Deuteronomy 20:19-20

20:19 If you besiege a city for a long time while attempting to capture it, you must not chop down its trees, for you may eat fruit from them and should not cut them down. A tree in the field is not human that you should besiege it! 20:20 However, you may chop down any tree you know is not suitable for food, and you may use it to build siege works against the city that is making war with you until that city falls.