Is it permissible to cut down harmful trees in graveyards?

Trees that harm visitors to graves should be cut down and their thorns removed. It is not permissible to plant trees or palm branches on graves, because the Prophet, peace and blessings be upon him, did not do so except for two graves that were known to be undergoing torment. He did not plant on the graves in Medina or Al-Baqi', nor did the Companions do so.