EFFECTS OF LAND USE CHANGES AND MANAGEMENT PRACTICES ON WATER YIELD IN NATIVE FORESTS AND EXOTIC PLANTATIONS IN SOURTHERN CHILE

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 important subject of study. The objective of this study was to evaluate the effects 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 deciduous native 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 experimental small 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%). Temperature of the stream in the thinned catchment increases 2° C in summertime, compared with the unthinned catchment.