The Gemara presents the following discussion:
If one person claims the trees on a field and the other one claims the land, Rav Zevid rules that each one owns the thing that he claims. Rav Pappa objects to this ruling, since the owner of the land can insist that the owner of the trees remove them from his property! Therefore Rav Pappa suggests that we must view the person who claims the trees as owning a share of the land, as well.
The language used by the Gemara in presenting this case is that each of the two people were maḥzik – took hold of – the thing that they claimed. The Rashbam understands that this is not a case of ḥazaka (presumptive ownership) of having worked the land for three years, which we have been discussing throughout this perek, rather that this is a discussion about two people, each of whom purchased a different part of the orchard from the original owner. The term ḥazaka in this case refers to the means of kinyan – of taking possession of the object at the time of purchase.
Tosafot disagree, arguing that the placement of this case here in the perek that deals with the idea of a ḥazaka of three years of working a field clearly indicates that the discussion is about two people, each of whom lays claim to the field based on their use of a different part of that field for three years. Rav Zevid’s ruling is that we accept each one’s argument with regard to the part that they had used.
The Ritva and the Meiri suggest that each of these explanations has merit, since they do not contradict one another. They are in fact complementary, for whatever action is effective for taking possession also is effective for establishing the presumption of ownership, as long as there is an accompanying valid claim as to how he became the owner.