Anastassia Makarieva, co-developer of the concept of “Biotic Pump” was recently interviewed in a film produced by the New England Forests Group that you may find at this link (and also at the bottom of this post). The biotic pump is a fundamental idea that illustrates the way ecosystems regulate themselves by networking. In the case of forests, trees are the nodes of a giant network that operates using the typical win-win mechanism of holobionts. Each tree evaporates water to keep its own metabolic system working, but in doing so, it benefits the whole forest by creating a mechanism that pumps water from the ocean. It is the way most ecosystems work, including the huge one we call “Gaia.” Above, Anastassia Makarieva in the beech forest of Abbadia San Salvadore, in Italy, in 2023 (photo by UB).
From “The Return of Old Growth Forests”
Transcription by Duen Hsi Yen
[Narrator Ray Asselin] But older unmanaged forests have a value that extends beyond their natural resilience, complexity, soil health, and habitat value. It's now becoming clear that natural, time-tested forests can significantly regulate our weather patterns. Photosynthesis draws in carbon dioxide, and releases large amounts of water vapor. Leaves evaporate and transpire the water. Vapor accumulates and rises with the sun's heat. When the water vapor encounters cool air, it condenses, forming clouds. If conditions are right, we get precipitation. Atmospheric physicist Anastassia Makarieva is the co-developer of the Biotic Pump theory, which explains the crucial importance of the role that old-growth forests play in the Earth's hydrologic cycle.
[Anastassia Makarieva, 37 minute mark] So, how plants get their water...Moist air must come from the ocean to land and then it rises and then as the air rises it cools, and water vapor condenses and precipitates. So this is how plants are watered. And so the Biotic Pump explains how this process is in fact regulated by forests themselves. The air moves governed by pressure gradients.
What is a pressure gradient? It is when somewhere there is less air than somewhere else. Then the air streams to the area of low pressure. If the air is moist, and it means that it contains a lot of water vapor, and if there is condensation of water vapor so the water vapor molecules condense into droplets and occupy much less space than before, then we have kind of a rarification of local air and a drop of pressure. And this process generates a pressure gradient that can drive winds. So by regulating the rate of condensation, forests can actually regulate the wind.
And how do forests regulate the rate of condensation? So with these green leaves... they have stomata... small openings and when there is photosynthesis the stomata open to catch CO2 molecules. But during the same time there are many water vapor molecules emitted into the air. And this process moistens the atmosphere. And when the atmosphere becomes moist, the probability of condensation and of the ascending air motion rises exponentially with the amount of moisture. So by regulating the rate of evapo-transpiration, forests can actually induce the ascending air motion. And when there is ascending air motion there will be also horizontal inflow of air. And it can lead to the moisture import from the water bodies like the ocean or a big lake. And so the forest will be supplying itself with water.
The problem is that the water store on land is very transient. So if we stop the import of moisture via the atmosphere, all the rivers would steal all the fresh water from the continent in just a few years. So there must be continuous process returning water to land. Natural forests and mature forests are especially important because they kind of "know" and evolved to know when and how to transpire to trigger the right inflow of moisture.
Because... imagine you have some randomly planted vegetation or an even-aged stand which just transpires whatever they have in soil. Then if the atmosphere is too dry and the transpired moisture cannot trigger the condensation, it can all be lost and blown away from the area without triggering any inflow of moisture. So the forest must get more moisture than it has transpired to also compensate for the losses to the stream flow. And if condensation is not triggered in sufficient amounts, then there will be drying of the forest and this is what happens when we have unnatural stands or tree stands that do not have this capacity to regulate the water cycle in comparison to natural systems that have evolved this capacity tuned to the local geophysical conditions. So when we have large contiguous forest it brings moisture even further inland.
For example, if we speak about New England forests, we can say that the process of succession that began 100 to 150 years ago is transforming these forests to a state when they are more and more competent buffering the extremes, both droughts and extreme winds and floods. So, as succession goes and we allow it to continue to transform these forests into their natural state we can expect a better and better regulated and stable regional water cycle.
