Effects of tree height on whole-tree water use of Acacia mangium

By using Granier's thermal dissipation probe, the sap flow of 14 sample trees in a 22-year old Acacia mangium forest in hilly land of South China was continuously measured in 2004. Environmental factors including the photosynthetically active radiation, air temperature, and air humidity above canopy and the water content in 0-30 cm soil layer were monitored simultaneously. Combining with the tree morphological features and sap flux density, the whole-tree transpiration, canopy stomatal conductance, and ratio of leaf area to sapwood area were calculated by simplified Whitehead and Jarvis equation, and the effects of tree height on these three parameters were analyzed. The results indicated that under sufficient soil water supply, the whole-tree transpiration increased in a quadratic polynomial way with tree height (P < 0.01), and the diurnal variation of canopy stomatal conductance was of one-peak pattern. Within the measured range of photosynthetically active radiation, taller A. mangium trees had higher reference canopy stomatal conductance and higher sensitivity of canopy stomatal conductance to vapor pressure deficit, compared with the shorter ones. The ratio of leaf area to sapwood area was (1.837 +/- 0.048) m2 x cm(-2), and increased in power function with tree height. A. mangium had no obvious hydraulic limitation and