Sustainable Growth of Medicinal and Aromatic Mediterranean Plants Growing as Communities in Shallow Substrate Urban Green Roof Systems

To date, the evaluation of the performance of Mediterranean native plants under urban green roof conditions has been limited to monoculture studies. However, plants grow naturally in plant communities and therefore it is of interest to evaluate their growth under realistic conditions, including interactions among plant species. The present study aims to evaluate the growth, flowering, and self-reproduction capacity of three artificially created plant communities consisting of native Mediterranean plants, as exemplified in Greece under shallow green roof substrate depths (8 and 15 cm) and two irrigation regimes (high, 20% ETo and low, 10% ETo). The plant communities (PC) were designed to resemble xerophytic vegetation found either in Chania, Crete (PC-1), as a combined pattern with plants from Attica, Crete, and the Cyclades (Kythnos) (PC-2), or to resemble the coastal vegetation of Attica and Cyclades (Kythnos) (PC-3). Each of the three artificial plant communities (PC-1, PC-2 and PC-3) consisted of nine species and subspecies. The deeper substrate significantly improved the growth, flowering and survival of most plant taxa. The irrigation regime was not significant for all species except one, indicating that minimal amounts of irrigation are required. Four species did not manage to bloom while 15 species were able to self-reproduce.