Deuteronomy 20:16-20

Only in the cities of these peoples that the Lord your God is giving you as an inheritance, you shall not leave anything that breathes alive.

Instead, you shall utterly destroy them, the Hittite and the Amorite, the Canaanite and the Perizzite, the Hivite and the Jebusite, just as the Lord your God has commanded you,

so that they will not teach you to do all the same detestable practices of theirs which they have done for their gods, by which you would sin against the Lord your God.

“When you besiege a city for 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, so you shall not cut them down. For is the tree of the field a human, that it should be besieged by you?

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