Monumental trees and tree-related microhabitats: their biodiversity value for urban areas of Veneto

Monumental trees, with their exceptional size, shape, and landscape and ecological values, provide several ecosystem services. While making up a small portion of the total tree population, monumental trees require specific management and planning to preserve and enhance their distinctive cultural and biological contributions. Due to their morphology and age, monumental trees provide crucial habitats for a wide range of species through the presence of tree-related microhabitats (TreMs). TreMs support a variety of animal, plant, and fungal species, playing a key role in terms of biodiversity conservation. In this study, we shed light on the biodiversity values tailored to the monumental tree community of urban areas of Veneto (northeast Italy). We used the Italian database of monumental trees as a reference, selecting those within Veneto’s urban areas. TreMs and dendrometric parameters (i.e., DBH and height) were assessed for 93 monumental entities (i.e., considering alignments and groups of trees as a whole) in urban areas, encompassing a total of 223 individual trees. We found positive correlations between DBH and TreM’s richness and abundance, particularly at the canopy level. Mosses, crown microsoil, and limb breakage were the most frequent TreMs, while trunk rot-holes were the most common among cavity types. These results highlight how large monumental trees constitute an ecologically significant element in urban areas. Furthermore, the importance of these trees, in terms of supporting biodiversity in environments where nature is scarce, highlights a potential use of TreMs as an indicator to assess ecological values (i.e., one of the criteria to identify trees as monumental). The monitoring and study of TreMs are crucial for implementing conservation measures for many species, improving the assessment of the provisioning of ecosystem services and urban biodiversity. Moreover, the identification and monitoring of specific TreMs, (e.g., dead branches, and cavities) can provide critical information for evaluating the structural stability of urban greenery, which is crucial for ensuring citizen safety.