If you take care of the land for a period of time (cannot precise) as
if it was yours, thinking it was yours and no one complais then you are
entitle to consider it yours and register it as yours... of course
there are some technical details, but it possible.

In the worst case scenario, the owner will appear and your problem is
solved, in the best scenario you should invite us all to a BBQ in your
new piece of garden