The imagery of "the rugged trunk" as well as personification of having "scars" indicate that the Casuarina Trees of the poem symbolizes the long passage of time. This is because the tree must be timeworn to have accrued the ruggedness and scars. With these descriptors, the first stanza introduces the tree as a symbol which manifests time long past. Another personification in the first stanza makes clear that the tree involves the present spring of life, too: as a giant, the tree thus
wears the scarf, and flowers are hung
In crimson clusters all the boughs among,
Whereon all day are gathered bird and bee;
It becomes clear in the subsequent stanza that the tree blends with the memories of the poet’s siblings with whom she played under the boughs of the tree long ago in her childhood:
Beneath it, we have played; though years may roll,
sweet companions, loved with love intense,
For your sakes, shall the tree be ever dear!
The poet wishes to connect the memories of her dead siblings to the present life of the tree—and for all time, at that. This seems to be her overarching aim for the tree: to include her past in this symbol that endures into the future.
Therefore I fain would consecrate a lay
Unto thy honor, Tree, beloved of those
Who now in blessed sleep, for aye, repose,
Dearer than life to me, alas! were they!
May'st thou be numbered when my days are done
Thus the poet projects her wish for the tree to endure with all that it represents of her past beyond her own death. It is not for her sake, as she makes clear, so much as for that of her dear siblings.