Assessment of first-year survival, growth, and physiological performance of seven species of graminoids within two substrate types on a green roof in the Flint Hills Ecoregion

Abstract

Native vegetation on green roofs is desired due to the functions and values that indigenous plant communities provide. This includes native warm and cool season grasses. Plant selection on green roofs needs to account for the likelihood that specified species will be able to survive water stress, limited soil or substrate depths, and potentially harsh rooftop conditions. There is insufficient research on specific plant species that can perform well on an extensive green roof approximately four inches (10.16cm) deep in Manhattan, Kansas (U.S.A.). Growing conditions are largely affected by substrate characteristics such as organic matter, nutrient content, and the ability to hold moisture. The goal of this study is to lay the groundwork for the appropriate selection of native graminoids for green roofs in the Flint Hills Ecoregion, and assess the performance of two engineered substrate types used on the Experimental Green Roof (composed of three beds of different substrate depths) atop the new Architecture, Planning and Design building at Kansas State University. The study measured plant survival, growth, and physiological performance of one native sedge and six grass species over the first growing season in two distinct types of engineered substrates. Visual assessments were used to quantify survival, and growth was determined by measuring the above-ground biomass, height, and coverage of the plants. Plant physiological performance was assessed by measuring stomatal resistance. The study was conducted for the first growing season (plants were installed on the Experimental Green Roof in October 2017 and a number of live plants were replanted in May and June 2018) with vegetation observations made and other data collected from late June to mid-October 2018. This research provides valuable baseline information for a longer-term study of this extensive green roof system.