Abstract/Summary

Insect pollination is a globally important ecosystem service, contributing to crop yields, production stability and the maintenance of wild plant populations. Ironically, agriculture is one of the major global drivers of wild insect pollinator decline. At the same time, increasing human population is driving ever greater demands on crop production. Agroforestry (AF) – a more diverse farming system integrating woody and agricultural crops – can theoretically reconcile high production with provision of ecosystem services such as pollination. However, empirical studies of pollination in temperate AF systems are almost entirely lacking. We sought to fill this knowledge gap by assessing whether AF can provide increased pollination service compared to monoculture (MC) systems. Six UK sites, each containing an AF and a MC system, were studied over three years. Wild pollinator abundance and diversity were used as proxies for the magnitude and stability, respectively, of the pollinating community. We also directly measured pollination service as seed set in a wild plant phytometer. We found that temperate AF systems can provide greater pollination service than MC: AF treatments had twice as many solitary bees and hoverflies, and in arable systems 2.4 times more bumblebees, than MC treatments. AF also had 4.5 times more seed set compared to MC in one of the two years. At 40% of site-by-year sampling units, species richness of solitary bees was on average 10.5 times higher in AF treatments. This provides evidence in favour of the expectation that AF systems can support higher pollinator richness, and therefore greater potential stability, of pollination service. For the other sampling units, and for bumblebees (Bombus spp.), there was no treatment effect on species richness. Further work is needed to investigate the effect of AF on species richness and its mechanistic basis. Our results also highlight the importance of AF system design, ensuring that ecosystem services outcomes are explicitly planned at the design stage. We suggest that AF has a role to play in improving the sustainability of modern farming and in mitigating the ongoing loss of wild pollinating insects, which is strongly driven by prevailing agricultural practices.