Clearcutting Northern Hardwoods: Effects on Hydrologic and Nutrient Ion Budgets
Two evenaged management systems, progressive strip cutting and block clearcutting, have been studied since 1970 on small watersheds at the Hubbard Brook Experimental Forest, New Hampshire. In the progressive strip cutting, all merchantable trees were harvested in a series of three strips over 4 years (1970-74). In the block clearcutting, all trees were harvested in a single operation in 1970. Block cutting caused an increase in water yield of 673 mm over 10 years compared to an increase of 397 mm for strip cutting. Maximum annual increases were 278 mm in the first year after block cutting versus 114 mm in the third year of the strip cutting sequence (two-thirds of watershed harvested). Nearly all of the increases on both watersheds occurred during the growing season months of June through September. For the 10-year period after strip cutting, nutrients lost as dissolved ions in streamflow were increased by 27 kg ha-1 for Ca2+, 30 kg ha-1 for K+, and 22 kg ha-1 for N. Corresponding increases after block clearcutting were 40 kg ha-1; for Ca2+, 48 kg ha-1 for K+, and 59 kg ha-1 for N. The combined losses of nutrients to product removal and increased leaching did not exceed 3 percent of preharvest capital for any of the nutrients studied. The losses assume greater importance when contrasted with plant-available capitals of nutrients. However, with careful logging and continued use of intervals of 70 to 120 years between harvests, clearcutting of northern hardwoods should not have adverse impacts on site nutrient capital. Forest Sci. 32:667-686.
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