Investigations on spatial heterogeneity of humus forms and natural regeneration of Larch (Larix decidua Mill.) and Swiss Stone Pine (Pinus cembra L.) in an alpine timberline ecotone (Upper Engadine, Central Alps, Switzerland)

Abstract. The north-west facing study area in the Upper Engadine (Central Alps, Switzerland) encompasses the whole timberline ecotone between 2200 m and 2400 m a.s.l.. By dendroecological methods, clear differences concerning quantity and age structure of the natural regeneration of the main tree species Swiss stone pine (Pinus cembra L.) and larch (Larix decidua Mill.) at different sites could be detected.The differing site conditions, closely linked to the microtopography, determine distribution and age structure of natural tree regeneration, as well as humus forms. On exposed sites characterised by Tenuic Humimors, an intensive natural regeneration of, in particular, Swiss stone pine occurs. In depressions with a Rhizic Leptomoder, the density of tree regeneration is low and a high tree mortality could be observed. The results indicate that the site conditions most important for the natural regeneration of trees in the timberline ecotone are reflected in the site-specific humus form.