The contribution of Sicilian historical gardens to biodiversity conservation

The potential value of private gardens for enhancing biodiversity has long been recognized, while, less investigated is the contribution of historical gardens. The complex history of Sicily, with its strategically central position in the Mediterranean basin, made the island an important crossroad of civilizations and also influenced the use of ornamental plants in gardens over the centuries. With the aim to investigate the biodiversity of historical gardens of Milazzo (North of Sicily), the flora of 31 gardens, dating from the late 19th to the early 20th century, were analyzed through a complete plant inventory. The gardens are localized in two areas: the first ('Piana' = 13 gardens) close to the rural area, the second ('Capo' = 18 gardens) close to the residential area. The determinants of taxonomic richness in individual gardens were carried out with the use of Shannon (H'), Simpson (D) and Evenness (J) indices. The values of the indices are, respectively for 'Capo' and 'Piana', 5.7 and 5.5 for H', 0.8 for J and 0.0046 and 0.0054 for D, and demonstrate the presence of a high biodiversity and an even distribution of individuals per species, with a few dominant species. In the 31 gardens, 529 taxa of ornamental plants were identified, belonging to 343 genera and 117 botanical families. The richness of species found in these green areas allow to consider them as "living plant collections". About 80% of the taxa were present in less than 10% of the gardens; 43.5% of species were present in a single garden. Only one species (Cycas revoluta Thunb.) was present in 87.1% of gardens to underline the species diversity.