Distribution Pattern of Urban Street Trees in Rome (Italy): A Multifactorial Evaluation of Selection Criteria

Street trees play a significant ecological role in modern urban ecosystems, but usually the selection criteria follow pragmatic reasons rather than bio-ecological suitability. Understanding the influence of such factors can be relevant, especially in cities having a certain complexity and area. This paper aims to analyze the variation in the distribution of street tree species within the city's municipia of Rome to determine the influence of some factors in the selection process. Here, we have described the species of street trees in fourteen municipia of Rome, and we created five clusters of factors (bio-ecological, aesthetic, historical-cultural, health, and economic) that could constitute selection criteria for street trees. From our data analysis, the municipia of Rome were grouped into four main groups and the choice of trees was based on multiple selection criteria. Foliage type, longevity, fruit type, autochthony, and economic value were the primary criteria. In 90-100% of municipia, deciduous species dominate, with 50-150 years longevity, dry fruits, exotic species, and prices of < Euro500 per tree. Additionally, the flower type, allergenicity, size class, and cultural value werethe secondary criteria. The biological and ecological characteristics of trees are key factors to consider in order to reduce the management of street trees and relative costs.