Tuyển tập các báo cáo nghiên cứu về lâm nghiệp được đăng trên tạp chí lâm nghiệp quốc tế đề tài: "Interpreting the variations in xylem sap flux density within the trunk of maritime pine (Pinus pinaster Ait.): application of a model for calculating water flows at tree and stand levels. | Ann. Sci. For. 1998 55 29-46 Inra Elsevier Paris 29 Original article Interpreting the variations in xylem sap flux density within the trunk of maritime pine Pinus pinaster Ait application of a model for calculating water flows at tree and stand levels Denis Loustau Jean-Christophe Domec Alexandre Bose Laboratoire d ecophysiologie et nutrition Inra-Forets BP 45 33611 Gazinet France Received 15 January 1997 accepted 30 June 1997 Abstract - Sap flux density was measured throughout a whole growing season at different locations within a 25-year-old maritime pine trunk using a continuous constant-power heating method with the aim of 1 assessing the variability of the sap flux density within a horizontal plane of the stem section and 2 interpreting the time shift in sap flow at different heights over the course of a day. Measurements were made at five height levels from to 15 m above ground level. At two heights . m and beneath the lower living whorl respectively sap flux density was also measured at four azimuth angles. Additionally diurnal time courses of canopy transpiration needle transpiration needle and trunk water potential and trunk volume variations were measured over 4 days with differing soil moisture contents. At the single tree level the variability of sap flux density with respect to azimuth was higher at the base of the trunk than immediately beneath the live crown. This has important implications for sampling methodologies. The observed pattern suggests that the azimuth variations observed may be attributed to sapwood heterogeneity caused by anisotropic distribution of the sapwoods hydraulic properties rather than to a sectorisation of sap flux. At the stand level we did not find any evidence of a relationship between the tree social status and its sap flux density and this we attributed to the high degree of homogeneity within the stand and its low LAI. An unbranched three-compartment RC-analogue model of water transfer through the tree is .
