The invasion of alien vascular species in agroforestry systems: the case of Erigeron sumatrensis Retz. and Sorghum halepense (L.) Pers. in Campania region (Southern Italy)

Biological invasions pose a major threat to the conservation of biodiversity worldwide, causing the extinction of native species, modifying ecosystem functions and high costs for containment. The introduction, either voluntary or accidental, of alien species in natural and agroforestry systems are favored by the globalization of trade, exchanges, and transports. Exotic weeds compete with the crop plants and, probably more frequently than known in the literature, they can be secondary hosts for viruses, insects, and fungi harmful to native flora and agricultural crops (e.g. Parrella et al., 2013). In this note, we will be focus on the dynamics of naturalization and the current alien status of Erigeron sumatrensis Retz. (Asteraceae) and Sorghum halepense (L.) Pers. (Poaceae) in Campania region (Southern Italy). E. sumatrensis (vernacular name Tropical horseweed, Saeppola di Sumatra) is an annual plant native of South America, from where it has spread to the warmer regions of all continents, except for Antarctica (neophyte in Europe). S. halepense (vernacular name Johnson grass, Sorghetto) is a perennial grass native probably of Near-East region, but today spread in almost all the world (archaeophyte in Europe). The spread into the wild of the two species in the Campania region was evaluated by comparing the present surveys (last 6 years) with the floristic lists published throughout the last century. The field surveys were carried out in 1230 randomly selected sample plots, having a circular shape of about 500 m2. Each sampling area was georeferenced using the central point as reference (datum UTM WGS84, UTM 33T). The exsiccata were identified and stored in the Herbarium Porticense (PORUN). The current invasive status in Campania was defined according to the terminology of Py?ek et al. (2004). The floristic surveys confirmed the presence of the two alien species all over the Campania region. Indeed E. sumatrensis and S. halepensis were respectively found in 787 (63,9%) and 309 (25,1%) of the 1230 totals plots. As the matter of the fact, data analysis shows a strong expansion of the two species in Campania Region during the last decades and demonstrate that E. sumatrensis and S. halepense have to be considered invasive alien plants. In particular, because of their remarkable and successful reproductive strategies, especially in the semi-abandoned rural environment the two alien species have the potential to spread over considerable areas.