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 approximate to 15 yr after harvest. Surface soil C concentration on the undisturbed watersheds varied significantly among sample years. Concentrations fluctuated on the south-faring 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 rutting. 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.