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Holobionts: a new Paradigm to Understand the Role of Humankind in the Ecosystem

You are a holobiont, I am a holobiont, we are all holobionts. "Holobiont" means, literally, "whole living creature." It ...

Showing posts with label holobiont. Show all posts
Showing posts with label holobiont. Show all posts

Tuesday, September 12, 2023

How to Freeze a Holobiont: The Great Proterozoic Catastrophe

 

Image created by Dall-E


One of the great features of climate science is that you always learn new things. It is the story of how our planet evolved, changed, and arrived where we are, silly naked apes as we are. One of the most fascinating moments of this long history is the "Snowball Earth" period. Some 700 million years ago, in the Sturtian period, at the end of the Proterozoic Eon, the whole planet got frozen, covered by an ice sheet. Yes, Earth was all white, ice-covered, and nicely frozen. The great holobiont that some call "Gaia" nearly died. It may have survived, barely, because some small areas, maybe volcanic hot springs, remained ice-free.

Why this event? An ongoing research effort is aimed at unraveling the story. The latest results show that the great freezing was preceded by the "Franklin Large Igneous Province" (Franklin LIP). It was another spectacular event but for the opposite reasons. It involved a gigantic volcanic eruption that spread molten lava over a huge region that went from the regions now called Alaska and Greenland. It lasted about one million years. Earth's history is never boring!

Now, some recent data show that the Franklin LIP took place immediately before the great Snowball Glaciation. And the proposal is that the LIP caused the snowball. 

Great, but one moment. There have been several Large Igneous Provinces, LIPs, in the later history of Earth. In most cases, the result was warming, not cooling. The "great dying" of the end of the Permian, about 250 million years ago (at the "Permian-Triassic" boundary) was caused by a giant LIP in the region called Siberia today. The demise of the dinosaurs (apart from birds) was caused by another huge LIP taking place in the Deccan region in what is now India (an asteroid may have helped, but the LIP was probably the main cause). Smaller LIPs also caused havoc in the ecosystem. 

The basic idea is that these huge eruptions inject large amounts of CO2 into the atmosphere, generating a rapid and catastrophic warming that, in turn, causes a dieoff in the ecosystem. So, what did the Franklin LIP have that is different from the more recent LIPs? Is this a new demonstration that climate science is all wrong, actually a hoax created by the appliance industry to force us to cook on induction stoves?

Well, no. If you know the basic mechanisms that control CO2 concentrations and consequently Earth's temperature, the story makes plenty of sense. The Franklin LIP was not different (not so much, at least) from the later LIPs. But the world in which these eruptions took place was completely different. 

Let's start from the beginning: How do LIPs emit CO2? It is because the volcanic lava contains carbonates, compounds that can decompose, producing CO2 and oxides. As for all chemical reactions, the equilibrium between CO2 release and uptake depends on temperature. At the high temperatures of molten lava, carbonates tend to decompose, but, when the lava cools down, the reverse reaction occurs. Now, CO2 reacts with silicates to form carbonates. If the mass of lava is truly huge, as it was in the Franklin LIP, then it is no surprise that the CO2 drawdown is massive. If the temperature is hot enough, but not too hot, the drawdown is also rapid, at least on the geological time scale. Starved of CO2, the atmosphere doesn't act any longer as a blanket to keep the Earth warm. Bang! It is snowball Earth. 

Now, there comes the fundamental point: at the time of the Franklin LIP, the interplay between CO2 release and uptake took place in a relatively simple world: There was no life on land; it only appeared a couple of hundred million years later. So, since the LIP took place mainly on land, it didn't interact with the land biosphere. Then, fast forward 400 million years in the future, and you are now seeing the huge, gigantic, enormous, appalling lava landscape that we call the Siberian LIP. Same thing as before, but with a profound difference. By then, life had spread on land and had plenty of time to create huge reservoirs of carbon that resulted from the decomposition of living matter. This carbon we call "coal." In addition, there were also reservoirs of kerogen (solid hydrocarbons dispersed in the soil) and those hydrocarbons that the naked apes living today on Earth call "fossil fuels." 

Imagine the lava spewing out from the Siberian LIP going through this mass of fossil carbon, and you see that there was a factor that didn't exist with the Franklin LIP: coal was burned by the hot lava and turned into CO2. The same thing happened some 190 million years later with the Deccan LIP. Huge amounts of carbon were turned into CO2 and the resulting warming wrecked the whole ecosystem. Bang! Another mass extinction (the poor dinosaurs were boiled alive). That was the rule with all the Phanerozoic LIPs; their correlation with mass extinctions is reasonably well established, although the details can be complicated. You can find more information in this paper by Ernst and Youbi.

And there we stand: the story of life on Earth is an incredible adventure that sees the geosphere, the atmosphere, and the biosphere interacting with each other, usually resulting in a certain degree of stability but sometimes leading to great upheavals. It is what's happening now, with a large tribe of naked monkeys having taken control of the biosphere and playing the role of a Large Igneous Province by burning the huge reserves of fossil hydrocarbons built over the Phanerozoic Eon. For sure, this new "artificial LIP" will not lead to cooling but to warming. A huge and rapid warming. Gaia will probably survive it, but the monkeys... well, it all to be seen


A simple discussion of the recent results on the Franklin LIP  can be found on Anton Petrov's blog.

How Gaia survived Snowball Earth is described in this post by Ugo Bardi https://theproudholobionts.blogspot.com/2022/12/how-gaia-saved-earth-from-cold-death.html

The paper on the Franklin LIP by Dufour et al. that stimulated this post can be found at https://www.sciencedirect.com/science/article/pii/S0012821X23002728

The link to the paper by Ernst and Youbi on mass extinctions is: https://www.sciencedirect.com/science/article/pii/S0031018217302857

If you cannot access these papers, ask me for a copy


Saturday, August 26, 2023

Lichens and Lichen Lovers. Holobionts Everywhere

 

Irene, a young biologist from Abbadia San Salvatore, embraces a beech tree growing on the slope of the Amiata Mountain in Tuscany, Italy. Note the white lichens growing on the surface. In addition to being a tree lover, Irene is also a lichen lover. And a holobiont, too. 


"Life did not take over the globe by combat, but by networking" -- Lynn Margulis, 1996


It is not so easy to find fellow lichen lovers. Lichens are so common and yet so misunderstood and ignored, despite being the quintessential example of a holobiont. They are creatures formed of two completely different species, a fungus and an alga (or a cyanobacterium, not the same thing as an alga, but functioning in a similar way). Algae and cyanobacteria are photosynthetic organisms that provide food for the fungus. The fungus, in turn, digs up mineral nutrients from the substrate and provides them to the algae/cyanobacteria. A perfect example of symbiosis, lichens have existed for hundreds of millions of years, possibly billions of years, and they probably were the first organisms to colonize the land in very ancient times. 

Once you discover lichens, you can't avoid being fascinated by their incredible variety of shapes and colors. They can have tiny, leafless branches (fruticose), flat leaf-like structures (foliose); they may form  a crust that adheres to the substrate, (crustose), have a powder-like appearance (leprose); and more. They give you some ideas of the overall health conditions of the biome in which they appear, especially if they appear in the foliose state. Some of them are edible and they have been appreciated as food by many traditional culture and also by reindeer. Below, a print shows Japanese lichen collectors


In our culture, lichen lovers are a little rare, but they do exist, and when they find each other they may engage in lyrical appreciations of the lichens they observe, as I did when I met Irene, in the woods of the Amiata mountains. There is a facebook site on lichens (unfortunately it has not been updated during the past three years), an active "società lichenologica italiana", a "British Lichen Society,"  and you can surely find many more sites on the subject by searching the Web. But the mere fact of seeing these little creatures for what they are is a source of endless wonder. You don't need to be in the wild. You can find plenty of lichens anywhere in urbanized areas. 

