Plant traits in a 300-year-old urban forest: insights for plant conservation in compact cities

Abstract As urbanization accelerates worldwide, reconciling urban growth with biodiversity conservation has become increasingly urgent. Urban forests offer a promising solution by supporting biodiversity and mitigating the negative impacts of urbanization. Historic urban forests, such as the Royal Park of Portici (Naples, Italy), founded in 1738, offer a unique opportunity to assess the long-term contribution of these green spaces to urban biodiversity. In the present study we investigated the role of the Royal Park in supporting urban plant diversity, focusing on the functional traits of species that use the Royal Park as a refuge versus those that disperse into the surrounding urban matrix. We recorded vegetative, pollination and dispersal traits and tested if specific traits were associated with species found exclusively in the Royal Park or in both the Royal Park and urban matrix. The results showed that annual plants with generalist pollination and animal-mediated dispersal strategies thrive in the urban matrix, while perennial species with specialized pollination are restricted to less disturbed areas such as the Royal Park. Urban forests can serve as critical refugia for species and as species sources for nearby green spaces. To maximize their ecological function, efforts should prioritize improving connectivity, reducing environmental stress, and minimizing human disturbance, particularly for species with specific ecological requirements.