Reclaiming urban vacant land to manage stormwater and support insect habitat

Urban green spaces can provide important wildlife habitat and ecosystem services. In legacy cities, built structures are demolished as populations dwindle, resulting in vacant land. Vacant land constitutes an opportunity to establish green infrastructure that provides multiple ecosystem services. Our objective was to determine whether establishing green infrastructure on vacant land to manage stormwater could provide insect habitat in the legacy city of Cleveland, Ohio, U.S.A. Two green infrastructure treatments were implemented on vacant land in the historic Slavic Village neighborhood in 2014 and 2015: rain gardens (lower cost) and bioswales (higher cost). We hypothesized that rain gardens and bioswales would support more abundant, species rich insect communities compared to unaltered vacant lots. Wild bees (Hymenoptera: Aculeata) and lady beetles (Coleoptera: Coccinellidae), two insect groups of conservation concern, were sampled during the summer (June–August) from 2014 to 2016 using pan traps and yellow sticky card traps. Local vegetation and temporal variables were measured. Generalized linear mixed effects models evaluated whether insect biodiversity varied with treatment, habitat variables, site, and time. We collected 3,004 bees from pan traps and 5,438 lady beetles from yellow sticky card traps during this study. Bee biodiversity was similar among treatments. In 2014, alien Coccinellidae abundance was higher in vacant lots compared to rain gardens. In 2015 and 2016, alien Coccinellidae were marginally more abundant in rain gardens compared to vacant lots and bioswales, while native Coccinellidae abundance was significantly higher in vacant lots. In the short term, establishing green infrastructure on vacant land can improve stormwater management without compromising the quality of vacant land as insect habitat.

Methods
Pan traps were set in 2014 (July 10, July 31), 2015 (June 9, July 6, Aug 5), and 2016 (June 9, July 26, Aug 8) to sample bees. Pan traps consisted of 96 ml plastic soufflé bowls (Solo®) painted fluorescent blue, yellow, or left white. One pan trap of each color was filled halfway with soapy water (1% blue Dawn dish soap/water solution) and deployed at ground level for 24 h in each quadrat used for vegetation sampling. At the time of collection, the number of viable pan traps per site was recorded to account for trap loss during each sampling. All bees from pan traps were washed, blown dry, pinned, and preserved with museum level archival labels. Bees collected using pan traps were identified using Discoverlife.org (Ascher and Pickering 2017), revisions by Jason Gibbs for Lasioglossum (Gibbs 2011; Gibbs et al. 2013), and Bumble Bees of North America (Williams et al. 2014). Voucher specimen identifications were verified by Sam Droege at the USGS Bee Inventory and Monitoring Lab in Laurel, Maryland and pinned bee specimens were deposited in the Museum of Biological Diversity in Columbus, Ohio. From the verified bee species data, total bee abundance, Halictidae abundance, Lasioglossum abundance, and native bee abundance were counted. Bee species richness and Shannon diversity were also calculated. Bycatch, including hoverflies (Syrphidae), longlegged flies (Dolichopodidae), minute pirate bugs (Anthocoridae: Orius), and rove beetles (Staphylinidae), were counted but not analyzed for the purposes of this study. To sample lady beetles (Coleoptera: Coccinellidae), Trece Pherocon ® Unbaited AM Yellow Sticky Traps (hereafter sticky traps) (23 cm W × 28 cm L with a 18 cm W × 23 cm L grid) were deployed for seven days at a time in 2014 (June 23, July 21), 2015 (June 10, July 6, Aug 3), and 2016 (June 9, July 14, Aug 2). One sticky trap was set per quadrat and secured to a step-in fence post above maximum vegetation height. At the time of collection, the number of viable sticky traps per site was recorded. Lady beetles were counted and identified to species using a stereomicroscope (Spring 2017). Bees were also counted and identified on these sticky traps, but the majority were only identifiable to genus due to the adhesive obscuring diagnostic features in the abundant Lasioglossum and Hylaeus specimens. This adhesive also made it challenging to remove bees collected from sticky traps without damaging them, and as a result, these specimens were not archived. From the lady beetle species data, total lady beetle abundance, lady beetle abundance by subfamily, lady beetle abundance by species, alien lady beetle abundance, and native lady beetle abundance were calculated. Some sampling equipment (pan traps, sticky traps, stakes) was lost due to theft or destruction by mowing equipment. Sticky traps on fallen stakes were not included in sticky trap analyses. Some traps had obvious contamination from animal fur or feathers but were still included in the analyses since a large portion of the sticky surface was still viable. Pan traps were also occasionally knocked over or washed out due to high rainfall during the sampling period, and these traps were not included in the analyses.