Hydrologic recovery of aspen clearcuts in northwestern Alberta

A 3-year study of evapotranspiration from aspen clearcuts 1 to 14 years of age indicated the following: (1) The annual evapotranspiration from 1- to 5 -year-old clearcuts ranges from 0 to 743 mm less than a mature forest on th e same site. Evapotranspiration is highly dependent upon the amount of prec ipitation. (2) These effects can vanish in as few as 2 years with low preci pitation (300 mm) or persist for 40 to 45 years with high precipitation (60 0 mm). These results were confirmed by data from the Spring Creek experimen tal watershed. Simulated water yield increase from the harvested catchment averaged 16 mm, compared with 16.3 mm estimated from the paired watershed d ata. In planning harvesting scenarios on flood-prone watersheds full hydrol ogic recovery should be assumed to occur 45 years after harvest. Harvesting sequences designed using this approach should not cause a measurable incre ase in flooding levels or flood frequency.