Here are some white lichens growing on the nearly forgotten tomb of Vernon Lee (1856- 1935) British writer and poet who lived most of her life in Tuscany. Poetry is a form of virtual holobiont growing in the mind. 



h/t Irene Mazza, Cinzia Mammolotti, and Miguel Martinez



 

Friday, June 30, 2023

Tickling Gaia's Feet. How to Deforest Oneself to Death



Image from Dezgo.com


A few years ago, I published the article reproduced below on my blog "Cassandra's Legacy" I think it is worth republishing it because the debate on global warming has entered a frenzied phase. On one side, the rapid rise of temperatures is evident, and it is worrying people a lot. On the other side, it has caused many people to take refuge in the usual cherry-picking. Hannibal's elephants crossing the Alps is a typical argument that revolves around the idea that "Climate has Always been Changing." 

But it is true that the climate has always been changing. A little, at least. The question is why. In this post, I advance the hypothesis that human actions were an important contribution to the creation of the "Roman Warm Period" (RWP) by deforesting the land, while after the collapse, the forests returned, creating the LALIA (Late Antiquity Little Ice Age). Small variations, but enough to affect humans a lot. These data may be seen as a confirmation of the importance of forests in affecting the atmosphere's temperature as an effect of the operation of the "biotic pump." Tickling Gaia's feet may be very dangerous if She decides to stomp you out. 


Sunday, February 14, 2016

The collapse of the Western Roman Empire: was it caused by climate change?



Image from the recent paper by Buentgen et al., published in "Nature Geoscience" on February 8, 2016. The red curves are temperature changes reconstructed from tree rings in the Russian Altai (upper curve) and the European Alps (lower curve). Note the remarkable dip in temperatures that took place starting with the 6th century AD. But, by then, the Western Roman Empire was past and gone. Its collapse was NOT caused by climate change. 


The relationship between climate and civilization collapse is a much-debated subject. From the recent collapse of the Syrian state to the much older one of the Bronze Age civilization, climate changes have been seen as the culprit of various disasters befalling human societies. However, an alternative view of societal collapse sees it as the natural ("systemic") result of the declining returns that a society obtains from the resources it exploits. It is the concept termed "diminishing returns of complexity" by Joseph A. Tainter.

On this point, there may well exist several causes for societal collapse. Either climate change or resource depletion may sufficiently weaken the control structures of any civilization to cause it to fold over and disappear. In the case of the Western Roman Empire, however, the data published by Buentgen et al. completely vindicate Tainter's interpretation of the collapse of the Roman Empire: it was a systemic collapse, and it was NOT caused by climate change. 

From the data, we can see that there was a cooling episode that probably affected the whole of Eurasia, starting at the beginning of the 6th century AD.  This period is called LALIA (Late Antiquity Little Ice Age), and it seems to have been stronger than the better-known LIA (Little Ice Age) that took place during the 18th and 19th centuries. The LALIA was caused, at least in part, by a series of volcanic eruptions that injected large amounts of particulate in the atmosphere; cooling it by reflecting sunlight. Overall, temperatures went down by a couple of degrees in comparison to the time that we call the "Roman Warm Period."

A brutal cooling, yes, and it surely had effects on human life, as discussed at length in the paper by Buentgen et al. But it had nothing to do with the fall of the Western Roman Empire, whose decline had started at least two centuries before. The Empire started its final disintegration phase at the beginning of the 5th century when it ceased to be able to garrison the fortifications at the borders. Then, Rome was sacked for one first time in 410 AD; and finally destroyed by the Vandals in 455 AD. That was the true end of the Western Empire, even though, for some decades, there were still individuals who claimed the title of Emperors. But all that took place in a period of relatively stable climate, at least from what we can say about the available data. So, the collapse was systemic, related to factors other than climate and, in my opinion, mainly related to the collapse of the Roman financial system; in turn caused by mineral depletion.

But could it be that, after all, there is a correlation between the Roman collapse and climate change? Just it would be the reverse of what it had been sometimes proposed: could the Roman collapse have caused the LALIA cooling (or, at least, contributed to it)? The idea is not farfetched: the population collapse that took place with the fall of the Empire could have led to a considerable level of reforestation of Western Europe, and that would have absorbed CO2 from the atmosphere. That would have been an added factor to volcanic cooling. It is an idea already expressed some time ago by William Ruddiman. It seems to be out of fashion nowadays, but I think that it should be explored more.

In the end, this story can teach us a lot: first of all, how fragile climate is. In the interpretation by Buentgen et al., just three volcanic eruptions - relatively large ones, but not truly gigantic - were sufficient to cause a two-degree cooling extending all over Eurasia. Think of what could be the effect if something similar were to happen in our times! Then, it shows also how the situation, today, has completely changed. Temperatures have taken a completely different trend with the start of large-scale emissions of greenhouse gases in the atmosphere. Incidentally, these data also confirm the "Hockey Stick" data by Michael Mann and others. Global warming is real, the earth's climate is fragile, and we are in big trouble.

Additional note: The data published in "Nature" generated a truly awful article in the "Daily Express" titled "Mini-ice age 1,500 years ago contributed to fall of Roman Empire". There, they put together an incredible mix of unrelated things, showing, for instance, gladiator games that had ceased to exist at least one century before the LALIA. Then, they say that the 6th-century cooling "contributed to the collapse of the Eastern Roman Empire." Which is an interesting extrapolation since the Eastern Empire didn't collapse until about a thousand years after the LALIA!!  At least, they should go back to junior high school, but, on the other hand, think of how they report about climate change: what would you expect from them when they discuss the Roman Empire?

(h/t Graham Readfearn)

Monday, June 26, 2023

How is the Great Holobiont Doing? Alive, but not so Well

 



This is a translation of a recent article I published in an Italian newspaper, "Il Fatto Quotidiano." It refers to the Italian situation, but I think it can be interesting for an international readership. Note how I tried to explain the situation in simple terms, remaining within very strict length limits. The article turned out to be popular, but, as usual, I received my daily dose of insults in the comments. It is like this -- people have an inner rage that they need to unleash in one way or another. I can understand them, but I wish they would find a better outlet for their sacrosanct rage.  Above, an image from the recent floods in Emilia Romagna in Italy, mentioned in the article as the cause of a quarrel between believers and unbelievers.


From "Il Fatto Quotidiano


Climate Change: Where do we stand?

By Ugo Bardi June 05, 2023


The environment and climate are not often mentioned in the media, apart from particular moments such as in the case of the controversy that followed the flooding in Emilia-Romagna. However, on longer time scales, we see that concern about climate change is gradually spreading. The latest Eurobarometer data (you can find them at this link) show that 12 percent of Europeans put climate change among their top concerns, with Italy exactly in the middle. This is not so small as it sounds: 10 years ago, only 6 percent of Europeans gave this answer, and in Italy, 4 percent. Even compared to pre-covid times (now remote), this year we gained a couple of "worry points."

The reaction to the perception of a serious problem can be simply to deny that it exists, but it may also be to exaggerate it. This was the case with the flooding in Emilia-Romagna where it was obvious to some that climate change was to blame while, for others, it was all the fault of the Greens, or perhaps the river rodents called "nutria." More generally, it seems clear that the rise in the number of worried people is going in parallel with that of the number of skeptics. The latter are very active in the discussion, albeit at a rather superficial level, with various accusations of conspiracies of the strong powers and reasoning about things like the Alps with no ice in the Middle Ages, and why don't you consider the effect of the sun, and then today it is raining, so what? On the other side, the reaction is not so much better. "The IPCC says so, hence it's true," or, worse, in Italy there came the proposal to ban by law "climate denialism." 

But instead of launching into talk of conspiracies or invoking censorship, shouldn't we try to better understand what we are talking about? Climate science was not invented by the WEF in cahoots with the Lizard People. And climate models are quite a different matter compared to the two hand-drawn curves that were used as an excuse to lock us at home at the time of the pandemic. Climate science has more than a hundred years of history of studying a difficult and complex subject and is now one of the most active and fruitful fields of study in modern science. It has given us a grand and fascinating picture of the behavior of Earth's climate over a time span of hundreds of millions of years and more. It allows us to interpret how the biosphere was able to survive all this time and to understand how phases of climate instability led to the great mass extinctions. That of the dinosaurs, 66 million years ago, was only one of many and not even the largest. 

