could reach a tipping point and face collapse. In February, a study in the journal Nature estimated that by 2050, up to 47% of the Amazon “will be exposed to compounding disturbances that may trigger unexpected ecosystem transitions and potentially exacerbate regional climate change.” How likely is such a scenario?
Hans ter Steege: I was a co-author of the paper published by Nature, which says a lot of things about how things could go. Could the Amazon collapse before 2050? Yes, it certainly can. However, regarding these huge systems, we should realize there is a lot we do not know. We know there is an interaction between vegetation and the atmosphere. All kinds of things are happening there.
But, for example, as a consequence of climate change, we are also facing the Atlantic Ocean, which last summer was 1°[C, or 1.8°F] warmer than any model had predicted. These are the most complicated models we have. Numerous scientists and departments work on these models, which were unable to predict such a huge deviation.
When it comes to the Atlantic Ocean heating up, the Gulf Stream [the warm ocean current originating in the Gulf of Mexico and running north] is slowing down, could potentially stop, and even change course. If that happens, it means that in the Netherlands, the temperature could drop by some 15°C [27°F].
This would also have a major impact on the Amazon region. Would it get colder? Hotter? Drier? There are many theories about that. But no one knows for sure. So to go back to the Amazon tipping point: Yes, that is a very real scenario. But it is very hard to predict how and when.
Mongabay: What are the consequences for Brazil if such a scenario is to become a reality?
Hans ter Steege: I think the most important thing for Brazil is to realize that, if the forest collapses, the whole water supply system of the country, and most of the continent, will arguably collapse. Brazil should seriously think about the aerial water highway, which is the water evaporated by the forests that travels by air to other parts of the country in the form of rain. The more forest is removed, the weaker the highway becomes, which is of crucial importance for the agriculture that has replaced the forest and even for the drinking water supply of a city like São Paulo. At some point, agriculture will no longer be feasible. Ironically, perhaps the most important reason for Brazil to save its forests is to save its agriculture.
Mongabay: What can we still do to stop such a scenario from happening?
Hans ter Steege: I think that with every solution we find for a problem we tend to create new problems. For example, driving electric cars in Europe creates slavery-like conditions for people mining minerals in Africa. So you solve one problem but you create others elsewhere. So let’s also look at existing systems.
About half of all food we produce today is thrown away. Also, only half of all agricultural fields are actually productive. So we could produce four times more food simply by using existing land and distributing food more efficiently. Bottom line: we don’t need deforestation. We have to stop deforestation. In addition, reforestation is a good option, but only when it does not lead to cutting primary forest elsewhere.
Mongabay: How long does it take for a field of weeds, which is the first stage of a forest, to become an actual forest?
Hans ter Steege: It depends a bit on where you are. But in terms of biomass, it takes about 100 years. In terms of species richness, it takes a bit less than 100 years. But if you want to return to the exact composition a forest once had, we are talking about thousands of years. The primary forest that once stood is extremely hard to get back. But late-stage secondary forest already delivers many positives, such as water and coolness.
Mongabay: Are you hopeful for the future?
Hans ter Steege: I maintain that a region as big as the Amazon with up to half under some form of Brazilian protection is a very good start. Even under the previous president, Jair Bolsonaro, there were less forest fires inside the protected areas than outside. There were more than before, and there was a lot of hostility towards local and Indigenous people, but the fact that half of the forest, under some form of conservational status, offered real protection gives me hope. Now, if we in Northern Europe can start doing a better job in protecting cod, herring and other fish stocks, we may still get the world turning in the right direction.
Are the Amazon’s biggest trees dying? Forest coroners investigate
Citations:
Ter Steege, H., Pitman, N. C., Sabatier, D., Baraloto, C., Salomão, R. P., Guevara, J. E., … Silman, M. R. (2013). Hyperdominance in the Amazonian tree flora. Science, 342(6156), 1243092. doi:10.1126/science.1243092
Heckenberger, M. J. (2009). Lost cities of the Amazon. Scientific American, 301(4), 64-71. Retrieved from https://www.scientificamerican.com/article/lost-cities-of-the-amazon/
Peripato, V., Levis, C., Moreira, G. A., Gamerman, D., Ter Steege, H., Pitman, N. C., … Vos, V. A. (2023). More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia. Science, 382(6666), 103-109. doi:10.1126/science.ade2541
Levis, C., Costa, F. R., Bongers, F., Peña-Claros, M., Clement, C. R., Junqueira, A. B., … Sandoval, E. V. (2017). Persistent effects of pre-Columbian plant domestication on Amazonian forest composition. Science, 355(6328), 925-931. doi:10.1126/science.aal0157
Flores, B. M., Montoya, E., Sakschewski, B., Nascimento, N., Staal, A., Betts, R. A., … Hirota, M. (2024). Critical transitions in the Amazon forest system. Nature, 626(7999), 555-564. doi:10.1038/s41586-023-06970-0
FEEDBACK: Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.
Credits
