The speaker walks through a patch of woods, noticing things one at a time. Spicebush grows where a big birch once stood, and its allspice smell hangs in the air. Then a stiff scientific phrase, "heteromorphic self-incompatibility," drops into the middle of the poem, as if the speaker's mind has supplied a botanist's label for what they see. Partridgeberry's red berries are called "pills," a small, wry image.
The sign reading "END OF PUBLIC ACCESS" is a human boundary, but the poem undercuts it. Sun shines "right through" the plastic, so the sign looks flimsy and almost transparent. The last image, a crayfish walking upstream where the road crosses the creek, ignores the road and the sign completely.
The mood is quiet, curious, and gently amused. The speaker doesn't lecture. They simply pay attention, and the poem suggests that nature carries on, filling gaps and crossing lines, whatever rules people post.