Distribution of overwintering invertebrates in temperate agroforestry systems: Implications for biodiversity conservation and biological control of crop pests

The dramatic decline of invertebrates at a global scale is mainly driven by habitat loss, agricultural intensification and urbanization. Alley cropping agroforestry is a land use practice in which arable crops are grown between tree rows. In such systems, understory vegetation strips (UVS) develop in the tree rows, providing habitats undisturbed by soil tillage. We investigated whether UVS are major overwintering habitats for invertebrates. We focused on carabid communities, which are dominant beneficial invertebrates in crop fields, but suffer from agricultural intensification. We described carabid communities with functional traits related to sensitivity to agricultural disturbances and ecological functions (i.e. pest control). Sampling of invertebrates were carried out from February to June 2018 over seven agroforestry fields in Restinclieres Estate (South France), one of the oldest experimental sites in Europe. The study revealed that 55% of invertebrate taxonomic groups were more abundant in UVS, whereas only 14% were more abundant in crop alleys. Crop pests were overwintering mainly in crop alleys while beneficial invertebrates were more dependent on UVS. Finally, UVS hosted carabids sensitive to agricultural disturbances, characterized by large body length, predominantly granivorous diet and overwintering in adult stage. On the other hand, crop alleys were home to smaller carnivorous species overwintering in both larval and adult stages, which can tolerate high levels of disturbance. Environmental and agricultural policies should consider agroforestry systems, especially understory vegetation strips, as valuable habitats for biodiversity conservation and biological control in agricultural landscapes.