The vegetation of a historic road system in the suburban area of Monte Pellegrino (Palermo, Sicily)

Knowledge of the processes by which plants colonize old structures is a key element for nature-based design both in urban and suburban contexts. This paper analyses the natural vegetation on walls and in other microhabitats of the roadway structures of Monte Pellegrino (606 m a.s.l.) near Palermo (Sicily), built in the first half of the 1900s. The historical road has particular construction and architectural features, and its characteristics have been maintained to this day. The route, approximately 16 kilometers long, is well integrated within a site of high naturalistic value which has been designated as a Special Area of Conservation (ITA020014) of the Natura 2000 network, and it is also a regional natural reserve. The survey was carried out on different homogeneous ecological contexts based on different microhabitats (masonry retaining walls, masonry guardwalls, road margins, and rock cut slopes) which are diversified according to other environmental factors (building materials, inclination, height, and exposure). The phytosociological and statistical analysis has led to the description of six new associations (Crepido bursifoliae-Parietarietum judaicae ass. nov., Athamanto siculae-Parietarietum judaicae ass. nov., Helichryso panormitani-Hypochaeridetum laevigatae ass. nov., Diantho siculi-Helichrysetum panormitani Gianguzzi ass. nov., Olopto miliacei-Pennisetetum setacei Gianguzzi ass. nov., Teucrio flavi-Rhoetum coriariae Gianguzzi ass. nov.) and one sub-association (Rhamno alaterni-Euphorbietum dendroidis Géhu & Biondi 1997 artemisietosum arborescentis subass. nov.). Other chasmophytic formations (Centranthetum rubri Oberd. 1969, Antirrhinetum siculi Bartolo & Brullo 1986) were reported for the first time in this area.