Seasonal Leaf Functional Trait Responses of Quercus frainetto Ten. to Urban and Natural Forest Environments and a Comparison with Quercus cerris L. in a Mediterranean Municipality

Among global biodiversity hotspots, the Mediterranean Basin is expected to become the one containing the largest extent of urban land, leaving natural forest fragments embedded within urban areas. Consequently, urban forests represent key reservoirs of biodiversity in rapidly urbanizing regions. However, how tree species adjust to the fragmentation and altered conditions of these forests remains poorly understood. We evaluated the seasonal variation in leaf functional traits of Quercus frainetto in an urban and a natural forest stand belonging to the same phytosociological association, Roso arvensis-Quercetum cerridis, in the municipality of Campobasso (Italy), and compared these patterns with those of the co-dominant Q. cerris sampled in the same stands and campaigns. Specific leaf area (SLA), leaf dry matter content (LDMC), leaf thickness, chlorophyll, flavonols and anthocyanins were measured in June, July and September 2023 and analysed using linear mixed-effects models, together with satellite-derived environmental variables. Q. frainetto showed a seasonal shift toward a more conservative leaf economy, with declining SLA and increasing LDMC and flavonols. In the urban forest, Q. cerris combined relatively high SLA with consistently higher LDMC and higher flavonol content than Q. frainetto in July and September, whereas in the natural forest these differences were restricted to single sampling dates. Overall, in the stands studied, the urban functional profile of Q. cerris was more consistent with tolerance to warmer and seasonally drier conditions than that of Q. frainetto, a pattern that requires validation across multiple sites and years.