Effect of clear cutting on snow accumulation and water outflow at Fraser, Colorado

Abstract. This paper compares of snowpack accumulation and ablation, evapotranspiration, and water outflow from clearcut and forested plots within a high elevation (2900 m) mixed conifer forest at the Fraser Experimental Forest near Fraser, Colorado, USA. Also presented is a method for defining contributing area where outflow is measured from unbounded plots. Plots were monitored from 1980 to 1990 and again in 1993. The clearcut plot was harvested in late 1984. Evapotranspiration (E_T) of the forested plot at zero discharge (E_To) was estimated at 426 mm while the E_T was 500 mm at the mean precipitation of 596 mm. E_T was dependent on precipitation with about 28% of precipitation input in excess of 426 mm contributing to increased E_T, while the remainder contributed to increased outflow. During the six monitored post-harvest years, Peak Water Equivalent of the snowpack averaged 36% higher on the cut plot than on the control, and the mean discharge increased from 85 mm to 356 mm. Area estimates were obtained from the slopes of the regression of outflow on precipitation inputs. Hydrologic parameters corresponded closely to those previously determined at Fraser Experimental Forest using other methods, lending credence to the validity of the area estimates.