Invasion Impact of the Nitrogen-fixing Shrub Genista aetnensis on Vesuvius Grand Cone

Vesuvius Grand Cone dominates the landscape of Napoli Gulf with its distinguishable grey bare slopes, exposed to continuous surface erosion processes and rock falls which have been hindering the development of the vegetation after the last volcanic eruptions (occurred in 1944). In the last 60 years the development of the vegetation became evident along some portions of the Grand Cone. This process is facilitated by the upslope expansion of the Genista aetnensis (Biv.) DC., a plant endemic of the Mt. Etna (Sicily) and of Eastern Sardinia, which has been imported to Mt. Vesuvio in 1906 as part of a reforestation program of the Vesuvius slopes. Vesuvio National Park, within the MED project For Climadapt, is conducting a multidisciplinary research program aiming at evaluating the effect of the aetnensis invasion of the Vesuvius Grand Cone, both at landscape and ecosystem level, also in light of current and predicted climatic changes. An intensive field investigation has been designed to explore the eco-hydrological conditions facilitating the expansion of the G. aetnensis. Plant species and soils have been collected both underneath and outside the cover of G. aetnensis canopies to gather relevant information about the interaction of the G. aetnensis with the other species as well as to explore the small scale spatial gradients of soil fertility induced by the G. aetnensis. Two permanent stations have been installed to monitor the differences in soil water content, soil temperature and air temperature between inside and outside the canopy cover. The collected data evidence that G. aetnensis tends to create an island of fertility by increasing the organic matter content in the soil and improving the soil water retention properties. Moreover, the G. aetnensis mitigates the daily soil temperature excursions, reducing the exposure of seeds to extremely high temperature values, particularly during the growing season, and the direct soil evaporation loss. These results suggest that the invasion of G. aetnensis can promote alternative successional trajectories that may dramatically affects vegetation dynamics. Further studies are needed to identity specific management practices that can limit the spread and impact of this species.