There have been a number of studies that found hedgerows had higher numbers of bees and more diverse community composition than field margins without habitat enhancements, but a recent studies shows that this effect may extend into fields.
Farmers have expressed concern that if they place hedgerows along field borders, the hedgerows might actually compete with crops for pollination. Working in the same system that I work in around Davis, California, Dr. Lora Morandin and my PI Claire Kremen, tested whether hedgerows concentrated bees from the landscape, functioning as a sink, or created a source of bees, actually exporting them into surrounding fields.The evidence they collected suggests that bees were actually more abundant in fields that were next to hedgerows. Although most of the bees were concentrated along field edges (about 10 m into fields), the increase was noticeable up to 200 meters into fields. As for honey bees, they too were more common in hedgerows and adjacent fields- indicating that they too may be attracted to the floral resources restoration provides.
On a methodological note, the researchers found that specimens collected with pan traps (a standard passive bee collection method that involves setting out colored bowls filled with soapy water) were not different in any of the study types, however bees collected with nets that were actually foraging on plants were different. Morandin and Kremen found more bees pan traps placed in sites with fewer flowers, indicating bees might be more attracted to these traps when there are fewer available resources. They caution that pan traps may not be an accurate way of “assessing differences in pollinator communities among areas that differ in floral display.”
Overall, this study adds to the body of evidence showing that increasing vegetative diversity within agricultural landscapes increases bee diversity, which likely benefits crop pollination.
Morandin and Kremen. 2013. Hedgerow Restoration Promotes Pollinator Populations and Exports Native Bees to Adjacent Fields. Ecological Applications 23(4): 829-839