Plantaciones forestales y rendimiento hídrico

Water supply is one of the largest and most valued ecosystem services from forests. This paper presents a systematization of scientific studies about the effects generated by exotic fast-growing forest plantations of Pinus radiata and of Eucalyptus spp. on water yield in south-central Chilean watersheds (33 - 41º S), at different spatial and temporal scales. We compiled scientific studies that have at least one year of observations on large catchments, small catchments and experimental plots. Studies in experimental plots of Pinus radiata plantations showed that annual evapotranspiration increased from south (41° S) to north (33° S), while in this northernmost site almost the entire incoming precipitation was evapotranspired, and the percolated water was negligible. Studies of water balance in small catchments documented a negative linear relationship between total streamflow and forest plantations coverage. Catchments with forest coverage of Pinus or Eucalyptus spp. stored less water than catchments with mixed species, mainly due to high interception loss, more net evapotranspiration and reduced percolation. Forest plantation management can alter the accumulation of water in the catchment (soil and groundwater) and forest cover is the fundamental factor in the dynamics water accumulation. Long-term studies focused on changes in forest coverage from native to plantation forests in large catchments located in the Mediterranean area (33 - 38º S) of Chile showed a sustained reduction in water yield, especially during summertime.