OOS 15-2 - Native prairie-like green roof dynamics and performance in Manhattan, Kansas (Flint Hills Ecoregion)

Green roofs are increasingly common as cities seek environmentally sustainable approaches to mitigate climate change impacts while providing urban amenities. However, water availability is one of the most limiting factors in a green roof system and understanding the substrate-plant-water relationships within green roof ecosystems is key for understanding plant success and failures for individual green roofs. To provide insight on green roof plant and substrate selection for green roofs in the Flint Hills Ecoregion (Kansas, USA) and similar climates, three experimental research green roof beds were designed for the Kansas State University (KSU) College of Architecture, Planning and Design (APD) building and were initially planted in October 2017, with replacement plantings completed by June 2018. The three green roof beds provide three different depths (4, 6, and 8 inches [approximately 10.2, 15.3, and 20.4 cm]). Each green roof depth contains two substrates (Rooflite® Extensive MC and Kansas BuildEx), and three different species mixes (all-Sedums, Sedums and native grasses, and all-natives). Each of the three specified mixes contain 6 different species planted in triplicate within each replication cell.
The main objectives for this APD Experimental Green Roof research are twofold: (1) understand how a locally blended substrate (Kansas BuildEx) and a commercially provided, regionally mixed substrate (Rooflite® Extensive MC) vary in the way they store and dispense water; and (2) understand how growth of the three mixed-species plantings change over time. Initially, some differences in cover between the two substrates overall and the mixes planted within each substrate type was observed. However, as time has progressed differences in plant cover between the two substrates and between the mixes planted within each substrate have decreased. Using lessons learned from this experimental study of the two different substrate types, three different substrate depths, and three species mixes, the desire is to improve our collective understanding of the selected plants and substrates and ultimately to improve the design, implementation, and management of green roofs in the Flint Hills Ecoregion and in locations with similar climates.