Analysis and modelling of tree succession on a recent rockslide deposit

Dendroecological methods were combined with vegetation and soil mapping to study recolonisation of European larch (Larix decidua), silver birch (Betula pendula) and Norway spruce (Picea abies) on a recently formed rockslide cone (deposit of 30 x 10(6) m(3)) in the Valais Alps (Switzerland). Tree density and tree height were predicted with regression models that we derived using an information-theoretic model selection approach. Results demonstrate that the deposits of the 1991 rockslide have been colonised relatively rapidly with larch (ecesis time 2 years), birch (5 years) and spruce (2 years). Most of the colonisation occurred 5-11 years following the rockslide. Clast size was the primary factor driving tree colonisation with the highest tree densities found on plots with mainly smaller (<30 cm) clast sizes. Tree height was affected by a combination of different influences, with tree age and tree density showing the most obvious effects. This study demonstrates how dendroecological methods allow reconstruction of spatio-temporal patterns of tree succession on rockslides, which may ultimately facilitate a more accurate dating of similar landforms of unknown age.