Constructed communities of geophyte and succulent mixes are suitable for non-irrigated extensive green roofs in Mediterranean cities

Research on extensive green roofs has largely focused on cooler, wetter climates, leaving Mediterranean conditions underexplored. This four-year study addresses this gap by evaluating the performance of a constructed community of Mediterranean geophytes and Sedum species on an unirrigated extensive green roof. Known for their resilience to dry periods, geophytes and Sedum have been assessed separately. We studied the combined performance of 15 Mediterranean geophytes with one native Sedum on an extensive unirrigated green roof. Data collection included plant survival, number of plants, spread, number of inflorescences, and new species recruitment. Results revealed that seven out of 15 geophytes survived throughout the experiment. Five geophytes increased in number and spread, the remaining two either did not change or declined. Of the seven surviving geophytes six flowered. Sedum spread vegetatively and flowered consistently. Seven native species were recruited and colonized the green roof. After four years, the constructed plant community and the colonizing native species fully covered the roof area with some vegetation overlap (47% Sedum, 44% geophytes, 21% colonizing native species). These findings offer new insights into green roof planting design in Mediterranean cities, highlighting the importance of conducting studies over several growing seasons to observe plant dynamics and revealed the potential to create sustainable urban habitats.