"though once they are bowed
So low for long, they never right themselves:..."
See in text (Text of the Poem)
This description of the birches represents an example of both personification and the pathetic fallacy. The speaker subtly imagines the birches as people “bowed/so low for long, they never right themselves.” As the poem unfolds, it becomes increasingly clear that the speaker views himself as such a person, particularly when comparing himself to the carefree, birch-swinging boy he once was.