Logging of mature Douglas-fir in western Oregon has little effect on nutrient output budgets

Abstract

Precipitation and streamwater quantity have been sampled continuously on three adjacent watersheds since 1964 at the H. J. Andrews Experimental Forest on the western slopes of the Cascade Mountains of Oregon. The chemistry of streamwater has been sampled since 1972, and the chemistry of precipitation since 1973. These watersheds were covered primarily by a mature 130-year-old forest of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco). In 1974, one of the watersheds was clear-cut, the logs being removed primarily by a high-lead cable system. At the same time, 60% of the basal area was removed in a shelterwood cut from the adjoining watershed. The third watershed remained uncut for reference. Both harvested watersheds were broadcast burned in 1975 and planted to Douglas-fir in 1976. Streamwater chemistry data and input–output budgets for the three watersheds are presented for 10 years after cutting. Nitrate nitrogen was the only measured solute affected by logging. Despite a 30-fold increase, nitrate nitrogen concentrations were so low that more than twice as much nitrate nitrogen was added to the clearcut from precipitation as was lost in streamwater.