Climate research: What the stress of the trees is doing to the rainforest

In Amazonia, floating rivers are part of the water cycle, which scientists are researching in great detail. There, the forest itself can produce rain – for now.

Chapter:

Dawn in the rainforest

Over all the treetops is peace

Photo: Nyani Quarmyne

Dawn in the rainforest

By ANDREAS FREY (text) and NYANI QUARMYNE (photos)

Photo: Nyani Quarmyne

October 31, 2022 Floating rivers are part of the water cycle in Amazonia, which scientists are researching in great detail.

There, the forest itself can produce rain – for now.

But it is already failing as a natural carbon sink: the sensitive ecosystem is disturbed.

Sometimes Jonathan Williams leaves the camp while it is still dark.

He climbs out of his hammock, slips on sturdy shoes and starts walking.

His way through the night takes him past giant trees, hidden snakes, spiders and beetles that grow to the size of plates when they spread their wings and buzz around buzzing.

After a short walk, Williams reaches a red steel tower that rises up into the pale sky in the middle of the rainforest.

From the darkness of the forest, Williams then climbs step by step until he reaches the viewing platform at a height of 325 meters.

The ascent takes half an hour, but he has never regretted it, says Jonathan William on the phone.

When he gets to the top, it's already getting dark.

He always enjoys this moment: only the sky and the forest and right in the middle he, the scientist.

As soon as the first rays of sun fall on the treetops, the endless dark nothingness turns into the green carpet that he saw from the plane when he arrived.

Then steam forms over the treetops, the air carries scents upwards, and he discovers little spots of color: parrots flying from tree to tree.

It is the moment when the size and beauty and uniqueness of the rainforest in the Brazilian Amazon region are most understandable.

He cites "tourist reasons" for his nightly outings, but Williams is there on business.

Once or twice a year, the Englishman moves from his desk at the Max Planck Institute for Chemistry in Mainz to the tropical Amazonia to explore the largest contiguous rainforest on the planet up close and at dizzy heights.

ATTO is the name of the project, short for Amazonian Tall Tower Observatory, which Williams is coordinating and which the Max Planck Society initiated together with the Brazilian government a few years ago.

At the heart of the project is the 325-meter-high steel tower in Brazil, which “we use to measure the breath of the rainforest,” as the atmospheric chemist puts it, at different heights.

What is meant are the complex cycles in this vast ecosystem, such as carbon,

The water cycle is also fascinating.

Even children learn that the rainforest produces its own weather, since fallen rain evaporates quickly, so new clouds grow in the sky or more precisely: a separate moist atmosphere layer forms.

Floating rivers are what scientists call this hydrological marvel, which ensures that rain fronts approaching from the Atlantic can penetrate far into the continent and intensify - creating their own circulation that ensures rain supplies and reduces the risk of drought.

Photo: MPIC/Jonathan Williams

Photo: Nyani Quarmyne

In order to measure the "breath of the rain forest", researchers in Brazil had a 325 high steel tower built in red.

But even from a height of 55 meters, the sea of leaves looks impressive, that's how high the platform of the measuring tower is in the Congo Basin.

The green jungle giants recycle the rain by allowing the water to evaporate again immediately or by pumping it through the roots into the crowns, where it evaporates through the leaves.

Hydrologists call this process evapotranspiration: the forest sweats, forms clouds, and rain falls.

This system regulates the water cycle and forms the basis of life for humans and animals.

In addition, the leaf canopy shields the thin, sensitive soil layer from the vertical sun in the tropics, thereby protecting it from drying out and erosion.

However, this regional water cycle is still not precisely understood.

How much rain does the forest itself produce and which mechanisms are involved are research questions that the scientists led by Jonathan Williams are pursuing - and which they would like to answer soon.

Estimates of recycled rain, for example, vary widely, ranging from one to three quarters.

It is also unclear at which critical point the cycles break down, i.e. when the loss of forest threatens the entire system.

In order to be able to answer these questions, the ATTO project was launched.

With the aim of gaining a more detailed understanding of the rainforest and its exchange processes with the soil and atmosphere - and to clarify the influence of climate change in order to be able to model it more precisely.

That is why the scientists have chosen this place far away from civilization.

A place with no factories, chimneys, or exhaust fumes to interfere with their sensitive measurements.

The monstrous structure was erected 150 kilometers north-east of Manaus, in the middle of the almost endless rainforest with its unique ecosystem.

Arriving by plane, boat and jeep is expensive and takes a long time, but this is the only way to obtain unadulterated data.

