We have an older established tree whose roots are starting to grow
above the surface of the lawn. We have been told that we need to
cover the roots with soil to protect the tree's health.

*SNIP*

You were given misinformation. Surface roots serve a function on
certain trees. One of the major functions, it is thought, is to have
better gas exchange capacity. I don't recommend covering surface
roots on trees, not ever.

Thank you! I was hoping someone who knew for *sure* would answer.

Cindy