Tuesday, May 25, 2021

The Secret of Holobionts: How Excessive Efficiency can Kill


Five minutes are enough to take a look at this amazing video. It is extremely well done and it tells you about things that you would never have suspected. How can it be that trees exist? Well, it turns out that their metabolism is truly alien and it exploits physical phenomena that you wouldn't have imagined could be used in that way. But Mother Gaia has many tricks!

One point that has fascinated me most is how this behavior of threes highlights a fundamental characteristic of holobionts: the individual organisms that form the holobiont do not act with a purpose, they do not have "in mind" to benefit the group. But, if it is true that what's good for the hive is good for the bee, also the reverse is often true. And especially in this case. 

Trees pump water by evaporating water, which means they lose most of it. From the video, you'll learn that just about 5% of the pumped water is used by the tree for its needs. The rest evaporates away -- it is the process of evapotranspiration. 

So, trees are highly inefficient pumping machines. But, curiously, this inefficiency is what benefits the forest. This huge evaporation is what puts in motion another pump: the biotic pump. It is a mechanism that generates a depression that, in turn, pulls water from the humid atmosphere near the sea all the way to the inner areas of the forest. Without this mechanism, forests could hardly exist inland. 

If trees were 100% efficient, they would evaporate nothing and the forest would die. I think there is a deep message here, not valid just for forests: too high efficiency can kill. Living is sharing, and if there is no sharing there is no life.





  1. Good piece and video.

    But there is also cavitation happening, https://www.kew.org/read-and-watch/the-tree-listener so I'm still a bit confused.

    Vital point about the biotic pump; I think there is too much focus on forests for biodiversity and carbon sequestration whilst the hydrology tends to get sidelined ... the former services won't function without water.

    Some experts think the Amazon is approaching a tipping point - when more than maybe 20% is cut then rainfall declines and the biome flips to savannah. Maybe the increasing droughts in Brazil (coffee price is shooting up due to drought) are the start of this, as the 'aerial rivers' wane.

    1. Yes, there is also this story of cavitation. The video I posted makes the point that the physics of water transportation in trees is completely known. It is not. Some points are still unclear, including the role of cavitation



Ugo Bardi is a member of the Club of Rome, faculty member of the University of Florence, and the author of "Extracted" (Chelsea Green 2014), "The Seneca Effect" (Springer 2017), and Before the Collapse (Springer 2019)