What once was an open pasture on a long abandoned farm has changed over time without the direct influence of humans. After the cattle had been removed, shrubs and bushes could be seen dotting the grass-covered hillsides. A few years later, small pine trees and then larger deciduous trees appeared. Now, there are so many trees and shaded regions it is difficult to tell that this was once a field. In this wooded region that was once pasture, a mature forest of towering oaks and hickory trees eventually takes over. However, change is still apparent, as a large patch of young shrubs and small trees are growing where several large trees were toppled by a storm several years ago. Collectively, this wooded region represents?