Growing season water balance of an inner alpine Scots pine (Pinus sylvestris L.) forest.

We estimated components of the water cycle of a 150-year-old Pinus sylvestris forest in an inner Alpine dry valley of the Tyrol, Austria throughout five growing seasons. Forest canopy transpiration (TC) was measured by sap flow measurements scaled to the stand canopy level. Estimates of understory transpiration and forest floor evaporation (ETU) were derived from the soil water budget method, while interception (I) was modelled. Growing season cumulative evapotranspiration (ET = TC + ETU + I) varied between 256 and 322 mm or 51 to 79% of the growing season precipitation. The contribution of TC, ETU, and I to ET were 33, 40 and 27% respectively. Although these values of each layer (evapo)-transpiration are in good agreement with studies carried out in other European Scots pine forests, our estimated growing season total forest water use (Ttot = Tc + ETu) of 200-244 mm is at the lower end of values reported for coniferous forest ecosystems, and thus reflects an adaptation to the low shallow soil water availability. We conclude that Scots pine forests in inner alpine dry valleys are able to cope with high evaporative demand, even when shallow soil water availability is limited.