Concrete Driveway Heaving

I have a concrete driveway with four section separated by expansion joints. One of the upper sections is rising up at the bottom edge, about 2 inches. The climate here is not cold enough for this to be due to frost. We do have a liquidambar, or sweet gum, tree about 20 ft. away. This tree is known for having surface roots. But the sidewalk and walkway up to the house aren't moving. Is there anything else that could cause the concrete to lift up?