2012 Annual Report for GW12-024
Ecosystem Services in Hedgerow Restorations: Pollination Function and Nesting Habitat
We evaluated the ability of hedgerow restorations to augment hybrid sunflower pollination by the native bee community. We also investigated whether rates of nesting were increased in fields adjacent to hedgerows, as well as whether the presence of hedgerows enhanced the diversity and abundance of the native bee community at different distances into fields. Field work will be continued in 2013, therefore we only report milestones at this juncture.
1. Assess the spatial distribution of pollinators in agricultural fields
2. Assess pollination function in fields with and without hedgerows
3. Generate an economic model that evaluates the marginal benefits of hedgerow restoration along field edges
4. Assess the nesting bee community in hedgerows and fallow field edges
5. Correlate habitat features in hedgerows and fallow field edges to nest occurrence
Field work was carried out in 10 sunflower fields in California’s Central Valley from June – August 2012. Over 800 bee specimens were collected. They have been pinned and sorted and are currently being identified by collaborator Dr. Robbin Thorp.
We also used fluorescent dyes to mark 100 bees along field edges in eight of our study sites. We then recorded the amount of dye deposited over a single day, up to fifty meters into the field. Kathleen Tom, a participant in UC Berkeley’s Undergraduate Research Apprentice Program, has adopted this part of the project as her Senior Thesis and is currently conducting statistical analyses.
At each of four locations (ten, fifty, one hundred and two hundred meters into the field) along two parallel transects, we assessed the bee community using three complimentary methods: visitation plots, aerial netting and blue vane traps. Visitation gives an estimate of the community of bees pollinating female sunflowers. Aerial netting directly from sunflower heads also yields a direct assessment of bees at different distances. Blue vane traps have been shown to be effective at trapping bees in sunflower (Stephens and Rao, 2007), yet it is unknown whether they attract bees to them from various distances, therefore they are better indicators of community diversity and abundance within fields.
We conducted pollen limitation experiments along two transects in each field. After a 2011 pilot study indicating that female sunflowers do not self-pollinate, we only had two closed control sunflowers in each study site that were covered by mesh bags. At each distance on the two transects, we left three sunflowers heads open to determine ambient levels of pollution. We also added pollen to three experimental plants to assess maximum pollination levels. To determine pollen limitation, we will subtract the ambient seed set rate from the experimental seed set rate. A lower pollination deficit indicates higher yield. Sunflower seeds have been harvested and cleaned; they will be counted in spring 2013. Pollination deficit data will then be incorporated into economic models that account for the added value of additional pollination given the costs of installing and maintaining hedgerows adjacent to fields.
We used emergence traps (Bug dorm) to assess the nesting community in each study site. The traps were deployed for 18-22 hours, from sunset until the afternoon the following day. We found 116 individuals in emergence traps. There was no difference between bees caught in fields with or without hedgerows (p = 0.492, t = – 0.688). In addition, we did not find evidence that bees nested at different rates at different distances into the field versus the edge, or at different distances into the field (p = 0.2795, F = 1.289).
Soil was collected at each site from within the field and the edge. Soil analyses are being conducted at UC Davis. In addition, within each emergence trap, we recorded nesting proxies as defined by Potts et al. (2005). These proxies comprise potential nesting resources or habitat required by ground-nesting native bees, such as bare ground, slope, available nesting cavities and floral resources. These proxies will be correlated to native bee nesting incidence, diversity and abundance.
Impacts and Contributions/Outcomes
In 2012, all known hedgerows in the Yolo County study region were GPSed, and the data has been complied into GIS maps which will be given to the California Crop Improvement Association (CCIA) this spring to incorporate into maps utilized by growers to determine sunflower planting selection.
We send all of the companies participating in our study annual updates related to our research. Last year, we participated in a conference held by a multi-national corporation, presenting on the benefits of hedgerow installation to agriculture. Upon completion of our field work, we plan to hold a workshop for regional sunflower producers to disseminate our findings. In addition, our findings will be incorporated into education pamphlets distributed by the Xerces Society for Invertebrate Conservation. Thus far, feedback from growers has been positive, with a few contacting us to indicate sites with large numbers of ground-nesting sunflower-specialist bees.
Our findings will be useful to the NRSC, specifically WHIP and EQIP programs that participate in habitat enhancement projects, including hedgerows. Findings may be relevant to other mass flowering crop systems. In particular, they shed light on nesting dynamics within till and irrigated crops.
We also created a website focused on our research and findings (nativebeeresearch.wordpress.com), which is updated during the active field season. It also serves as an educational tool with information about hedgerows and native bee biology. To date, we have received 794 unsolicited views, with a high of 62.
Potts, S.G., B. Vulliamy, S. Roberts, C. O’Toole, A. Dafni, G. Ne’eman,and P. Wilmer. 2005. Role of nesting resources in organizing diverse bee communities in a Mediterranean landscape. Ecological Entomology 30(1): 78-85.
Stephen, W.P. and S. Rao. 2007. Sampling Native Bees in Proximity to a Highly Competitive Food Resource (Hymenoptera: Apiformes). J. Kansas Entomological Society 80(4):369-376.
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