A new mishnah! Things in the natural world that were worshipped - and whether that worship made them prohibited for benefit. For the most part, the hills and so on are permitted - the worship doesn't change them, but the obligation to destroy the idolatry itself kicks in. Adornment in the name of idolatry would be different - and prohibited. Also, a redundancy in the Torah: a prohibition against trees that are forbidden because they have been worshipped - and then another verse prohibited "each leafy tree," which appears to be redundant. So Rabbi Akiva provides an explanation that presents a need for both verses. Plus, the question of intent - is the tree planted in the name of idolatry, in which case, it needs to be destroyed, or, alternatively, is the tree already there and then someone decides to worship it?