Urban green infrastructure includes both natural inputs and artificial supplements, including irrigation, synthetic substrates, and drainage layers. Green infrastructure aims to make cities more resilient and less dependent on outside resource inputs through more efficient use. Over the past 2 decades, these constructed ecosystems have expanded to include green roofs, elevated urban parks, and rooftop vegetable farms. This paper outlines opportunities and challenges for advancing the science of these constructed ecosystems with particular emphasis on rooftop agriculture. Although in concept rooftop agriculture could contribute to urban food security, water management, and biodiversity, research comparing design and management strategies across climate zones and regional economies is necessary to fully integrate ecological understanding into urban planning policy.

Constructed urban ecosystems can be different from traditional subjects of ecology in terms of environmental and economic performance, but they are direct outcomes of urban planning and design intentions, which are important and testable subjects for understanding and improving coupled human-natural systems. Among those constructed ecosystems are rooftop intensive vegetable production systems aiming to achieve diverse goals of sustainability within the practices of urban green infrastructure projects, while the scientific community has little information for instructing and navigating urban planning and design. Future research could be motivated by the following questions:

(1) What are the optimal levels of yield, water and nutrient use efficiency, and stormwater management for balancing environmental and economic costs of rooftop intensive agriculture?

(2) How do economic and environmental returns of rooftop intensive agriculture differ in specific system design, climate zone, regional economy, and distance to major agricultural areas?

(3) What are the specific contributions of rooftop farming to enhancing urban biodiversity?

(4) What are the best ways of involving scientists and designing experiments in rooftop intensive agriculture for understanding and improving social ecological systems?

(5) How could urban planning and design integrate different options of rooftop intensive agriculture and other green spaces for achieving diverse goals of urban sustainability?