COS 26-7
Fifteen-year patterns of soil carbon and nitrogen following organic matter removal in upper Great Lakes forests

Tuesday, August 6, 2013: 9:30 AM
L100F, Minneapolis Convention Center
Valerie J. Kurth, Department of Forest Resources, University of Minnesota, St. Paul, MN
Anthony W. D'Amato, Department of Forest Resources, University of Minnesota, St. Paul, MN
John B. Bradford, Southwest Biological Science Center, U.S. Geological Survey, Flagstaff, AZ
Brian J. Palik, Northern Research Station, USDA Forest Service, Grand Rapids, MN
Background/Question/Methods

A growing interest in the substitution of forest-derived biofuels for fossil fuel energy has led to related concerns about the impacts of increased organic matter removals on forest structure and function. In particular, whole-tree removal (bole, tops and branches) may cause greater nutrient and organic matter depletion over time than conventional bole-only harvests. We assessed the effects of varying levels of organic material removal associated with harvest on soil carbon (C) and nitrogen (N) over a medium-term time frame (15 years) at three aspen-dominated sites in the Great Lakes region of the U.S. The sites were part of the Long-Term Soil Productivity network and each had distinctive soil texture (loam, clay, or sand). Organic matter removal treatments consisted of conventional main-bole harvest, total tree harvest, and total tree plus removal of the forest floor. Organic horizon and mineral soil C and N were sampled pre- and postharvest and every five years thereafter.

Results/Conclusions

Organic matter removal affected C and N in the organic horizon, but effects were site-dependent. Whole-tree harvest plus forest floor removal was associated with the lowest levels of organic horizon C and N at two of the sites. Organic matter removal did not alter C or N in the mineral soil, but site-dependent temporal changes emerged over the 15-year post-harvest measurement period. Our results are consistent with the current literature suggesting that harvest-related debris retention is more influential to C and N in the organic horizon than the mineral soil. Although residues do not appear to contribute to mineral soil C or N in this time frame, changes in these relatively large pools may be difficult to detect using traditional sampling designs. Also, the relatively fast regeneration of aspen following harvest may allow aspen-dominated systems to be buffered from substantial losses of mineral soil C and N.