Here we’ll talk about three opinions on what happens if you have branches overhanging a public street. Mishnah says that if branches of a tree overhang a public street, we cut them down and trim them enough so that a camel and its rider can pass through. The rider is the tallest thing that would pass through the street. Once we trim the branches back, they may grow back a little, but we continuously trim them so that a camel and its driver can fit through. This is the opinion of Tanna Kama (first tanna).
Rabbi Yehuda says we don’t have to trim the branches back far enough for a camel and its rider to pass through. Rather, we only have to trim them enough so that a camel passing through with bundles of flax or twigs on its back can get through. We don’t have to clear the branches to that very high level, because a rider can simply duck between them. Therefore, we can just trim them enough for a camel and the bundles it’s carrying to pass through.
Rabbi Shimon made a third opinion of Rabbi Shimon. Rabbi Shimon says: Every tree that overhangs a public domain must have all its branches cut back along the mishkolet, the plumb line. Like we said earlier, that means anything overhanging the street at all is cut back all the way to the sidewalk, to the boundary. The reason is Tumah (ritual impurity). Rabbi Shimon is concerned that branches overhanging the street could halachically (according to Jewish law) become an ohel, a roof. If they’re overhanging a source of Tumah, let’s say there’s a corpse—a baby bird that is dead in the street—and these branches are directly over it. So there’s an ohel over a corpse. Then let’s say somebody rides under that branch, passing through the street. There’s a roof over them, and there’s a source of Tumah under them. Therefore, he’s going to become Tameh (ritually impure) without knowing it. So Rabbi Shimon says that, to make sure people don’t become Tameh without knowing it, all branches that overhang a public domain have to be trimmed back, regardless of their height. It all becomes irrelevant; we have to trim them back fully, all the way to the property line.