Ground beetles in agroforestry system show functional traits and activity-density differences according to distance to trees

Abstract

Alley-cropping systems are arable agroforestry systems in which tree rows and associated grassy strips are established within cropped fields. This constitutes a promising approach to promote biodiversity and associated services in the vicinity of crops. However, there is still little knowledge on the functioning of these systems, especially when they are developed in combination with other agroecological practices or models. We studied ground beetle ( Carabidae ) communities in such silvoarable systems (SAS), with a particular focus on the effect of distance to tree rows. The studied fields were managed using conservation agriculture practices, namely no-tillage, cover crop maximisation, and crop diversification, carried out over the long term. This study aimed to assess the response of carabid beetle communities to these specific but promising agroecological systems. Ground beetle activity-density, which reflects both abundance and activity, was higher in crop alleys than in tree rows. We did not detect clear differences in species richness or overall community composition along the distance gradient from tree rows. However, diversity patterns based on effective diversity revealed marked structural differences, with communities near tree rows being more diverse, whereas carabid assemblages within crop alleys, especially at 20m from tree rows, were increasingly dominated by a limited number of abundant species. Consistent with these structural patterns, functional trait composition varied with distance to trees, with crop alleys harbouring less winged, less zoophagous communities and a higher proportion of adult-overwintering species, while larger species were more frequent in the middle of crop alleys. SAS associated with conservation agriculture therefore exhibit strong potential to support biocontrol services and promote carabid communities that are resilient to climatic or agronomic perturbations. Further studies are needed to understand the functioning of ecosystems by integrating other taxonomic groups and abiotic factors.