WSARE report on pollinator projects they have funded

Western SARE (which stands for Sustainable Agriculture, Research & Education) just released a report highlighting the pollinator projects they have funded, including short courses on pollinator monitoring put on by the Xerces Society for Invertebrate Conservation (excellent opportunities to learn about different bee species). WSARE funded my graduate research, which was also highlighted.
Check out the details here!

National Pollinator Strategy

Today the White House released it’s National Pollinator Strategy, a comprehensive document outlining the governments’ plans to decrease losses from Colony Collapse Disorder, help Monarch butterflies, and increase acreage for pollinators through restoration and enhancement (goal = 7 million acres in the next 5 years!). How will they accomplish this? Through “USDA resources applied to CRP and EQIP pollinator enhancements, and national forest and grassland acreage; DOI actions to restore or enhance lands through direct restoration action, along with the inclusion of pollinator-friendly native seeds in all post-fire re-vegetation and fuels/green stripping projects; U.S. Army Corps of Engineers (USACE) implementation of pollinator best management practices at its facilities.”

However, the strategy had already been criticized for not doing enough to alter the use of pesticides currently being used today (that are having deleterious effects on pollinator populations).

Read the whole strategy here (pdf).

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.

 

 

 

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.