The water-use of plantations compared to alternative land uses is an important natural resource management issue in central Chile. The need for local data is heightened by a drying trend in the local climate, the potential for planted forests to store carbon and local plans to replace plantations of Pinus radiata D. Don with Eucalyptus globulus Labill. This paper compares the growth and water balance of P. radiata and native forest (Hualo – Nothofagus glauca (Phil.) Krasser) at a low rainfall site (1016 mm) and of P. radiata, E. globulus and native forest (Roble – N. obliqua Mirb.) at a medium rainfall (1395 mm) site.
Evapotranspiration of plantations of P. radiata in the north and of P. radiata and E. globulus further south was greater than in the local native forest by about 100 mm per year. This difference in total water use was due to greater transpiration by the plantation species; the sum of interception and soil evaporation was very similar for all forest types. Pinus radiata used more water than native forest throughout the year, owing to a more than two-fold greater stand sapwood area in the P. radiata. The difference between E. globulus and native forest was due to much higher sap flux density in the E. globulus during spring and early summer. Although there was no annual difference between the water use of E. globulus and P. radiata, the much greater transpiration of E. globulus in spring may result in earlier drying of soils and catchments planted with E. globulus than P. radiata species.
The annual growth rate of all forest types increased in the years after the end of Chilean mega drought. During the first year of this period, E. globulus produced significantly more wood per unit of water used (3.5 g wood kg−1) than P. radiata (2.1 g kg−1) which was, in turn, more than five times more efficient then the native forest (0.4 g kg−1).