Urban tree diversity reduces invertebrate leaf herbivory

Global rise of urbanization and climate change are strongly affecting biodiversity, species interactions and species survival. Urban areas are socio-ecological ecosystems which often result in climate novelty and unique artificial species assemblages through tree plantation. This unique tree species pool can be used as a tool to counterbalance the aforementioned impacts. Enemies hypothesis and Host Dilution hypothesis post that higher tree biodiversity can reduce herbivory by reducing host detectability or by having a positive effect on natural enemies of herbivores. Oppositely, the Resource-Concentration hypothesis claims that higher plant diversity increases overall herbivory. The aim of this study was to test the effect of urban tree diversity in trophic interactions. This was assessed by measuring herbivory rates in 3153 leaves of 30 Quercus robur trees surrounded by different tree diversity levels. Urbanization level was included to consider local warming due to urban heat island effect. Estimation of the surrounding vegetation or water was also considered as a reductor of this artificial heating. Herbivory was negatively affected by local tree diversity, with Shannon’s index having the strongest effect. Host Dilution hypothesis supports these results, as more even tree communities suffered from less herbivory. Higher levels of tree diversity can be used as a nature based solution to avoid the ecosystem disservice of herbivory in urban areas. Our results suggest that urban managers need to avoid monocultures and consider relative abundance in urban plantations in order to increase urban tree fitness by reducing herbivory.