Shade tolerance and herbivory are associated with RGR of tree species via different functional traits

Relative growth rate (RGR) plays an important role in plant adaptation to the light environment through the growth potential/survival trade-off. RGR is a complex trait with physiological and biomass allocation components. It has been argued that herbivory may influence the evolution of plant strategies to cope with the light environment, but little is known about the relation between susceptibility to herbivores and growth-related functional traits. Here, we examined in 11 evergreen tree species from a temperate rainforest the association between growth-related functional traits and (i) species' shade-tolerance, and (ii) herbivory rate in the field. We aimed at elucidating the differential linkage of shade and herbivory with RGR via growth-related functional traits. We found that RGR was associated negatively with shade-tolerance and positively with herbivory rate. However, herbivory rate and shade-tolerance were not significantly related. RGR was determined mainly by photosynthetic rate (A_max ) and specific leaf area (SLA). Results suggest that shade tolerance and herbivore resistance do not covary with the same functional traits. Whereas shade-tolerance was strongly related to A_max and to a lesser extent to leaf mass ratio (LMR) and dark respiration (R_d ), herbivory rate was closely related to allocation traits (SLA and LMR) and slightly associated with protein content. The effects of low light on RGR would be mediated by A_max , while the effects of herbivory on RGR would be mediated by SLA. Our findings suggest that shade and herbivores may differentially contribute to shape RGR of tree species through their effects on different resource-uptake functional traits.