Miscellaneous to the vegetation of hard surfaces in old towns in North Portugal (Porto, Braga, Guimarães)

A short excursion to the historic centres of Porto, Braga and Guimarães in spring 2024 showed a relatively lush vegetation of urban hard surfaces due to mild winters (winter hardiness zone 10a: -1,1°C to 1,7°C) and high rainfall (approx. 1237 to 1706 mm p.a). In the meanwhile most of the people of the world are living in cities. Urban ecosystems are therefore a very important habitat. The urbanization process involves a remarkable reduction of potential areas for spontanous vegetation, surface sealing and use of hard construction materials where only the joints can be used by plants.The later is often mentioned as „urban hard surfaces“ (LUNDHOLM 2011). Indeed urban ecology started with the investgation of the flora of walls (DEAKIN 1855) after the very early work of PANAROLI (1643). The aim of this paper is to document vegetation pattern from the historic centres; mainly of Porto. The vegetation of stone walls in Porto belongs primarely to the alliance Centrantho – Parietarion enriched by some vigorously growing alien species.