is it safe to build a flower garden around a tree?

i am just talking about a few inches of soil around the tree and a littlemulch on top will it kill the tree
or is it safer to just add mulch only
finally found answer –

http://www.greensboro-nc.gov/Departments/Planning/forestry/care/tree+myths.htm

http://www.jackeden.com/cgi-bin/sheets/viewdata.cgi?id=1088108675

Marisela