Examining mineral-associated soil organic carbon pool dynamics following clearcut harvesting in a temperate red spruce forest chronosequence

Abstract

Clearcut forest harvesting is a common practice in temperate forests. Whereas the mineral soil contains a substantial proportion of total forest carbon (C), little is known about the effects of harvesting disturbance on the quantity and character of mineral-associated C pools. This thesis documents changes in the size and chemical character of four pools (water soluble, organo-metal, poorly crystalline, and crystalline) within the organo-mineral fraction through 50 cm mineral soil depth (0-5, 5-10, 10-15, 15-20, 20-35, and 35-50 cm) profiles from a chronosequence of Podzol soils representing important stages of forest development (1yr, 15yr, 45yr, 80yr post harvest and a 125+yr reference stand). At all sites, the dominant C pool was the organo-metal complexed, and significant losses were documented following disturbance, particularly in the deeper (>20 cm) mineral soil. Trends of decreasing C concentration, along with chemical character and isotopic data support the hypothesis that increased microbial processing is responsible for C losses following disturbance. These findings suggest that soil C associated with minerals can become destabilized with a change in soil environmental conditions, and that this can increase susceptibility to microbial decomposition. The sheer size of the mineral C pool, as well as the observation that deeper soil dynamics appear to drive trends at these sites, warrants further investigation.