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SOIL SCIENCE
Tree stands with ages 0, 2, 4, 6, 8, 10, 12, 14, 16 and 18 years with similar species composition and management practices will be studied. Soil variables (including humic acids, bulk density and coarse fragments) at 0-20, 20-40, 40-60, 60-80, and 80-100 cm depth will be measured using standard procedures. The initial ecosystem C stock will be quantified. When the 2-year-old stands are well established, soil respiration will be intensively monitored because soil disturbance has a serious impact on C cycling. Humic acids and the stable C in the acids will be quantified using standard procedures. For each year, the spectral characteristics of SOM will be analyzed using NMR or FT-IR (high intensities of functional groups such as carboxylic and phenolic indicate SOM enrichment). At this stage, C gained in the vegetation, detritus, and losses in soil respiration will be quantified and this will enable the calculation of net change in ecosystem C storage. To be able to determine the rates of detrital biomass C turnover, litter decomposition rates will be quantified. Detrital quality for all ages of tree stands will be determined by analyzing lignin content, C:N ratio, lignin : N ratio, content of polyphenol and tannin of root and aboveground litter. This will enable the assessment of the relationship between lignin content (and other litter variables) and soil C residence time. CO2 emission will be measured throughout the study period using portable respiration chambers. Based on the inputs and outputs of C into and out of the system and compared with what was in the soil before stand establishment, the transition of the stands from being a net source to neutral or a net sink of C will be calculated.