Nothing about climate science is beyond criticism. In fact, without criticism, there is no progress. So, let us maintain a healthy skepticism, but let us also avoid destructive polemics that serve only to demonize, not to build. If we take the correct attitude, we see that climate change is not something that models predict for the more or less distant future. It is happening here and now: we can see it, and we can measure it. We have reached a CO2 concentration not seen in millions of years before our time, when temperatures were 4-7 degrees higher than today. And the temperature continues to rise. This year, the development of the condition called "El Niño" in the Pacific Ocean is already causing particularly high temperatures, and it could lead to 2023 breaking all historical records. 

The change is already doing us major damage, for example, making Italian cities unlivable in summer unless in conditioned environments. Not to mention the return of mosquitoes, now victorious everywhere. But the worst damage is being done by the tropicalization of the climate, with prolonged periods of drought alternating with periods of heavy rains. That these intense rains played a role in the disaster in Emilia Romagna is at least likely, although rain was certainly not the only factor at play. Add to that the disappearance of snow in the mountains that used to act as a water reservoir in the summer, and you understand the problems that drought brings to agriculture and why there is talk of ongoing desertification for southern Italy, and perhaps not only for the South. 

These problems can only get worse if we continue to behave as we have been doing, which is to ignore the impact of human activities on the ecosphere. CO2 emitted by fossil fuel combustion is probably the main factor causing warming, but others, such as deforestation and loss of biodiversity, have their weight. 

But let's end on a few optimistic notes. The first is that the global transition to renewables is going great. We have passed the $1 trillion per year level of investment in the transition. If we keep it up, we can reasonably hope to get rid of fossil fuels in a reasonable timeframe. Plus, we are seeing some "greening" of the planet, almost certainly caused by the fertilizing effect of CO2 (see this link). So it seems that the goddess Gaia is trying to lend us a hand in avoiding the worst. But we have to work on it, otherwise, the old lady might decide she can't stand us anymore and make us go the way of the dinosaurs.


Friday, April 7, 2023

Trophic Rewilding: A Cure for a sick Planet?

 


The Mammoth Steppe was a huge area that extended over most of Northern Eurasia, including part of Alaska. It existed during the last glacial period, 126,000 YBP–11,700 YBP. Then, it was superseded by modern boreal forests during the thaw that led into the Holocene. The question of what factors led to this huge switch in the dominant biome is far from being clear. If "rewilding" some areas of the Earth is a good idea, should we strive for forests or steppes? After all, they are both "natural" environments?   


You may have already seen this paper just appeared on "Nature" with the title: "Trophic rewilding can expand natural climate solutions." The study is led by Oswald Schmitz of Yale University and is an assessment of the role of natural trophic chains on climate and of the perspectives of using "rewilding" as an important method for the mitigation of global warming. It has been described as a "landmark paper," and in several respects, it is. It is part of a general movement in favor of rewilding, and there is even a "Global Rewilding Alliance." 

The concept makes plenty of sense. It provides an alternative to the multiple bizarre ideas that have been proposed as "solutions" for the climate change problem, including cutting down the Boreal  Forests to increase Earth's albedo. On the other hand, it is still a subject in its infancy. One problem is that the authors do not mention that there is not just carbon sequestration at play in the climate game. They miss the effects of forests on the hydrological cycle (the kind of effects studied by Gorshkov, Makarieva, and others). But I think that it could be possible to merge these concepts together. In both cases, the idea is to restore the ecosystem to its maximum metabolic rate, balancing the disturbing effect of human activities. 

A deeper problem lies in understanding why exactly trophic chains have the effects claimed in the paper. The paper reports several estimates of the amount of carbon stored by various biomes, noting how it increases when a more diverse ecosystem is restored. To give an idea of the approach of the paper, the authors write that: 

The dividend of creating dynamic landscapes and seascapes is illustrated by the 1.2 million Serengeti wildebeest still found in Africa. This population annually migrates throughout the 25,000 km2 savannah– woodland landscape tracking lush vegetation created by seasonally and spatially varying rainfall. During the migration, wildebeest consume large amounts of grassland carbon and return it as dung that is incorporated by insects into soil storage. In the early twentieth century this dynamic was halted when the wildebeest population plummeted to 300,000 animals, decimated by rinderpest disease transmitted from domestic cattle. Consequently, there were too few animals to fully graze the landscape. The increased standing grass fuelled more frequent and intense wildfires that released carbon stored in the biomass across 80% of the landscape, which rendered the Serengeti a net source of atmospheric CO2 (ref. 47). Similar alterations of fire regimes followed the near-prehistoric extinctions of other large herbivores, the legacies of which persist today. Fire is an essential natural process in most of these systems, but the loss of natural grazing increases their frequency and intensity. Restoring the wildebeest population through disease management led to less frequent and intense wildfires, and gradually restored the Serengeti back to being a carbon sink. The Serengeti now stores up to 4.4 MtCO 2 more than when the wildebeest population was at its lowest. 

Which is truly fascinating. But why exactly should more diverse ecosystems store more carbon? One could say that if there were no wildebeest, then the forest would cover the Serengeti Park, and wouldn't a forest store more carbon than a savanna? Not necessarily. Large herbivores can sequester a lot of carbon in the soil, and it seems that the deep, fertile soil that Europeans found in the central area of North America was the result of the work of the huge herds of large ungulates living there. So, in terms of carbon storage, is a forest better than a savanna, or is it the reverse? 

Probably there is no clear-cut answer, and maybe there will never be one. Biomes are always dynamic; they change all the time. Although, in general, the ecosystem strives for stability, it may not be able to reach it except as an average -- it is sensible to even minor triggers such as the Milankovich oscillations that triggered the cycles of ice ages of the past two million years or so. But the Milankovich effects are just that: triggers. For the huge Earth ecosystem to move from a cold to a warm status, and the reverse, it takes enormous forces at play. In any case, the trophic chain remains the crucial factor in the ecosystem, the backbone of holobionts in their extended definition.


h/t John Day and Михаил Войтехов

Saturday, March 11, 2023

How Forests Create Rain: a New Study Demonstrates the Effects of Evapotranspiration


Image created by Dall-E

The idea that forests create rain has been known by peasants for hundreds, perhaps thousands, of years. The first scientific studies go back to Alexander von Humboldt (1769–1859), but the subject remains controversial. Nevertheless, we are starting to understand the deep and complex interactions between the atmosphere and the biosphere. They form a true "holobiont," a system of connected elements that affect each other in non-linear ways. A recent paper published by a research group led by Anastassia Makarieva shows how evapotranspiration, the evaporation of water by trees, modifies the water vapor dynamics and may generate high moisture content regimes that provide the rain needed by the land ecosystem. There is still much that we need to understand about these mechanisms, but one point is clear: forests are a crucial element of the stability of Earth's climate, and they must be preserved as much as possible (U.B.)


This is the press release about the new study. You can find the complete text here.

Forest transpiration and the terrestrial water cycle: A non-trivial relationship

Link

As water scarcity globally grows, and deforestation threatens the remaining natural forests, understanding how vegetation impacts the water cycle becomes increasingly important.  In their new paper, “The role of ecosystem transpiration in creating alternate moisture regimes by influencing atmospheric moisture convergence” published in Global Change Biology, an international and interdisciplinary team led by TUM demonstrated the existence of two potential moisture regimes – one drier, with additional moisture decreasing atmospheric moisture import, and one wetter, with additional moisture enhancing atmospheric moisture import. In the drier regime, water vapor behaves as a passive tracer following the air flow. In the wetter regime, it modifies atmospheric dynamics.


The team based their analysis on the previously established non-linear dependence of precipitation on atmospheric moisture content – increasing absolute humidity leads to a negligible precipitation increment if the atmosphere is dry, but to a large increment when the atmosphere is sufficiently wet. Combining this dependence with a full consideration of the water budget, the researchers showed that an increase in precipitation in humid conditions facilitated by increased evapotranspiration, should lead to enhanced moisture import. They illustrated these patterns with the data from the Amazon basin and the Loess Plateau in China.

