Abstract

In several parts of the world, drinking water is obtained from springs in natural and managed mountainous forests. Since forests regulate quality as well as quantity of water, the effects of forest management activities on water yield are an essential subject of study. The objective of this study was to evaluate the impact of land-use changes and forest management on water yield in managed and unmanaged temperate native rainforests and exotic fast-growing plantations of Eucalyptus spp. in both the Coastal and the Andean ranges of southern Chile. The study areas are located in Bonifacio on the Coastal range of southern Chile (39° 50' S, 73° 10' W, 71-297 m a.s.l.) and San Pablo, a forest reserve of 2,184 ha located on the Andean range of southern Chile (39° 35' S, 72° 07' W, 600-925 m a.s.l.). In the Coastal range, during the period January 2010 - December 2011 we measured transpiration rates and water use efficiency for different native and exotic tree species and water yield in three small headwater catchments covered by Eucalyptus globulus plantations, evergreen and native deciduous forests. According to our results, E. globulus has the highest transpiration rate, but the lowest water use efficiency values compared to native evergreen and deciduous species. During the period January through December 2010, the water yield was 1346, 572 and 247 mm in the Eucalyptus plantation, the native evergreen and the deciduous forests, respectively, and in the period January through December 2011, water yield was 1501, 1100 and 177 mm, respectively. In the Andean range, from October 2005 to October 2010, two small experimental catchments were monitored for rainfall, throughfall, stemflow, soil water infiltration, soil water percolation and runoff. In November 2006, a watershed covered with evergreen old-growth forests was thinned extracting 40% of the total basal area whereas another adjacent catchment remained unthinned as a control. Both watersheds are located at 725 - 910 m a.s.l. and have the same aspects. Thinning of the evergreen old-growth forest increased the streamflow for the period November 2006-October 2010 with 14.1%, ranging from 4.4% to 24.6%, with greater differences during summertime (15.4 to 160.5%). The temperature of the stream in the thinned catchment increases 2° C in the summertime, compared with the unthinned catchment.