In many of Dylan Thomas' poetry, nature is heavily used in regards to imagery.
For example, in the poem "But Being Men" Dylan speaks of men walking through the forest afraid of waking the birds. The imagery used here represents men who wish to enter into things without causing problems for the things around them. In the poem, men are worried about the rooks, fearful they will wake them because of their heavy footfalls. Thomas reflects on children who would not wake the birds with their lighter footfalls. The point of the poem is that men walk with a heavy weight on their shoulders which can reek havoc on the things around them.
In another poem, "All All and All", Thomas begins the poem reflecting on the world around him: the the ocean, the ice, the lava, and the oil. This imagery speaks to the natural aspects of the world intermingled with the artificial: synthetic blood, ribbing metal, and seeded milling. Here the imagery used recognizes the imbalance between the natural and artificial world.