Human trees in the Bible?

DR. SHAI SECUNDA: “Are Trees of the Field Human?” (TheTorah.com).

Deuteronomy 20:19 forbids the chopping down of fruit trees during war-time, and offers the cryptic explanation כי האדם עץ השדה (ki ha-adam etz hasadeh), but what does this mean?

I was waiting for Ents to come up, but they didn't. Nevertheless, a timely essay.