That tree was planted 4 years before the bed was placed around the trunk...at ground level??????
You guys in upstate NY must get a hell of alot of rain and have hard soils. What is funny--is the 3 separate layers of root growth and a layer of rock...........then another layer of roots and rock.
The layering of rock kept the moisture at the surface and obvious surface watering posed an easy access for the roots to grow on top of the ground rather than grow downward. I bet the previous owners fertilized the tree over the top of that face stone bed. However, the roots did well above ground considering the winter weather months.......so I tip my hat to this species of MAple. I can guarantee that this tree would have died down here planted like that.
From here, considering an Arborist in your area with native soil familiarity should advise you to level off the slope on those roots out to the dripline. Leaving these roots exposed will become dry and brittle if not covered with some burlap until the decisions are made on what to do. Extending the bed to the dripline will be the best advise I can give you, so you better hurry and make a calculated decision based on the growing conditions of your area.