Answer: Mistletoe

Among all the Christmas-related decorations millions will string, stand, and otherwise arrange this holiday season, only one of them is capable of wiping out entire swathes of forest. Mistletoe, an evergreen plant commonly hung in North American and European homes around Christmas, is a a hemi-parasitic plant that survives by driving its root structure right into the bark of a host tree and siphoning nutrients off of it–a large enough infestation can easily take down a healthy tree.