I should add, it is actually some sort of Juniper tree as it has those little bluish gray berries.

Just plant and add compost on top of the soil. Worms and other soil organizms will do the rest.
Linda C

When you say you'll take out the juniper does that mean you'll excavate the roots - or do a quick swish with the saw at ground level?

If the roots will be staying (smart move!) then it may be useful to create a temporary raised bed from bricks, rocks, logs - whichever suits your yard style and fill that with your compost.

Before you apply the compost you could also add a layer of blood and bone fertiliser directly on top of the tired soil. It won't hurt the worms. The worst that could happen would be 'critters' coming by to dig up the bed for the snack they can smell. If that has no appeal - then use a fertiliser with a reasonably high Nitrogen portion so the microbes breaking down the roots have a source of Nitrogen and aren't robbing your plants. (The plus on the organic mix is that it is slow-acting over months instead of a quick jolt.)

Just grow annuals for a year or two until the smaller roots at least have had a chance to start rotting down.

If you also add your grass clippings and leaves from the maple to this 'temporary bed' then you'll begin to see an improvement in the underneath soil quality probably as soon as next spring.