Till shallow yard?

Sounds like you will need to put more dirt in your yard. I had some sandy soil put in some low spots on my property. I had lots of Tulip Poplar trees planted. After the bulldozer smoothed it off about 6 months later the poplars started to die where the soil was pushed over the standing roots of the poplars. I had to hire a tree cutter to saw the huge trees down. He told me the trees died because of the dirt covering the tree roots. He said the same thing happens to Oak trees.