SOIL-EROSION AND OVERLAND-FLOW IN FORESTED AREAS WITH PINE PLANTATIONS AT COASTAL MOUNTAIN-RANGE, CENTRAL CHILE

The effects of timber-cutting on sediment concentrations, soil loss an overland flow in an insigne pine (Pinus radiata) plantation were stud ies in a mountain watershed of the Cordillera de la Costa, central Chi le. Soil formation rates for the lithological conditions of the waters hed were estimated. Soil loss measurements on the plantation were take n in 100 m(2) plots, equipped with Coshocton samplers, during the year s 1991 and 1992. Treatments were: clear-cutting no residues/burned, cl ear-cutting with residues and undistorted controls. First-year soil lo sses were greater from the no residues/burned (2128 kg ha(-1)) than fr om the residues (1219 kg ha(-1)) or undisturbed (48 kg ha(-1)) plots. During the second post-treatment year, soil loss was greater from the burned plots (1349 kg ha(-1)) than from the residues (243 kg ha(-1)) o r the undisturbed (72 kg ha(-1)) plots. Sediment concentrations for th e three treatments were 561, 340 and 59 mg l(-1) during the first year , and 400, 150 and 83 mg l(-1) in the second year. Runoff from the no residues/burned plots was greater than from residues or undisturbed pl ots during the two post-treatment years. Long-term soil losses were pr ojected to average 240 kg ha(-1) yr(-1) from areas without residues/bu rned and 120 kg ha(-1) yr(-1) in areas with residues treatment, over a 25 year rotation period, whereas control areas were projected to aver age 60 kg ha(-1) yr(-1).