Much of the finest soil in the midwest was built up from the forests and ages of leaves being added to the soil.
When I was a kid, our back yard was basement fill subsoil. It was endless mud when wet and hard as cement when dry. All we did was rototill leaves by the pick up load into it for several years and it became unrecognisable. Dark, crumbly garden soil of the first order.
Can not say enough good things about leaves.