Urban plant heterogeneity influences cavity nesting bees and wasps

Urban greenspace is critical in supporting ecosystem services such as pollination and pest regulation. Yet, greenspace management can limit the value of these patches for conservation. This study investigated how redesigning plant communities within vacant lots influenced their ability to support insect pollinator and predator communities. The Biodiversity Ecosystem Function (BEF) hypothesis proposes that increasing biodiversity stabilizes and increases the productivity of an ecosystem. However, biodiversity’s influence is context dependent and varies amongst trophic levels. Our research examines BEF theory in urban Cleveland, OH by quantifying how patch and landscape scale heterogeneity impact cavity nesting bees and wasps, two taxa responsible for pollination and resource capture of arthropod pests. We seeded forty vacant lots in eight neighborhoods with one of five planting treatments. We then determined how both local vegetation and landscape features influenced wasp and bee nesting productivity. To monitor nesting, we established one trap nest filled with twenty cardboard nesting straws in each lot. Once per month, from May-August 2015, we collected all occupied straws and X-rayed their contents. We found that larvae abundance increased with vegetation height and dominant plant species diversity. Larvae within trap nests were also more abundant in landscapes dominated by built structures versus landscapes composed of more vegetation. Our results indicate green space is more valuable in increasingly built landscapes and can be used to guide management of vacant land to support (1) urban conservation of wasps and bees, and (2) increased ecosystem functioning in urban environments.