Dr. Anja Rammig (TUM School of Life Sciences and study author) considers these results as having profound implications for the ongoing studies of the resilience of the Amazon forest in the face of the danger of deforestation and climate change. Dr. Scott Saleska (University of Arizona, study author) believes that the new results are in agreement with the profound role of leaf phenology in the Amazon forest for water cycle regulation. By forcing a decline in forest evapotranspiration, deforestation can dehumidify the atmosphere and thus drive the forest into the drier regime where transpiration of the re-growing vegetation would further aggravate aridity by decreasing moisture import. Getting out of this landscape trap could be impossible. Dr. Ruben Molina (University of Antioquia, Colombia, study author) hopes that the study findings will raise the awareness of the importance of tropical forest conservation.

Dr. Andrei Nefiodov (Petersburg Nuclear Physics Institute, Russia) participating in the study says that the new results corroborate the concept of the biotic pump of atmospheric moisture that emphasizes the dominant role of natural forests in transporting moisture inland. Dr. Antonio Nobre (INPE, Brazil, study author) compares this biotic moisture pumping to a beating heart, and highlights the good news: even in arid lands, by restoring the vegetation one should be able to enhance the atmospheric moisture convergence and streamflow. To achieve that, the ecological restoration strategy should be carefully designed to guide the ecosystem transition from the dry to wet regimes.

“I suspect that natural vegetation will be best for maintaining a moist and productive environment as these systems kept the world green and productive long before people got involved” – emphasizes Dr. Douglas Sheil (Wageningen University, author), collaborating on the research. “We do need to take into account the holobiontic relationships among all ecosystem elements that allow for an efficient regulation of the water cycle,” adds another author Dr. Ugo Bardi (Club of Rome, University of Florence).

Anastassia Makarieva (Institute for Advanced Study, TUM, lead author) emphasizes the need for a broad international cooperation in the studies of the ecology of the water cycle: “We have shown that the non-linear precipitation dependence on atmospheric moisture content, first noted by our co-author Dr. Mara Baudena (CNR-ISAC, Italy) and her colleagues, has widely ranging implications. The atmospheric water flows do not recognize international borders, thus deforestation disrupting evapotranspiration in one region could trigger a transition to the drier regime in another. Our results indicate that natural forests of the Earth, in both high and low latitudes, are our common legacy of pivotal global importance as they support the terrestrial water cycle. Their preservation should become a widely recognized priority for our civilization to solve the global water crisis.”

Thursday, February 16, 2023

Trees Come from Air

 


Richard Feynman, 1983. He didn't have the concept of "holobiont" -- but in this clip, he shows that he clearly understood the metabolism of the biosphere. (the part about trees starts at 3:50).

Monday, December 19, 2022

The Holobiont's Decisional System: A Comment by Helga Ingeborg Vierich




Helga in Botswana with two Kua friends (image source)

A post by Helga Ingeborg Vierich


Here, Helga comments on my previous post "Why do we Always Choose the Decisional System that do the Most Damage," where I discuss the case of the sinking of the "El Faro" ship, caused by the way the command structure was organized. "Pyramidal" decisional systems place the power in the hands of a single person, (typically a man) and the person in charge doesn't have the flexibility to change his opinion, nor the capability to access the data on what's really happening. A Holobiont-like decisional system is much more flexible and attuned to the real world, as Helga describes here.  



Dear Ugo; this is wonderful.

It explains the danger of hierarchies of powerful authority so clearly! I am teaching introductory sociology this term and will be making this one of the supplemental readings, for the topic right now is the development of state-level societies. It is, indeed, in state-level societies that we see the development of these kinds of hierarchies.

People have frequently pointed to the pecking order of chickens, and the evidence of hierarchies based on aggression in chimpanzees and baboons, and used this as a justification for human hierarchical social organization. As if it were, thus, "natural". But everything we know now, about the social organization and behaviour of people in "tribal" and "band" level societies (based on hunting, gathering, fishing, swidden horticulture, or nomadic pastoralism) suggests that before the state developed, seniority-based hierarchies of authority rare, and socio-economic and power-based hierarchies were unknown. Decisions were rarely made without extensive discussion.

The whole dynamic of morality in forager economies is to enforce a degree of social equality: the networks are based on relationships of mutual support, not chains of authority. There are no permanent leadership positions. Group actions to enforce punishment of transgressors appear to arrive through consultation and consensus.

We find these forms of consensus-creation preserved in tribal societies as well, even those with more permanent leadership positions. This is perfectly articulated in the following:

“...Roland Chrisjohn, a member of the Iroquois tribe and the author of The Circle Game, points out that for his people, it is deemed valuable to spend whatever time necessary to achieve consensus so as to prevent such resentment. By the standards of Western civilization, this is highly inefficient.

“Achieving consensus could take forever!” exclaimed an attendee of a talk Chrisjohn gave. Chrisjohn responded, “What else is there more important to do?”” (quoted from
http://www.filmsforaction.org/articles/the-more-a-society-coerces-its-people-the- greater-the-chance-of-mental-illness/ )

Unlike the hierarchical systems in many larger primates, like chimpanzees, ranking systems among foragers and even among pastoral and horticultural peoples, are not derived from intimidation and aggression, but by acquired reputation for demonstrated moral virtues - like articulating a consensus. Such people are valued by the community and thus listened to, only after a history of demonstrated integrity involving a list of highly valued signs of good character: generosity, diplomacy, honesty, loyalty and recognized proficiency at important skills (hunting, gathering, cooking, singing, trance-dancing, music, storytelling or comedy).

In other words, they are people of high rank and good reputation. Among hunter-gatherers, therefore, differences in social rank rarely result in social inequality of access to vital goods and services, but instead, ensure such access.

Indeed, aggressive hierarchies are not even innate, even in baboons. Such behaviour is cultural - learned and shared. This was shown very clearly in Richard Sapolsky's story of his Keekorok baboon troop, and how after the alpha males died from tuberculosis, the troop very quickly transformed into a very peaceful troop, and since then, a peaceful approach has become a cultural norm for them. This was in contrast to the normal high levels of stress in the aggressive hierarchies of baboons. Sapolski's research indicates that stress created by hierarchies is a killer in human societies, and he is not alone in saying this. Gabor Mate has been very clear on this too, and has linked stress, addictions, and even the addiction to power.

Yes, our societies, in the world today, need to become more of a holobiont: the integration of many co-dependents is always going to produce a less dangerous and stressful alternative.


regards, Helga



Friday, November 4, 2022

Forest Recovery: A quote by Anastassia Makarieva

 




You see, there is a succession process for forest recovery. We first have shrub grasses after some disturbance like fire, then it takes time for that to be replaced by trees. So if we are lucky, our grand grandchildren will be walking in such a forest, so this dimension should also be stressed. We are working for the future we are not just securing for ourselves some two dozen years of better comfort. Rather, we send a message through centuries such that people will remember us, and walking into this forest along the brooks and rivers they will remember us with gratitude for our care and dedication.

Anastassia Makarieva  




Tuesday, October 25, 2022

Can HolobiontsThink?

 


My wife, a holobiont called Grazia, hugs another holobiont, a Cupressus Sempervirens, in the hills near Florence, Italy

This is an excerpt from the chapter I am writing for a multi-author book 



I started this chapter by examining trees and forests as holobionts, then looking at human beings. Trees and humans are as alien to each other as we could possibly imagine. Humans are mobile creatures with an extravagantly powerful metabolism that makes them able to sustain protracted efforts longer than any other living animal. That turbo-charged metabolism is also used to maintain their large brains, of which they are very proud. They use their brains to control their muscles and their sophisticated sensory apparatus, as well as to deal with each other in complicated social rituals.

Trees are the opposite in almost all respects: they are immobile, their metabolism is slow: and they can’t even control their internal temperature. They don’t have eyes, nerves, brains, and not even muscles. Yet, they move, they sense their environment mainly by chemical signals, but also visual and mechanical ones -- including vibrations in the acoustic frequency. They "know" what's going on around them, but in ways that are mostly alien to mobile mammals, including humans.

