Anything you plant there will probably grow very well. Even without adding any dirt. It sounds like a
hugelkultur with a 10-year build.
There is a new housing development a mile down the road from me. When they went to clear all the pine and oak forest and subdivide it into building lots, they chipped all the
trees and brush and pushed the wood chips to the back of the lots as they graded them. Each lot has a wood chip dump at the back of it that is anywhere from 1' to 3' deep. Now, two years later, the lots are still mostly dirt with some weeds on them, grasses and and an occasional pokeweed, but the wood chip piles at the back of the lots have big, big weeds, 5 and 6 feet tall. That's the fertility of a wood chip dump.