Effect of clear-felling on runoff in two small watersheds in Central Sweden

Small watersheds were used in a study of the effect of clear-felling on runoff from coniferous forest areas in Central Sweden. After a 3-year calibration period, two watersheds were clear-felled (on one of them the slash was left and on the other slash was removed) and a third was left as a reference.Runoff under forested conditions was 271 and 246 mm year^?1, respectively for the treated watersheds, while the precipitation measured 732 mm year^?1 as a mean for the investigated period. Clear-felling resulted in an increase in runoff of 119 and 75% (371 and 215 mm per year), respectively. The increase occurred during the period of snowmelt (April–May) and the period without snow (June–October). During winter (November–March) a very small increase in runoff was noted. The effect of clear-felling on runoff appears to be greater than has been reported from most other Scandinavian investigations.The increase in runoff during snowmelt is probably due to an increased snow accumulation in the clear-felled area as compared to the forest. The increased runoff for the period without snow is explained by reduced transpiration from the vegetation and reduced evaporation caused by an increased aerodynamic resistance.No effects of slash removal could be detected, probably because of the natural variation between the two treated watersheds.