Transpiration and canopy conductance in an inner alpine Scots pine (Pinus sylvestris L.) forest

Canopy transpiration (E_c) of a 150-year old Pinus sylvestris L. stand in an inner alpine dry valley, Tyrol, Austria was estimated throughout two growing seasons 2011 and 2012 by means of xylem sap flow measurements. Although there were prolonged periods of limited soil water availability E_c did not show a clear trend with respect to soil water availability and averaged 0.4 ± 0.19 mm day^-1 under conditions of non-limiting soil water availability and 0.37 ± 0.17 mm day^-1 when soil water availability was limited. This is because canopy conductance declined significantly with increasing evaporative demand and thus significantly reduced tree water loss. The growing season total of E_c was 74 mm and 88 mm in 2011 and 2012, respectively, which is significantly below the values estimated for other P. sylvestris forest ecosystems in Central Europe, and thus reflecting a strong adaptation to soil drought during periods of high evaporative.