Impacts of intensive harvesting on hydrology and nutrient dynamics of northern hardwood forests

Whole-tree clear-cutting and progressive strip-cutting of northern hardwood forests at the Hubbard Brook Experimental Forest in central New Hampshire resulted in measurable changes in physical and chemical conditions of fores t streams. As a result of reduced transpiration and interception, water yie ld for the first year after whole-tree harvesting increased by >150 mm, the majority of which occurred during the growing season. Peak flows increased only moderately. Water yield and peak flow increases disappeared within 4- 6 years as a result of rapidly regrowing vegetation. Sediment yields increa sed during and after harvesting but can be maintained within normal ranges of reference streams by careful use of best management practices. Stream ch emistry changes occurred immediately following harvesting, most notably in the form of increases in concentrations of Ca2+, K+, NO3-, and H+. The conc entrations return close to preharvest levels within 3-5 years. The above ch anges are discussed in terms of their causes and implications for aquatic h abitat and fisheries.