Abstract: Aims Urban forests serve as ecological barriers that mitigate urban heat island effects and enhance ecosystem services, attracting increasing attention to their structure and function. Plant functional traits are essential for characterizing plant ecological strategies and revealing their regulatory mechanisms on ecosystem functioning. However, most existing studies have focused on natural ecosystems, while the ecological strategies and functional roles of dominant tree species in urban forests remain poorly understood. Methods This study focused on six key species (Robinia pseudoacacia, Eucommia ulmoides, Styphnolobium japonicum, Acer truncatum, Pinus tabuliformis, and Ginkgo biloba) in Beijing plain forests. Four categories of leaf functional traits, including morphological, elemental, chemical defense, and hydraulic traits, were measured to elucidate interspecific differences in ecological strategies and to characterize the network structure of leaf functional traits. Important findings Significant interspecific differences in leaf functional traits and corresponding ecological strategies were found: P. tabuliformis exhibited the lowest specific leaf area and lowest water potential at turgor loss point, reflecting a resource conservation and drought resistance prioritized strategy; A. truncatum showed high specific leaf area and the highest total phenolic content, representing a rapid resource acquisition with strong chemical defense; R. pseudoacacia demonstrated the highest leaf nitrogen content with moderate total phenolic levels, indicating fast growth with basic chemical defense strategy; S. japonicum possessed the highest phosphorus content and lowest total phenolic content, suggesting rapid growth with low chemical defense investment; E. ulmoides displayed high leaf dry matter content and carbon concentration, reflecting moderate resource conservation and structural defense; G. biloba exhibited intermediate-low values in growth-defense traits, representing balanced growth with low chemical defense. The leaf trait network constructed from the six species (edge density = 0.37, diameter = 4, average path length = 1.90, clustering coefficient = 0.59, modularity = 0.26) revealed a relatively simple structure, with specific leaf area acting as the central hub connecting different functional modules. This pattern reflects an initial stage of functional differentiation under the “fast-growth and high-efficiency” management orientation of Beijing plain forests, while also implying potential ecological vulnerability. Overall, this study provides new insights into the functional positioning of urban forest species and offers a theoretical basis for enhancing the multifunctionality of plain forests.

Key words: leaf functional traits, Beijing plain forests, urban forest transition, multifunctionality enhancement, leaf trait network