What does the poplar tree in poem Mariana South by Alfred Lord Tennyson symbolize?

In the poem "Mariana South" by Alfred Lord Tennyson, the poplar tree symbolizes Mariana's solitary confinement and her longing for escape from her secluded existence. The tree stands tall and isolated in the landscape, much like Mariana herself, who is trapped within the walls of her grand but lonely ancestral home. The poplar's slender, upward-reaching branches suggest her yearning for freedom, while its restless leaves create a sense of unease and frustration. Throughout the poem, the tree becomes a recurring motif that reinforces the themes of isolation, longing, and the oppressive weight of time that Mariana is forced to endure.