The atmospheric researchers, biologists and chemists also want to answer the question of what will become of the rainforest if climate change continues to heat it up.

Heat and drought threaten the natural paradise;

Conquest of land, deforestation and fires will take care of the rest. The future is not certain and only one thing is clear: Amazonia has no chance without the jungle giants.

Some scientists assume that the delicate ecosystem of the Amazon is already tipping.

Then the gigantic carbon reservoir could turn into a carbon source from which more CO2 escapes than can be stored in it.

You wonder what will happen to the rainforest when drought is the norm: will the hydrological cycle collapse and the rainforest turn into a savannah?

What will become of biodiversity?

The drought is one of the main questions Williams' research is also addressing.

In any case, climate models indicate that this is to be expected more frequently in the future, which is supported by observations from recent years: in 2005, 2010 and 2015 three severe droughts hit the Amazon.

In some regions, the dry season lengthened from four to almost five months.

Anyone interested in the exchange of greenhouse gases between the atmosphere and trees must take into account the direction and speed of the wind.

Photo: Nyani Quarmyne

All of this has consequences, neither for the estimated 400 billion trees nor for the cycles associated with them.

In summer 2021, a research team from the Brazilian space agency INPE calculated in the journal Nature that a turning point could already be reached for carbon.

Accordingly, Amazonia has already turned into a region that, on balance, emits more CO2 into the atmosphere than it removes.

The researchers led by Luciana Gatti came to this conclusion after 590 measuring flights over four different rainforest areas in the period from 2010 to 2018 and thus determined the respective carbon balances.

The researchers found that the eastern part in particular had higher carbon dioxide emissions.

The whole of Eastern Amazonia is therefore already a carbon source,

and the fire years 2019 to 2021 were not even included.

But the high emissions are not surprising because deforestation in the eastern areas has been faster than in the west over the past 40 years.

About one-sixth of the rainforest in the east has been destroyed and converted to farmland or pasture.

Temperatures and the risk of fire have risen sharply since 1979, the open country is warming faster than the dense, humid rainforest;

Drought and heat are increasingly affecting the region.

Temperatures and the risk of fire have risen sharply since 1979, the open country is warming faster than the dense, humid rainforest;

Drought and heat are increasingly affecting the region.

Temperatures and the risk of fire have risen sharply since 1979, the open country is warming faster than the dense, humid rainforest;

Drought and heat are increasingly affecting the region.

NASA researchers came to similarly depressing results in 2021 using satellite data.

"The ability of tropical rainforests to store carbon is dwindling," the study, published in Science Advances, concludes.

This mainly affects the rainforests in South America and Southeast Asia, where deforestation has increased significantly.

The bottom line is that these authors assume that the Amazon forest now stores as much carbon as it releases into the atmosphere.

This eliminates this as a natural sink.

Illustration: FAS

South American rainforests emit a particularly large amount of carbon during El Niño.

The dreaded weather phenomenon occurs every few years, causing Amazonia to dry out while heavy rain falls on the west coast.

In 2015, El Niño was particularly violent, even in the deepest rainforest not a drop fell from the sky for weeks.

Jonathan Williams was at the camp at the time and is still shocked at what he saw.

The leaves drooped sadly, the shoots were all dead.

"It usually rains even in the dry season," he says, but at that time no rain cloud strayed into the rainforest.

The Amazon Basin was also hit so hard by the drought in 2015 because it was dry there before El Niño began.

It was also shockingly dry in the wooded area where Freiburg professor Christiane Werner stayed two years ago.

The biologist affectionately calls this rainforest “small earth”. It grows in the middle of the Arizona desert, surrounded by a huge glass dome, the Biosphere 2 research laboratory. In this building complex, thirty years ago, eight scientists wanted to simulate life on an alien planet and failed miserably, a tropical ecosystem thrives under artificial conditions in which humans hardly intervene.

Here, under controlled conditions, it is possible to research the strategies with which the trees react to drought.

So Christiane Werner played the weather gods, turned off the water in the forest, drained rivers and waterfalls, simulated five months of drought.

The first reaction was not long in coming: "When it gets dry, the tree closes its stomata," she says, which is a typical protective function.

Some tree species reacted immediately, others were much more tolerant, for example those with thick sclerophyllous leaves.

But that has its price: good drought adaptation always comes at the expense of productivity.

To the researchers' surprise, this was evident even during the drought in Biosphere 2: the extremely productive, large trees in particular reacted most sensitively, immediately closing the stomata through which water vapor escapes and which are used for gas exchange, and shed their leaves.

