AN ECOPHYSIOLOGICAL EVALUATION OF THE SUITABILITY OF EUCALYPTUS-GRANDIS FOR PLANTING IN THE TROPICS

Water use by eucalypts has received a lot of attention in tropical cou ntries during the past decade because of the large-scale introduction of these trees for afforestation. Eucalyptus grandis, widely used as a plantation item in tropical southern India, is the subject of a detai led ecophysiological study in this paper. A 4-year-old coppiced planta tion was used for measurements. Microclimate data collected above the canopy were used along with stomatal conductance measurements to estim ate the transpirational water loss by the Penman-Monteith equation ass uming a two-layer canopy model. Leaf photosynthesis was measured diurn ally and seasonally to understand the limitations in photosynthesis in the field. Results show that the water loss from the plantation range s between 2.5 and 6.5 mm day(-1) depending on the season. When suitabl y extrapolated, this amounts to 1181 mm annually in the study location , where annual rainfall averages 1302 mm. The stomatal conductance mea surements showed that the increase in atmospheric vapour pressure defi cit induced stomatal closure. This was probably regulated by the leaf water potentials also. Based oil the above results it is concluded tha t E. grandis need not be a high water consumer because of its good sto matal control of transpirational water loss, especially during the dry season when the atmospheric vapour pressure deficit is high. The phot osynthesis measurements led to a conclusion that the dry period experi enced in the study location does not seriously affect the photosynthet ic rate of the trees on a leaf unit area basis. (C) 1997 Elsevier Scie nce B.V.