Die Alpenpflanzen des Tössberglandes. Einhundert Jahre nach Gustav Hegi
At the beginning of the 20th century, Gustav Hegi – later becoming one of Europe's most important botanists – completed his dissertation on the flora of the mountainous area of the Canton of Zürich and its adjacent areas, i.e. the Tössbergland at the headwaters of the river Töss. Hegi described the flora as well as the plant biogeography and history of this mountainous region in north-eastern Switzerland in great detail. One hundred years later, general economic developments have triggered profound changes in the land use of this area. These land use changes caused changes in the regional flora and vegetation, but no detailed investigations have so far been carried out despite the excellent historical data by Gustav Hegi and other botanists. First, we describe the land use changes that occurred in the Tössbergland area within the last 150 years and put them into a larger historical context. This qualitative assessment shows that land use has never been stable in the region and that the flora and vegetation has constantly been influenced and changed by humans according to economic needs and cultural traditions. However, land use change accelerated at the end of the 19th century, when the river Töss has been regulated, extensive afforestation took place and agriculture experienced drastic intensification. We illustrate these landscape changes with historical, so far partly unpublished photographs from the Tössbergland area. Additionally, an account of the history of botanical research in the area and brief descriptions of the lifes of its most prominent botanists are given. Second, in order to investigate the effects of changes in land use practices on the regional flora during the last one hundred years, we selected a group of hundred plant species, i.e. alpine plants in a broad sense, and assessed changes in the number of their occupied sites. A loss of species was revealed (16 % extinct species), whereas the surviving species lost 42 percent of the formerly occupied locations. This loss in species diversity and the number of occupied sites was different among three landscapes within the Tössbergland area. Species which had only a few sites a century ago were more negatively affected than more common species formerly occupying ten or more sites. Regarding different habitat types, i.e. nutrient poor meadows and pastures, other grasslands, rocks and forests, similar patterns of extinction and population losses were generally found. Populations became spatially more fragmented during the last one hundred years as based on former and current distribution maps of all studied species. Third, the important contemporary habitats of alpine species in the Tössbergland area are described, and reasons for the loss in species and population number are given and discussed in relation to nature protection management and conservation biology. A set of suitable measures to halt a further species decline is outlined. The most important causes for the identified floristic losses are the darkening of forests, the abandonment of various traditional agricultural practices such as woodland pasture and the intensification of pastures and grasslands during the 20th century. Especially, the nutrient poor, extensively managed mountain pastures, besides the proper rocky habitats being the most important habitat of alpine species in the Tössbergland, have been destroyed to a large extent. Moreover, natural landscape dynamics is shown to be an important factor favoring the survival of many alpine species of the area. Furthermore, the text illustrates that measures can result in conflicts of aims, both with respect to conservation goals as well as the goals of different stakeholders. We conclude with five potential scenarios on the future development of the Tössbergland area.