Effects of forest management on soil carbon: results of some long-term resampling studies
The effects of harvest intensity (sawlog, SAW; whole tree, WTH; and complete tree, CTH) on biomass and soil carbon (C) were studied in four forested sites in the Southeastern United States: (mixed deciduous forests at Oak Ridge, TN and Coweeta, NC; Pinus taeda at Clemson, SC; and P. eliottii at Bradford, FL). In general, harvesting had no lasting effects on soil C. However, intensive temporal sampling at the North Carolina and South Carolina sites revealed short-term changes in soil C during the first few years after harvesting, and large, long-term increases in soil C were noted at the Tennessee site in all treatments. Thus, changes in soil C were found even though lasting effects of harvest treatment were not. There were substantial differences in growth and biomass C responses to harvest treatments among sites. At the Tennessee site, there were no differences in biomass at 15 years after harvest. At the South Carolina site, greater biomass was found in the SAW than in the WTH treatment 16 years after harvest, and this effect is attributed to be due to both the nitrogen (N) left on site in foliar residues and to the enhancement of soil physical and chemical properties by residues. At the Florida site, greater biomass was found in the CTH than in the WTH treatment 15 years after harvest, and this effect is attributed to be due to differences in understory competition. Bio-mass data were not reported for North Carolina. The effects of harvest treatment on ecosystem C are expected to magnify over time at the South Carolina C and Florida sites as live biomass increases, whereas the current differences in ecosystem C at the Tennessee site (which are due to the presence of undecomposed residues) are expected to lessen with time.