Deuteronomy 20:19-20

19When you lay siege to a city for a long time, fighting against it to capture it, do not destroy its trees by putting an ax to them, because you can eat their fruit. Do not cut them down. Are the trees people, that you should besiege them? 20However, you may cut down trees that you know are not fruit trees and use them to build siege works until the city at war with you falls.