If the maple roots are in there, you may be in for a tough fight. Maple roots will seek out (or, in this case, up) and into any nice rich soil they find.

Perhaps a large decorative stone or three?

Do you have any pix of the area?

tj

If you aren't in a dry climate, ferns would probably work.

lily of the valley, spiderwort. you may need to plant them in bottom open containers to keep roots out

periwinkle (vinca minor) will grow there. Their roots are very shallow & they'll tolerate just about any soil that's not too compact. Loosen the top inch, or throw a half inch of garden soil on top to get them started.

They like to send runners out to conquer new territory. Fortunately they are shallow rooted & can be kept in check with a twice annual trim & pull.

oh periwinkle sounds lovely! i hope i can loosen even the top inch though. otherwise, i was thinking...moss? i'll try to get outside and take some photos when all the snow has melted.

Ferns and hostas are your best choices.

I hear the Cardinal Climbing vine will do ok in shade. I have some planted in front of a trellised window, part shade/indirect sun. I'll let you know how they come out once they start sprouting. I also have some in hanging pots in the front (full sun) so that's how I'll know if they are thriving or not :)

Cardinal climber needs sun.....and full, hot sun at that.

Any shade tolerant groundcover will work in your shallow beds. And you can always add a few shade loving annuals for some summer color.

we had a concrete yard with a foot high layer of soil in a raised bed and we raised rocket lettuce basil spinach and chard in there. if you have about two or three foot you could try anything just buy some seeds and see how they fair seeds are fairly cheap and if nothing comes of it theres little lost. just top up whats already there with a good layer of compost and sprikle your seeds on top. wildflowers native to your area will grow almost anywhere they can find footing even out of walls and many are shade loving you could try collecting seeds from wildflowers along shaded woods that take your fancy or if your permitted taking the plants and a good chunk of soil with them and replanting beside your trees. beans will also grow in shade and climbers will creep up the trees and find light something like honeysuckle or jasmine so long as they have enough food to feed the roots while they are climbing up. you may get less of a crop of flowers or fruit from anything in shade like kale will grow much smaller but it will still grow.

I have yet to see my Lamium maculatum find a spot it hates. Being related to the mint family, it tends to get crazy, so if you have a lot of ground to cover, that may be your plant. Zone 5 here, part shade, north side of a house, but thriving too in my west-facing, full sun butterfly garden. Oddly, it is changing color in places. Must have cross-pollinated with a darker flowering variety. Kind of cool, I think, and provided fast erosion control perfectly, which is what I needed!

Nicki B, my lamium has done the same thing. This patch is mostly purple, with a bit of pink on the left side.

I planted just a little lamium years ago, and it has spread in delightful ways, often jumping 10 or 15 feet and spreading under a different fir tree. This patch came up at the edge of the lawn (and desperately needs the grass pulled out of it, but our weather has been too cold and rainy to work outside much).

It's the weirdest thing! The bees love this plant too

I have a different variety maple but a cousin nonetheless with fibrous roots galore. I planted some asters around the base of the trees successfully. The asters were too aggressive in my traditional garden beds without a challenge to keep them in check.

I also have planted successfully within a few feet spring bulbs, gaura, and between two of them a large hydrangea.

Dont overlook a large ceramic pot or two strategically placed.