Nevertheless, humans and trees are both holobionts at their core, and they share more than it would seem at first sight. It is not even forbidden to ask whether trees and other plants might be “conscious” in some way. This is a subject of wide debate, nowadays, and it would be out of the scope of the present text to enter into the details of a question whose answer depends primarily on the definition of the entity being debated. For what we are concerned, we can rather ask the question of whether some creatures store somewhere a schematic representation of at least some elements of the outside world, and modify their behavior depending on the sensor input they receive. That implies a certain level of “consciousness.”

In the case of human beings, there is no doubt that this capability exists. Assuming that most of the readers of this text are human, they should be familiar with the typical sensation of being encased in a bodily container. We have no direct perception of having a brain, but somehow we perceive that we are “inside” a body, that we are a sort of "homunculus" that resides someplace behind the eyes. And, surely, we do keep representations of the outside world, sometimes even too much, as when our political leaders claim that they can “create their own reality.”

How about a tree, then? Where would a tree have its representation of the outside world? As I said, trees have no brains and no nervous system, but they can transmit electric signals from cell to cell. It is a still scarcely known field, but it is known that the phloem and xylem cells form a network to transmit electrical signals long-distance within the plant. At the root level, the mycorrhizal system shares chemical signals within single plants and also from one plant to another. Would such a network be able also of storing information, just like a neural network does in animals? There is no reason to deny that it could. In this case, the representation of the outside world would be stored in the plant as a configuration of the network, continuously changed by sensorial inputs, and leading to signals being transmitted to the various parts of the plants instructing them, for instance, to release volatile organic compounds to fight an insect attack.

If that were the case, apart from the slippery concept of consciousness, a plant would not have the sensation of being encased in a bone cage that humans have. Its intelligence would be delocalized all over the structure. The plant would “feel” the conditions of the leaves, and the presence of sunlight. It would “smell” chemicals floating in the air and perceive the sound of living creatures moving in the vicinity. It would also be actively sending and receiving chemical signals through the mycorrhizal system. In short, it might have a representation of the external world of complexity comparable to the one that humans can build in from their sensorial input. Whether plants could also “create their own reality,” that is, dream, is impossible to say. Communicating with trees is a challenge that was never met, at least in terms compatible with the scientific method. Nevertheless, there seems to be a certain empathy between trees and humans. In the photo, the author’s wife, Grazia, communicates with a specimen of Cupressus sempervirens, in Tuscany.

About this encounter of these two holobionts, we may speculate about their reciprocal sensorial experience. For the human, the tree holobiont is perceived mainly as a visual entity -- but her sensorial system has no capability of detecting the underground root system. Nor she can detect the complex chemical signaling that the tree is operating inside and outside itself. For the tree, instead, the human cannot generate as a visual image, but it is possible that the tree perceives the human from the vibrations she generates and, maybe, detecting the chemical signals she produces. Whether the tree knows that it is being hugged is impossible to say, but we cannot completely discount this possibility. As a further note, both humans and trees use sunlight for chemical processing on their surfaces. Trees use it for photosynthesis, while humans need it to synthesize the compound called "Vitamin D" that they need for their survival.   

We can gather from this discussion that creating a representation of the outside world is a fundamental survival element of holobionts. And since holobionts are the main form that life on Earth takes, we should admit that all holobionts have this kind of capability. In other words, holobionts can “think.” Not in the same way as humans think, of course. But the process of thinking is part of the homeostatic adaptation that all living beings tend to attain. To accomplish that, they need to process information: it is the basic idea of the “dissipation structures” as defined by Prigogine. These structures process entropy and dissipate it, and entropy is basically information. So, holobionts are structured in such a way as to modify their internal structure to obtain homeostasis and maintain it despite changes in the structure of their environment. The holobiont itself is the holobiont’s “brain” and its internal structure stores a representation of the outside world.

Seen in these terms, the hypertrophic brain of which humans are so proud is not an exception to the rule that holobionts store information in their networked structure. All the neurons in the human brain are the same: there is no “super-neuron” that controls the other neurons. In a sense, you could say that the brain is a holobiont, possibly the biggest one known in the ecosystem in terms of the units it contains, with a total of some 86 billion neurons. It is still a small number if compared to the genetic information stored by the whole biosphere has been estimated as Thus, the total amount of genetic information stored in the natural biota is of the order of 1016 bit (Gorshkov et al., 2000) and coincides as an order of magnitude with the information stored in a human brain. This similarity may give us some interesting insights about the idea that the world in which we live is a single, extremely large, holobiont to which we sometimes give the name of Gaia, the Earth Goddess (Castell et al., 2019)



Friday, September 30, 2022

The Brain, the Gut, and How we get Old





A message sent to the "Proud Holobionts" forum. If you are interested in joining it, write at prudentlobster(thingette)gmail.com. Image from the Leverhulme Center for the Holobiont (yes, there exists such a thing!!)


Dear colleagues,

while every day humans demonstrate more and more their stupidity in the way they deal with each other, there is still such a thing as "real" science that moves onward. I found a recent paper by Dilara Hasavci and Thomas Blank of the University of Freiburg, Germany, that I think may be of interest to you at:

https://www.frontiersin.org/articles/10.3389/fncel.2022.944526/full

I do not claim to have been able to able to read and digest the whole paper, but it is surely fascinating. It is about how the health of the human brain is correlated to the gut microbiota. It sounds strange: why should these two organs be so strictly related to each other? And, yet, the brain is far from being a squishy version of the central processing unit of a computer. It is continuously kept, managed, maintained, repaired, and upgraded by a hugely complex system of specialized cells, mainly the "microglia," but also a host of macrophages: the authors say:

"Parenchymal microglia and perivascular, meningeal, and choroid plexus macrophages, representing non-parenchymal CNS-associated macrophages (CAMs), are among the innate immune cells of the brain (Kierdorf et al., 2019). Together, they significantly influence cerebral inflammation and can be targeted by gut-derived metabolites, especially with increasing age (Mossad and Blank, 2021). Activities connected with macrophages' highly developed lysosomal compartment are among their main tasks. Microglia and macrophages express a number of receptor families that help them degrade old, necrotic tissues and harmful substances from the circulation and their surrounding milieu (Prinz et al., 2017). The CNS is usually only mildly affected by transient activation of brain macrophages. Aging, on the other hand, is associated with chronic systemic inflammation and persistent brain macrophage activation, which can cause major physiological, behavioral and cognitive dysfunctions"

Surprisingly, or perhaps not, this apparatus is deeply affected by the gut microbiome. The connection is through the blood circulation system:

"Studies in germ-free (GF) mice revealed the importance of the microbiome in microglial development and maturation, as well as function in the adult brain. Microglia from adult GF and specific pathogen-free (SPF) mice display different morphologies including branch points, dendrite length, segment number, and cell volume. Additionally, the transcriptomic profile of microglia in GF mice shows a downregulation of several genes involved in cell activation and induction of immune response (Erny et al., 2015). The lack of mature gene expression in these microglia is linked to the absence of microbiota in the gut intestinal tract and disrupts their ability to respond to immunostimulants"

and

"Countless bacteria, viruses, yeasts, bacteriophages, and fungi inhabit our bodies. While microorganisms can be found on almost all environmentally exposed surfaces of our body, the gastrointestinal tract (GIT) shows the highest number and density of microbiota. These communities have significant impact on numerous physiological mechanisms, such as function of the immune system and metabolism (Zhuang et al., 2018; Dabke et al., 2019). The gut modulates several functions in the brain by bacteria-derived metabolites, hormones, and neuroactive substances reaching the CNS via the vagus nerve, enteric nervous- and circulatory system, and immune system"

And finally, note that

"Several studies have found that microbial metabolites can affect gut–brain responses, affecting the morphology and function of brain macrophages. These changes include their polarization and phagocytic capacity, which, in turn, controls behavior and emotional processes."

