A methodological approach for mapping alien plants in Sardinia (Italy)

In this paper we analyse and discuss the methodology used for the first project of mapping a set of 109 alien species of the alien flora of Sardinia (Italy). This project, funded by the Nature Conservation Service of the Italian Ministry of the Environment, started in 2000 and ended in December 2002. It has highlighted peculiar problems and stimulated the search for possible methodological solutions. This strategy is of national concern, because the island of Sardinia is a pilot study area for a mapping project methodology that may be extended to other Italian regions. In this paper we focus on project data and metadata definitions, sets of mapped aliens, geocoding of data, GPS surveys, GIS-oriented field surveys and features, chosen between raster and vector analysis. The presence of alien species, according to previous studies ranges from 70 to 184 species. We present and discuss some preliminary results of the mapping of a set of 109 species selected from a set of ca. 900. They have been mapped over the whole island according to a 10 x 10 km grid (3 10 cells), taking into account the topology of the community, cover, habitat and land use of the invaded site. By 2002, we had located a network of 12,065 GPS locations, which included 3,485 sites where none of the given aliens had been found at the time of the survey. Alien distribution in the island has been ranked in eight empirical classes according to the total number of records, the number occupied cells and other features. Some species, e.g. Opuntia ficus-indica, have been recorded in so many sites (> 1,000) and are present in so many 200 cells (> 200), that it can be defined a landscape alien, due to the great visual impact on the landscape all around the island. The project has highlighted the feasibility of the described and used methodology, the underestimated values given to the Sardinian alien flora by previous studies and the uneven distribution of most of the 109 mapped species at the Regional scale. Most of the aliens occur at higher frequencies close to the main settlements of Sardinia, along road and riparian networks, in irrigated agricultural areas, along the coastline and at lower altitudes, in natural and semi-natural habitats. Future monitoring and further studies will constitute a first priority, as the importance and abundance of the Sardinian alien flora has been clearly shown by this study.