Deuterium tracing for the estimation of transpiration from trees Part 3. Measurements of transpiration from Eucalyptus plantation, India

Measurements of transpiration from individual trees of Eucalyptus from plantations at four different sites in Karnataka, Southern India, are presented. These show large (as much as tenfold) differences in the transpiration between premonsoon and postmonsoon periods, a reflection of the effects of soil-moisture stress in the premonsoon periods. For trees with diameters at breast height (DBH) less than 10 cm the transpiration rate of individual trees is proportional to the square of the DBH. For trees which are not experiencing soil-water stress the daily transpiration rate of individual trees, q, is well represented by the relation: q = (6.6 ± 0.3)g (m³ day^?1 where g (m²) is the tree basal area. On a unit ground area basis the transpiration rate, expressed as a depth per day is given by the relation: E_t = (0.66 ± 0.03)G (mm day^?1 where g(m²ha^?1) is the total basal area per hectare. For all the sites studied, although there is evidence for the ‘mining’ of soil water as roots penetrate deeper depths in the soil each year, there is no evidence for direct abstraction from the water table.