Eucalyptus trees and the consumption of water
Water is essential for life – for humans and for plants. In plants, the binding of atmospheric carbon, in the presence of water and sunlight, occurs through the process of photosynthesis. There are several factors that influence the amount of rainfall that reaches the forest soil. First is the amount of water intercepted by the canopies of the trees. Of the amount of this water that reaches the soil surface, part is absorbed and part runs off directly to streams and rivers. Of the amount of water absorbed, part evaporates from the soil and part is More rainwater is absorbed into the soil in planted forests. In native forests, a greater portion of the water is collected in the tree canopies and evaporated back into the atmosphere used by plants, to grow and to reproduce. This part is call “transpiration.”
Transpiration occurs in the leaves. It is the evaporation of water that is used by various processes inside a plant, including protecting it from excessive sunlight. The evaporation (soil) and transpiration (plants) processes may be combined, in a phenomenon known as “evapotranspiration,” which reflects the amount of water a plant uses per unit of area. The water that is absorbed into the soil can also reach the underground water table (the portion of soil that is saturated with water). The opposite (“ascending flow”) can also occur. This entire “water cycle” is shown in Figure 3.
Aracruz has scientifically studied and quantified the components of this water cycle (hydrological cycle) in its eucalyptus plantations in the state of Espírito Santo since 1995. These studies were part of an initiative called the “Watershed Project” aimed at better understanding the relationship between eucalyptus trees and the atmosphere. The study area is representative of the total utilized land (i.e. eucalyptus plantation intermingled with native forests) and encompasses 286 hectares. The studies involve evaluation of the complete eucalyptus cycle from planting to harvesting.
Several other experiments have been carried out in partnership with universities, research centers, NGOs, and environmental agencies – from inside Brazil and internationally. These are listed at the end of this publication. The studies specifically related to the eucalyptus hydrological cycle have been an important part of the work by the National Institute of Space Research (INPE) and by CSIRO, a respected Australian research institution.
