The installation of extensive green roofs is becoming more popular in urban areas globally, for many reasons. Some appealing elements of green roofs include reduction in cooling costs for buildings and attractive scenery for people. While previous studies have shown that variations in solar radiation can affect green roof plants, few studies have examined plant performance on green roofs in the Rocky Mountain region. The combination of an urban heat island and continental climate make this a harsh environment for vegetation (summer temperatures can exceed 50° C) which could result in reduced survivability. Based on our understanding of this extreme environment, we hypothesized that many of the species and varieties initially planted would be absent after 6 years and that those remaining would be spatially sorted due to differences in temperature. In October of 2011, 13 species and varieties of Sedum were planted on the roof of the Student Success Building at Metropolitan State University of Denver, in Colorado. In 2016 and 2017, we sampled 2 meter by 2 meter quadrats, distributed across the green roof. In each of 30 quadrats we identified all Sedum species and varieties, estimated cover and recorded temperatures.
Results/Conclusions Of the 13 species and varieties of Sedum (Sedum album var. 'Coral carpet', Sedum sexangulare, Sedum acre, Sedum kamtschaticum, Sedum spurium var. 'Fuldaglut', Sedum spurium var. 'John Creech', Sedum spurium var. 'red carpet', Sedum spurium var. 'tricolor', Sedum takesimensis var. 'golden carpet', Sedum x Immergrunchen, Sedum fioriferum var. 'Weihenstephaner gold', Sedum reflexum var. 'blue spruce', Sedum rupestre var. 'Angelina'), only Sedum acre var. 'Goldmoss' was absent. Sedum reflexum and Sedum rupestre had cover of less than 1% in any plot while the remaining 10 are widespread and abundant, occurring in an average of 16.5 plots each. Total cover does not vary as temperatures increase with distance from the northeast wall (F=0.7, p=0.716, df=10). The MSU Denver green roof continues to support a diverse and well distributed mix of Sedum species and varieties. This suggests that a green roof plant mix developed for broad use across North America can be successful in the Rocky Mountain region.