The poem seems to be about trees, probably nine of them, that the speaker has known for a long time and thought of as companions. They stand together "like school kids in line," and the speaker imagines them watching from above, maybe amused, maybe judging. Mostly, though, they agree with whatever the speaker says, nodding in the breeze like loyal friends who never argue back.
The speaker assumed they would always be there. The turn comes in the last stanza, where a calm summer dusk is broken by the image of "men down, chopped up." The "beloved palms" suggests the trees were palms, and that they have been cut down. The word "heartbreak" in the title lands hard here.
The mood begins gentle and affectionate, even playful, then shifts to quiet shock and grief. The short, blunt ending leaves the loss feeling sudden and unfinished, like the speaker is still trying to take it in.