What to plant alongside fruit tree seedlings before they grow into their space

In regards to my first Forest Garden in the works, I've already sprouted some apple seeds, hoping more fruit trees and bushes will come. I know it will take a decade or so for them to grow into a more substantial size, hence I'm wondering what could I grow alongside the tiny trees until that happens? I'm looking into succession planting knowing that if the tree survives to adulthood, it will do best with a wide radius of root space, however, until then it seems like wasted space that I'd like to make better use of? Any ideas?

You can probably help the apple out by planting some garlic or similar allium family foods with it. The space will be productive, and the shared root space will provide for the exchange of some of the pungent factors of the allium into the apple to dissuade insects and other pathogens from damaging your young trees.

Basically any annual would be great. I planted 200 pawpaw seedlings this year, and so far between them I've planted lettuce, collards, basil, peppers, and tomatoes.

You can plant nitrogen fixers, pollinator plants, annuals, any support plants for your fruit trees like comfrey.  Do a Google search for "Apple tree guild" for lots and lots of suggestions, along with the reasoning behind the plants suggested.  Daron Williams, among others, posted about guilds here on Permies, and his post is a great starting point that covers the basics.  Starting a fruit tree guild

I like to plant peas with them.

Awesome advice, thank you everyone. That's a good link Trace. I like how he recommends creating nests for predators. I wonder if there's a way to make a home for somebody to scare the deer off, though I think that's just wishful hoping. Peas grow the easiest here, I'll go wild with them :D

Maruf Miliunas wrote:I wonder if there's a way to make a home for somebody to scare the deer off,

There is.  It's called a doghouse :)