Figure 19.14 Changing species composition in a climax forest. There are many species of trees in the canopy of a forest in Pennsylvania, as indicated by the importance value of each species. However, in the understory there are few oak trees and no tulip poplar or hickory trees because when they are young these species are not tolerant of deep shade and they are susceptible to herbivory by deer. This suggests that the future forest canopy will experience a substantial change in the composition of dominant trees.

Data from Z. T. Long et al., The impact of deer on relationships between tree growth and mortality in an old-growth beech-maple forest, Forest Ecology and Management 252 (2007): 230–238.