Evaluating native plant survival on a mid-western green roof

Green roofs have many ecological benefits that address numerous modern environmental issues. Many studies have evaluated Sedums on green roofs; on the other hand, there is much interest in native plant performance on a green roof. In my study, Green Roof Blocks were planted with 3 experimental treatments: native plants only; native species plus Sedums; and Sedums only. The native species only treatment consisted of Eragrostis spectabilis, Coreopsis lanceolata, Penstemon pallidus, Penstemon hirsutus, Koeleria marcantha, Rudbeckia hirta, Aster laevis and Carex muhlenbergii. These areas were planted with one plug per native species for a total of eight plugs per Green Roof Block. Natives were interspersed between existing Sedum plantings in the native species plus Sedum planting treatment. There was again one plug per six species, but only six native plugs per block. The species in these planting areas were Bouteloua gracilis, Buchloe dactyloides, Asclepius verticillata, Bouteloua curtipendula, Geum triflorum and Sporobolus cryptandrus. All native plants were planted in the two treatments on 5/29/2013 and 6/5/2013. All plants in the study plots were irrigated weekly as needed in 2013 and 2014. On November 7 and 8, 2013, June 10 and 23, 2014, June 2015, November 2015, and April 2016 native plant survival was measured. In the plots with natives only, survival ranged from 0 to 86 percent at the end of the study. To date, Coreopsis lanceolata and Penstemon pallidus have the greatest percent survival in the natives only planting area at 86 and 45 percent respectively. In the plots with natives plus Sedums, native plant survival ranged from 0 to 70 percent at the end of the study. Survival of the four native grasses was greater than 99 percent in the first growing season. To date, the only native species remaining in the natives plus Sedums planting area is Buchloe dactyloides, with about 70 percent survival. In addition, the forb Coreopsis lanceolata has rapidly spread outside the initial planting areas, indicating that this native species not only survives on the roof, but is able to reproduce successfully