Landscape conservation and orchard management influence carob tree yield through changes in pollinator communities

Abstract

Worldwide pollinator declines are a major problem for agricultural production. However, understanding how landscape characteristics and local management influence crop production through its pollinators is still a challenge. By sampling 20 orchards in Mallorca island (Spain), we evaluated how the landscape (habitat loss) and orchard local management (farming system: conventional vs. ecological; male-to-female ratio) influenced pollinator communities and production in carob trees (Ceratonia siliqua), a crop of high economic importance in Mediterranean areas. We found that orchards surrounded by larger natural areas received more visits by wild bees and butterflies and fewer by honeybees. Ecological farming tended to increase overall pollinator abundance in the orchards. High male-to-female ratio enhanced overall pollinator abundance and shaped pollinator composition, by increasing hoverfly abundance and decreasing wasps and flies. Male-to-female ratio showed hump-shaped relationships with fruit and seed production per female tree (peak at 0.7 males/female), whereas total orchard production maximized with 20-30% of males. Seed weight (farmers highest economic value) increased in conserved landscapes where wild pollinators prevailed, and with overall pollinator abundance; however, it decreased with male-to-female ratio, likely due to seed number-size trade-offs. Management strategies to enhance carob production may optimize sex ratios and favor wild pollinators by reducing pesticide use and preserving natural landscapes.