An amount of material similar to the forest floor is fine around trees, especially since it's not dirt, not raising the level of dirt around the roots. Nobody rakes them up out in the wild.
Once you 'improve' some soil with such little effort, it's addicting, at least that's what happened to me. Too exciting to not share how easy it is, though not instant. All started with smothering a small patch of grass instead of trying to shovel it up. And I've never done that double-digging thing that was all the rage in garden books when I was a buyer of garden books, but have ended up with some amazing patches of dark 'dirt.' I have more time than strength :+)
Yeah, add what you can when you can, the wider variety, the better.
