Direct and cascading impacts of landscape heterogeneity and agrochemical use on multi-trophic biodiversity in the patchy agroecosystem

Abstract

Farmland biodiversity is declining globally due to intensified agricultural practices, landscape homogenization, and simplification. However, the direct and cascading effects of landscape heterogeneity and agrochemical use on various interacting taxa and trophic levels remain unclear. This study investigated the richness and abundance of taxa across trophic levels, including weeds, epigeic invertebrates, and birds, within a patchy agroecosystem in Pengzhou, Sichuan, China. Structural equation modeling was used to analyze the responses of multi-taxa and trophic levels to agrochemical use, edge density and cropland diversity, and quantify the direct and indirect effects therein. Results showed that landscape heterogeneity and agrochemicals influenced the abundance and richness of weeds, epigeic invertebrates, and birds through direct impacts and bottom-up cascading effects. Agrochemicals negatively affected weeds and invertebrates at lower trophic levels, while edge density had positive effects. Both factors also exerted cascading effects on invertebrates and birds, and the magnitude of net effects diminished as trophic level increased. Cropland diversity reduced weed and invertebrate abundance, likely through competition between weeds and crops and frequent soil disturbances during farming, but exerted positive effect on crop-feeding birds probably due to additional food supply. These findings reveal varied responses of trophic groups with distinctive traits in size, mobility, and resource utilization to landscape heterogeneity and agrochemical use, and highlight the importance of biotic interactions in regulating these ecological processes. This study indicates that reducing agrochemicals use alongside enhancing landscape heterogeneity can promote multi-trophic biodiversity and sustain ecosystem services in patchy agroecosystems.