I recently published a paper in the journal Agriculture, Ecosystems and Environment posing this very question, Can hedgerows support native bee conservation and crop pollination? What I found was that in conventionally managed monoculture sunflower fields, the answer is “mostly no.” This finding, however, is likely do to a variety of factors unique to sunflower grown in intensively managed agricultural landscapes such as the California Central Valley.
First, hedgerows are just 1% of the size of a sunflower field, so the amount of blooms they provide bees is dwarfed by the number of flowers available in the sunflower field. In addition, I found that the bees visiting sunflower were different species from those visiting the hedgerow. The bees in sunflower fields were mostly sunflower specialists– species that only visit sunflower, taking the pollen and nectar back to their nests as the exclusive source of food for their young. Conversely, the bees in hedgerows were mostly generalists (visit many different species of plants). Hedgerows in my study didn’t contain sunflower due to concerns about contamination with the field varietals. New sunflower species containing a different number of chromosomes than the field plants are being tested. I hypothesize that once sunflower is available in hedgerows, they too will support sunflower specialist bee populations.
I did find that native bees increased sunflower yield- both indirectly, through the interaction between native bees and honey bees, and by having more native bee species present. Native bee species richness likely enhances crop pollination because different species pollinate different parts of the plant, complimenting the efforts of one another. But because hedgerows didn’t increase the number of native bees in fields, these benefits from native bees are likely due to other factors. I am currently exploring what might affect sunflower-pollinating bees through additional analyses.
Past studies have found that hedgerows and other small-scale field-edge habitat enhancements can contribute to increased seed set in canola and blueberry crops in different landscapes. In addition, hedgerows not only increase bee diversity but also the diversity of different traits the bee community has. I therefore conclude that hedgerows could contribute to both bee conservation and crop pollination, but their efficacy likely depends on their location and crop-context.
In sum, hedgerows are a good idea in some situations but not in others. We ought to hedge our bets and use multiple diversification strategies instead of relying on a single method. Thus, while hedgerows are an important tool in our toolkit, they should be utilized in tandem with other techniques, such as cover cropping, crop rotation, and polyculture.
H.S. Sardiñas and C. Kremen. 2015. Pollination services from field-scale agricultural diversification may be context-dependent. Agriculture, Ecosystems and Environment, 270: 17-25.
Hillary Sardiñas 