All ETDs from UAB

Advisory Committee Chair

Stephen A Watts

Advisory Committee Members

Jason T Kirby

Daniel D Jones

Robert A Angus

Document Type


Date of Award


Degree Name by School

Doctor of Philosophy (PhD) College of Arts and Sciences


Green roofs offer the opportunity to transform impervious surfaces into multifunctional constructed ecosystems. Plant selection for green roofs is often limited to drought-tolerant succulent species, but more diverse assemblages enhance habitat and biodiversity in urban areas and have the potential to improve green roof performance. Nineteen taxa were evaluated under irrigated and non-irrigated conditions over three growing seasons. Individual taxa were evaluated for survival and amount and mechanism of colonization, and the effect of irrigation on plant community structure and vegetation coverage was examined. Only succulent species survived under non-irrigated conditions. Irrigated plots had more taxa, higher diversity index, less bare ground, and more individuals than non-irrigated plots. Irrigation is recommended on extensive green roofs to increase the palette for plant selection by protecting against plant mortality due to drought and extreme soil temperatures. To provide an estimate of the capacity of a photosynthetically diverse selection of plants to transpire water, maintain photosynthetic functionality, and mitigate stormwater in green roof systems, three species were selected for evaluation: Bouteloua curtipendula, a C4 bunchgrass; Phlox bifida, a C3 forb; and S. album `France', a facultative CAM succulent. Gas exchange was measured over a cycle of drying down and rehydration during spring, summer, and fall experimental seasons. B. curtipendula had higher rates of net carbon assimilation (An) and stomatal conductance (gs) than P. bifida and S. album, particularly in the summer season, and recovered rapidly following rehydration. In general, An and gs of S. album were low. In the southeastern U.S., B. curtipendula and P. bifida could be utilized on a green roof with limited irrigation to gain evapotranspirative benefits in spring, summer, and fall. Sedum album was found to contribute little transpiration, but could be included for winter cover to improve soil stabilization and increase morphological diversity. While differences in stormwater mitigation among the different species could not be discerned, each of the species reduced the total volume, delayed the start, and extended the duration of stormwater runoff compared with impervious roof surfaces.



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