Although there are many trees that reach more modest heights of tens of meters, cases that exceed 100 meters are anecdotal. Is there a maximum height that trees can reach? And if it exists, what is it?
You might think that the answer is related to the resistance of the wood. But every good carpenter knows that wood with the grain is very resistant; Wood is not as limiting as it might seem. The true limit is marked by water.
What is the maximum height that trees could reach?
The vascular system of plants is made up of two types of tubes. The xylem, which starts from the roots, goes up the stem and branches and ends in the leaves, is responsible for transporting the raw sap, a fluid composed of water and mineral salts that are absorbed from the soil, to the photosynthetic part. The phloem runs parallel, in the opposite direction. Its function is to transport the nutrients synthesized in the leaves, in the form of , to the rest of the plant tissues. The processed sap descends due to the gravitational effect, so height is not an obstacle to growth. However, raw sap does have limitations.
Hypotheses abound that attempt to explain how water ascends through the xylem vessels. Unlike the circulatory system of animals, which have a pumping station, the heart, plants lack muscles that allow them to generate an active impulse that makes water rise. The xylem is structured by cell walls of dead cells. There is no pumping system.
At first it was thought that water rose by mere capillarity; Because the tubes are so thin, the surface tension of the water exceeded the force of gravity, and the water rose. However, the height that can be reached by this means, taking into account the thickness of the xylem tubes, is only 10 or 12 meters, which is insufficient. It takes extra effort to get the water to the leaves.
Taking all this into account, a theoretical approximation can be made about the maximum height that a tree can reach. It would be conditioned by the height at which, in the xylem tubes, the force of gravity is equal to the cohesive tension force of water.
That height that, if exceeded, the plant suffers cavitation. In thinner xylem tubes, and with smaller stomata, the height will be greater. Thus, the theoretical maximum height will not be the same for all tree species: depending on the specific features that that tree has, it may reach a different height. Therefore, it stands to reason that the best candidates for this calculation are redwoods and sequoiadendrons.
According to a research team led by George W. Koch from the University of Northern Arizona, the theoretical maximum that a sequoia could reach under optimal conditions is between 122 and 130 meters in height, as indicated in its publication in the scientific journal Nature.