Ki HaAdam Etz HaSadeh?

When 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? However, 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.

כי האדם עץ השדה FOR IS THE TREE OF THE FIELD A MAN [THAT IT SHOULD BE BESIEGED BY THEE]? — כי has here the meaning of “possibly”, “perhaps” — is the tree of the field perhaps a man who is able to withdraw within the besieged city from before you, that it should be chastised by the suffering of famine and thirst like the inhabitants of the city? Why should you destroy it?

"man is a tree of the field"...in my view this interpretation is not correct, because it makes no sense to explain a prohibition against destroying a fruit tree, on the grounds that a tree is not a man (and is thus incapable of running away). In my opinion there is no need for any of this. The meaning, rather, is as follows: You may eat of them, but do not cut them down, for man is a tree of the field (i.e., the life of man depends on the trees of the field). A similar construction appears in “for it is taking a life in pawn” [24: 6], which clearly means “it is taking the means of a man’s livelihood in pawn”. The phrase but do not cut them down is conceptually tied to the phrase to come before you in the siege, to wit: You may not destroy fruit-bearing trees, which are a source of life to mankind, but you may eat of their fruit; you are forbidden to destroy them so that the besieged city will surrender before you. The subsequent phrase cut to build up siegeworks is proof that this is the correct interpretation.

§ The Gemara relates another story about Ḥoni HaMe’aggel. Rabbi Yoḥanan said: All the days of the life of that righteous man, Ḥoni, he was distressed over the meaning of this verse: “A song of Ascents: When the Lord brought back those who returned to Zion, we were like those who dream” (Psalms 126:1). He said to himself: Is there really a person who can sleep and dream for seventy years? How is it possible to compare the seventy-year exile in Babylonia to a dream?One day, he was walking along the road when he saw a certain man planting a carob tree. Ḥoni said to him: This tree, after how many years will it bear fruit? The man said to him: It will not produce fruit until seventy years have passed. Ḥoni said to him: Is it obvious to you that you will live seventy years, that you expect to benefit from this tree? He said to him: That man himself found a world full of carob trees. Just as my ancestors planted for me, I too am planting for my descendants.