From pollinators to predators: On-farm diversification adds value to California's crops

Background/Question/Methods

Together, habitat destruction and fragmentation comprise the primary causes of global biodiversity declines.  Modern experience tells us that the nature preserve model does not adequately meet the goals of conservation, setting aside only a tiny fraction of the land necessary to support the world’s flora and fauna.  In response, conservationists have extended conservation and restoration practices to privately owned and managed ecosystems with an aim to facilitate species movement and avoid extinction across a larger segment of the landscape. Agroecosystems are the most abundant human-managed systems on the planet. The proliferation of industrial crop fields is well-established as a leading cause of habitat destruction and fragmentation, and traditional and “biodiversity-friendly” agriculture is seen to provide wildlife refuge and movement corridors. Ironically, in the last 5 years, on-farm “food safety” initiatives have threatened to undo many of the advances gained by farm diversification. It has become increasingly important to document how agricultural practices designed to enhance biodiversity can provide farms with ecological services such as pollination and natural biological control of insect pests that enhance human health and food safety. Higher trophic level species, such as arthropod predators, and insect pollinators in particular are both indicators of ecosystem health as well as food safety in light of their reliance on an intact food web and co-evolved relationships with plants, respectively. This study documents different ways that agricultural diversification affects ecosystem services in California farm fields in the form of native plant hedgerows and trap cropping. For the first part of the study, bees were collected from six organically managed farms in Central California, four of which had hedgerows and two that did not, and at varying distances out from the hedgerows.  Effects of on-farm diversification on predators was further explored through a study of spiders in organically managed strawberries near to and more distant from alfalfa strip crops. 

Results/Conclusions

Native bee abundance and diversity were markedly greater on hedgerow sites, and native bee presence and species richness were higher in samples collected within the hedgerow than in those collected at further distances from native plantings. Similarly, spider abundances were supported by trap crops, but patterns differed among spider taxa. This research strengthens the observation that on-farm biodiversity can provide ecosystem services that enhance food safety in predictable ways that outweigh the uncertain fears currently driving some agricultural policy.