Does Root Carbon from Harvested Trees Replace Mineral Carbon? Effects of LTSP Treatments in a Western Oregon Douglas-fir Forest.

Although soil carbon is known to hold at least two times as much carbon as that held in the atmosphere, the source and fate of soil carbon remains loosely understood. Forest soils in particular are subject to colossal shifts in nutrient cycling as more land area is involved with natural resource extraction. The goal of this study is to determine how the sources of soil carbon shift following varying levels of organic matter removals, and what representative soil organic matter (SOM) pools are most affected by these perturbations. We investigated how lignin biomarkers and stable isotopes changed in soils separated into three density fractions representing ideal pools of SOM from a newly installed Long-term Soil Productivity (LTSP) site on a Southern Oregon Cascades timber area. There was an overall decrease in the mass of recoverable heavy fraction (>2.60g/cm3) material 2-years following the forest harvest. The proportion of total soil carbon from the light fraction (<1.85g/cm3) decreased, with an approximately proportional increase in the soil carbon stored in the intermediate fraction (1.85-2.60g/cm3). Stable isotope (13C and 15N) and cupric oxidation data on whole soils and SOM pools (density fraction) are forthcoming.