Urban Food Security and Informal Green Ecosystems in Secondary Cities: Negotiating Sustainability through the Green Optimum Economy

Urban food insecurity is an increasingly pressing challenge in secondary cities of the Global South, where fragile supply chains, rapid urbanisation, and uneven urban governance disproportionately affect low-income populations. This paper examines how Khon Kaen, a secondary city in Northeastern Thailand, developed an informal green food ecosystem that supports urban food security and ecological transition through peri-urban agriculture, informal markets, green logistics, and community-based initiatives. The study operationalises a Green Optimum Economy framework, emphasising negotiated balances between ecological integrity, economic viability, and social equity. Using a mixed-methods action research design that integrates food value-chain mapping, participatory action research, an Urban Lab approach, and tactical urbanism, the study analyzes upstream–midstream–downstream dynamics in Khon Kaen’s organic vegetable system. Empirical work involved collaboration with peri-urban producers, mobile vendors, green markets, local restaurants, school canteens, and vulnerable groups to prototype locally embedded mechanisms such as green logistics and small-scale green entrepreneurship. The findings demonstrate that informal and semi-formal food networks function as critical urban infrastructure, particularly during periods of disruption. During the COVID-19 pandemic, these networks enabled continued food access when conventional supply chains were destabilised, revealing both adaptive capacity and underlying precarity. The pandemic thus served as a stress test, exposing structural vulnerabilities and risk redistribution within urban food systems. The paper contributes by conceptualising the Informal Green Food Ecosystem in secondary cities, applying the Green Optimum Economy as a critical analytical lens beyond formal planning, and deriving insights for governing informal food systems as contested arenas of urban sustainability transitions.