| I investigated the effects of two contemporary disturbances to soil systems: forest clearing in the northeastern U.S. and climate-driven plant succession in the Arctic. To test the effects of clear-cutting forests on mineral soil carbon (C) storage, I collected deep mineral soil cores from twenty forest stands, representing seven geographic areas and a range of times since harvest. I compared recently harvested forests to >100-year-old forests and used an information theoretic approach to uncover controls on C pool dynamics over time since disturbance. I found no significant differences between total soil C pools in >100-year-old and clear-cut forests. However, I found a significant negative relationship between time since harvest and the size of mineral soil C pools, which suggested a gradual decline in mineral soil C pools across the region after harvesting.;To test differences in grass- versus shrub-dominated Arctic soils, I collected twenty deep mineral soil cores in western Greenland and determined soil texture, pH, C and N pools and C:N ratios by depth. To understand if vegetation type was associated with physiochemical mechanisms of soil C storage, I employed a novel sequential extraction method for measuring organo-mineral pools of increasing bond-strength within the soil strata. I found that: (i) total mineral soil C and N storage was significantly lower under shrubs than under grass, and the magnitude of this difference would likely outweigh any positive increases in aboveground C storage with shrub expansion; (ii) chemical mechanisms of C storage in the organo-mineral fraction of the soil did not differ between grass and shrub soils, and (ii) weak adsorption to mineral surfaces accounted for 40-60% of C storage in the organo-mineral soil fraction in both treatments, which is a pool that is relatively sensitive to environmental disturbance.;My research suggests that both direct soil disturbance, such as forest harvest, and indirect disturbance, such as climate-driven shifts in species ranges, does cause changes to biogeochemical cycling and may result in C loss from the landscape. These results have implications for understanding the flux of greenhouse gases from Arctic and temperate soils in a changing environment. |
