Forest Management Effects on Surface Soil Carbon and Nitrogen

Changes in surface soil C and N can result from forest management practices and may provide an index of impacts on long‐term site productivity. Soil C and N were measured over time for five watersheds in the southern Appalachians: two aggrading hardwood forests, one south‐ and one north‐facing, undisturbed since the 1920s; a white pine ( Pinus strobus L.) plantation planted in 1956; and two regenerating hardwood forests, a whole‐tree harvest in 1980, and a commercial sawlog harvest in 1977. Soils on harvested watersheds were sampled before and for ≈15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south‐facing and decreased on the north‐facing watershed. The pattern for total N was similar. Total N decreased significantly on the north‐facing but was stable on the south‐facing watershed. In the white pine plantation, C increased while N concentrations decreased during the 20‐yr period. Soil C and N concentrations generally declined the first year following whole‐tree harvest. Fourteen years after cutting, C remained stable, while N was greater compared with reference watershed soils. The commercial sawlog harvest resulted in large increases in surface soil C and N concentrations immediately after cutting. Carbon levels remained elevated 17 yr following cutting. Our data suggest that the forest management practices examined do not result in long‐term decreases in soil C and N. However, the high interannual variation on all watersheds suggests that care must be taken in selecting control sites to determine long‐term treatment impacts.