I was on my way to the sea and it occurred to me what Tosphot [Rosh Hashana 13a] means. In fact, it is true that Tosphot is saying that the Gemara in Avoda Zara 23b is referring to the "asherot"  אשרות שמדורות הראשונים in the question of the Gemara, not the answer. For like Rav Shach is saying, the answer refers to the trees that were on the land at the time it was given to Avraham. The thing that made this a little confusing is that the gemara itself qualifies the question after it has already given the answer. That is it asks, "Why did Israel have to burn the asherot? After all, no one can cause to be forbidden that which does not belong to him. And you can not answer "It refers to the ashrot that were planted after the land was given to Avraham and those trees in fact belonged to the Canaanites," because bitul [nullification would have been enough]. So then the Gemara answers that it refers to trees that were in the land at the time of Avraham, and then those trees were worshiped after Israel worshiped the golden calf, and thus those trees would have been required to be burnt.] This is why Tosphot refers to the "asherot from the previous generations" since he is talking about the question of the Gemara, not its answer.

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