Comparing sap flow of European larch with evergreen conifers at different elevations in an inner-alpine dry valley

European Larch (Larix decidua) is considered as an anisohydric species which hardly reduces transpiration during moderate dry periods. In contrary, evergreen Pinus-species have a more conservative stomatal control. We used sites at different elevations within the LTER platform 'Matsch|Mazia' (LTER IT25) in Vinschgau/Val Venosta (Province of Bozen/Bolzano, Northern Italy), to compare sap flow and tree growth of larch with pines under different climatic conditions. At a lower site (1160 m a.s.l.) larch and introduced black pine (Pinus nigra) were investigated, while larch and Swiss stone pine (Pinus cembra) were investigated at a higher site (2000 and 2100 m a.s.l.). Sap flow was measured with trunk tissue heat balance sensors and stem radius variations with automatic band dendrometers for four trees per species at each site. Overall sap flow and yearly growth was higher for larch than for the two co-occurring pine species. During 15-day dry periods black pine showed a quick and strong reaction to limited water availability, but sap flow of larch decreased more slowly. At high elevation, larch hardly reacted at all to a 10-day drought, while Pinus cembra reduced both sap flow and stem radius. Repeated dry periods led to limited water availability and reduced tree growth for larch and black pine at low elevation, while water supply did not restrict growth at high elevation.