Effects of herbivory on leaf life span in woody plants: a meta‐analysis

Abstract

Summary Premature abscission of leaves damaged by herbivores can increase the degree of defoliation beyond that imposed directly by insect feeding. Our aim was to explore the general patterns and sources of variation in the effects of insect herbivory on leaf life span in woody plants. Meta‐analysis of published data demonstrated that herbivory significantly reduced the life span of damaged leaves; insect feeding had a greater effect than the same level of herbivory simulated by mechanical wounding. The effects of both natural and simulated herbivory became stronger with increase in the proportion of damaged leaf area. Damage to young leaves and to plant species with higher specific leaf area resulted in a greater reduction in leaf life span than damage to mature leaves and to species with lower specific leaf area. Herbivores differed in the magnitude of their effects on leaf life span, but this variation was not explained by herbivore feeding guilds or specialization. Natural herbivory similarly reduced leaf life span in deciduous and evergreen trees, thereby questioning the hypothesis that premature abscission as a defence response is primarily a characteristic of evergreen trees. However, simulated herbivory imposed stronger effects on evergreens, suggesting that they are more sensitive to non‐specific wound‐induced elicitors than deciduous trees. Synthesis. We demonstrated that, in spite of pronounced variation between study systems, herbivory in general reduces the life span of the damaged leaves of woody plants. Our results suggest that variability in plant responses to herbivory may be linked with the leaf economic spectrum. Premature abscission of damaged leaves can be seen as a tolerance strategy that reduces the negative consequences of local damage on the whole plant. This phenomenon should be accounted for in estimation of losses of net primary production caused by herbivory.