There are tons of understory/edge-of-woods trees native to Mass. Mountain Laurel and some azaleas and rhodos are evergreen. I think the PJM series from the Weston Nurseries are evergreen (they are hybrids, not 100% native). I'd recommend an undulating border. Pick an array of shrubs, maybe 5 or so that you like, preferably with different sizes and then play (on paper) with an arrangement, taking into account their final heights.

I'd start with hosta as ground cover in front of the trees to start a bed. There are so many varieties and sizes that you could use. Plant them as a row. Then add seasonal annuals in colors. Assuming this will work and that you have more shade than sun.

These trees look mature and well-established, so the soil underneath could be packed with roots, dry and depleted. This may limit what you can do there.

I lost quite a few shrubs in similar conditions, so I ended up planting shade-tolerating perennials (hostas, hellebores, ferns, and lots of crocus, bluebells and daffodils for spring). I looked for root-free pockets of soil, and planted nursery-grown mature plants (not seeds or seedlings). I watered well to help them get established, and I still water that area a lot, as these plants can't compete with the trees for moisture.

The azaleas and pieris in this picture? All dead now except the small magenta one :( But the perennials have spread and are doing great. However, during the summer I have to water that area at least once a week and keep it well mulched with shredded leaves.

Hi...also in MA here. I unfortunately agree with Festiva's comments above. Trying to get anything growing close to established maples is very difficult...esp this many. I've given up pretty much over 40 yrs and resigned myself to the hardiest of hostas and mulch. And even then hostas normally need to be dug up occasionally to pry the tree roots away from their root balls....letting them breathe for a year or 2! Piling soil on top of tree roots, especially within 10' of the trunk is a no no if you want to keep the trees healthy. As Festiva did, you can dig around to see if you can find any less root filled areas but with the number of trees there and the wide spread roots it might be rather futile. As she found, early bulbs and woodland type plants are easiest...but even then take extra care. You'd need to break up tree roots and add a lot of compost before planting. And yes,....you'd need to water frequently since tree roots steal the water and rain won't penetrate well through all the tree leaves. You could try Soil Moist granules to help the plants when young; they expland and hold moisture...usually used in pots but it works anywhere. It's a heck of a lot of ongoing work though with not much reward I'm afraid. You could consider some large pots with hostas, annuals concentrated in a particular area under the trees...maybe with some chairs. It would give interest, a focal point, color and break up the monotony of that line up.

Oh forgetting one of my favs....yews can make it there. Above is a young one. "Densiformis" yews are lovely, spreading ones with a graceful habit. Normally they're sheared into box shapes around here but they're beautiful when allowed to "go". They do OK in dry, total shade and are the most unfussy evergreens about although you will have to water...esp initially. They won't grow fast as they would without tree competition but they shouldn't die either!

Because of the tree roots, you might find digging to plant anything other than seeds difficult and/or you might end up damaging enough roots of the trees to damage the trees. Do not be tempted to add dirt around the trunk of a tree -- that would likely eventually kill the tree.

You might consider adding mulch near the base of the trees -- just not against the tree trunk

http://www.state.nj.us/dep/parksandforests/forest/community/Pruning.htm

or the fence -- if mulch or dirt holds moisture against the tree trunk or fence, it can cause rot.

If you have a ground cover you like that spreads that you can plant in front of the trees, that might be worth considering.

It's safe to create a bordered planting bed on top of your soil if it's not too high & not at the tree dripline, bordered by edging and plant the hostas in the brand new soil mix