RUMMO, ROSARIO (2026) Urban plant ecology and biodiversity: multiple approaches to investigate role, functional traits, responses and conservation of plants in cities. [Tesi di dottorato]

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Abstract

Urbanization is the process through which human populations increasingly concentrate in cities, driving extensive land-use conversion, infrastructure expansion, and profound alterations of ecological dynamics. Since this process is constantly accelerating worldwide, there is an urgent need to reconcile urban growth with biodiversity conservation and to deeply investigate plant ecology in urban ecosystems, as vegetation represents the base component in sustaining biodiversity, maintaining ecosystem functions, and improving human well-being. Expanding over natural habitats, urbanization reshapes landscapes, ecosystems, and threats biodiversity worldwide. Habitat loss and fragmentation, reduction in the quality of air and soil, biotic homogenization, biological invasions and intense human disturbance are well-known outcomes. Collectively, these factors expose plants to multiple interacting pressures that limit their growth, reproduction, survival and alter species richness, community composition, and functional trait diversity. While urban pressures generally challenge species survival, they also create a unique combination of extreme and novel conditions that strongly and rapidly interact with plants, making cities a valuable opportunity for studies on plant reaction and adaptation to specific environmental factors. From an ecological perspective, urbanization is a complex and multifaceted phenomenon, presenting hostile conditions for most species while simultaneously offering opportunities for others, owing to their heterogeneous structures, diverse habitats, and varied microclimates. Within this dynamic environment, urban plants provide essential ecosystems functions but are also subjected to strong environmental stresses. Plants are fundamental components of Urban Green Spaces (UGS), being able to mitigate adverse effects of urbanization and to support biodiversity functioning. For example, urban forests can provide suitable habitats for plants, support ecological communities, and promote species movement across the urban matrix. Of course, many years are necessary to verify the long-term ecological effects of planting new urban forest. In this scenario, historic urban forests, being planted many decades ago, can represent important case studies for assessing their long-term contribution to urban biodiversity. Among the numerous environmental disturbances, plants in cities also must deal with soil deterioration and urban soil substrates, including asphalt and foundry sand. Moreover, UGS often relies on the unsustainable practice of importing topsoil from natural areas to ensure plant growth, raising concerns on natural soil depletion. Considering this, targeted experiments are truly important to identify viable alternatives to the current overexploitation of natural topsoil. 8 Urban conditions generally exert a negative effect on richness and relative abundance of native plant species. However, high habitat heterogeneity, human intervention and the establishment within regions with naturally high biological diversity, make cities favorable to host rare or threatened species. Nevertheless, it is not totally clear how endangered species are distributed across such heterogeneous environments and large-scale floristic data analysis can help fill this gap. Given the above, a deep understanding of the risks and opportunities exerted by urban environments on plants requires urban ecology studies to operate across multiple spatial scales, addressing both community-level and species-level dynamics. Such research should integrate field sampling, data analyses, and applied botanical experiments. It should also bring together diverse expertise in a multidisciplinary framework. Collaboration with relevant institutions is also essential to ensure that this knowledge can be translated into practical applications that enable people and nature to coexist harmoniously in urban settings. The study and research activities carried out during this Ph.D. project followed the approach described above. Specifically, I approached urban plant ecology first by in-depth bibliographic research, which resulted in a review of the role of plants in the city (chapter 1). Next, a field sampling was conducted to investigate the functional traits of plant communities in a city with a historic urban forest (chapter 2). Moreover, an experiment was done to analyze the effect of alternative substrates, typical of the urban environment, on the growth of a single species (chapter 3). Finally, floristic data were collected from several European cities to investigate the conservation role of different urban environments (chapter 4). To achieve this variety of goals, I collaborated with researchers from the University of Naples Federico II, Department of Agricultural Sciences, and expanded to other scientific institutions, mainly the University of Primorska, the Ca’ Foscari University of Venice and Royal Botanic Gardens “Kew”. Additionally, I attended the Training school in Biology and Pollination Ecology (Module II) at the University of Coimbra promoted by the COST Action ConservePlants CA18201, during which I have acquired knowledge and methodologies in pollen biology, pollination experiments, plant-pollinator interactions, and nectar dynamics. Some results obtained during the activities of the Ph.D. period have been presented at two international conferences: the 21st Annual Meeting of the Spanish Group for Floral Ecology (EcoFlor 24) and the X International Plant Science Conference (IPSC) and the XI IPSC. 9 Main activities and results gathered during my PhD period can be shared in four parts that constitute the chapters of this thesis. Aims and content of each chapter are reported hereby. Chapter 1 is a review which presents the current state of knowledge on plants and urban environments. It started considering what is known about urban plants as threatened organisms and therefore underlining the potential of plants both as bioindicators of environmental changes and as mitigators of the same stressors. By focusing on the dual and interconnected role of urban plants, gaps in current research and opportunities for future investigations were identified and discussed. The article has been submitted for publication in Urban Ecosystems. Chapter 2 presents evidence on the role of The Royal Park of Portici (an urban forest planted three centuries ago) as critical refuge for species less adapted to urbanization. The study investigated the role of the Park in supporting urban plant diversity, focusing on the functional traits of species that use the Park as a refuge versus those that disperse into the surrounding urban matrix. The Royal Park of Portici was used as an ideal study case for investigating the contribution of an ancient urban forest to biodiversity, being a unique example of a long-established forest within a Mediterranean city. Specifically, it was underlined how urban forests can serve as critical refugia for species and as species sources for nearby green spaces. The study was performed in collaboration with the Ca’ Foscari University of Venice, where I learned how to design and execute the analysis. Results of the work were published in Journal of Urban Ecology (Rummo et al. 2025). Chapter 3 refers to an experiment which assessed the effects of asphalt and two types of sands frequently used in pavement construction, namely standard sand (SS) and recycled sand (RS), on the germination and early development of Borago officinalis. The aim was to investigate the possibility of reusing these materials as alternative substrates for urban green infrastructure, focusing on problems related to landfill pressure, and the environmental costs of natural soil exploitation. The article reporting this study has been published in Urban Ecosystems (Rummo et al. 2026). Chapter 4 presents a conservation-based study that focuses on urban environmental heterogeneity and on the opportunities that cities can offer for conservation of IUCN threatened species. Specific habitat types within the European cities were investigated by adopting two habitat classifications. The aim was to determine whether climatic or demographic factors or habitat-level differences within cities play a stronger role in shaping the distribution of species of conservation concern and which of the different types of urban habitat favors their occurrence. The study was performed in collaboration with the 10 University of Primorska, the Ca’ Foscari University of Venice and Royal Botanic Gardens “Kew”, where I acquired knowledge and methodologies on urban ecology and on plant conservation. The manuscript is being finalized for submission for publication in Current Plant Biology. Finally, in Chapter 5 some general comments and considerations are given. In addition, an Appendix outlooking the activities conducted during the Ph.D. program is also reported.

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