In short, the way we get old strongly depends on our gut microbiota. It seems also probable (although they do not say it in this paper) that the fact that some of us lose our brain capabilities with age also depends on that. I was just discussing today with a distressed colleague whose mother (88 years old) is going down the dementia road -- and yet, my wife's mother reached 101 years old without losing her mind. Is it all due to the gut microbiota? It would be wonderful if we could cure dementia with gut bacteria but, as they say in the paper,

" A roadblock in today's microbiota-based biomedical research is the modest and long-term impact on psychological and cognitive performance. Probiotic and microbiota-based therapies may take months to years to affect neuropsychiatric illnesses"

So, there are many things we still don't know about this story. It is another facet of the complexity of holobionts.



U.B.


Saturday, March 19, 2022

Holobiont Science: Stefania Consigliere on Bio-Anthropology

 




An image of the talk given today in Florence by Stefania Consigliere, who teaches at the University of Genova, Italy. A talk at a remarkably high level: an interdisciplinary romp on many facets of the modern crisis, touching individual health, the management of the pandemic, the cultural structure of our world, and how diet-based Chinese medicine is superior to our pill-based medicine. 

Note how the talk was given in the open, in a public garden, with all sorts of people attending. It would not have been possible to give it in a University: the bureaucratic rules would have prevented the general public from attending. And it is hard to see how a standard university department would have been able to stomach such a wide-ranging, heretic talk. It is sad to say that the Western universities have completely lost the role of keeper of knowledge and wisdom they once had. By now, they are completely self-referencing entities whose main purpose seems to turn smart people into idiots. 

What we did today is what I call "holobiont science." Science for human beings, with human beings, for the good of human beings. The people attending the talk were not scientists, they were a holobiont-like assemblage of varied people who wanted to learn something. And Stefania Consigliere did her best to transmit her knowledge to them. It is the same approach we took with a talk that Anastassia Makarieva gave in Florence a few months ago. No university, no bureaucracy, no permissions, no QR-codes. Just people getting together to learn. That's the definition I use for "social holobiont:" people collecting to do something together. 

I briefly intervened in the debate and I mentioned the concept of "holobiont" (Stefania had not used the term, but she had hinted at it using the concept of "symbionts"). And, you know? It turned out that several people in the audience knew what a holobiont is! Don't say that science does not progress!!


Monday, February 14, 2022

Holobiont Music

 



A clip that I just discovered, cited by Merlin Sheldrake in his book "Entangled Life" -- Sheldrake is an expert in fungi and he wrote a truly amazing book about the intricacies of fungal life - I am still reading it and I am more amazed after every page. The author uses the term "holobiont" only occasionally, but it is clear that it is a concept that merges very well with his description of how "mycobionts" merge with "photobionts" to form the fundamental unit of life on Earth: plants and fungi.

This song by Baka women is titled "Song for Gathering Mushrooms" -- it is a completely different idea from what we call "music" -- I'd say that our music is an organism where all players act according to an overall plan under a central control. The Baka music is something where everyone sings something different: there is no "rhythm," no synchrony, nothing like that. The result is a "sound holobiont" an entity that somehow mingles the various sounds in an organic and fascinating entity. It takes some time to get used to that, though!

Wednesday, February 2, 2022

Thinking like a Tree. Old-Growth Forests as Holobionts



A "holobiont" is a living creature formed of independent, but cooperating, organisms. It is a wide-ranging concept that can explain many things not just about the ecosystem of our planet, but also about human society, and even more than that. Photo courtesy of Chuck Pezeshky. This post was modified and improved thanks to suggestions received from Anastassia Makarieva.



When was the last time that you walked through an old-growth forest? Do you remember the silence, the stillness of the air, the sensation of awe, the feeling that you are walking in a sacred place? The inside of a forest looks like a cathedral or, perhaps, it is the inside of a cathedral that is built in such a way to resemble a forest, with columns as trees and vaults as the canopy.  If you don't have a forest or a cathedral nearby, you can get the same feeling by watching the masterful scene of the forest-God appearing in Miyazaki's movie, "Mononoke no Hime" (The Princess of the Ghosts). 

In a way, when you walk among trees, you feel that you are at home, the home that our remote ancestors left to embark on the mad adventure of becoming human. Yet, for some humans, trees have become enemies to be fought. And, as it is traditional in all wars, they are demonized and despised. It was the English landlord Jonah Barrington who commented about the destruction of Ireland's old forests that "trees are stumps provided by Nature for the repayment of debt." And, as it is traditional in all wars of extermination, not a single enemy was left standing. 

The war metaphor is engrained in our minds of primates, the only mammals that wage war against groups of their own species. So much that sometimes we imagine trees fighting back. In the "Trilogy of the Ring" by Tolkien, we see walking trees, the "ents," standing in arms against humanoid enemies and defeating them. Clearly, we feel guilty for what we have been doing to Earth's forests. A sensation of guilt that goes back to the time when the Sumerian King Gilgamesh and his friend Enkidu were cursed by the Goddess for having destroyed the sacred trees and killed their guardian, Humbaba. From that remote time, we have continued to destroy Earth's forests, and we are still doing that. 

Yet, if there is a war between trees and humans, it is not obvious that humans will win it. Trees are complex, structured, adaptable, tough, and resourceful creatures. Despite the human attempts to destroy them, they survive and even thrive. The most recent data indicate a greening trend of the whole planet [3], probably the result of humans pumping carbon dioxide (CO2) into the atmosphere (this greening is not necessarily a good thing, neither for trees nor for humans [4], [5]). 

But what are trees, exactly? They have no nervous system, no blood, no muscles, just as we have no capability of doing photosynthesis, nor of extracting minerals from the soil. Trees are truly alien creatures, yet they are made of the same building blocks as we are: their cells contain DNA and RNA molecules, their metabolism is based on the reduction of a molecule called adenosine triphosphate (ATP) created by mitochondria inside their cells, and much more. And, in a certain sense, trees do have a brain. The root system of a forest is a network similar to that of a human brain. It has been termed the “Wood-Wide Web” by Suzanne Simard and others [1]. What trees “think” is a difficult question for us, monkeys but, paraphrasing Sir. Thomas Browne [2], what trees are thinking, just like what song the Sirens sang to Ulysses, though puzzling questions are not beyond all conjecture. 

Whether trees think or not, they have the basic characteristics of all complex living systems: they are holobionts. "Holobiont" is a concept popularized by Lynn Margulis as the basic building block of the ecosphere. Holobionts are groups of creatures that collaborate with each other while maintaining their individual characteristics. If you are reading this text, you are probably a human being and, as such, you are also a holobiont. Your body hosts a wide variety of creatures, mostly bacteria, that help you in various tasks, for instance in digesting food. A forest is another kind of holobiont, vaster but also structured in terms of collaborating creatures. Trees could not exist alone, they need the all-important "mycorrhizal symbiosis." It has to do with the presence of fungi in the soil that collaborate with plant roots to create an entity called the “rhizosphere,” the holobiont that makes it possible for a forest to exist. Fungi process the minerals that exist in the soil and turn them into forms that plants can absorb. The plant, in turn, provides the fungi with energy in the form of sugars obtained from photosynthesis. 

So, even though trees are familiar creatures, it is surprising how many things are scarcely known about them and some are not known at all. So, let’s go through a few questions that disclose whole new worlds in front of us. 

First: wood. Everyone knows that trees are made of wood, of course, but why? Of course, its purpose is the mechanical support of the whole plant. But it is not a trivial question. If wood serves for mechanical support, why aren’t our bones made of wood? And why aren’t trees, instead, made of the stuff our bones are made of, mainly solid phosphate?

As usual, if something exists, there is some reason for it to exist. Within some limits, evolution may take different paths simply because it has started moving in a certain direction and it cannot move back. But, as things stand on Earth, wooden trunks are perfectly optimized for their purpose of support of a creature that doesn't move. Tree trunks (not palms, though) grow in concentric layers: it is well known that you can date a tree by counting the growth rings in its trunk. As a new layer grows, the inside layers die. They become just a support for the external layer called the “cambium” which is the living part of the trunk, containing the all-important “xylem”, the ducts that bring water and nutrients from the roots to the leaves. The cambium also contains the "phloem," another set of ducts that move water loaded with sugars in the opposite direction, toward the roots. The inner part of the trunk is dead, so it has no metabolic cost for the tree. Yet, it keeps providing the static support the tree needs. 

