When we walk through a forest and look up, we find a very curious image: the trees seem to have been designed to maintain a small and constant distance between them. This artistic picture of lines drawn in the sky is due to a natural phenomenon that has been universally baptized as "timidity". In fact, "shyness" is the phenomenon by which treetops avoid touching each other and the "crack or groove of shyness" is the distance they leave between them. These separations usually measure between 10 and 50 cm.
Botanists have been studying this phenomenon since the 1920s, but it was not until the late 1950s that it was named. The word comes from the English "crown shyness", term coined by the Australian biologist Maxwell Ralph Jacobs, who began the study of this phenomenon. The Australian studied the cracks of shyness in the eucalyptus forests. Their results were collected in the book "Growth habits of the eucalypts", where he explained that these cracks were due to direct physical contact between treetops. The botanist concluded that the shoots were sensitive to the friction of the wind-blown branches, which caused their rupture. This theory suggests that the empty space between them would not be "premeditated", that is, the branches would not have grown voluntarily avoiding each other. At first, the border branches would touch but the continuous shock induced by the wind would damage their tissues limiting the growth.
However, despite the efforts of Ralph and many other botanists, the exact origin of shyness, one of the most curious phenomena of the plant world, is still unknown.
Currently, there are several theories that try to respond to this phenomenon. Ralph's theory implies some unconsciousness of trees: shyness would be the result of their own limitations. However, subsequent studies with the camphor tree (Dryobalanops sumatrensis) found no evidence of friction on contact between the branches.
And if it is the trees themselves that decide to stay away from each other for reasons of coexistence? It may not be so far-fetched.
Plants may not make decisions the way humans do, but they do take the initiative when it comes to choosing one direction of growth or another. They have sensors, photo-receptors that operate and are activated depending on the available light (they are the ones that allow the flowers to orient in relation to the sun, for example). It is known that many plants know where their neighbors are and dodge them on purpose. The objective is to avoid competition for light, an essential resource for the survival and development of vegetables.
In fact, in studies with the camphor tree it was observed that the shoots were especially sensitive to solar radiation, since they are in a stage of very active growth. When they approach other branches they detect that the amount of light diminishes and they "decide" to grow towards another direction more illuminated.
With its leaves from the prized photoreceptors phytochrome, the growth of treetops would shoot in two different directions. On the one hand, it would look for spaces where the incidence of sunlight is greater. On the other hand, it would avoid the shadow zones (precisely those that would generate the presence of their forest companions). The result would be group shyness, a reasonable way of sharing the light that hits their respective cups.
It is believed that shyness also prevents the spread and spread of certain diseases, being a defense mechanism that would slow the rapid development of epidemics. In this sense, timid trees would have a selective advantage over those that do not avoid contact. And the phenomenon of shyness only affects certain species of trees. Many species are not shy and their crowns touch and entangle without complexes. Even so, it is rare that two glasses are completely intermixed.
Be that as it may, trees are aware of their peers, and the spaces and silhouettes would be the result of a competition for survival. In Europe, oaks and pines are good examples of timid trees, unable to touch their nearest neighbors.