TDP Measurements to Determine Nighttime Sap Flow and the Impact of Fog in Tree Transpiration of a Laurisilva Forest.

摘要

The evergreen ‘laurisilva’ forests of the Canary Islands (Spain) are frequently immersed in fog. However the role of fog precipitation remains yet unanswered, despite the belief that fog is important for the survival and distribution of endemic ‘laurisilva’ tree species. Granier’s sap flow measurements carried out in Erica arborea L. and Myrica faya Ait. trees of the Garajonay National Park (La Gomera), during a ten month period, show that diurnal tree transpiration is greatly reduced, down to nighttime values, during fog occurrence as compared to fog-free periods. Additionally, nighttime sap flow was detected in laurisilva tree species with an ad hoc method which combines evapotranspiration and Granier’s Thermal Dissipation Probes (TDP) measurements. To our knowledge this is the first time that a study shows under natural field conditions and for a long measuring period the effect of fog on whole-tree transpiration using sap flow techniques.