Question
I have built a ring around my very large soft maple tree and when I asked to have dirt brought in around it I was told it would kill the tree.  The timbers are about 6-7 timbers high and the tree is very mature.  Is this true seeing how the ring is already built and ready for dirt?

Answer
Putting fill dirt more than 2-3 inches around established trees will cause at the least die back to mortality of the tree. The deep will kill the tree. You can actual leave the space open and not fill it with soil. This is called a tree well and will work. Here is a web link to information on tree wells.  http://www.wvu.edu/~agexten/hortcult/treeshru/treewells.htm