Inner ring MUST have a layer of large river stones for air +water to get to trunk, otherwise it will suffocate + kill the tree. The soil will support small shallow rooted plants like Allyssum or Primrose.
Dead old trees may seem like a problem but there is always a way to make the most of the worst situation. Dead wood isn’t necessarily have to be unsightly and if it is there are ways to make it work for your landscape. Whether you have a tree stump or a w