Enhancing Pollination Supply in an Urban Ecosystem through Landscape Modifications

The authors modeled the effect of converting lawn/turf areas to flowering habitat on bee abundance within the greater Chicago, Illinois area, specifically to test the “pollination supply” for urban agriculture (defined as home food gardens, community gardens, and urban farms). 

Scenarios examined included:

• Scenario 1: Convert existing grass cover in city parks to flower gardens.
• Scenario 2: Convert existing grass cover in residential yards to flower gardens. 
• Scenario 3: Convert existing grass cover within 250 m, 500 m, 750 m, or 1000 m of community gardens/urban farms to flower gardens.

Each scenario was tested for conversion rates of 1% and 5% of existing grass cover.  

The assessment utilized a crop pollination model known as InVEST.  Based on the distribution of source habitat and the foraging range of pollinators, the model calculates a relative index of bee abundance for each location (pixel) in the landscape. This map can be interpreted as an index of pollination supply. 

Results showed that a 5% conversion of turf to flower gardens produced statistically significant increases in pollination supply when floral enhancements were within proximity of urban agriculture sites.  Residential food gardens experienced the largest increase in pollination supply if floral enhancements were conducted at the 5% level under Scenario 2 (i.e. highly dispersed enhancements result in better pollination supply for the similarly highly dispersed home gardens) or within 1000 m of community gardens/farms under Scenario 3. Pollination supply abundance was also increased at community gardens and urban farms, but only at statistically significant levels if conversion occurred within 250 m of these urban agriculture sites and at the 5% level. 

The results highlight tradeoffs in strategies if a pollinator enhancement campaign includes the goal of increasing the supply of pollinators for urban agriculture. If the objective is to enhance pollination supply for home gardeners, then converting turf grass in residential yards to flower gardens or within 1km of urban farms and community gardens would be beneficial. However, to enhance pollination at existing urban farms and community gardens, the best strategy is to concentrate the increased floral resources close to the farms themselves.