The increase of plant invasions in cultural heritage sites in Italy
Cultural heritage sites such as historic sites or sacred areas can be important habitats for a range of plant and animal species due to their size, heterogeneity and moderate human disturbance. However, they can also harbour invasive alien species which can degrade structures over time. In particular, woody species can grow in crevices and in walls where the roots can displace stonework. The flora of 26 heritage sites in the city of Rome, Italy was surveyed at the same sites over three periods in 1988–1990, 1994–1995 and 2004–2005. The 26 sites were chosen from a larger sample of 40 sites which had been surveyed by a botanist between 1946 and 1950. A total of 119 woody species, of which 35 (29.4%) were non-native, were detected on the walls of the 26 heritage sites from 1950 to 2019; 27 of the total number of species were trees, 55 were shrubs, 20 were dwarf shrubs and 17 were vines. The study showed that although the species richness remained relatively constant over time, the composition of species changed with a decrease in native species and an increase of non-native species (30 occurrences in 1950 compared to 224 in 2019). Acer negundo (Sapindaceae), Ailanthus altissima (Simaroubaceae: EPPO List of Invasive Alien Plants), Ligustrum lucidum (Oleaceae), Lonicera japonica (Caprifoliaceae), Parthenocissus quinquefolia (Vitaceae), Platanus hispanica (Platanaceae) and Robinia pseudoacacia (Fabaceae) were the non-native species that showed the highest increase in occurrences. Additionally, the study showed that there was an increase over time of non-native species that had originally been introduced into the region for ornamental purposes, and species that are dispersed by birds and wind.
Celesti-Grapow L, Ricotta C (2020) Plant invasions as an emerging challenge for the conservation of heritage sites: the spread of ornamental trees on ancient monuments in Rome, Italy. Biological Invasions, https://doi.org/10.1007/s10530-020-02429-9