Figure 13.4 Age structure in an old-growth forest. By dating the ages of existing trees in an old-growth forest in Pennsylvania, researchers could determine the years in which populations added individuals. For simplicity, not all species of trees are shown. The thickness of the bars indicates the relative abundance of each species.

Data from A. F. Hough and R. D. Forbes, The ecology and silvics of forests in the plateaus of Pennsylvania, Ecological Monographs 13 (1943): 299–320.