Urban Ecology for Conservation: Evaluating Social and Ecological Drivers of Biodiversity Change Over Time

Global biodiversity is threatened by anthropogenic impacts, as the global population becomes increasingly urbanized. Conservation researchers and practitioners increasingly recognize the potential of cities to support biodiversity and foster human-nature interactions. However, further understanding of social and ecological mechanisms driving change in urban biodiversity over time is needed. In this dissertation, I first synthesized evidence for the urban homogenization hypothesis, which proposes that cities are more similar across space and time than are the natural communities they replace. I found that approaches to testing urban homogenization varied widely, but there is evidence for convergence at regional spatial scales and for some taxa. This work revealed a lack of long-term urban studies, as well as support for social and ecological mechanisms driving homogenization.

Building from this systematic literature review, I tested the effects of a long-term nutrient enrichment experiment in urban and near-urban desert preserves to evaluate indirect urban impacts on natural plant communities over time. Urban preserves and nitrogen-fertilized plots supported fewer annual wildflower species, limiting their effectiveness for biodiversity conservation and nature provisioning for urban residents.

Finally, I conducted research on residential yards in Phoenix, Arizona, to explore the effects of individual management behavior on urban plant community dynamics. Using a front yard vegetation survey repeated at three time points and a paired social survey, I asked, to what extent are yard plant communities dynamic over time, and how do attitudes and parcel characteristics affect native plant landscaping? Front yard woody plant communities experienced high turnover on a decadal scale, indicating that these managed communities are dynamic and capable of change for conservation benefit. Residents held positive attitudes toward native plants, but cultivated few in their yards. Priorities such as desired functional traits, attitudes toward native plants, and household income predicted native plant abundance, while knowledge of native plants did not.

This body of work contributes to the growing understanding of how urban ecosystems change over time in response to local- and city-scale impacts, demonstrating opportunities to engage urban residents and land managers in local conservation action to improve the value of cities for people and biodiversity.