Species-specific effects of genetic diversity and species diversity of experimental communities on early tree performance

Aims Changing biodiversity can affect ecosystem functioning. However, the role of genetic diversity within species, relative to the one of species diversity, has hardly been addressed. Methods To address the effects of both genetic diversity and species diversity during the important stage of early tree life, we used eight seed families (SF) taken from each of 12 evergreen and deciduous tree species of subtropical forest to perform a factorial experiment. We established 264 communities of 16 trees each. Each community had a species diversity of either one or four species and a genetic diversity of either one, two or four SF per species. We measured plant survival, growth rate, final biomass and herbivory 20 months after sowing. Important Findings Species differed from each other in biomass, growth rate, herbivory and survival (P < 0.001). Deciduous species tended to have much higher biomass (P < 0.1) and experienced higher herbivory (P < 0.05) than evergreen species. Species diversity affected the performance of different species differently (species diversity by species interaction, P < 0.001 for all variables but survival). Biomass differed between SF and increasing genetic diversity from one to two, and from two to four, SF per species increased biomass for some species and decreased it for others (P < 0.001). Our study showed pronounced species-specific responses of early tree performance to species diversity and less pronounced responses to genetic diversity. These species-specific responses suggest feedbacks of species diversity and genetic diversity on future species composition.