ref - wonderful article and great poems. I would like to talk more about your choices but I am struck by your final question

What do forests mean, I wonder? What about swamps?

We are surrounded by weather and landscape. Weather and landscape create moods as effectively as music. If we are bent towards interpreting symbolism, weather and landscape add depth, atmosphere, and meaning to poems and dreams.

Weather: fog, sun, rain -- sun can be bright and sunny or scorching and arid. The Hollow Men comes to mind - a poem full of weather and landscape:

    There, the eyes are
    Sunlight on a broken column
    There, is a tree swinging
    And voices are
    In the wind's singing
    More distant and more solemn
    Than a fading star.

The forest is the place where we find ourselves, stopping, going, choosing: -- "Two roads diverging in a single wood" or "Whose woods are these I think I know."

and the unforgettable opening lines of Dante's Inferno:

In the middle of our lives, I found myself in a wood so dark, the way ahead was blotted out.

  Nel mezzo del cammin di nostra vita
  mi ritrovai per una selva oscura,
  ché la diritta via era smarrita.

If it seems difficult in the woods, you sure don't want to find yourself in the poetic jungle:

  Now this is the Law of the Jungle -- as old and as true as the sky;
  And the Wolf that shall keep it may prosper, but the Wolf that shall break it must die.
  As the creeper that girdles the tree-trunk the Law runneth forward and back --
  For the strength of the Pack is the Wolf, and the strength of the Wolf is the Pack.

Kipling

so much to read, share, and discuss and so little time.