Boundaries Between Gardens and Landscapes: A Case Study of Horticultural Diversity on Koločep Island

The protection of landscape and biological diversity on small Mediterranean islands represents a significant challenge in the context of intensive anthropogenic pressure and land-use change. The aim of this study was to determine the composition of ornamental flora in private gardens on the island of Koločep (IPA, Natura 2000 site), the smallest inhabited island in the Croatian part of the Adriatic, with special emphasis on invasive (IAS) and potentially invasive (PIAS) plant species, and to analyse their relationship with landscape changes and property types. A total of 161 private gardens were analysed, representing all private gardens on the island. In total, 2095 plant records corresponded to 255 unique horticultural taxa from 82 families. Allochthonous species dominate in the gardens (73%). Private gardens represent the primary pathway for the introduction of IAS and PIAS taxa on the island. The taxa with the highest invasion intensity were Ailanthus altissima and Carpobrotus edulis, while among PIAS species, high invasive potential was observed for Mirabilis jalapa and Diospyros virginiana. The study highlights the need for systematic monitoring of ornamental flora and landscape transformation, and the promotion of horticultural practices focused on autochthonous species in gardens, in order to preserve island biological and landscape diversity.