Don't we overvalue the leeward? It may seem like everything. There are also malignant trees such as walnut (Juglans regia). In addition to the simple memory of the savage torture of the colonizers under his name, the usual saying of not showering under him: “Sleeping under the nut is bad.” The old Pliny also picked it up: “Its shadow is compact and causes headaches to people and damages everything planted in the area.” Otherwise, the walnut is formed by the expression “Intxaurra etxe txarrak”, “the nut tree does not want friends”, which José Kruz Etxeberria wrote in 1821, “the nut severely harms the vineyard and the countryside where it is transformed”. We know that the walnut does not want anyone around him to compete to take food from the earth. To do so, it accumulates in its leaves and roots a substance called juglone. The puff will fall on the ground, attacking the seagulls under the tree, and as in the roots… What is contained in the expressions we call today “alelopathy” and we know how it works little more. Walnut is a negative alelopathy, that is, it uses substances to harm them. Some eucalyptus (Eucalyptus spp.) The alelopathic “sweats” that segregate the foliar remains and the roots that accumulate beneath them are responsible for the “desert” plant of Eucaliptadi, which directly attack some microbes from the soil and above all many plant species until life itself cannot be carried away.

There are also positive alleopathies when one plant helps another. Green Bean (Phaseolus vulgaris) and strawberry (Fragaria x anananananassa) are great friends who, if they live together, will make their life much better and the harvest richer. There are many examples of this kind.

The most important help from trees and trees is what makes us. Alelopathy, the shadow that alelopathies give us, is not, as Beñat Sarasola says, a sneezing at noon on the bat. According to measurements from the Cooltrees program led by the French INRAE, when in a city street with trees planted on both sides the temperature drops about 7ºC, of course. Arborist Augustin Bonnardot, who worked on this program, told us the figure of 7: “This impact is only from trees of respectable size. These trees have to reach maturity in order to offer their full potential, so it is necessary to take good care and plant trees compatible with urban life”.

We have had a lot of work in this country, in the hands of most of our trees and trees, in the custody of arboricides, criminals, murderers. Do you know big trees in your city? Please at least the shadow.