Study On Changes Of Sap Flow Density And The Evapotranspiration Of The Fir Stands In The Upper Reaches Of Minjiang River, Sichuan Province

By using ICT-2000TE(Transpiration-Environment) measurement system which was designed on basis of Thermal Dissipation Method, the sap flow density (SFD) of main arbor species(Abies taxoniana, Betula platyphylla and Rhododendron balangense) and environmental factors were studied during growing seasons in 2004 and 2005 in upper reaches of Minjiang area. Meanwhile, the SFD variety in radial sapwood and whole-tree evapotranspiration intensity of A. taxoniana and the stand water use were investigated. Major conclusions are described as follows:The diurnal variety SFD of the arbor species were alternate in daytime and nighttime and exhibited mono-peak patterns. In different seasons, the SFD of A. taxoniana and B. platyphylla had relatively notable fluctuation. Based on regression analysis and grey relationship analysis, the function models between environmental value and SFD of the three trees were established. The solar radiation was the most significant environmental factor to SFD, and then were air temperature and air relative humidity. The role of soil water content, soil temperature and rainfall were relatively insignificant.There was a close relation among the SFD of different points in radial positions of sapwood. On the other hand, there was no distinct regulation of the SFD in different dimensions of the stem and the diameter at the breast height. Through dyeing xylem by FeCl₃, the function model between sapwood thickness (SWT, cm) and diameter at the breast height (D, cm) was established (SWT = 1.572lnD-2.03). And then the function of calculating the whole-tree evapotranspiration quantity was: F_out=4.686F_d3(D-1), F_in=7.054F_d3[4.596D+2.556-4.596D(1.572lnD-2.03)^0.217-2.556(1.572lnD-2.03)^0.782],F=F_out+F_in.The stand water use model was established from whole-tree water use and the DBH distribution model in the stand. Considering the transpiration of Fargesia nitida and herbaceous (including Cystopteris moupinence, Cacalia latipes and Ligularia franchetiana), the average stand water use per day by transpiration was...