Invasiveness of Salpichroa origanifolia (Lam.) Baillon in the forest of San Rossore (UNESCO Biosphere Reserve ‘Selve Costiere di Toscana’)

Salpichroa origanifolia (Lam.) Baillon is a perennial herb of the Solanaceae family, native to the temperate regions of South America, where it grows from 0 to 2500 m asl, frequently behaving as a ruderal species. The introduction pathways were, probably, both unintentional, through the trade of seed and potted plants containing propagules, or intentional, as ornamental, or melliferous plant. The species is now naturalized in Europe, USA, Australia, and New Zealand. Its introduction is forbidden in Australia and Japan, while in Europe it is not listed as an invasive alien species of EU concern, and it is not included in any of the EPPO lists. Though reports from European countries are scarce, S. origanifolia was found to spread rapidly in southern Switzerland, and in the Canary Islands. In Italy, it is present in most regions, and recently its status was changed from naturalized to invasive in Campania and Calabria (Laface et al., 2020). The first report for Tuscany dates back to 1923 (Chiarugi), but around 2000, the species was still considered rare (Pedullà and Garbari 2004). More recently, S. origanifolia was frequently recorded in the urban and rural sites of the coastal provinces, and around Florence. We studied the spread of S. origanifolia in the nature reserve of San Rossore, which is part of a 23,000 ha wide forest system extending along the Tuscan coast from Viareggio to Livorno (UNESCO Reserve of Biosphere “Selve Costiere di Toscana”). The species was not recorded in San Rossore before 2000 (Garbari, 2000), though there is an anonymous herbarium specimen dated 1996. In 2010, S. origanifolia was accidentally found in cut stone pine plantations (Orlandi and Arduini, 2010) and a single plant was observed near the buildings at the reserve entrance. Ten years later, S. origanifolia showed a clear invasive habit, forming dense stands under isolated trees at the edges of the forest, and inside the forest, especially in correspondence of fallen trees. Phenological and morphological traits contributed to the invasiveness of this species. Shoots grew from March to December, and the flowering period was very long, from June to October. Plants spread rapidly producing both scrambling and rooting aerial stems, and two types of hypogeal stems: fine fleshy stolons (3-4 mm) just below the soil surface, and up to 7-mm-thick deep growing woody rhizomes. The recent invasion in San Rossore was probably also favored by forest dieback and by wild boars, which scavenged hypogeal stems during winter, thus increasing their fragmentation and diffusion. Preliminary findings highlight three key points: 1. Salpichroa origanifolia resembles a rhizome-geophytic Liana, rather than a suffruticose Chamaephyte (Ellenberg and Müller-Dombois, 1965); 2. Alien species can become invasive long after their introduction; 3. Potential invasiveness could be inferred from distribution patterns and ecological amplitude in the native range. Ongoing controlled condition experiments are investigating the resistance of S. origanifolia propagules to low temperatures and drought, and their competitiveness towards native forest species, by analyzing the plantlets emerging from the soil seed bank in the presence or absence of hypogeal propagules.