Deuteronomy 20:19; Deuteronomy 20:20

19 "When you besiege a city a long time, to make war against it in order to capture it, you shall not destroy its trees by swinging an axe against them; for you may eat from them, and you shall not cut them down. For is the tree of the field a man, that it should be besieged by you?

20 "Only the trees which you know are not fruit trees you shall destroy and cut down, that you may construct siegeworks against the city that is making war with you until it falls.