Responses to defoliation of species-rich and monospecific tropical plant communities.

Floristically rich and monospecific tropical plant communities both responded to partial defoliation with increases in rates of production of new leaf area. Even after 50% of the leaf area had been removed three times, the leaf area increments were still higher in defoliated plots than in controls. Mean leaf area increment after defoliation, on a leaf area per unit ground area basis, was 905 cm m d in diverse successional vegetation and 536 cm m d in a cassava monoculture. Although defoliation stimulated leaf area development, on a per unit ground area basis, in both the cassava monoculture and the successional vegetation, the effect was more pronounced in the successional vegetation. On a per unit leaf area basis, leaf area increments following defoliation in both the diverse successional vegetation and the monoculture were approximately five times those of controls. The diverse plant community continued to respond vigorously after repeated defoliation, while the amount of stimulation of leaf are development in the monoculture declined. Because of their ability to respond even after repeated defoliation, diverse communities may in the long term be more homeostatic with respect to leaf area than are monocultures. The enhanced responsiveness of the species-rich community was due to changes in plant species abundance and very rapid leaf area development by some species.