In this work a series of functions is proposed to predict growth in young plantations of Eucalyptus globulus and Eucalyptus nitens, based on soil water content. The functions were built combining a) relationships that consider the increase in diameter and height of the plant based on the soil water content. and b) the relationships proposed by Ribalta (1983) and Schonau and Boden (1982) that calculate the increase in biomass based on the diameter and height (of the plant). The constants of every function were determined on the basis of field measurements taken over three years, at three forest sites representing typical conditions of the Coastal Dry Land, Central Valley and Andean Piedmont of the VIII Region of Chile.
Fitted independently, the diameter and height increase relationships showed average R2 values of 0.36 when using the diameter at the neck and 0.69 when using the basal area. On the other hand, the Ribalta's and Schonau and Baden's relationships showed values of R2 over 0.98 in all cases. Combining both types of relationships, a) and b), it was possible to estimate the biomass with errors less than 10% for the 30-month period, and R2 values were over 0.93. Since the results for the three sites evaluated were similar when using Ribalta's or Schönau and Baden's relationships, and considering that the Schonau and Baden's function uses less explanatory variables, the use of Schönau and Baden's function is recommended for conditions similar to those studied here.