"After a short time it looked like autumn," remembers Werner.

The researchers also observed how the trees slowed down their metabolism, curbed consumption and only tapped into the last reserves of the deep water at the very end.

Each tree reacted differently.

Werner is convinced that it is precisely this interaction that gives a forest the buffering function it needs to survive a prolonged drought.

Intact, species-rich forests can therefore survive droughts better than damaged ones.

In the Democratic Republic of Congo it is still common to clear fields with a fire after harvest.

And here, as in Brazil, there is often slash-and-burn clearing to gain arable or grazing land.

Photo: Nyani Quarmyne

A similar inertia was observed in the carbon cycle: "All processes slowed down as soon as there was no rain," says Werner.

The roots recognized the drought early because the topsoil was drying out, and they quickly passed their information on phytohormones to the leaves.

Using outrageously expensive tracer gases, the biologists were able to trace the path of the carbon and witnessed how it was transported from uptake by photosynthesis in the leaves to the branches and trunk and from there it migrated further and further down.

It went on forever, Werner remembers.

The trees also reacted sluggishly to the end of the drought.

When Werner turned on the tap again, some trees initially remained in protection mode, not immediately pumping the water that fell on them into the leaves,

Although the metabolism was downregulated during the drought, the production of the volatile organic compounds was dynamic.

Trees emit such "volatile organic compounds", or VOCs for short, and release them into the atmosphere as gas or vapor, where they react with molecules in the air.

These substances sometimes attract insects or are used for communication from tree to tree.

As an initial reaction to the drought, Christiane Werner's team measured a sharp increase in the hydrocarbon compound isoprene, which plants use to protect themselves from heat and strong UV radiation.

The plants then released large amounts of monoterpenes, which you can smell in pine oil, for example, or perhaps know as the resin that glues the tent together on summer vacation: a sign of stress.

Organic carbon compounds originating from vegetation are under the special observation of Christiane Werner and her colleague Jonathan Williams, who also researched in Biosphere 2.

The monoterpenes mentioned in particular play an important role in the formation of aerosols, which in turn create clouds and then rain.

The two researchers even hypothesize that trees under drought stress specifically secrete more monoterpenes to form clouds and trigger rain.

How this process works and at what time of day is what Williams would like to finally understand better, namely on the steel tower under real conditions.

Because no UV light penetrates through the glass roof of the Biosphere 2 - many of the chemical reactions that normally take place in the open atmosphere therefore do not occur.

This is another reason why Jonathan Williams likes to climb the tower early in the morning.

He wants to be there when the fragrance cocktail and the highly reactive organic compounds it contains flow up the tower.

This always happens just after sunrise.

When the rainforest awakens.

This article was first published on January 21, 2022.

Next chapter:

Above all treetops is peace

By LAURA SALM-REIFFERSCHEIDT (text) and NYANI QUARMYNE (photos)

October 31, 2022 · The importance of the extensive rainforest area in the Congo Basin for the global climate has hardly been researched to date.

That is changing now, thanks to a modern measuring tower.

Fabrice Kimbesa only needs two minutes for the 221 rungs towards the sky.

With practice, the 26-year-old climbs one after the other until he reaches the end of the ladder, releases his safety rope and climbs onto the platform of the CongoFlux tower.

A green, almost endless sea of treetops now stretches out in front of his eyes on all sides, and even the highest treetops are still 15 meters below him.

For more than a year, Kimbesa, who studied at the University of Kisangani, has been working as a technician of the 55-meter high measuring tower in the Yangambi Biosphere Reserve in the Democratic Republic of the Congo.

He climbs the tower almost every day, checks the sensors mounted there and checks the computers in the ground station, which store all the data.

The sensors and a so-called eddy-covariance technique make it possible to collect precise data on the exchange of greenhouse gases such as methane, carbon dioxide (CO2), nitrous oxide and water vapor between the forest and the atmosphere.

"This tells us how the forest will help us in times of climate change," explains Kimbesa.

Until now, the tropical forest areas in the Congo Basin have received little attention – from science and the public – compared to those in Asia and Brazil.

This rainforest here is the second largest contiguous one in the world and covers almost 200 million hectares, the global importance of which is to be recorded with the help of the flux tower.

In order to maintain devices and sensors, Fabrice Kimbesa has to climb 221 rungs to the platform of the flux tower – and from there, 55 meters above the ground, he can see an almost endless forest area in the Congo Basin.

