Abstract

Significant areas of Latin America, and especially of Chile, have been forested with exotic plantations to provide timber and fibber and to decrease soil erosion after deforestation. Despite their potential contribution to reducing erosion processes, the magnitude of this decline has not been adequately assessed. In this study, we estimated soil loss and mobility for one year on steep hillslopes using the traditional erosion-pin approach at five micro-catchments planted with Pinus radiata with different stand ages and compared them to an adjacent secondary broadleaf Nothofagus sp. native forest. Annual net soil loss (ASL) positively correlated with cumulative rainfall (R2=0.49, p<0.001). ASL averaged 65.03 ± 9.8 Mg·ha-1·yr-1, with the lowest ASL in the natural forest with 21.4 ± 3.1 Mg·ha-1 yr-1 and the highest in one of the 1-year-old plantation micro-catchments (88.9 ± 9.3 Mg·ha-1·yr-1). ASL under plantation stands of different ages displayed no significant differences. All areas showed similar net soil loss index values, averaging 83.0 ± 1%, suggesting that most of the sediment left the hillslope. The RUSLE model predicted ASL moderately well across all sites and conditions (0,41, p=0,018), but it tends to underestimate ASL, particularly for native forests. On average, plantation forests in hilly terrain could result in soil losses up to 4 times greater than natural forests. The latter stresses the need to improve our understanding of erosive processes in planted forest, and to better assess the effect of intensive management practices on soil erosion, particularly on previously degraded and highly erodible soils. Keywords: erosion, forest plantations, erosion pins, soil mobility, land-use intensification.