WHOLE-TREE CLEAR-CUTTING EFFECTS ON SOIL HORIZONS AND ORGANIC-MATTER POOLS

Timber harvest results in physical disturbance and relocation of soil materials. This study was undertaken to assess the degree to which logging altered soil horizonation, bulk density, and organic-matter pools at a northern hardwood forest site underlain by Spodosols. Soils were sampled immediately before and 3 yr after the commercial whole-tree harvest of Watershed 5 at the Hubbard Brook Exerpimental Forest in central New Hampshire. The activity of logging machinery resulted in redistribution of organic matter within the solum. Thus, the thickness of the O horizon decreased from 6.9 cm to 5.5 cm, while O horizon mass and organic-matter content increased (from 8.7-12.2 kg m-2 and from 5.4-5.7 kg m-2, respectively). One-fourth of the postharvest soil pits exhibited an Ap horizon, which was not present prior to harvesting and was formed from soil of the O, E, and Bh horizons. Compaction of the soil during the logging operation resulted in increased (5-15%) bulk density in the upper 20 cm of mineral soil. The total pool of organic matter in the solum did not change following harvesting. Thus, losses of organic matter via streamwater and respiration were approximately balanced by inputs from decaying roots and leaf litter. The conservation of organic matter following harvesting is important in preserving soil fertility, since labile nutrients in northeastern Spodosols are generally associated with organic matter.