The penultimate stanza of "The Trees" could be viewed as a volta, or turn, in the direction of the poem. The first two stanzas introduce the extended metaphor of the trees, and readers come to understand that the poem is about an oppressed group who are about to achieve a sort of freedom to grow as they are destined to. In the second-to-last stanza, the speaker self-references with the introduction of the first-person pronoun "I." It is arguable that then, readers come to understand that the speaker identifies with the trees that are about to break out of the artificial environment that has held them and move into their natural habitat: the forest that they will populate.
In the final paragraph, the speaker observes that the trees' moment of escape has come, and any voices in her head that speak against it will be silenced the next morning, the first day of freedom. The natural world has come to greet them, and the watchful moon has disintegrated into shards that reflect the immensity of the oaks which are now allowed to tower.
Traditional analyses of this poem postulate that the poet is writing about the situation of women from a feminist perspective. Women are moving out of the oppression that has held them unnaturally from their rightful place in the world.