Tree species richness effects on pre-dispersal seed predation are mediated by tree fruit type

FEILONG JI, Noga Abecassis-Monteyne, Xiaojuan Liu, Finn Rehling , Tim Diekötter, Alexandra Erfmeier

Forest BEF experiments are only now reaching a stage at which natural tree regeneration can be studied, offering new opportunities to understand how biodiversity shapes trophic interactions during early demographic filtering. Here, we quantified seed productivity and insect-mediated pre-dispersal seed predation on 12 tree species across a tree species richness gradient from 1 to 16 in the BEF-China experiment, using 589 seed traps across two sites and 2,356 seasonal samples. Across 12 tree species, tree diversity did not exert a uniform effect on pre-dispersal seed predation. Instead, tree richness effects varied strongly among species and were significantly influenced by fruit type. Pre-dispersal seed predation rate on nuts declined with increasing tree species richness (95% CI: 10.96-30.89%), whereas fleshy fruits (95% CI: 10.34-25.37%) and capsules (95% CI: 7.78-17.12%) showed the opposite tendency. Seed productivity followed similar fruit-type-specific patterns and seed predation was generally negatively related to seed productivity. Seed predation was also negatively related to canopy cover, whereas seed productivity declined with increasing soil pH. Here, we are one of the first regeneration-feedback studies in mature forest BEF systems that shows that pre-dispersal seed predation, as one of the earliest demographic filters in forest regeneration, is interactively affected by tree species richness and fruit type. Together with future insights into seed predator identity and their resource specialisation, our data open new avenues for data-based forest restoration.