Hedging our bets: Can hedgerows support native bee conservation and crop pollination?

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.





USGS Pollinator Library

The USGS has just launched the Pollinator library for the Mid-West- it is a searchable database of occurrences of pollinators to help facilitate research, while documenting species distributions and interactions. Check it out at: http://www.npwrc.usgs.gov/pollinator/

Hedgerows don’t disperse weeds into agricultural fields

A study published last year by UC Davis alumni Marit Wilkerson has shown that although hedgerows contain weedy species, they don’t cause those weeds to invade agricultural fields. Wilkerson suggests that instead, hedgerows may be functioning as filter fences, trapping the weeds. However, in hedgerows with larger plants that cast more shade, the amount of weedy species dropped dramatically. She suggests that if it were possible to create conditions in hedgerows to allow woody plant species to thrive, then smaller herbaceous weeds would likely decline. These findings provide an interesting goal for growers putting in hedgerows- to figure out ways to ensure the best growth of their plant species. This might be hard in California, where drought is likely making establishment of new hedgerows without irrigation a challenge.

Another interesting finding to come out of this study was that what was planted next to a hedgerow affected the weed composition and density. Hedgerows next to row crops and vineyards had fewer weeds than those next to sloughs or grasslands. These more natural habitat types are not only less-managed, but also provide more habitat for species likely to disperse weed seeds, such as birds. However, other studies have shown that proximity to natural habitats is highly beneficial for pollinators, leading to increased yields in crop fields. Therefore a balance between biodiversity and ecosystem service benefits and weed suppression needs to be struck. Fortunately, taking actions to reduce weed populations before planting a hedgerow can create a “legacy effect,” limiting weeds in the hedgerow to volunteers from the landscape.

Knowing the history of your hedgerow and the landscape context (whether it is likely to be invaded by weeds), and managing it so that woody native plants grow large enough to shade out unwanted herbaceous weeds seems like a good recipe for making the planting more successful at limiting ingress of weeds into agricultural fields.

Learn more by reading the full paper:
Wilkerson, M.L. 2014. Using hedgerows as model linkages to examine non-native plant patterns. Agriculture, Ecosystems & Environment 192: 38-46.

Managing Small Farms for Pollinators

On Monday I had the pleasure of attending at the California Small Farms Conference, a gathering of growers, government/non-profit/extension personnel and marketers. I was delighted to run into my favorite vendor at my local farmers market (lake Merritt) from Say Hay Farms.

Together with Katarina Ullmann, a Pollinator Conservation Specialist with the Xerces Society for Invertebrate Conservation, and Ben Munger, Farm Manager of Midland School, I hosted a workshop about managing small farms for pollination. Katharina began the workshop by discussing the importance of wild bees for crop pollination (1/3 of our food is pollinator-dependent) and going over the key players (discussing the differences between wild bees groups as well as how to differentiate them from honey bees, wasps, and flies). Next I went over specific techniques to increase floral resources and nesting habitat on farms, largely drawing from an infographic series I recently published in collaboration with UC Cooperative Extension and the Berkeley Food Institute (with input from the Xerces Society). You can download the infograpics on the Resources page of this website. After this Ben shared pictures of his multi-hedgerow project, discussed the goals (to increase aesthetics on the farm while improving pollination of tomato, squash and pepper crops). He also talked about the importance of partnership- he worked with NRCS and Xerces, but also found working with a local landscaper greatly improved the installation and maintenance of hedgerows. He talked about some poor plant choices that have become weeds and escaped, as well as plants he really likes (non-cultivar plants from the native scrub surrounding the school’s property). Finally, Katharina finished up by discussing all the resources available to help for installing hedgerows, like NRCS and Xerces. It was fun to put this workshop together, hopefully we will give more in the future.

Scientists call on White House to take Pesticide Action

Today over 100 scientists (myself included) sent a letter to the President asking him to have his Bee Task Force protect bees by

1. establishing a moratorium on the use of neonicotinoics (like the one currently in place in the EU)

2. suspending currently approved agricultural and cosmetic uses of neonicotinoids

3. increasing research funding that looks at alternatives to pesticides that are toxic to bees.

These represent important steps in the quest to protect bees and our food supply. Other important foci include diversifying farmed areas to provide more floral and nesting resources for wild bees.

Read the full letter and summary here: http://www.panna.org/press-release/100-scientists-call-obama-bee-task-force-take-action-pesticides