Abstract

The large scale introduction of eucalypts has been attracting criticism from the public by alleging several negative ecological effects including high water consumption. This report presents the results of a detailed investigation on the alleged excessive water consumption by the two eucalypt species planted in Kerala. Three eucalypt plantations were chosen for intensive monitoring. Using a scaffold tower in the plantations, microclimate parameters like temperature, relative humidity, wind speed, total solar radiation and net radiation were measured 2m above the canopy level. The temperature at the ground level was also measured. All measurements were made using eletronic sensors connected to a datalogger. Data were collected at 5 seconds interval and averaged hourly. Along with the above microclimate parameters, hourly measurements of the stomatal conductance were made. In E. grandis, the canopy was treated as a two layer structure and appropriate measurements were made in both the layer. In E.tereticornis, a single layer model was followed. The data collected thus were applied in the Penman-monteith equation to get the hourly water loss due to transpiration. The canopy leaf area index was also measured for the above computations. The daily transpirationn rates were extrapolated to monthly values. The tran spiration loss during the nine months of the year was estimated by totalling the monthly values In all the three locations, the water potentials were maintained at relatively higher levels even during the non rainy months. This means that the plants were not under water stress during any part of the year. Even the midday water potentials never reached the turgor loss point(-1.75 MPa) The stomatal control of transpiration in response to increasing atmos-pheric vapour pressure deficit when examined shows that in E.tereticornis apparently the control was not existing at the available soil water content. In E.grandis, relatively good control existed with nearly complete closure at values above 4.0 kPa irrespective of the soil water availability. The relatively high water potentials and the stomatal conductance values throughout the year indications for abstraction of water from deeper layers of the soil. The maximum net photosynthetic rate in both the species was around 20umol m powerof -2 s powerof -1. The water use efficiency was better for E.tereticornis. Complete cessation of growth in girth was found during the pre monsoon period in both the species. Extension growth was maintained regardless of the seasons