The disadvantage is that, because the internal part of the wood is dead, when a branch or a trunk is broken, it cannot be healed by reconnecting the two parts together. In animals, instead, the bones are alive: there is blood flowing through them. So, they can regrow and rebuild the damaged parts. It is probably a necessary feature for animals. They jump, run, fly, fall, roll, and do more acrobatic feats, often resulting in broken bones. Of course, a broken bone is a major danger, especially for a large animal. We don’t know exactly how many animals suffer broken bones and survive, but it seems that it is not uncommon: live bones are a crucial survival feature [6], [7]. But that's not so important for trees: they do not move and the main stress they face is a heavy gust of wind. But trees tend to protect themselves from wind by shouldering against each other – which is, by the way, another typical holobiont characteristic: trees help each other resisting wind, but not because they are ordered to do so by a master tree. It is just the way they are.

That's not just the only feature that makes wood good for trees but not for animals. Another one is that bones, being alive, can grow with the creature they support. They can even be hollow, as in birds, and so be light and resilient at the same time. If our bones were made of wood, we would have to carry around a large weight of deadwood in the inner part of the bone. That's not a problem for trees which, instead, profit from a heavier weight in terms of better stability. And they do not have to run unless they are the fantasy creatures called "ents."  Spectacular, but Tolkien would need to perform some acrobatic feats of biophysics to explain how some trees of Middle Earth can walk around as fast as humans do.

So, there is plenty of logic in the fact that trees use wood as a structural material. They are not the only creatures doing that. Bamboos (bambusoideae), are also wooden, but they are not trees. They are a form of grass that appeared on Earth just about 30 million years ago, when they developed an evolutionary innovation that makes their "trunk” lighter, being hollow. So, they can take much more stress than trees before breaking and that inspired many Oriental philosophers about the advantages of bending without breaking. Among animals, insects and arthropods use a structural material similar to wood, called "chitin." They didn't solve the problem of how to make it grow with the whole organism, so use it as an exoskeleton that they need to replace as they grow.

Now, let's go to another question about trees. How does their metabolism work? You know that trees create their own food, carbohydrates (sugar), by photosynthesis, a process powered by solar light that works by combining water and carbon dioxide molecules. One problem is that sunlight arrives from above, whereas trees extract water from the ground. So, how do they manage to pump water all the way to the leaves? 

We animals are familiar with the way water (actually, blood) is pumped inside our bodies. It is done by an organ called "heart," basically a "positive displacement pump" powered by muscles. Hearts are wonderful machines, but expensive in terms of the energy they need and, unfortunately, prone to failure as we age. But trees, as we all know, have no muscles and no moving parts. There is no “heart” anywhere inside a tree. It is because only the feverish metabolism of animals can afford to use so much energy as it is used in hearts. Trees are slower and smarter (and they live much longer than primates). They use very little energy to pump water by exploiting capillary forces and small pressure differences in their environment. 

"Capillary forces" means exploiting interface forces that appear when water flows through narrow ducts. You exploit that every time you use a paper towel to soak spilled water. It doesn't happen in human-made ducts, nor in the large blood vessels of an animal body. But it is a fundamental feature in the movement of fluids in heartless (not in the bad sense of the term) plants. But capillary forces are not enough, by far. You need also a pressure difference to pull the water high enough to reach the canopy. That you can attain by evaporating water at the surface of leaves. The water that goes away as water vapor creates a small difference in pressure that can pull more water up from below. This is called a "suction pump." You experience it every time you use a straw to drink from a glass. It is, actually, the atmospheric pressure that pushes the water up the straw. 

Now, there is a big problem with suction pumps. If you studied elementary physics in school, you learned that you cannot use a suction pump to pull water higher than about 10 meters because the weight of the water column cannot exceed the atmospheric push. In other words, you wouldn't be able to drink your coke using a straw longer than 10 meters. You probably never made the experiment, but now you know that it won't work! But trees are far higher than ten meters. You just need to visit your local park to find trees that are far taller than that. 

That trees can grow so tall is a little miracle that even today we are not sure we completely understand. The generally accepted theory for how water can be pumped to such heights is called the “cohesion-tension theory” [8].  In short, water behaves, within some limits, as a solid in the live part of a tree trunk, the “xylem.” The ducts do not contain any air and water is pulled up by a mechanism that involves each molecule pulling all the nearby molecules. The story is complicated and not everything is known about it. The point is that trees do manage to pump water to heights up to about 100 meters and even more. There is a redwood tree (Sequoia sempervirens), in California, that reaches a height of 380 feet, (116 m). It is such an exceptional tree, that it has a specific name “Hyperion.” 

Could trees grow even higher? Apparently not, at least not on this planet. We are not sure of what is the main limiting factor. Possibly, the cohesion-tension pumping mechanism that brings water to the leaves ceases to work over a certain height. Or it could be the opposite problem: the phloem becoming unable to carry sugar all the way down to the roots. Or, perhaps, there are mechanical limits to the trunk size that can support a crown large enough to feed the whole tree. 

Nevertheless, some works of fiction imagined trees so huge that humans could build entire cities inside or around the trunk. The first may have been Edgar Rice Burroughs, known for his "Tarzan" novels. In a series set on the planet Venus, in 1932, he imagined trees so big that an entire civilization had taken refuge in them. Just a couple of years later, Alex Raymond created the character of Prince Barin of Arboria for his "Flash Gordon" series. Arboria, as the name says, is a forested region and, again, trees are so big that people can live in them. More recently, you may remember the gigantic "Hometrees" of the Na'vi people of planet Pandora in the movie "Avatar" (2009).  In the real world, some people do build their homes on trees -- it seems to be popular in California. The living quarters must be cramped, to say nothing about the problems with the static stability of the whole contraption. But, apparently, a section of our fantasy sphere still dreams about the times when our remote ancestors were living on trees. 

But why do trees go to such an effort to become tall? If the idea is to collect solar light, which is the business all plants are engaged in, there is just as much of it at the ground level as there is at 100 meters of height. Richard Dawkins was perplexed about this point in his book “The Greatest Show on Earth” (2009), where he said:
“Look at a single tall tree standing proud in the middle of an open area. Why is it so tall? Not to be closer to the sun! That long trunk could be shortened until the crown of the tree was splayed out over the ground, with no loss in photons and huge savings in cost. So why go to all that expense of pushing the crown of the tree up towards the sky? The answer eludes us until we realize that the natural habitat of such a tree is a forest. Trees are tall to overtop rival trees - of the same and other species. … A familiar example is a suggested agreement to sit, rather than stand, when watching a spectacle such as a horse race. If everybody sat, tall people would still get a better view than short people, just as they would if everybody stood, but with the advantage that sitting is more comfortable for everybody. The problems start when one short person sitting behind a tall person stands, to get a better view. Immediately, the person sitting behind him stands, in order to see anything at all. A wave of standing sweeps around the field, until everybody is standing. In the end, everybody is worse off than they would be if they had all stayed sitting.”
Dawkins is a sharp thinker but sometimes he takes the wrong road. Here, he reasons like a primate, actually a male primate (not surprising, because it is what he is). The idea that trees “compete with rival trees – of the same and other species” just doesn’t work. Trees can be male and female, although in ways that primates would find weird, for instance with both male and female organs on the same plant. But male trees do not fight for female trees, as male primates do with female primates. A tree would have no advantage in killing its neighbors by shadowing them -- that wouldn't provide "him" or "her" with more food or more sexual partners. Killing the neighbors would perhaps allow a tree to grow a little larger, but, in exchange, it would be more exposed to the gust of wind that could topple it. In the real world, trees protect each other by staying together and avoiding the full impact of gusts of wind. 

It doesn’t always work and if the wind manages to topple a few trees, then a domino effect may ensue and a whole forest may be brought down. In 2018, some 14 million trees were destroyed in Northern Italy by strong gales. The disaster was probably the result of more than a single cause: global warming has created winds of a strength unknown in earlier times. But it is also true that most of the woods that were destroyed were monocultures of spruce, plantations designed for wood production. In the natural world, forests are not made of identical trees, spaced from each other like soldiers in a parade. They are a mix of different species, some taller, some less tall. The interaction among different tree species depends on a number of different factors and there is evidence of complementarity among different species of trees in a mixed forest [9], [10]. The availability of direct sunlight is not the only parameter that affects tree growth and mixed canopies seem to adapt better to variable conditions. 

