Yes, he is bound to try and dismiss this and probably thinks your friend will sit back and take it. I would advise your friend to pay a visit to the adjuntament, make sure he has all his paperwork with him to prove the land is his. Take some 'photos of the piece of land in question that the Spanish/ Catalan guy has been using. Ask them to please confirm in writing that this is indeed your friends piece of land and that the other chap has no legal claim to be using it. It may well be that he had some verbal arrangement with the last owner. That is all very well but now it is your friends land and he wants to use it. Once he has some type of letter from the adjuntament he needs to take  a copy and pass it by hand to the other chap. Try and be polite but firm and say you will give him for example up until the end of the growing season to quit his use of the land. If he agrees then you need to hold him to this, if he does not you need to point out clearly that you will issue a 'denuncia' at the adjuntament. The threat of this is often enough to resolve issues. If he still refuses issue your denuncia, you may need some help here if your language skills are not up to scratch. What you want to aim for is resolving the issue without having to pay costly solicitors fees. Does your friend have any local friends who could help to mediate for him? ie. talk to the Catalan bloke?

Hope this helps!

HI everyone, i have a good story on the same topic, i bought a piece of land up the tip road near ginestar,
i purchased 1.74h of land from a dodgy estate agent from benifallet area,at the time of purchase my neighbour cultivated part of the land which was on my map,and it so happens there was water on this piece of land but well within my boundaries,he also planted trees on the same bit,on the other side of the land the other neighbour claimed a large part of the land was his.
the combined size of stolen land being 6000 square metres,leaving me with 1.1h ,this was 4 yrs ago ,and guess what the tree neighbour has never touched his cultivated part and now it is all overgrown,
all the while the estate agent never once helped to resolve any issues with the neighbours ,no after sales service,she speaks fluent catalan and could have at least tried as i speak none ,so 4 yrs later the land lies deserted and worthless ,i cant even build on it.
so it seems that this is a common problem in that area.