Leaf traits and herbivory rates of tropical tree species differing in successional status

Abstract

We evaluated leaf characteristics and herbivory intensities for saplings of fifteen tropical tree species differing in their successional position. Eight leaf traits were selected, related to the costs of leaf display (specific leaf area [SLA], water content), photosynthesis (N and P concentration per unit mass), and herbivory defence (lignin concentration, C:N ratio). We hypothesised that species traits are shaped by variation in abiotic and biotic (herbivory) selection pressures along the successional gradient. All leaf traits varied with the successional position of the species. The SLA, water content and nutrient concentration decreased, and lignin concentration increased with the successional position. Herbivory damage (defined as the percentage of damage found at one moment in time) varied from 0.9-8.5% among the species, but was not related to their successional position. Herbivory damage appeared to be a poor estimator of the herbivory rate experienced by species, due to the confounding effect of leaf lifespan. Herbivory rate (defined as percentage leaf area removal per unit time) declined with the successional position of the species. Herbivory rate was only positively correlated to water content, and negatively correlated to lignin concentration, suggesting that herbivores select leaves based upon their digestibility rather than upon their nutritive value. Surprisingly, most species traits change linearly with succession, while resource availability (light, nutrients) declines exponentially with succession.