Urban trees and green spaces provide a wide range of ecosystem services. Among urban green infrastructures, monumental trees represent key elements in these environments. Despite the growing recognition of their value, monumental trees in urban areas face multiple challenges, underscoring the need for targeted research to inform conservation and management strategies. This study investigates the ecological role of 124 urban monumental trees in the Veneto region (Italy) using tree-related microhabitats (TreMs) as a proxy for potential biodiversity support. Our analysis demonstrated that dendrometric characteristics (namely, diameter at breast height) and monumental tree configuration (namely, individual trees vs. those in groups) strongly affect the richness, abundance and composition of TreMs, highlighting that both native and non-native species contribute substantially to urban ecosystem functioning. Furthermore, complex relationships between monumentality criteria and TreMs were observed. These results are intended to support the management of urban green spaces, helping to enhance the biodiversity potential of monumental trees while preserving their multifaceted values.