The Value of urban greenspaces to support biodiversity and ecosystem services
With the Earth’s surface so significantly shaped by human activity it is critical to understand how to preserve and promote species within urban ecosystems. Urban conservation also offers direct human benefits by connecting people with nature and enhancing provision of diverse ecosystem services. Although we see a rise in urban living across the globe, due to protected economic downturn and the recent foreclosure crisis, many cities have lost substantial population in recent decades. This has left municipalities with the task of demolishing abandoned residential structures, creating parcels of vacant land. One such city is Cleveland, Ohio which has over 20,000 vacant lots covering 1,450 hectares of land area. These newly formed green spaces have the potential to serve multiple environmental functions including species conservation, storm water retention and local food production. Worldwide urban agriculture has grown rapidly as access to nutritious food is especially limited in low-income communities, where many residents lack access to personal or public transportation or supermarkets within walking distance that carry fresh produce. In Cleveland, 209 community gardens and 55 for-profit polyculture farms are producing fruits and vegetables on formerly-vacant land within inner city neighborhoods. These sites require the work of beneficial arthropods such as pollinators and predators to produce crops sustainably. We quantified the current ecological value of vacant land to support beneficial arthropod biodiversity and assessed how its conversion to support urban agriculture affected these species and the pollination and biological control services they provided.
We found that urban vacant lots supported a high arthropod diversity, with 30% of spider and 42% of bee genera known to occur in the state of Ohio found within them. Additionally, the conversion of vacant land to planted food gardens affected the abundance and diversity of these predators and pollinators, their food resources, and the biological control and pollination services they provide. Of particular concern was a low level of pollination services found within urban gardens, indicating that establishing pollinator habitat on vacant land near farms and gardens may be necessary to improve the yield of bee pollinated crops. In addition, we documented high concentrations of heavy metals within the soil and the arthropod biota within vacant lot and urban garden habitats. This could affect factors such as longevity and pollination and predatory efficiency and is a key concern when considering the development of additional urban green spaces to support conservation and community health.