Edward Thomas's poem "Aspens" is autobiographical in the sense that the aspens metaphorically represent Thomas's understanding of himself as a poet. In stanza five, Thomas declares that "Aspens must shake their leaves and men may hear / But need not listen, more than to my rhymes." This is the first point in the poem where Thomas explicitly compares himself to the aspens. Just as it is the nature of the aspens to "shake their leaves," so too it is in Thomas's nature to write poetry, or "rhymes." The aspens do not "shake their leaves" for the benefit of the men in "the inn, the smithy, and the shop," and in the same way, Thomas does not write his poetry for the benefit of any and all readers. The implication is that both the aspens and Thomas are simply compelled to follow their nature, regardless of who might or might not hear them.

The connection between the aspens and the poet is confirmed in the sixth stanza, with the lines, "Whatever wind blows, while they and I have leaves / We cannot other than an aspen be."

The alternating rhyme scheme of the poem, whereby every other line rhymes, possibly reflects the aforementioned union between the poet and the aspens. They are as inextricably linked, as inter-dependent and as complementary, as are the rhymes in the poem. This simple rhyme scheme, in combination with the regular quatrains and the regular syllabic meter, all possibly allude to the simplicity of the aspens and the poet. They are both simple in the sense that they both simply, without question, abide by their nature.

"Aspens" by Edward Thomas is a poem that, at its most simple level, is about aspen trees and how they constantly blow in the wind, no matter who is near or what is going on in the world.  The meaning is that aspens are an eternal part of this world, and as everything else changes, dies or fades away, the aspens will still be there

"at the cross-roads talk[ing] together/Of rain, until their last leaves fall from the top."

Edwards strikes a rather ominious tone in the poem when he declares that

"The whisper of the aspens is not drowned,.../No ceasing, calls their ghosts from their abode."

Here he is saying that the whispering of the aspen leaves is never stopped, and it always calls ghosts out from hiding.  That is an interesting and creepy thought.  Edwards thinks that their noise is like "grieving", and that no matter who or what is near, the aspens will continue to grieve forever.

Edwards uses a rhyming scheme of ABAB, which means that the first and third lines, the A lines, rhyme, and the 2nd and 4th lines, the B lines rhyme.  He uses personification to give the trees human-like traits.  They "whisper" and "grieve".  He uses imagery (the five senses) to make the aspens seem more alive, and the atmosphere more mysterious.  He describes the "bare moonlight" and "thick-furred gloom," of the nighttime, the "lightless pane" of abandoned houses, the "empty lane" of deserted streets.  Using imagery like that creates a more lonely and mysterious mood.

I hope that those thoughts can help to get you started on the path towards understanding the poem more fully.  Good luck!