This study is framed within a broader strategic effort to develop a citywide network of monumental trees in Lisbon. Within urban ecosystems, monumental trees—including those formally classified in Portugal as Trees of Public Interest (AIP) under Law n. 53/2012—function as key elements of sustainable planning. However, current management approaches remain largely reactive, focusing on the protection of existing specimens rather than on the identification of future candidates. In this context, the project proposes a shift towards a more proactive framework by assessing monumentality beyond purely biological criteria.

Jacaranda mimosifolia represents a fascinating paradox within Lisbon’s urban forest. Despite being an allochthonous species native to South America, it has become one of the city's most iconic visual symbols. According to the municipal street tree inventory, Lisbon hosts 3,981 specimens, making it the second most frequent species and accounting for approximately 5% of the total street tree population. Its abundance produces a profound sensory transformation of the urban landscape during the flowering season. At the same time, the presence of jacarandas increasingly intersects with socio-political dimensions. Recent conflicts, such as the 2025 controversy involving the redevelopment of 5 de Outubro Avenue, demonstrate how these trees can act as catalysts for civic mobilization, reflecting their integration into Lisbon's collective visual identity.

This study adopts a mixed-methods approach around a specific case study: an exceptionally large, enigmatic, and controversial jacaranda specimen in Lisbon’s historic center, currently under pressure from urban development. To evaluate its potential eligibility for AIP classification, the analysis expands across three complementary axes. The socio-political and historiographical dimension explores the tree’s cultural significance through interviews, surveys and archival research, highlighting how local narratives and collective perceptions shape its value. The spatial dimension analyses the distribution of jacarandas across the city using GIS, linking their presence to socio-economic patterns and broader processes of urban landscape formation. The ecological dimension considers the species’ long-term performance under Mediterranean climate conditions, including its resilience to drought stress and potential risks associated with future shifts in invasiveness.

The results indicate that the value attributed to urban trees cannot be understood solely through their biological characteristics. Rather, monumentality emerges from the intersection of ecological function, spatial context and socio-cultural meaning. The case study further illustrates how certain species, although non-native, may become embedded in the visual identity and collective memory of a city, while simultaneously raising ecological and management challenges.

In Lisbon, Jacaranda mimosifolia transcends its biological status, positioning itself as a complex biocultural entity. Transitioning to a proactive management of "future monumental trees" requires balancing aesthetic value against ecological risks. Ultimately, protecting specimens like the case-study jacaranda is a vital negotiation regarding the visual identity, socio-ecological resilience, and democratic space of the future city.