Growth performance of multi-species plant mixtures on an extensive vegetated roof: A two-year experimental study

Abstract

Assessing and selecting plant species for mixed planting on vegetated roofs is essential for integrating nature-based solutions into urban environments. This study evaluated the growth performance of multi-species mixtures on an extensive vegetated roof in a semiarid region at the campus of the Catholic University of Córdoba, Argentina over two years. Three native species with different growth forms and stress tolerance (Phyla nodiflora, Grindelia cabrerae, Eustachys retusa) and exotic Sedum mexicanum were planted in 11 microcosms containing two, three and four species combinations. Green cover and survival rate were assessed at seven benchmark times over two annual growing seasons at the microcosms and individual-species levels. At year one end, significant inter-microcosms and inter-species differences in green cover were found. Nine microcosms attained > 80% total green cover, and six achieved > 80% total survival rate. At year two end, five microcosms sustained 60 − 80% total green cover and survival rate (P. nodiflora/E. retusa; G. cabrerae/E. retusa; G. cabrerae/E. retusa/S. mexicanum; P. nodiflora/E. retusa/S. mexicanum; and P. nodiflora/G. cabrerae/E. retusa/S. mexicanum). For intra-microcosms species performance, E. retusa and S. mexicanum attained notably higher green cover than the other two species. Eustachys retusa was notably a key driver among microcosms. The commensal and complementary roles of some species toward others were demonstrated. The combination of P. nodiflora and E. retusa showed the best performance after two years. Our findings indicated that some species perform better in less diverse plant mixtures.