Question: In the neighborhood in which I reside there are neighbors with fruit trees whose branches extend into the sidewalk and make passage for pedestrians most uncomfortable. What is the right thing to do if the owners of the trees refuse to trim those branches?
Answer: When this question was put to Rabbi Yitzchak Zilberstein, rav of the Ramat Elchanan community in Bnei Brak, he compared the situation to that of someone harboring a dangerous animal. The ruling of our Sages is that one may take the law into his own hands and eliminate the danger. The basic concept of this ruling is that the rabbis have the power to expropriate a danger to the public.
Rabbi Zilberstein even went a step farther. Should the offending branches be that of an etrog tree, he noted, the civic-minded Jew who trims them can use an etrog from the tree for the fulfillment of the mitzvah on Succot. Even though one must own the etrog he uses on the first day of the Festival, the trimmer is considered the owner because of the rabbinical expropriation.