The possibility that occurs to me is that these trees were browsed pretty hard when they were seedlings. Based on the fairly flat slope, this woodland could easily have been a pasture or summer grazing lot for cows in the not-too-distant past. When seedlings get continually munched, they take on a bushy, multi-stemmed form. Once the pasture was abandoned, those multi-stemmed trees grew up to form these clumps. Logging could be another possibility, since a lot of hardwoods produce stump sprouts. These trees could conceivably be the grown-up stump sprouts from larger trees that were cut down and removed. But I feel like in that case you would see some sign of the old stumps, so right now I'm leaning toward old pasture.