Answer: I don't know whether or not your oak tree will adjust to the change in grade. While you did the right thing in trying to keep moist soil away from the trunk (which can cause rot), changing the grade over the root system can suffocate the roots. Oaks (and many other trees) have feeder roots which are close to the surface of the soil. This, coupled with the fact that the rest of the roots grew into spaces containing just the right ratio of oxygen and moisture, and they became accustomed to it, they may be suffocating, as well. You can only wait and watch. It may adjust. There's nothing you can do for your tree at this point - except remove the excess soil over the root system. That doesn't sound like it's a feasible solution, though, so let's just hope for the best.
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