The leaves they were crispèd and sere— The leaves they were withering and sere; (lines 2-3)
When this poem starts out, it isn't dealing with people or feelings or plot. It's just giving us a look around at the natural world, letting us absorb the landscape. Still, even though we haven't gotten to the action yet, these descriptions are preparing us for it. Dead leaves are a pretty obvious symbol for death, loss, and all that good stuff. By putting us in a late-October mood, Poe prepares us for the terrible things to come.
It was down by the dank tarn of Auber, In the ghoul-haunted woodland of Weir. (lines 8-9)
The lake and the woods almost feel like characters in this poem to us. The speaker brings them up over and over again, and they start to take on a kind of personality. We never meet these ghouls, but we can just imagine them lurking behind these spooky trees. This isn't really a nature poem per se, but the landscape really helps to make it rich and moving.
These were days when my heart was volcanic As the scoriac rivers that roll— As the lavas that restlessly roll (lines 13-15)
Honestly, this is our favorite part of the poem. What a great image. The speaker's heart isn't just bubbling with passion – it's exploding, erupting! We don't stop there. This epic simile rolls on and on. We can almost feel the heat from the lava as it rolls down the mountain. By the end, we've got a vivid sense of how strongly the speaker felt back then. Maybe we also feel like we've been on a little side-trip, an expedition to Mt. Yaanek at the North Pole.
And now, as the night was senescent (line 30)
The speaker doesn't know where he is or what month or day it is, but he's really plugged into the natural world. He's watching the stars, and he can feel the night fading. In a way, this poem seems to move to the rhythms of nature and the world much more than to clock time. If this guy wasn't so crazy with sadness, he'd be at home in bed, instead of out wandering in the lonesome forest.
Then my heart it grew ashen and sober As the leaves that were crispèd and sere— (lines 82-3)
This is one of a bunch of moments where the poem uses a simile to tie the natural world to the speaker's feelings. It's like the trees and his heart are vibrating at the same frequency. Suddenly, in this moment, they are joined, and the death and sadness outside becomes the same as what's happening inside the speaker.