Arthropod communities and arthropod-mediated ecosystem services in urban vacant lands

Background/Question/Methods: Within Midwestern cities, decades of job loss and economic decline have resulted in significant areas of vacant land. Currently, there are more than 3,300 acres of vacant land within Cleveland, OH alone. Across the U.S., municipalities are critically examining vacant property, with the goal of incorporating these lands into a healthier, safer, and environmentally-sound urban revitalization. The goal of this project was to examine how the conversion of vacant land to community gardens and farms influenced beneficial insects and the arthropod-mediated ecosystem services they support. Data were collected in 2009 in 6 vacant lot and 6 first-year community garden sites and in 2010 from 8 vacant lot and 8 established (3+ years of cultivation) community gardens in Cleveland, OH. The diversity and abundance of both generalist predators and bee pollinators were measured. The amount of predation services was studied by comparing consumption of Lepidoptera eggs (Helicoverpa zea) in open (predator accessable) and caged (to expose eggs to environmental conditions but prevented predation) treatments. Pollination services were measured by comparing seed production in bagged (no insect pollination) and open (pollinator-accessable) dwarf sunflower (Helianthus annuus var. “Sunspot”) plants.

Results/Conclusions: Generalist predator communities were reduced in both new and established community gardens compared with vacant lots. However, the conversion of a vacant lot to a first-year community garden did not result in a loss of egg predation activity. In 2009, a significant reduction of egg prey was detected in the open versus caged treatments in both newly-established gardens (P=0.013) and vacant lots (P=0.003). An average of 36% of eggs were removed by predators within 48 h. In 2010, significant egg predation was detected in vacant lots and established gardens in mid-June (P=0.05 gardens, P<0.001 vacant lots) and mid-July (P<0.001 for both gardens and vacant lots). Egg predation increased throughout the season, with 15% of eggs removed within 48 h in mid-June and 44% in mid-July. A total of 17 bee genera were collected; two of which were more abundant in the community garden sites. This included the squash bee (Peponapis pruinosa) which provides pollination to plants such as zucchini and pumpkin. There was not a significant difference in the amount of pollination services provided within the habitats (P=0.6204). These data suggest that the conversion of a turf-based vacant lot to a community garden can have a negative impact on some arthropod taxa but not necessarily on the associated arthropod-mediated ecosystem services provided.