preparing for woodland garden under giant redwood
i am planning to install a woodland type garden under a giant redwood in my back yard in the san francisco bay area this coming spring. the tree is about 80 years old and there are about 2 or 3 inches of needles under it. should i till the needles into the heavy clay soil or should i clear them off and enrich it with nursery bought soil ammendments? i'm also concerned that tilling or preparing the bed might possibly damage the roots of the tree.
what steps should i go through to ensure a successful woodland garden and preserve the health of my giant redwood?