Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp Original article đề tài: Hourly and daily variations of xylem sapflow in sweet chestnut coppices using a thermal measurement method. | 350s Ann. Sci. For. 1989 46 suppl. 35ŨS-352S Forest Tree Pysiology E. Dreyer et al. eds. Elsevier INRA Hourly and daily variations of xylem sapflow in sweet chestnut coppices using a thermal measurement method V. Bobay and B. Saugier Laboratoire d Ecologie végétale bât. 362 Université Paris-XI 91405 Orsay France Introduction A new method for measuring xylem sapflow Granier 1985 has been tested to calculate forest transpiration. Two coppices of sweet chestnut Castanea sativa Mill. in the south of Ile-de-France were studied. One of them was thinned to a density of 3500 stems ha the other 6000 stems ha was used as a control. This paper presents preliminary results of hourly and daily variations of xylem sapflow in the thinned coppice. Materials and Methods A xylem sapflow measurement sensor comprises two cylindrical probes inserted into the conducting xylem of the trunk. One of the probes is heated at constant power the other is unheated and used as a reference. The temperature difference between both probes is a measure of sap velocity around the heated probe. It is recorded using differential thermocouples connected to a data logger. This method allows investigations of the variability of the sap velocity within a stem or between stems. Sapflow is calculated with the following formula and may be averaged on hourly or daily time scales Bobay and Granier 1987 F X SA X Ợ-231 where F sapflow cm3-h-i SA sapwood area at heated probe level cm2 K - flow index without dimensions . K ATM - AT u AT u where ATM temperature difference without any sapflow C AT U temperature difference with sapflow u C . Psychrometer and net-radiometer were installed on a tower in the thinned coppice. Potential evapotranspiration Ep was calculated using Priestley-Taylor s equation 1972 with a hourly time step Ep A zl x fìn  where Rn net radiation Wm-2 A change of saturation vapor pressure per C kPa- C-i Ỵ psychrometer constant kPa- C-1 A latent heat of vaporization of water J g-1 . .
