Urban Forestry & Urban Greening 3 (2005) 103–111 Comparison of establishment methods for extensive green roofs in southern Sweden Tobias Emilsson à , Kaj Rolf Department of Landscape Management and Horticultural Technology, Swedish University of Agricultural Sciences, Box 66, SE 23053 Alnarp, Sweden Abstract The most common technique for establishment of thin extensive green roofs in Sweden has been using prefabricated vegetation mats. Our study investigated (1) how the establishment of green roofs in Sweden was influenced by the establishment method (prefabricated vegetation mat, plug-plant, shoot), substrate composition and species mixture, and (2) whether on-site construction was a possible alternative. The establishment of the vegetation, which in all cases consisted of succulent species, was recorded using the quadrate point intercept method in fixed plots and the success measured as frequency cover. Prefabricated vegetation mats had higher succulent plant cover than on-site constructed roofs. There was no difference in succulent plant cover between plots established using plug-plants compared to shoots. Shoot-established plots had more moss than the other establishment methods. The commercial substrate ‘Roof soil’ had significantly higher succulent plant cover than the other substrates, which might be related to a higher nutrient content. The organic content of the non-commercial substrates was rapidly decomposed. The standard species mixture produced a higher cover than both the mix developed for northern conditions and the mix with an increased proportion of big leaved species. The total cover of the plots was mainly dependent on the cover of two species: Sedum album (L.) and Sedum acre (L.). Few species managed to establish spontaneously but the establishment of woody species highlighted the need for proper maintenance. r 2004 Elsevier GmbH. All rights reserved. Keywords: Crassulaceae; On-site construction; Sedum; Vegetated roofs Introduction Green roofs are becoming increasingly popular in many countries. The interest for green roofs has been related to their capacity to reduce stormwater runoff volumes and peak flows (Bengtsson, 2002), mitigate urban heat island effects (Akbari et al., 2001) and cool buildings during summer months (Eumorfopoulou and Aravantinos, 1998; Onmura et al., 2001). Green roofs can also be designed to improve urban biodiversity (Mann, 1998; Brenneisen, 2003). Installation of green roofs requires larger investments than conventional roofs (Wong et al., 2003). Systems with thick substrate layers and large plants are especially expensive since they generally require reinforcement and reconstruction of the building unless it was designed for the extra load from the start. Thin extensive systems can generally be built without making any adjustments to buildings and this reduces the cost of the system and increases the number of possible roofs that can be vegetated. Even though the initial cost is high, ARTICLE IN PRESS www.elsevier.de/ufug 1618-8667/$ - see front matter r 2004 Elsevier GmbH. All rights reserved. doi:10.1016/j.ufug.2004.07.001 à Corresponding author. E-mail address: tobias.emilsson@lt.slu.se (T. Emilsson).