Pizarro-Tapia,R. (reprint author). Univ Talca, Fac Ciencias Forestales, Departamento de Gestion Forestal & Ambiental, Casilla 721, Talca, ChileThis article analyzes the influence of wooded masses in the water production of the Purapel River watershed, located in the central zone of Chile, This watershed has an area of 264 km(2) and has been affected by processes of vegetation replacement, going from native forests to massive forestation, mainly of Pinus radiata (D.Don). The multitemporary analysis made showed that the vegetal cover varied from 0 per cent of forest plantations in 1957 to 51.7 per cent for the year 1997. The methodology studied land use in 1957, 1978, and 1997, precipitations were analyzed and flow and hydrographs were studied on an hour by hour basis; the variation of water reserves was analyzed monthly and annually, monthly and annual runoff coefficients were analyzed, the maximum flow was studied, and finally, their relationship with the vegetal cover and the water production between the years 1960 and 2000 was studied. The results allow to conclude that for the Purapel River watershed there are no differences in the observed hydrology behavior in the 40 years studied. The oscillations observed in the hydrologic variables are due to precipitation amounts and intensities and to the high intermonthly variability. Only the monthly reserves show a different behavior, since they tend to increase in the 1979-2000 period. This had to do with important precipitations in the 80's, and not directly with a change of the type of vegetal cover.