I agree with plantladylin, in that sooby identified this tree, resulting as Celtis australis; My acknowledgement by that.
The comment by Leftwood seems unfocused; I never pretended that the fungus I want to identify was in the photos attached with the purpose of identifying the tree; that's why I wrote "The leitmotiv to identify this tree is to identify a fungus living on it". It happens that I'm also a lichen lover and know very well that the photo with the trunk of the tree as many lichens attached and not only one crustose and one foliose. In fact, among the foliose we can see several of the genus Parmotrema (the grey ones on the right) and also several of the genus Physcia (the light bluish dispersed by the trunk); Among the crustose there are mainly two of the genus Pertusaria (one with the thallus clearly yellow, probably P. heterochroa) and one with whitish thallus; in addition at the bottom of the photo one can see one with black apothecia (probably, of the genus Buellia) and another with tan coloured thallus that is not possible to identify to genus only on the basis of a photo.
Best regards to all,