The question that occurred to me at the police station was implicitly asked by Tosphot and answered. Just to give a background let me explain. The Gemara in Avoda Zara [page 23 side b] says when Israel came into the land of Canaan why did they have to burn all the asherot [worshipped trees] of the Canaanites? After all, no one can make forbidden that which belongs to his neighbor, and the land was given to Israel from the time Abraham. So it must be that since Israel worshipped the Golden Calf that makes the worship of the trees [asherot] OK to them, so  the Canaanites were acting as messengers for them.

Now the Gemara in Rosh Hashanah asks. how can it be that Israel brought the Omer [a offering of grain] right away when they came into the land? After all the only produce was grown by the Canaanites, and the verse says to bring the Omer from your produce, not the produce of a gentile.

On this Gemara in Rosh Hashana [page 13], Tosphot asks:  we know from the Gemara in Avoda Zara that the land belongs to Avraham from before Israel came into the land.(So the produce does in fact belong to them) Still the question is valid since the gentiles have ownership in the grain that they grow even if the land belongs to Israel. But if that is so then what is the question in Avoda Zara if after all the land is of Israel then the asherot are forbidden and need to be burnt. But the Gemara's question is from the asherot that were planted before the time of Avraham Avinu [Abraham the Patriarch]] that would be permitted in use by just nullification. [An idol of a gentile becomes permitted by simple nullification, without burning. Only an idol of a Israeli needs to be burnt]

So you see that it is implicit in the answer of Tosphot that trees that were outright owned by the Canaanites would come under the same category that tosphot brings about the trees that were planted before the time of Avraham