Vegetation on Alpine rock glacier surfaces: a contribution to abundance and dynamics on extreme plant habitats

Abstract

In the area of Piz Corvatsch (Upper Engadin, Grisons, Switzerland), the actual vegetation on active and inactive rock glacier surfaces has been mapped. The floristic composition (vascular plants and lichens) of the different rock glacier surfaces has been mapped and compared with photogrammetrical measurements of surface movements of the active rock glaciers. In general, the active rock glacier surfaces show a very low cover of vascular plants. Most of them are located at the edge and at the front of the rock glacier where fine-grained soil material occurs in small pokkets.
Lichenometry has been used as an additional method on Murtèl rock glacier and on the protalus rampart. Measurements of Rhizocarpon geographicum thalli revealed increasing sizes from the root zone of the rock glacier to its front. On the Murtèl rock glacier, Rhizocarpon geographicum thalli with a diameter >4cm occur on surfaces with ages between 5000 and 6000 years B.P.
The statistical analysis (MULVA-5) of the dense vegetation cover of the inactive and relict rock glaciers revealed four plant sociological groups, which are composed of species reflecting well consolidated sites: alpine grassland, subalpine dwarf shrubs and small patches with single small trees of Swiss stone pine (Pinus cembra) and larch (Larix decidua).