Changes in ecosystem carbon and nitrogen in a loblolly pine plantation over the first 18 years

Eighteen years after the establishment of a loblolly pine (Pinus taeda L.) plantation, ecosystem C content had approximately tripled (from 54 to 161 Mg C ha(-1)) primarily because of increases in tree biomass. Ninety-three percent of the net ecosystem C accumulated in biomass (100 Mg C ha(-1)) and 6% of net ecosystem C accumulated in the forest floor (13 Mg C ha(-1)). No statistically significant changes in soil C were found. Growth responses to fertilization noted in Year 4 were no longer statistically significant in Year 18. Nitrogen accumulation in aboveground biomass and forest floor were approximately equal (averaging approximately 270 kg N ha(-1) each) and could have come from a combination of atmospheric deposition, soil N mineralization, and, in the treated plots, fertilizer input. No statistically significant changes in soil N content were found. The results of this study are similar to those from a previous study in a loblolly pine plantation in South Carolina but contrast with those in nearby deciduous forests where substantial changes in soil C and N over similar time periods have been noted.