Twenty years after a storm brought it down, an oak tree has almost entirely rotted away. All that remains is the knot of its roots, which the speaker pictures in two striking images: the spokes of a wheel with no rim, and a crippled star. Both suggest something that was once whole and now isn't, a shape that still hints at the structure it used to have.
The last stanza turns the scene into a small puzzle. The roots are what's left because something in them was hard, and that same hardness once kept them from gripping the ground firmly enough to hold the tree up in the wind. Now, even as everything else decays, that stubbornness refuses to let go. The poem leaves it to us to wonder whether this is a flaw or a kind of endurance.
The mood is quiet and observant, a little sad but not dramatic. The speaker doesn't say how they feel outright. They simply look closely, and the careful, spare description lets a sense of loss and grudging respect come through.