Enhancing pollination supply in an urban ecosystem through landscape modifications

Although urban agriculture is growing in popularity, little is known about the distribution of insect pollinators across urbanized landscapes. We used the pollination module of InVEST (a suite of software models used to map and value ecosystem services), along with fine-scale land cover data and empirical data on bee distributions, to assess different scenarios of urban pollinator management in Chicago, Illinois (USA). Specifically, we simulated the partial conversion of lawn/turf-grass to floral resources in city parks only, in gardens managed by individual households only, and in any available turf grass within buffer distances of 250-1000 m of urban farms, community gardens, and home gardens across Chicago. We found that the output of InVEST's pollination model was significantly related to empirical measures of bee richness (explaining 46% of the variation) but not bee abundance in Chicago. To increase pollination supply at urban farms and community gardens, our results indicate that, out of the scenarios presented here, the best strategy for the City of Chicago would be to concentrate floral resources nearby (within a 250 m buffer rather than within a 1 km buffer). In contrast, for home gardens, the model indicates that it may be better to increase floral resources throughout the city. This discrepancy may be due to the smaller size of home gardens and their more dispersed spatial arrangement throughout the city. Generally, our results indicate that converting turf grass to a more florally-rich land cover would support increased supply of pollinators and urban agriculture.