Extensive vegetated roofs in Sweden

Emilsson, Tobias (2006) Extensive vegetated roofs in Sweden. Doctoral diss. Dept. of Landscape Management and Horticultural Technology, SLU. Acta Universitatis Agriculturae Sueciae vol. 2006:37.

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Abstract

This thesis discusses extensive vegetated roofs, i.e. vegetation systems placed on top of buildings as an aesthetical and/or ecological cover. Specific objectives was to (1) quantify how establishment techniques, substrates and plant mixes influence establishment and development of extensive vegetated roofs, (2) investigate effect of vegetated roofs on stormwater quality, and quantify how maintenance and starting fertilisation influences stormwater quality, and (4) investigate the role of vegetated roofs in planning tools for urban green space. The studies on vegetation establishment and development was carried out at the Augustenborg Botanical Roofgarden, Malmö (55°34’34’’N, 13°1’42’’E), the nutrient runoff was investigated on commercially installed systems in the Malmö-Lund region and in a greenhouse study. The role of vegetated roofs in planning of green areas was performed as a literature study. Vegetation establishment and development was investigated in relation to substrate, species and establishment method. Nutrient runoff was in the greenhouse study investigated in relation to fertiliser type, vegetation type and fertiliser amount.

Prefabricated vegetation mats had an advantage in establishment in creating high plant cover during the first year, which can be important on exposed sites. Establishment was similar for plug plants and cuttings. The commercial substrate was beneficial for establishment. The advantage in succulent cover of vegetation mats had disappeared after 3.5 years. All establishment techniques achieve the same long-term succulent cover. Moss cover increased over time and was at the end of the study dominating the system with approx 50-80% cover. Maintenance fertilisation can cause degradation of stormwater quality if conventional fertilisers are used. Conventionally installed vegetated roofs were found to be a source of potassium and phosphorous, and a sink for nitrogen. Vegetated roofs had a minor influence on heavy metal runoff. Spontaneous establishment on extensive vegetated roofs was low, which is beneficial from a maintenance perspective but unfavourable from a biodiversity perspective. The Green Space Factor tool was found to overestimate the environmental functions of thin vegetated roofs.

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