Sap flow of montane pine and oak forests in NE Spain

Papers published in Hydrology and Earth System Sciences Discussions are under open-access review for the journal Hydrology and Earth System Sciences Abstract Stand transpiration was measured during the 2003 and 2004 growing seasons using heat dissipation sap flow sensors in a Scots pine (Pinus sylvestris L.) and a pubescent oak (Quercus pubescens Willd.) forest located in a montane area of the Eastern Pyre-nees (NE Spain). The first aim of the study was to assess the differences in quantita-5 tive estimates of transpiration (E c) and the response to evaporative demand of the two stands. Over the studied period of 2003, characterised by a severe drought episode during the summer, the oak stand E c was only 110 mm compared to the 239 mm transpired by the Scots pine stand, although the ratio of transpiration to reference evapo-transpiration (E c /E T 0) in the oak stand compares well with the expected values pre-10 dicted for low leaf area index (LAI) oak forests in southern Europe. Scots pine showed a strong reduction in E c /ET 0 as the drought developed, whereas pubescent oak was less affected by soil moisture deficits in the upper soil. As a second objective, and given the contrasting meteorological conditions between 2003 and 2004 summer periods, the interanual variability of transpiration was studied in the Scots pine plot. Rainfall 15 during the summer months (June–September) in 2003 was almost 40% less than in the same interval in 2004. Accordingly, transpiration was also reduced about 25% in 2003. Finally, Scots pine data from 2003 and 2004 was used to calibrate a simple transpiration model using E T 0 and soil moisture deficit (SMD) as input variables, and implicitly including stomatal responses to high vapour pressure deficits (D d) and soil 20 water status.