2013 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.
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
Fieldwork was carried out in eight sunflower fields in California’s Central Valley from June – July 2013. We collected 250 bees from nets, 29 bees from emergence traps and 1,000 bees from blue vane traps.
Kathleen Tom completed her senior thesis on this portion of the project; fieldwork was completed in 2012. She used fluorescent dyes to mark 100 medium-sized bees along field edges in eight sites, half adjacent to hedgerows. She then recorded the amount of dye deposited over a single day up to fifty meters into the field. She found that native bees declined with an exponential decay rate of 0.9 from the field edge (Fig. 1). The majority of the marks were within 10 m of where the bees were marked, less than 1% of their predicted foraging range. She did not find any effect of hedgerow presence on the movement of native bees within sunflower fields.
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, 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 are still completing identification from blue vane traps. To accomplish this we have trained four interns in bee identification and specimen curation. Data analysis is projected to begin in spring 2014.
We continued our seed set experiment in 2013 at eight sites. After combining the data with 2012, we did not find a difference between seed set at hedgerow or control sites (Fig. 2). This could be partially explained by the high number of honey bees present at all sites, as colonies are rented and brought in to pollinate. We plan to assess what role native bee abundance and species richness had on seed set this coming year.
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 29 individuals in emergence traps in 2013, compared to 116 in 2012. We did not detect a difference between bees caught in fields with or without hedgerows. 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 (Fig. 3).
We began an additional project evaluating the role of irrigation on nesting rates within fields. Collette Yee, through the Sponsored Undergraduate Projects Program, is conducting this related research as part of her senior thesis project. She set out 20 traps along two parallel transects into fields, from 0 – 100 m. Her study was carried out in 10 sites, half of which were furrow irrigated and half of which were drip irrigated. She did not find a difference in nesting rate or the abundance or foraging bees in sites with either irrigation management style (Fig. 4).
Soil was collected at each site from within the field and the edge. Soil analyses are currently being conducted. In addition, within each emergence trap, we recorded nesting resources, such as bare ground, slope, available nesting cavities and soil hardness. We did find that hedgerows had more nesting resources available than weedy/bare field margins but have yet to detect an effect on native bee nesting incidence, diversity or abundance.
Impacts and Contributions/Outcomes
We are currently preparing an annual update for all growers who participated in our study over the last two years. Each report contains preliminary findings and data on species collected at each individual farm.
We participated in a pollination workshop put on by UC Extension to over 30 growers. We presented on our nesting and movement results. Participants were very interested in our results. We also presented our work at the 2013 Entomological Society of America Conference and EcoFarm 2014. These presentations reached academics, practitioners and farmers.
We also published a popular article on Objective 2 in the Berkeley Science Review http://sciencereview.berkeley.edu/article/flight-of-the-sunflower-bee/
We shared our data with two meta-analyses that are examining native bee crop pollination and the role of habitat enhancements. These studies combine data across a variety of crops and ecoregions and will allow better understanding of trends affecting native pollinators that can translate into management actions.
Last year we created a website focused on our research and findings: http://nativebeeresearch.wordpress.com Originally it was updated during the field season, but we are currently updating it at least twice a month with summaries of current scientific research on pollination, other relevant news stories and pertinent information or web-based resources. It also serves as an educational tool, with information about hedgerows and native bee biology. To date, we have received 2,494 unsolicited views from 32 countries. We average eight views per day.
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 irrigated crops. Our findings will be incorporated into fact sheets distributed by the Xerces Society for Invertebrate Conservation. We are also currently working on an info-graphic about habitat restoration and native bee conservation.
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