Deuteronomy 20:19-20

19Perhaps you are preparing to attack a city. Your soldiers may have their camp around the city for a long time. If so, you must not cut down the fruit trees. Then you can eat the fruit from them. These trees are not people, like your enemies! So do not attack them!

20But you can cut down the other trees that do not provide any food. You can use the wood to make things that will help you to attack the city. You can do this until you go into the city and you take it for yourselves.