Quantifying bee assemblages and attractiveness of flowering woody landscape plants for urban pollinator conservation.

Bernadette M Mach,Daniel A Potter,Iratxe Puebla

doi:10.1371/journal.pone.0208428

Abstract

Urban and suburban landscapes can be refuges for biodiversity of bees and other pollinators. Public awareness of declining pollinator populations has increased interest in growing plants that provide floral resources for bees. Various publications and websites list “bee-friendly” plants, but such lists are rarely based on empirical data, nor do they emphasize flowering trees and shrubs, which are a major component of urban landscapes. We quantified bee visitation to 72 species of flowering woody landscape plants across 373 urban and suburban sites in Kentucky and southern Ohio, USA, sampling and identifying the bee assemblages associated with 45 of the most bee-attractive species. We found strong plant species effects and variation in seasonal activity of particular bee taxa, but no overall differences in extent of bee visitation or bee genus diversity between native and non–native species, trees and shrubs, or early-, mid-, and late-season blooming plants. Horticulturally-modified varieties of Hydrangea, Prunus, and Rosa with double petals or clusters of showy sterile sepals attracted few bees compared to related plants with more accessible floral rewards. Some of the non-native woody plant species bloomed when floral resources from native plants were scarce and were highly bee-attractive, so their use in landscapes could help extend the flowering season for bees. These data will help city foresters, landscape managers, and the public make informed decisions to create bee–friendly urban and suburban landscapes.

Highlights

Many wild bee species, including important crop pollinators such as bumble bees (Bombus spp.), are declining in abundance or range [1,2,3,4,5,6]
We identified 45 species of trees and shrubs that could be useful for augmenting floral resources for bees in urban and suburban settings
While it is unlikely that a sample of 250 bees collected from five sites would capture the full bee species richness and diversity of a given plant species during the entirety of its bloom, our data do provide a measure of which tree and shrub species attract and support robust bee assemblages

Summary

Introduction

Many wild bee species, including important crop pollinators such as bumble bees (Bombus spp.), are declining in abundance or range [1,2,3,4,5,6]. Loss of floral resources, associated with agricultural intensification and habitat loss, is one of the major drivers of pollinator decline [5,7]. Protecting natural areas and restoring agricultural lands are important strategies for pollinator conservation, but urban landscapes, which offer a variety of forage and nesting sites, can be refuges for bees [8,9,10]. Substantial portions of native bee communities can persist and even thrive in urban and suburban areas with support from gardens [11,12,13,14,15,16], parks [17], low-input lawns [18,19], and other properly designed and managed urban green spaces.

Methods

Results

Conclusion