Photos: Nyani Quarmyne

Gas concentrations and wind speeds are measured in three dimensions ten times per second.

In this way, the vortices or “eddies” that transport gases such as CO2 and water vapor can be recorded and quantified.

During the day, when the sun shines, trees and microorganisms in the soil respire, but photosynthesis also takes place and the leaves absorb CO2, which is stored in the trunk, branches and roots.

Photosynthesis stops at night, trees and microbes release CO2.

The net ecosystem exchange, short NEE for Net Ecosystem Exchange, is obtained by continuously measuring the gas exchange.

In May 2022, special soil chambers are to be installed around the flux tower to determine the CO2 respiration of the soil,

with nocturnal eddy-covariance measurements one wants to determine the CO2 emissions from trees and soil.

From this, together with the NEE, the gross primary production can be calculated, i.e. the total amount of carbon that is fixed by trees in the ecosystem over a certain area in a certain period of time.

"This number is the most important to provide information about the CO2 storage potential of a forest," explains Pascal Boeckx, head of the isotope bioscience laboratory ISOFYS at the University of Ghent in Belgium, which, among other things, is the scientific and technical director of the CongoFlux towers.

It is crucial that the data is obtained without interruption over longer periods of time.

However, guaranteeing this is difficult: the Congo Basin has one of the highest rates of lightning strikes in the world.

In May 2021, lightning struck a tree, which subsequently damaged the 2.5-kilometer power cable connecting the tower to a solar farm on the edge of the forest.

The sensors failed for weeks and replacement cables now have to be transported to the biosphere reserve.

That may take until March or longer.

To ensure that the measurements are not interrupted for too long, Kimbesa and his colleagues have installed a few solar cells directly on the tower.

The eddy-covariance measurements are made for different ecosystems such as grasslands, peatlands and forest landscapes.

There are more than 1400 such stations worldwide,

on the African continent there are only about ten, and these are mostly in savannas or in other non-comparable areas.

This is what makes the CongoFlux tower so unique.

The technology is operated with solar energy, the electricity has to be routed through a 2.5 kilometer long cable through the forest to the CongoFlux tower.

Photo: Nyani Quarmyne

The raw data from the Congo Basin is regularly stored, uploaded to the cloud and subjected to quality control.

The processed data is then made accessible via the "Integrated Carbon Observation System" and Fluxnet, so that researchers can create Earth system models, for example.

These are climate models that also simulate chemical and biological processes on earth.

So far, data from the Amazon region has often been used for this.

"However, there are still no measurements to validate the results of these models for the Congo Basin," says Boeckx.

But this is important: This forest differs significantly from the Amazon forest in terms of structure, tree species and human influences.

The measurements of the tower could therefore become an important anchor point for models that serve, for example, to forecast

How climate change will affect forest CO2 uptake.

In May 2022, additional sensors will be installed for eddy-covariance measurements of methane and nitrous oxide.

Additional information is collected in the measuring radius of the tower, for example about leaf surfaces and soil conditions, and there is also a tree inventory.

Data to assess air pollution is also collected.

Ozone in the troposphere is a greenhouse gas, but also a pollutant that can cause respiratory problems and, above a certain concentration, impairs the photosynthesis of trees.

So far, there has been a lack of reliable measurements for this region, but the first data are now available: the ozone values here are sometimes as high as those measured in Europe.

"Everyone thinks just because it's a tropical forest means it's untouched."

PASCAL BOECKX

“Everyone thinks just because it's a tropical forest means it's untouched.

But the atmospheric pollution over this forest is actually quite high,” says Boeckx.

The reason for this is the burning of biomass, not necessarily in the forest itself, but north and south of it, where smallholders traditionally practice fire clearing before tilling their fields: their fires release nitrogen oxides into the atmosphere.

At the same time, tropical forests produce volatile organic compounds that their leaves release.

If these now meet nitrogen oxides under the influence of sunlight, ozone is formed.

According to Boeckx, this leads to high ozone concentrations of up to 60 ppb;

anything above 40 ppb affects photosynthesis.

The Belgian researcher reports on models

according to which, as ozone increases, the photosynthetic capacity of these forests will decrease in the future because the population increases and so more fields are burned to increase yields.

Therefore, measuring actual ozone concentrations is important to support such models.

On the flux tower, which with its struts is reminiscent of a high-voltage pylon, a device also takes care of the soot, because this provides information about the amount of biomass burned.

"The burned areas that our station notices can be 2,000 or 3,000 kilometers away," says Boeckx.