One thing that is important in the biotic pump mechanism is that the forest moisture store is an extremely valuable capital, or treasure of the forest, which shouldn't be wasted. It should be used wisely. And so when there is logging in the forest which opens the canopy, this leads to huge losses of soil moisture.
Why? When there is a closed canopy, the canopy is warmer than the soil. And because of the soil- air above the soil- is colder, it doesn't readily go up and so the soil is moist and the trees transpire from the underground layers. So we have moist ground surface in the soil and the fire probability is low.
Now, when we cut the trees and open the canopy the ground heats directly by the sun, it's heated, and then there is a much stronger convection, which just brings moisture away, the soil dries up- the upper layer-and so the temperatures can rise up to like 50° centigrade (122F) and the flammability increases abruptly. So, actually, fires follow logging.
There was a study made in Russian so-called intact forest landscapes which are landscapes where you cannot see any human disturbance when you use satellite images, so during the last like 50 or 30 years, depending on the images that you use, and they found that in intact forest the number of fires is 10 times less than in the forest that are exploited and logged and so not intact. So this is very important. The planet does warm, so there can be warm and dry periods, but still, if the forest is intact it can withstand it, because it has powerful mechanisms of how to stabilize its moisture store. But if we add to the global warming also disturbance by logging, we just undermine the forest capacity to manage drought, which it does have. There is a natural fire dynamic in a forest, which is like relatively infrequent fires, but then you add logging and the tree stands become even-aged and young and they have much higher flammability, and at a certain point the threshold is, like, passed and the ecosystem is put on a self-degradation trajectory and the landscape is trapped into a drier, depauperate state. So when we hear about the Canadian fires, huge fires, huge carbon emissions from these fires, this is packaged as global warming message but in reality if you look at the Canadian forests they are logged at a rate of about 1% per year, which means actually that in the steady state that the mean age of these forests is 50 years. So these are not natural forests but basically intensely exploited forests, and this dramatically reduces their capacity to regulate the water cycle and to keep moist, just because the climate regulating capacity cannot be maximized simultaneously with the commercial value of timber. These are different things.
The commercial tree stand is what we grow like a tree garden or something and just consume for our human needs. And we need to decide how much natural forest we need for climate stabilization and how much land we can allocate for these commercial and economic needs. These are separate categories. We... shouldn't mix them up, pretending that any forest can do this climate regulating job. This is not so!
Forests can only function normally and most efficiently in terms of climate regulation when they have the structure to be stable and to perpetuate in time, together with their climate. When we arbitrarily change what is in the forest we decouple these mechanisms, and forests' ability to stabilize environmental and climatic conditions deteriorates. So we need to keep these natural forests on sufficiently large territories for them to continue regulating our climate for us. So there is a red line which we cannot cross if we don't want our climate to destabilize to a state which will prohibit our normal existence.
...
It takes about 400 years to get the point of a fire resistant old growth forest! New England forests are now about 150 years old. The boreal forests of Canada are only 50 years old, which is why there are so many recent fires!
https://newenglandforests.blogspot.com/
https://en.m.wikipedia.org/wiki/Ecological_succession
#BioticPump #Holobiont
I´ve read Makarieva´s biotic pump theory and the forest age point got my attention.
In my understanding of agroforestry practices, some techniques can enhance a forest canopy age more than letting the trees left to their own devices.
For example, in syntropic agriculture, it states that frequent canopy and branch prunnings in specific seasons, can have a multiplying effect on growth hormones in conjunction with biodiverse plantings in creating more canopy strata and enhancing photosyntesis with more leaves and flushing more carbon in the soil, elevating its Carbon to Nitrogen ratio.
Older forests tend to have its C:N ratio above 100:1 and its moist soil have huge fungal mycelia networks, sometimes spanning kilometers.
More to the biodiversity point: a tree plantation, like eucaliptus monoculture isn't a forest at all.
Thank you for the transcript, Ugo.
Thank you for the insights, Anastassia.
:-)