Italian monumental trees and biodiversity: a focus on origin and landscape settings

The scientific community, policy-makers and citizens have increased their attention on monumental trees and their ecological, landscape and socio-cultural values. Monumental trees represent only a small portion of the population of trees but require specific planning and management to maintain their notable and specific cultural and biodiversity values. These trees are generally identified for their exceptional size (e.g., trunk diameter, height), shape (e.g., crown and trunk shape), age, and/or for their intrinsic cultural values having witnessed important historical events. Because of their specific structural and functional traits (e.g., tree-related microhabitats), monumental trees are essential for supporting complex and distinct assemblages of a wide range of species. However, little attention has been paid to the importance of monumental trees for biodiversity, especially in urban environments. In the project “MONUVERSITY - MONUmental and urban trees for biodiveRSITY: improving our knowledge on their origin and microhabitats”, we aimed to analyse and describe the monumental tree community of Italy, highlighting their importance for the conservation of biodiversity. We analysed the most updated version of the database of Italian monumental trees as identified according to the Italian Ministerial Italian administrative regions on the basis of the two recently published national check-lists for the native and non-native flora of Italy. The original urban/non-urban classification, based on personal assessment of the operator, was updated according to the Corine Land Cover map 2018. We selected the category “Artificial Surfaces" and applyed a 500m buffer around each monumental tree. Urban context = Artificial surface’s cover > 50%. Urban context: Our classification method identified 995 records in urban environment across Italy. Out of these, 727 records (73%) are non-native species, among which 11 individuals are considered invasive within the corresponding region. F i g . 1 : S c h e m a t i c representation of tree’s buffer, clipped with the Corine Land Cover 2018 500m * Agr. S.: Agricultural Surface; Art. s.: Artificial surface; W.a. / SN e.: Wooded areas / Semi-natural environments * Native Non-native Fig.2: Relationship between Biogeographical origin and Context of 4006 records. (107) are the commonest non-native species. Friuli-Venezia Giula is the region with the highest number of non-native individuals. Fig.3: Monumental Platanus hispanica Mill. ex Münchh in Vigodarzere’s Carthusian monastery (Padua, Veneto). ID: 01/L892/PD/05. Criteria of monumentality in urban areas: Circumference and age are the most frequently used criteria for identifying trees as monumental, 79% and 67% of urban’s records, respectively. The criterion botanical rarity was adopted for the identification of 21% of urban non-native species (152) and only 5% of urban native species (15). Distribution map of 995 urban monumental trees, differentiated according to the biogeographical origin. Dimensions in urban areas: Urban non-native species seem to be generally larger and taller than native species (Figure 4). The current database includes 4,006 monumental trees, both as single (ca. 90%) and group of plants (ca. 10%). Quercus is the most representative genus (29%). The most frequent species are native: Quercus pubescens Wild. subsp. pubescens (609), Fagus sylvatica L. (220), Quercus ilex L. (195). 1369 records (34.1%) are non-native species, distributed among 144 species, among which, Platanus hispanica Mill. ex Münchh and Cedrus deodara: Distribution of dimensional traits of monumental trees, differentiated between native (red) and non-native trees, with relative 95% confidence ellipses. H: 32m D: 198.9cm Knowledge of the composition and spatial distribution of monumental trees, distinguishing between native and non-native species allowed us to understand better their cultural value and their potential role in biodiversity. These results help proposing management practices that aim to protect individual trees and their cultural and biodiversity values.