SUMMARY

From 1984 to 1998, a square-kilometer base floristic map of the city of Zurich was completed, after which, from 1999 to 2011, the mapping was continued south of the city of Zurich, into the region of the Sihl Valley towards Höhronen, a mountain range that straddles the borders of the cantons of Zurich, Zug and Schwyz. In total, an area of 249 km2 was investigated. A «Flora» of all species of the region, with morphological and ecological descriptions, a key, and distribution maps, was created (approx. 1500 pages). The «Flora» will be distributed at ZDSF (Zentrum des Datenverbundnetzes der Schweizer Flora, http://www.crsf.ch) in Geneva and at the Canton of Zurich Office of Landscape and Nature (Amt für Landschaft und Natur des Kantons Zürich), from where it will be accessible by download for the general public. In this paper sonne results of the investigation are presented.
The «Flora» contains 2113 species altogether. Of these 615 are frequently cultivated or ephemerophytes. The rest of 1498 species are native or have been established in the study area for at least 30 years. Of these species 177, or 13 %, are extinct and 284 are newly introduced and established within the last 160 years. During this time, the flora became richer, especially in the city of Zurich. However, of the presently occurring species, 42 % decreased and only 30 % increased in frequency. The average number of species per km2 is larger in the city, (approx. 450), than in the regions further south (about 400 in the middle part of the study area and 350 in the southern part). 48 % of the 204 species growing only within the city and not outside of it are Neophytes, 32 % Archaeophytes, and only 20 % indigenous species. Of the 99 species occurring only outside the city 91 % are indigenous species and Archaeophytes and Neophytes comprise only 4 % and 6 %, respectively. Of the species in the City of Zurich (1400 species, including extinct species) and in the whole study area (1500 species) nearly 60 % are indigenous species, about 20 % Archaeophytes and a little more than 20% Neophytes. In the densely populated inner city with a high percentage of sealed soils, the Neophytes consisted of more than 50 % of the species. Hütten, the highest situated and sparsely populated community of the study area had 738 plant species, of which 81 % were indigenous species, 7 % were Archaeophytes and 12 % were Neophytes.
The study area was divided into 7 landscapes according to geomorphological, climatic and floristic properties.
The study demonstrates the reduction of plant diversity in various vegetations, outlines the reasons of the loss, and discusses possible countermeasures.
The distribution of invasive Neophytes and possibilities of controlling the expansion are shown. Generally, invaders are less important in cooler and higher regions. Various critical species not previously, or very rarely distinguished are presented shortly.

Key words: Albis – Hirzel – Hütten – Höhronen – Üetliberg – Zimmerberg – Wetlands – Steep Slopes – Flora Change – Flora Mapping – Biodiversity – Invasive Species – Flora Protection