As a further advantage of being tall, a thick canopy that stands high up protects the ground from sunlight and avoids the evaporation of moisture from the soil, conserving water for the trees. When the sun makes the canopy hotter than the soil, the result is that the air becomes hotter higher up, technically it is called "negative lapse rate" [11].  Since the cold air is below the hot air, convection is much reduced, the air stays still, and water remains in the soil. If that's not completely clear to you, try this experiment: on a hot day, scorching if possible, stand in the sun while wearing a thick wool winter hat for several minutes. Then wear a sombrero. Compare the effects. 

So, you see that having a canopy well separated from the ground is another collective effect generated by trees forming a forest. It doesn't help single trees so much, but it does help the forest in conserving water by generating something that we could call a "holobiont of shadows." Each tree helps the others by shadowing a fraction of the ground, below. And that creates, incidentally, the "cathedral effect" that we experience when we walk through a forest. Again, we see that this point was missed by Dawkins when he said that "That long trunk could be shortened until the crown of the tree was splayed out over the ground, with no loss in photons and huge savings in cost." Another confirmation of how difficult it is for primates to think like trees. 

That doesn’t mean that trees do not compete with other trees or other kinds of plants. They do, by all means. It is typical for a forest especially after an area has been damaged, for instance by fire. In that area, you see growing first the plants that grow faster, typically herbs. Then, they are replaced by shrubs, and finally by trees. The mechanism is generated by the shadowing of the shorter species created by the taller ones. It is a process called "recolonization" that may take decades, or even centuries before the burned patch becomes indistinguishable from the rest of the forest.

These are dynamic processes: fires are part and parcel of the ecosystem, not disasters. Some trees, such as the Australian eucalypti and the African palms seem to have evolved with the specific purpose of burning as fast as possible and spreading flames and sparks around. Have you noticed how palms are “hairy”? They are engineered in such a way to catch fire easily. So much, that it may be dangerous to prune a palm by using a chainsaw while climbing it. A spark from the engine may set on fire the dry wood filaments and that may be very bad for the person strapped to the trunk. It is not that palms could have evolved this feature to defend themselves from chainsaw-yielding monkeys, but they are fast-growing plants that may benefit from how a fire cleans a swat of ground, letting them re-colonize it faster than other species. Note how palms act like kamikaze: single plants sacrifice themselves for the survival of their seed. It is another feature of holobionts. Some primates do the same, but it is rare. 

Other kinds of trees adopt the opposite approach. They optimize their chances for survival when exposed to fire by means of thick bark. The ponderosa pine (Pinus ponderosa) is an example of a plant adopting this strategy. Then there are more tricks: have you ever wondered why some pinecones are so sticky and resinous? The idea is that the resin glues the cone to a branch or to the bark of the tree and keeps the seeds inside. If a fire burns the tree, the resin melts, and the seeds inside are left free to germinate. More evidence that fires are not a bug but a feature of the system. 

In the end, a forest, as we saw, is a typical holobiont. Holobionts do not evolve by the fight for survival that some interpretations of Darwin’s theory had imagined being the rule in the ecosystem. Holobionts can be ruthless when it is necessary to eliminate the unfit, but they aim at an amicable convivence of the creatures that are fit enough. 

The “holobiontic” characteristic of forests is best evidenced by the concept of “biotic pump,” an example of how organisms benefit the holobiont they are part of without the need for hierarchies and planning.



The concept of biotic pump [11] was proposed by Viktor Gorshkov, Anastassia Makarieva, and others, as part of the wider concept of biotic regulation [12]. It is a profound synthesis of how the ecosphere works: it emphasizes its regulating power that keeps the ecosystem from straying away from the conditions that make it possible for biological life to exist. From this work comes the idea that the ecosystemic imbalance we call "climate change" is caused only in part by CO2 emissions. Another important factor is the ongoing deforestation. This is, of course, a controversial position. The general opinion among climatologists in the West is that growing a forest has a cooling effect because it removes some CO2 from the atmosphere. But, once a forest has reached its stable state, it has a warming effect on Earth’s climate because its albedo (the light reflected back into space) is lower than that of the bare ground. But studies exist [13] that show how forests cool the Earth not only by sequestering carbon in the form of biomass but because of a biophysical effect related to evapotranspiration. That is, the water evaporates at low altitudes from the leaves, causing cooling. It returns the heat when it condenses in the form of clouds, but the heat emissions at high altitudes are more easily dispersed towards space because the main greenhouse gas, the water, exists in very small concentrations. It may be a minor effect compared to that of the albedo, but it is a point not very well quantified. 

The concept of biotic pump states that forests act as "planetary pumping systems," carrying water from the atmosphere above the oceans up to thousands of kilometers inland. It is the mechanism that generates the “atmospheric rivers” that supply water to lands that are far away from the seas [14]. The biotic pump mechanism depends on quantitative factors that are still little known. But it seems that the water transpired by trees condenses above the forest canopy and the phase transition from gas to liquid generates a pressure drop. This drop pulls air from the surroundings, all the way from the moist air over the sea. This mechanism is what allows the inner areas of the continents to receive sufficient rain to be forested. It doesn’t work everywhere, in Northern Africa, for instance, there are no forests that bring the water inland, and the result is the desert region we call the Sahara. But the biotic pump operates in Northern Eurasia, central Africa, India, Indonesia, Southern, and Northern America.

The concept of the biotic pump is an especially clear example of how holobionts operate. Single trees don’t evaporate water in the air because they somehow “know” that this evaporation will benefit other trees. They do that because they need to generate the pressure difference they need to pull water and nutrients from their roots. In a certain sense, evapotranspiration is an inefficient process because, from the viewpoint of an individual tree, a lot of water (maybe more than 95%) is "wasted" in the form of water vapor and not used for photosynthesis. But, from the viewpoint of a forest, the inefficiency of single trees is what generates the pull of humidity from the sea that makes it possible for the forest to survive. Without the biotic pump, the forest would quickly run out of water and die. It often happens with the rush to "plant trees to stop global warming" that well-intentioned humans are engaged in, nowadays. It may do more harm than good: to stabilize the climate, we do not need just trees, we need forests. 

Note another holobiontic characteristic of trees in forests: they store very little water, individually. They rely almost totally on the collective effect of biotic pumping for the water they need: that's because they are good holobionts! Not all trees are structured in this way. An example is the African baobab, which has a typical barrel-like trunk, where it stores water more or less in the same way as succulent plants (cacti) do. But baobabs are solitary trees, 

Incidentally, evapotranspiration is one of the few points that trees have in common with the primates called "homo sapiens." The sapiens, too, "evapotranspirate" a lot of water out of their skins -- it is called "sweating." But the metabolism of primates is completely different: trees are heterothermic, that is their temperature follows that of their environment. Primates, instead, are homeotherms and control their temperature by various mechanisms, including sweating. But that doesn't create a biotic pump! 

The concept of "biotic pump" generated by the forest holobiont is crucial the correlated one of "biotic regulation," [12] the idea that the whole ecosystem is tightly regulated by the organisms living in it. Natural selection worked at the holobiont level to favor those forests that operated most efficiently as biotic pumps. Plants other than trees and also animals do benefit from the water rivers generated by the forest even though they may not evotranspirate anything. They are other elements of the forest holobiont, an incredibly complex entity where not necessarily everything is optimized, but where, on the whole things move in concert. 

It is a story that we, monkeys, have difficulties in understanding: with the best of goodwill, it is hard for us to think like trees. Likely, the reverse is also true and the behavior of monkeys must be hard to understand for the brain-like network of the tree root system of the forest. It does not matter, we are all holobionts and part of the same holobiont. Eventually, the great land holobiont that we call “forests” merges into the greater planetary ecosystem that includes all the biomes, from the sea to land. It is the grand holobionts that we call “Gaia.” 



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