Wood stake decomposition twenty years after organic matter removal at the Lake States LTSP sites

Organic matter (OM) is an integral part of site productivity for a forest, and understanding the effects of OM removal on various forms of carbon (C) cycling is important for land managers and for policy makers. In this study, we utilized the Lake States Long-Term Soil Productivity (LTSP) study sites, located along a gradient in soil texture (clay, silt loam and sand) and high to low productivity, to evaluate the impacts of two OM removal treatments on belowground wood decomposition. In 2013, approximately 20 years after the LTSP treatments had been installed, we placed standardized aspen and loblolly pine wood stakes in the mineral soil of plots receiving the bole only harvesting treatment (BO) and the whole tree harvesting with forest floor removal treatment (WT + FF), and in plots in an adjacent unharvested reference area (1350 wood stakes total). Soil was also sampled to characterize the microbial community composition in the various treatments. From 2014 to 2018, wood stakes were removed from each treatment, and mass loss determined. We found significant differences in wood stake decomposition among the three sites, and between the two wood species, but little impact of timber harvesting and surface OM removals on decomposition. Soil microbial composition also reflected site differences in stake decomposition. We conclude that clearcut harvest and surface OM removal had little effect on stake mass loss in the mineral soil 20 years after the treatments were initiated, and the inherent soil factors are now controlling decomposition