Almost all ecological processes are amplified in urban areas, with nutrients, resources, energy and biomass densely packed into an environment that changes rapidly in both space and time. Although ecological communities in urban areas might not be a tightly integrated web of interactions like the tropical rainforest, the urban ecosystem as a whole is like a taut string where a gentle pluck in one spot quickly reverberates through the whole. Our Ignite session will focus on these taut connections: how a subtle change in building materials or an invasive species can alter hydrology, climate, biogeochemical cycling, ecology, and the human experience of the urban environment, and how urban planning leads to a mix of intended and unintended consequences that only careful study and modeling can predict. Our speakers will highlight two key ways to understand these consequences: use of theory, and interactions between policy and ecology. The rapid-fire pace of an Ignite session is perfect for this complex subject, because each speaker will flash light upon one piece of the puzzle, and the combined after-images will form the basis of the new cognitive map that we will construct after the presentations.