Effects of Agroforestry Systems on Biodiversity and Ecosystem Services in Subtropical Agricultural Landscapes

Abstract:

Subtropical agricultural landscapes are facing severe biodiversity loss and degradation of ecosystem services due to intensive monoculture practices. Agroforestry systems (AFS), which integrate trees with crops and/or livestock, are considered potential solutions to mitigate these issues by enhancing habitat complexity. However, the effects of different AFS types on various biodiversity components (plants, insects, soil microbes, birds) and associated ecosystem services (pollination, pest control, soil nutrient cycling, water regulation) in subtropical regions remain inadequately explored, especially the trade-offs and synergies among these services. This study investigated the effects of three typical AFS (alley cropping, silvopasture, forest garden) on biodiversity and ecosystem services in subtropical agricultural landscapes across China, Spain, and Japan, with a 12-year monitoring period. Biodiversity was assessed using species richness, Shannon-Wiener index, and community composition. Ecosystem services were quantified through field experiments and model simulations. Results showed that compared to monoculture, AFS significantly increased overall biodiversity, with species richness increasing by 32-58% and Shannon-Wiener index by 28-45%. Forest garden exhibited the highest biodiversity enhancement (species richness +58%, Shannon-Wiener index +45%), followed by silvopasture (species richness +43%, Shannon-Wiener index +36%) and alley cropping (species richness +32%, Shannon-Wiener index +28%). For ecosystem services, AFS improved pollination service by 25-42%, pest control service by 22-38%, soil nutrient cycling service by 30-45%, and water regulation service by 18-32%. Alley cropping performed best in soil nutrient cycling, silvopasture in water regulation, and forest garden in pollination and pest control. Structural equation modeling indicated that AFS enhanced ecosystem services mainly through increasing biodiversity and improving habitat complexity. Synergies were observed between pollination and pest control services, while trade-offs existed between water regulation and soil nutrient cycling in some regions. The effects of AFS on biodiversity and ecosystem services varied with climate zones and AFS management practices, with humid subtropical regions showing greater biodiversity gains and semi-arid regions exhibiting more significant improvements in water regulation. These findings highlight the multifunctional benefits of AFS in sustaining biodiversity and ecosystem services in subtropical agricultural landscapes, and provide insights for optimizing AFS design to maximize synergistic ecosystem services.