Long-Term Vegetation Research on Two Extensive Green Roofs in Berlin

by Manfred Köhler

University of Applied Sciences Neubrandenburg, Brodaer Str. 2, 17041 Neubrandenburg, Germany

Abstract

The long-term vegetation dynamics of two extensive green roof (EGR) installations in Berlin were evaluated. The first, installed on two inner-city residential buildings in 1985, consisted of ten sections ("sub-roofs") with a combined area of 650 square meters. The ten sub-roofs differed in exposure and slope. Observations were made twice yearly (with a few exceptions) from 1985 to 2005. Ten species were initially sown on the sub-roofs. Altogether, 110 plant species were observed over the 20-year time period; however, only about 10 to 15 of these were dominant over the long term and could be considered typical EGR flora in Berlin. Allium schoenoprasum was the dominant plant species over all dates and all sub-roofs. Festuca ovina, Poa compressa, and Bromus tectorum were also typically present over the time of the study. Statistical tests revealed that weather-related factors such as temperature and rainfall distribution were the most important factors affecting floral diversity. The size, slope, and age of the EGRs had no significant statistical influence on plant diversity. This EGR installation was virtually free of technical problems after 20 years. The success of this low-maintenance green roof is a good argument for greater extension of green roof technology in urban areas. The EGRs of the second study were installed in 1986, but investigation of the flora only began in 1992. Observations were again made twice yearly until 2005. The six roofs studied were on top of a cultural center located in a park area in the Berlin suburbs, and they were irrigated during the first few years to support plant establishment. These EGRs had a higher degree of species richness than the inner city ones. Both of these early German projects in urban ecology demonstrate that relatively diverse EGRs are possible on city buildings. They also show that species richness can be increased by a minimal amount of irrigation and maintenance. They also suggest that enhanced initial plantings, the creation of microclimates (shaded and sunny areas), and the presence of surrounding vegetation also increase plant diversity.

Key words: extensive green roofs; Germany; plant community dynamics; urban ecology; vegetation science