People design urban ecosystems to promote many social, economic, and environmental benefits, with a recent surge of interest in supporting biodiversity. The role of intentional design in urban ecosystem structure and function spans a continuum from completely spontaneous dynamics in derelict land, to parks and gardens where design and management are important, to green roofs and bioswales that are completely manufactured and employ artificial substrates. Many publications document the performance of ecosystem services by designed systems, but the relationships between the properties of designed ecosystems and their ability to provide habitat for various kinds of biodiversity in cities has been less explored by ecologists. Descriptions of the habitat value of designed ecosystems, species inventories and comparisons with other habitats (natural or designed) represent part of the necessary baseline studies that ground more complex ecological research. Ecologists have also described ecosystem processes such as nutrient export and linked plant community composition to ecosystem functions, and begun to identify the design elements that make a difference for habitat provisioning. The speakers in this organized session will review and synthesize these "low-hanging fruit" studies from various perspectives, including biogeochemistry and landscape ecology. The speakers will then articulate the frontiers of these fields and outline the next research questions that will challenge ecological designers of these urban systems. How does ecological novelty shape the utility of designed habitats as refuges for urban biodiversity and what does this tell us about the nature of urban environments? For example, plant-microbe-soil feedbacks are key to understanding the material cycling in designed ecosystems but several features of these systems such as isolation from nearby habitat, artificial substrates and anthropogenic inputs mean that they may work quite differently compared with natural ecosystems. Ecosystems that start out as highly designed and managed often show spontaneous dynamics as other species colonize or as management regimes shift due to changes in budgetary priorities. Recognizing a continuum from designed to completely spontaneous/unmanaged ecosystems, ecologists need to explore the role of spontaneous assembly of communities in the overall provision of ecosystem services, as well as the effects of relatively subtle management interventions into ecosystems with largely spontaneous dynamics. Speakers will scale up to consider the landscape context of designed urban ecosystems, including the export of services beyond designed systems (e.g. pollination, urban cooling), and discuss spatial prioritization in three-dimensions (e.g. on and in buildings and infrastructure) as a key to optimizing habitat value.