Long-term performance of selected old Berlin greenroofs in comparison to younger extensive greenroofs in Berlin

In Germany, the construction of extensive greenroofs has been a tradition for over 100 years. This study picked up older Berlin research conducted in 1960, 1982, 1986, 1987, 1990, 1995 and compared it with current findings (Poll, 2008). The older research was made either on the old “Tar-Paper-Greenroofs” (TPG-roofs), established between 1880 and 1930, or on the first systematically vegetated Modern Extensive Greenroofs (MEG-roofs), established in the 1980s. This survey compares both roof types and supplements the chronology of analysis. The research showed that MEG and especially TPG are resilient roof types and can last up to 100 years. About 70 vascular plant species were found on the surveyed roofs (>10%>10% resp. consistency). Regarding the growing media, we could show that total porosity rises over a period of 10 years from 50 to 60%. In the meantime C/N-ratio falls from initially 25 down to 13. While the pH of the slightly acidic TPG-media rose to neutral, the slightly alkaline MEG-media sank down to neutral.With the help of a specially developed vegetation quality index, which incorporates both relative plant coverage and species quantity, we could show that media depth and the grade of sunlight exposition influence floral quality of greenroofs as well as how. According to the specified criteria, the quality of the modern extensive greenroofs is significantly higher than the quality of the 100-year-old ones. Nevertheless, a significant correlation between water holding capacity and vegetation coverage was shown for both roof types.