Large book, about a sequoia or redwood in the pacific rainforest, it drops its nuts on the forest floor and several trees grow up around it, forming a circle. Ultimately it dies in a lightning storm, then becomes a nurse log. Beautiful artwork, animals, trees. Poignant story.
Well, it’s an oak tree, not a redwood or sequoia, but I think you must be looking for A Log’s Life by Wendy Pfeffer, with illustrations by Robin Brickman. The book starts out with the oak tree in the forest and shows some of the creatures that live in and around it, including a family of squirrels, a porcupine, carpenter ants, a woodpecker, beetles, and even fungi, slugs, and snails. One night there’s a huge storm and the tree is struck down by lightning, turning it into a log. The animals move in, boring and tunneling, as the log grows spongy and falls apart, finally becoming a layer of rich earth from which an acorn sprouts and grows into a new oak tree.