The cattle were removed from a field and shrubs and bushes were 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. What once was an open pasture on a long abandoned farm has changed over time, without the direct influence of human. In this wooded region that was once pasture, a mature forest of towering trees has taken 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 regions represents
(a) a climax ecosystem
(b) primary succession
(c) a sustained biome
(d) intermediate succession
