Abstract ID: 3.11911 | Accepted as Talk | Talk/Oral | TBA | TBA

The Swiss Rhone valley is one of the driest regions of the European Alps, surrounded by high mountain ranges which intercept precipitations. For more than 100 years, the forests on the steep slopes between Hohtenn and Brig have successfully protected the BLS railway line from natural hazards thanks to careful management and continuous irrigation. However, water is becoming increasingly scarce and the climate in these extreme locations hotter and drier. Questions are increasingly being asked about the future tree species composition and management of these forest areas. As part of an afforestation experiment, nine possible future tree species have been tested since 2011, Acer opalus, Fraxinus excelsior, Fraxinus ornus, Pseudotsuga menziesii, Pinus nigra, Pinus sylvestris, Quercus ilex, Quercus pubescens and Sorbus aria. Half of the more than 2’000 plants were irrigated while the other half was exposed to natural weather conditions.

The results of this experiment show that after more than ten years, Fraxinus ornus and Quercus pubescens had both a high survival rate as well as rapid height and diameter growth under both treatments. While Pseudotsuga menziesii had a high mortality under dry conditions, these didn’t affect the growth of the surviving plants, making this species a valuable option for forest management at dry sites. Pinus sylvestris didn’t reach the high survival of the first two species, nor quite the impressive growth of Pseudotsuga menziesii. Nevertheless, it still proved a valuable addition and as an important native tree species, deserves to be included in the management of these protection forests. These results are not only relevant for the Swiss Rhone valley, but also for other dry alpine valleys, as well as an early response area to climate change, indicating what future conditions and challenges might look like at less extreme sites in central Europe in the future.