Not to add to the topsoil amount in a forest debate.....
However I do know that in a forest (and I too live in one) the vast majority of the nutrients are in the vegetation. Being stored in the living vegetation and not in the soil at any given point in time. This system keeps these nutrients safe from being washed away with the heavy rains that most forest get. It's just a different ecosystem than a prairie, not worse just different. Haul off the trees and burn the brush and you are left with very little nutrients, as well as no soil erosion protection.....there goes your topsoil IMO.
What if one chopped and dropped most of that forest matter right where it grew....? Now you have basically the same system as the
Back to Eden folks use for the best food production.
Back to the subject: I would bring in as much organic matter to place on top of the soil as possible, use what you have, but don't like and chop 'n drop it or
compost it for soil covering. Leave no soil uncovered, ever! Add in sand to the clay in specific places for a faster amending, like under plants when planting, and cover with organic matter. Plant Nigerien fixers, both plants and trees. Grow a variety of deep rooting plants. And have animals free range to distribute their manures. I hope this helps give you some ideas.