Gemara in Bava Batra page 26

There is an argument between עולא and רבין if one has a tree within 16 cubits of his neighbour, if he can bring first fruits, עולא said no. רבין said yes because יהושוה בו נון made a stipulation that one can bring first fruits in such a case. Besides that, there is another argument between תוספות and רבינו חננאל about the reason of עולא to forbid. To ר' חננאל, the reason is because of causing damage. To תוספות, the reason is ownership. If the reason is ownership, then עולא holds that when ר' יוחנן said the amount needed for a collector of the fallen fruit, that means 16 cubits. In the גמרא in בבא בתרא דף פ''א there is an argument what ר' יוחנן means. There are three opinions, 4 to eight cubits. Eight to sixteen or four to sixteen. עולא would hold the 16 is the only valid answer. As for רבין, we do not know what he holds. He might agree totally with עולא and disagree only on one account, that is the stipulation of יהושוה בו נון. Or there might be many other issues. The רמב’’ם holds the law is like רבין, and also that there is no law of distance of a tree from a neighbour except when the neighbour has trees also, and then the distance is four cubits. This is probably what the רמב’’ם thinks Rabin is in agreement with. Now there is also a different approach to this whole subject. It is רבינו חננאל that the reason for עולא is damages. But then it is hard to know from where the 16 cubits comes from. The משנה on page 25 holds 25 cubits if there is a pit in the field of his neighbour according to the חכמים, and zero cubits to ר' יוסי. If there are trees on the neighbour’s field, then the distance is four cubits according to a later mishna/ Rabin might hold like the ר' יוסי that a tree on one property causes no immediate damage to a neighbour’s field and so it does not have to be moved away