Natures wonders: trees and water supply stress (Introduction)

by David Turell @, Thursday, September 22, 2016, 20:44 (1385 days ago) @ David Turell

A great description on how trees learn to handle deluge and draughts:

"A mature beech tree can send more than 130 gallons of water a day coursing through its branches and leaves, and this is what it does as long as it can draw enough water up from below. However, the moisture in the soil would soon run out if the tree were to do that every day in summer. In the warmer seasons, it doesn't rain nearly enough to replenish water levels in the desiccated soil. Therefore, the tree stockpiles water in winter.

"In winter, the tree is not consuming as much water, because most plants take a break from growing at that time of year. Together with below ground accumulation of spring showers, the stockpiled water usually lasts until the onset of summer. But in many years, water then gets scarce. After a couple of weeks of high temperatures and no rain, forests usually begin to suffer. The most severely affected trees are those that grow in soils where moisture is usually particularly abundant. These trees don't know the meaning of restraint and are lavish in their water use, and it is usually the largest and most vigorous trees that pay the price for this behavior.


"If a tree does not pay attention and do what it's told, it will suffer. Splits in its wood, in its bark, in its extremely sensitive cambium (the life-giving layer under the bark): It doesn't get any worse than this for a tree. It has to react, and it does this not only by attempting to seal the wound. From then on, it will also do a better job of rationing water instead of pumping whatever is available out of the ground as soon as spring hits without giving a second thought to waste. The tree takes the lesson to heart, and from then on it will stick with this new, thrifty behavior, even when the ground has plenty of moisture—after all, you never know!


"A much more obvious lesson in tree school is how trees learn to support themselves. Trees don't like to make things unnecessarily difficult. Why bother to grow a thick, sturdy trunk if you can lean comfortably against your neighbors? As long as they remain standing, not much can go wrong. In natural forests, it is the death from old age of a mighty mother tree that leaves surrounding trees without support. That's how gaps in the canopy open up, and how formerly comfortable beeches or spruce find themselves suddenly wobbling on their own two feet—or rather, on their own root systems. Trees are not known for their speed, and it takes some species many years before they stand firm once again after such disruptions.


" If trees are capable of learning (and you can see they are just by observing them), then the question becomes: Where do they store what they have learned and how do they access this information? After all, they don't have brains to function as databases and manage processes. It's the same for all plants, and that's why some scientists are skeptical and why many of them banish to the realm of fantasy the idea of plants' ability to learn.
"Gagliano studies mimosas, also called “sensitive plants.” Mimosas are tropical creeping herbs. They make particularly good research subjects, because it is easy to get them a bit riled up and they are easier to study in the laboratory than trees are. When they are touched, they close their feathery little leaves to protect themselves. Gagliano designed an experiment where individual drops of water fell on the plants' foliage at regular intervals. At first, the anxious leaves closed immediately, but after a while, the little plants learned there was no danger of damage from the water droplets. After that, the leaves remained open despite the drops. Even more surprising for Gagliano was the fact that the mimosas could remember and apply their lesson weeks later, even without any further tests.

"It's a shame you can't transport entire beeches or oaks into the laboratory to find out more about learning. But, at least as far as water is concerned, there is research in the field that reveals more than just behavioral changes: When trees are really thirsty, they begin to scream. If you're out in the forest, you won't be able to hear them, because this all takes place at ultrasonic levels. Scientists at the Swiss Federal Institute for Forest, Snow, and Landscape Research recorded the sounds, and this is how they explain them: Vibrations occur in the trunk when the flow of water from the roots to the leaves is interrupted. This is a purely mechanical event and it probably doesn't mean anything.1 And yet?

"We know how the sounds are produced, and if we were to look through a microscope to examine how humans produce sounds, what we would see wouldn't be that different: The passage of air down the windpipe causes our vocal chords to vibrate. When I think about the research results, in particular in conjunction with the crackling roots I mentioned earlier, it seems to me that these vibrations could indeed be much more than just vibrations—they could be cries of thirst. The trees might be screaming out a dire warning to their colleagues that water levels are running low."

Comment: We don't know trees learn, but I would guess DNA studies may find epigenetic changes. We know they release warning gases which require biochemical manufacture, something which be guided by genes.

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