Forest succession and demographic groups interact to influence insect herbivory on woody seedlings

Most tropical forests are subject to human disturbances, creating successional communities of varying forest ages. Changes in abiotic conditions and dominant plant species over succession may drive shifts in insect herbivory with forest age, influencing patterns of forest recovery. We quantified leaf insect herbivory (incidence and percentage standing damage) on 4774 seedlings of 185 woody species within 10 1-ha forest plots spanning a successional gradient from 9 to 129 years since disturbance in lowland tropical moist forest in Panama. We classified species as lianas vs. trees and further divided trees into five demographic groups according to their position along the growth-survival and stature-recruitment trade-off axes (slow, fast, long-lived pioneer, short-lived breeder, intermediate). We measured understory light availability to determine whether differences in herbivory were related to decreasing light availability during succession. At the forest plot level, herbivory incidence, but not damage, on woody seedlings increased with forest age. Herbivory incidence increased similarly with forest age for seedlings of trees and lianas. However, the relationships between forest age and herbivory incidence varied among tree demographic groups. Specifically, fast and short-lived breeders had a significantly greater increase in herbivory incidence with forest age compared to slow species. Understory light availability decreased on average with forest age but did not explain variation in herbivory. Our findings improve understanding of how past human disturbance influences natural enemy pressure on seedlings and suggest that decreased herbivory in early-successional forests may contribute to forest recovery while increased herbivory in late-successional forests may maintain seedling diversity.