Why don't the trees grow back?

health : Why don't the trees grow into the sky?

The atmosphere is constantly absorbing water that rains down elsewhere. Moisture is constantly evaporating not only over the seas, but also over land. What if a forest covers the land?

Then the water is simply drawn through the plants, says Ernst Steudle, plant ecologist at the University of Bayreuth. The evaporation on the leaves creates a suction that draws the water up through a system of pipes in the wood. “Most of the water absorbed is passed on to the atmosphere and is no longer used by the plant.” For example, a 25 meter high beech tree with a leaf area of ​​1500 square meters evaporates 400 liters of water on a summer day - and ensures a pleasantly humid climate in the forest.

The plant also regulates its water balance via the roots and the pipe system, but above all via closable pores in the leaves. It is astonishing what enormous heights trees overcome with their water transport. The tallest living coastal sequoia is 113 meters high. Eucalyptus species are similar in size. The strong pull of the leaves and the cohesion of the water molecules make this growth possible.

Electric charges are distributed asymmetrically in water molecules. Therefore, the molecules attract each other and can withstand high tensile stresses. While technical suction pumps work with pressures close to the vacuum, which means that a height difference of up to ten meters can only be overcome, some trees bring it to more than 100 meters due to the negative pressure in their transport system.

However, the water pipe against gravity will eventually reach its limits. In order to reach clear heights, strong negative pressures are necessary. This also changes the boiling point of the water. If the pressure is too low, gas bubbles form in the water, which interrupt the flow. But if the transport deteriorates, the tree stops growing in height.

Deciduous trees have wide vessels through which water can rise 20 meters in an hour. The vessels of the conifers are narrower and only transport water at one meter per hour. Even so, the tallest deciduous trees and conifers are about the same size. One reason for this could be different transitions between the vessels. In the case of conifers, these valves offer very little resistance to water transport.

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