During the second half of the 20^th century, many processes have altered the species composition in the low-elevation (<1200 m a.s.l.) forests in the inner-Alpine dry valley Valais, which is located in the southwest of Switzerland. In the past, the pioneer Scots pine (Pinus sylvestris L.) benefited from historical forest managements, such as goat grazing, selective withdrawal of forest products and timber harvesting (Rigling & Cherubini 1999). In recent decades, deciduous species, in particular pubescent oak (Quercus pubescens Willd.), have spread as a result of the abandonment of past forest use and ongoing natural succession. In the mean time, the climate has changed towards longer summer drought periods, higher mean temperatures (Rebetez & Dobbertin 2004) and different seasonality for moisture availability. The direct and indirect effects of the factors mentioned above are believed to have led to the locally high mortality rates of pine. In this study, we investigate the differences between pine and oak in their growth response to moisture conditions along altitudinal gradients, to evaluate the influence of climate change on species composition.