Temperate alley‐cropping agroforestry improves pest control potential by promoting spider abundance and functional diversity

Abstract Intensive agricultural land use negatively impacts biodiversity, including arthropod predator diversity and their pest control potential. Alley‐cropping agroforestry systems (integration of tree rows into arable land) are increasingly considered an economically viable alternative for more sustainable and biodiversity‐friendly agriculture. However, their effectiveness in promoting generalist predator diversity and pest control, especially as a function of space (distance from tree rows) and time (across the growing season) remains poorly understood. We assessed how spider abundance, taxonomic and functional diversity (as proxies of pest control potential) respond to temperate alley‐cropping agroforestry systems as compared to open croplands. Additionally, we analysed whether spiders with different habitat preferences (eurytopic, forest and open‐habitat specialists) show distinct responses. Lastly, we analysed whether the influence of agroforestry changes with decreasing tree proximity and across the growing season. Tree row proximity generally benefited the abundance, as well as taxonomic and functional diversity of the overall spider communities. Alley‐cropping promoted the abundance and taxonomic diversity of forest specialists and eurytopic spiders, without negatively affecting open‐habitat specialists. The positive effect of alley cropping was strongest within tree rows and their immediate vicinity, but was still detectable at considerably farther distances. These patterns were temporally dynamic with spider abundance and taxonomic diversity being highest within tree rows in early spring and spiders spilling over to adjacent crop rows in subsequent periods. Synthesis and applications : Overall, our findings highlight that the inclusion of tree rows benefited spiders across the entirety of the 48 m crop rows, independent of crop type. Since the peak in spider abundance and taxonomic diversity in crop rows coincided with crop pest arrival, alley‐cropping agroforestry is expected to benefit agricultural production through increased pest control potential. Alley‐cropping agroforestry may therefore be an important management strategy to develop more sustainable agricultural systems benefiting farmers and biodiversity alike.