What a great idea! I read this comment on the National Gardening web site, and it's such a wonderful idea I thought I'd share it with you!
"When removing sod to plant a new tree or shrub, flip the sod clumps over -- root side out -- and lay them down in a wide ring around the tree on top of the soil and they will form a berm to hold water and also add organic matter as the grass decomposes. Top them with your mulch of choice."
Isn't that a super thought?