Answer: Some trees tend to develop surface roots as the tree matures. This is natural and there is nothing you can do to stop it without harming the tree. Typically grass will not grow well in competition with the surface roots, it is also usually just too dry and shady there under the tree for healthy lawn grass, and it will be difficult to mow. So, you may want to consider using a groundcover there instead of trying to grow lawn. Vinca, pachysandra and other low growing perennials will grow there without needing to be mowed.
Good luck with your landscape!
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