Urban Allotment Gardens with Turf Reduce Biodiversity and Provide Limited Regulatory Ecosystem Services

Urban gardens, including family allotment gardens (FAGs) and community gardens (CGs), play an increasingly important role in urban resilience to climate change—particularly through the delivery of regulatory ecosystem services. They occupy as much as 2.6% of Warsaw’s land area and thus have a tangible impact on the entire metropolitan system. These gardens are used in different ways, and each use affects the magnitude of the provided ecosystem services. This preliminary study explores how different types of allotment garden uses affect biodiversity and ecosystem services, addressing a critical knowledge gap in the classification and ecological functioning of urban gardens. We surveyed 44 plots in Warsaw, categorizing them into five vegetation use types: turf, flower, vegetable, orchard, and abandoned. For each plot, we assessed the floristic diversity, vegetation structure (leaf area index, LAI), and six regulatory services: air and soil cooling, water retention, humidity regulation, PM 2.5 retention, and nectar provision. Flower gardens had the highest species diversity (Shannon index = 1.93), while turf gardens had the lowest (1.43) but the highest proportion of native species (92%). Abandoned plots stood out due to the densest vegetation (LAI = 4.93) and ecological distinctiveness. Principal component analysis showed that the selected ecosystem services explained 25% of the variation in vegetation types. We propose a use-based classification of urban gardens and highlight abandoned plots as a functionally unique and overlooked ecological category.