Semester

Spring

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Brzostek, Edward

Committee Co-Chair

Peterjohn, William

Committee Member

McNeil, Brenden

Abstract

Forest carbon (C) credit markets have emerged as a tool to mitigate climate change by offsetting C emissions through improved forest management. However, the models used to estimate C gains in response to shifts in forest management focus on aboveground C pools while neglecting the role of changes in soil organic matter (SOM) pool. This absence of SOM dynamics in forest C markets is concerning given that soil holds nearly double the amount of C compared to vegetation. In addition, most research on the impacts of forest management on soil C has focused on bulk SOM concentrations. This focus overlooks recent research that shows that not all SOM has the same resiliency to future global change. As such, forest C projects that alter the distribution of particulate organic matter (POM), undecomposed litter that is more susceptible to microbial decomposition, vs. mineral associated organic matter (MAOM), microbial products that are protected from microbial decomposition by sorption to mineral surfaces, have the potential to build SOM that is less stable in the long-term. Given these omissions, the objective of this study was to quantify the impacts of different harvesting regimes on soil C stocks, MAOM, and POM. We sampled soils from long-term silviculture experiments at the Fernow Experimental Forest in WV including a recently harvested diameter-limit cut watershed, a single tree selection watershed last harvested a decade ago, and an unmanaged reference watershed. In each watershed we sampled the organic horizon, 0-20 cm mineral soil, and 20-40 cm mineral soil from 18 locations. For each sample, we measured root biomass, total soil C, total soil N, and the distribution of POM vs. MAOM. In the recently harvested diameter-limit cut watershed, we found that there was little difference between it and the reference watershed in total soil C but there was more undecomposed plant detritus in the 0-20 cm depth. By contrast, in the single tree selection watershed, which was last harvested over a decade ago, there was significantly less soil C, and a greater proportion of MAOM C to POM C at the 20-40 cm depth than both the other watersheds. Overall, these differential results between the managed watersheds that varied in their time since last harvest suggest that the impacts of harvest on soil C vary with time. Initially, harvest may lead to a short-term pulse in undecomposed plant detritus that is lost as the forest recovers from disturbance leading to less total soil C and a higher MAOM C to POM-C ratio.

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