Quantifying carbon sequestration of various green roof and ornamental landscape systems

Abstract

Interest in reducing carbon emissions and carbon trading programs has been increasing. In order to calculate the carbon benefits of landscapes, we must first understand how they sequester and store carbon. Carbon dynamics have been extensively studied in natural and agricultural landscapes, and urban and community forests. Relatively little is known about carbon sequestration in ornamental landscapes. This study compared the carbon content of nine in ground and three green roof landscape systems of varying complexity to determine their carbon sequestration potential. Soil or substrate samples were analyzed prior to planting in 2009 and soil/substrate, below- and above-ground biomass were analyzed at the end of the 2010 and 2011 growing seasons. Landscape systems containing more woody plants, such shrubs (65.67, 78.75, and 62.91kgm−2) and herbaceous perennials and grasses (68.75 and 67.70kgm−2 for the in-ground and green roofs, respectively) had higher carbon content than other landscape systems. The native prairie mix (28.57kgm−2) also had high carbon content, because of the high volume of plant biomass. The vegetable and herb garden and vegetable green roof contained a moderate amount of carbon (54.18 and 11.03kgm−2, respectively). The Sedum and prairie green roofs contained less carbon than their counterpart in-ground landscape systems, suggesting that although green roofs do sequester a small amount of carbon, greater benefit can be achieved in ground level landscape systems. Ornamental landscapes have good potential for carbon sequestration but management practices can affect their net carbon sequestration and the permanence of the carbon sequestered.