Positive effects of plant diversity on productivity increase over time through stronger complementarity among species 1 . However, whether these temporal dynamics propagate across trophic levels towards higher-order ecosystem functions remains largely unexplored. Here we tested how tree diversity drives attack rates and trophic interactions of host-parasitoid communities over the course of a decade in a young large-scale forest experiment. We found that the effect of tree species richness on parasitism increased over time, driven both by accelerating stand productivity and changes in food web structure. Parasitism increasingly reflected an attenuation of consumer responses to accumulating resources and a shift towards tree and parasitoid diversity-dependent regulation. The influence of parasitoid species richness on parasitism rose over time as generalist parasitoids concentrated interactions on shared hosts, increasing overall resource use and network robustness to species extinctions. Our results reveal that the functional benefits of biodiversity strengthen over time through shifts in the mechanisms linking trophic levels, underscoring the long-term value of diversity-focused restoration.