Soil Carbon and Nitrogen Storage and Dynamics In Loblolly Pine Ecosystems As Impacted by Forest Management.

Carbon sequestration by forest ecosystems provides important ecosystem services by regulating atmospheric CO₂ concentrations and influencing the climate system; however, forest harvest practices could have profound effects on C and nutrient storage and turnover within these ecosystems.  The purpose of this study was to examine the effects of a 3 X 3 factorial combination of tree harvest method and soil compaction on C and N pools in the mineral soil and forest floor of a Pinus taeda L. (loblolly pine) forest in the western Gulf Coastal Plain 13 yrs after treatment.  We used chloroform fumigation extraction to quantify soil microbial biomass-C and –N (SMB-C, SMB-N), and elemental analysis/isotope ratio mass spectrometry to quantify mineral soil and litter C, N, and δ¹⁵N.  Soil total N, SMB-C and -N decreased significantly with increasing tree harvest intensity.  Soil C decreased appreciably, but not significantly, with increasing tree harvest intensity.  Soil and litter δ¹⁵N were more enriched with increasing forest harvest intensity, reflecting greater apparent N-losses in those treatments.  Litter mass, -C, and -N were unaffected by tree harvest method.  Neither soil compaction intensity nor tree harvest method x soil compaction intensity interaction affected any variables examined in this study.  Our data suggest that forest harvest practices that minimize removal of tree biomass will favor soil N-retention and the maintenance of the SMB pool.  Since N is a limiting nutrient for tree growth in the sandy soils of the western Gulf Coastal Plain, and because SMB plays a key role in making that N available, tree harvest practices that favor N-retention and SMB will help ensure the productivity of future rotations.  These results also suggest that soil fertility impacts resulting from tree harvest practices could affect the degree to which these southern pine forests can function as sinks for atmospheric CO₂.