PhD Thesis Defense: Thijs van den Bergh
The influence of climate and vegetation on the water balance of montane and alpine ecosystems
grosser Hörsaal Pharmazie-Historisches Museum, Totengässlein 3
Widespread abandonment of montane pastures and meadows causes the growth of tall grass swards that later become occupied by shrubs, most dramatically by Alnus viridis. Because of its N2-fixing capacity, this species halts further succession towards the original montane forest. At alpine elevations, above the treeline, grass swards also become taller. In my thesis, I investigated the effects of this land cover change on the water balance (evapotranspiration: ET) and I scaled these to an entire catchment (Ursern valley). In order to understand the determinants of ET, I separated the contributions from climate and vegetation. Also, in a manipulative experiment I quantified effects of tall grass sward growth on bright day ET and seasonal ET. For measuring Alnus ET, I used a combination of lysimeters, sap flow sensors and shrub allometery to scale sap flow rates from single stems to the full canopy. I show that abandonment and subsequent land cover changes lead to higher ET rates and thus, reduced runoff. This thesis underlines the so far unaccounted significance of sustainable land use for alpine hydro-electric schemes.