Deuteronomy 20:19-20

If you surround and attack a city for a long time, trying to capture it, do not destroy its trees with an ax. You can eat the fruit from the trees, but do not cut them down. These trees are not the enemy, so don’t make war against them. But you may cut down trees that you know are not fruit trees and use them to build devices to attack the city walls, until the city is captured.