Influence of water availability on native wildflower phenology and pollinator attractiveness

In 2017 and 2018, we performed a field study screening 23 garden-friendly, native Willamette Valley wildflowers (and four exotic comparators) for their attractiveness to pollinators. Flower phenology and pollinator visitation differed between the two seasons. There was a marked difference in both flowering timing and duration. The 2017 peak bloom began an average of 17.7 days later than 2018, and ceased 27.7 days later. Thus, the length of 2018 peak bloom was 10 days shorter on average, and ended a month earlier. We hypothesize that these differences are due to water availability. In 2017, we irrigated to ensure perennial establishment, while in 2018 we did not irrigate. Furthermore, in 2017 the region received 2.83 inches of rain across May-August, whereas in 2018 there was only 0.87 inches of rain in May-August. This may have accelerated flowering and attenuated its length. These phenological differences may have implications for the abundance and species-richness of attracted pollinators. In 2018, flowers opened earlier and for a shorter duration on average. However, across our timed pollinator counts we observed more native bee visitors per observation. When considering native bees, Gilia capitata, Madia elegans, Aster subspicatus, Eschscholzia californica, and Solidago canadensis attracted the greatest bee abundance in 2017. In 2018, Eschscholzia californica, Aster subspicatus, Phacelia heterophylla, Solidago canadensis, and Clarkia amoena were the most attractive to native bees. During our 2019 field season we will irrigate half the plots, to address both temporal variation and the impact of irrigation on bloom phenology and attractiveness

Screening Native PNW wildflowers for Attractiveness to Pollinators and Natural Enemies

Many organizations have published pollinator friendly planting lists for home gardeners. However, most of these lists lack empirical evidence to support their choices. To our knowledge no such list exists In the Pacific Northwest; thus, there is a need for baseline research on the relative attractiveness of native wildflowers to floral visitors in our region. Such data would better inform targeted plantings designed to increase habitat value in urban area. During the summer of 2017, we conducted the first field season of a study screening 23 native Willamette Valley wildflowers for their attractiveness to pollinators and natural enemies. We planted these species at the North Willamette Research and Extension Center in meter square plots spaced six meters apart. We monitored floral visitation, floral bloom, and vacuum sampled insects weekly between April and October Though this research is ongoing, we have early findings on the attractiveness of these wildflower species to bees and natural enemies. Solidago canadensis and Symphyotrichum subspicatum were two of the more attractive perennial species, and Clarkia amoena and Gilia capitata were annual flowers highly attractive to a variety of pollinators. This project will run for several more seasons, and will result in recommended pollinator planting lists for home gardens and for agricultural areas

Garden Pollinators and the Potential for Ecosystem Service Flow to Urban and Peri-Urban Agriculture

Hedgerows, flowering strips, and natural areas that are adjacent to agricultural land have been shown to benefit crop production, via the provision of insect pollinators that pollinate crops. However, we do not yet know the extent to which bee habitat in the form of urban gardens might contribute to pollination services in surrounding crops. We explored whether gardens might provision pollinators to adjacent agricultural areas by sampling bees from gardens in the Portland, Oregon metropolitan area, and estimating typical foraging distances in the context of commercial- and residential-scale pollination-dependent crops up to 1000 m from garden study sites. We estimate that garden bees could forage outside of the garden in which they were collected, and that when pollination-dependent crops (commercial-scale or residential-scale) are nearby, 30–50% of the garden bee community could potentially provide pollination services to adjacent crops, if urban bees readily cross boundaries and forage among habitat types. Urban gardens might thus be well-positioned to provision neighboring farms and food gardens with pollination services, or could serve as a refuge for pollinators when forage is scarce or crop management practices are inhospitable. The actual capacity of gardens to serve as a refuge for pollinators from agricultural fields depends upon the extent to which bees forage across habitat types. However, relatively little is known about the degree to which bees move among habitat patches in heterogeneous landscapes. We thus propose a research agenda that can document the extent to which gardens contribute to pollinator health and pollination services at the interface of urban, peri-urban, and rural landscapes. In particular, more data is needed on how landscape context impedes or promotes garden bee movement between habitat types