Soil carbon storage and dynamics in the western Gulf Coastal Plain as impacted by forest management

Background/Question/Methods

Carbon sequestration by forest ecosystems represents an important ecosystem service which regulates atmospheric CO₂ concentration and influences the climate system; however, disturbances due to land management practices could have profound effects on C storage and turnover within these ecosystems. North American forestlands currently cover ≈ 770 million ha, or 36% of the continent’s land mass, and hold 170 ± 40 Pg C. With litter and SOC combined accounting for ≈ 72% of these C stocks, perturbations could have profound effects on C and nutrient cycling. The purpose of this study was to examine the effects of a 3 X 3 factorial combination (N = 3) of tree harvest method and soil compaction intensity 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 dry combustion to quantify mineral soil and litter C and N.

Results/Conclusions

Soil total N and SMB-C and -N were significantly affected by tree harvest method, and decreased in the order:  bole only > whole tree > whole tree + litter. Although soil C decreased appreciably with increasing intensity of tree harvest method, this difference was not statistically significant. Litter mass, C, and N were unaffected by tree harvest method. Neither soil compaction intensity nor the harvest method x soil compaction intensity interaction had a significant effect on any of the variables examined in this study. Our data suggest that forest harvest practices that minimize the 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.