Hi Asier. I would say that hazelnuts bear fruit every year. And if it doesn't, we have a problem. For this to happen, I see three possible problems: that the evil of the earth be an alteration that is not that of the place and that is attacked by some fungus; that it has pollination problems, that it flourishes and pollinates at the end of the fall and that it has a special problem, especially associated with time; or that the fruit falls by the fall of the fruit, by the extraction of the fruit, when the leaf opens or the fruit appears dry environment.