In the stormy east-wind straining, The pale yellow woods were waning, (lines 118-119)
At this point, the natural world starts to reflect the mood of the Lady and the atmosphere of the poem. As her danger increases, as she gets closer to her doom, the sky gets dark and heavy, and a storm blows up. Making the natural world reflect human moods is a pretty old poetic trick, and Tennyson goes all out with it here.
The leaves upon her falling light-- Through the noises of the night (lines 138-139)
Although she won't make it to Lancelot, she does make contact with the natural world. The river rocks her, the wind blows her clothes and the leaves cover her. Even this close to death, she is feeling a kind of freedom and movement that was never there before. The story of her human isolation is really tragic, but maybe her meeting with the natural world gives it a little bit of a silver lining.