Effects of tree species and management practices on soil carbon dynamics in Upper Midwest forests

Understanding the ecology of northern hardwood forests and the effects of changing management practices on carbon (C) dynamics is critical to sustainable forest management and enhancing C sequestration of forests. The overall objective of this dissertation was to examine the effects of different forest management activities on soil C and microbial dynamics. Chapter 1 examined the effect of overstory species on the structural storage of soil C in aggregates. Total soil C did not differ significantly among the five tree species. C and nitrogen (N) stabilization and storage in forest soils, especially in the free microaggregate fraction and the associated particulate organic matter did differ significantly among species. Tree species may be one forest management opportunity to increase C sequestration and using total C content instead of the structural component may not be adequate to detect small, but important changes in soil C dynamics.;Chapter 2 examined the effects of selective harvests on soil microclimate and soil surface CO2 flux (Sflux) in a northern hardwood forest. Annual (+1 std. err.) Sflux differed by only 4% among treatments and averaged 967 + 72, 1011 +72, and 1012 +72 g C m-2 yr -1 in the control, mechanized and gap treatments, respectively, for the two year post-treatment period but was not significant. The small difference among treatments was less than the 9% difference in S flux among the three sugar maple forest types used in the study. Chapter 3 examined the effects of selective harvest on microbial biomass and community composition in a northern hardwood forest. Microbial biomass and community structure are important regulators of soil C dynamics. The ratio of Gram-positive to Gram-negative (Gm+:Gm-) bacteria and relative abundance of three Gm+ bacteria was significantly greater in harvested gaps than control and mechanized plots for August post-treatment. Small selective group tree harvests that created canopy gaps of 200-350 m2 influenced the microbial composition but did not significantly change total microbial biomass.