On 542 sites established by the USFS’ Forest Inventory Analysis (FIA), we used structural equation models to investigate the effects of climate, soil conditions and forest composition on MSC and FFC pools in the temperate forests of the Northeast. Forest diversity effects were measured through phylogenetic diversity, functional trait dispersion and community weighted mean trait values of 11 functional traits. We assessed (1) which group of variables (climate, soil or forest conditions) had the largest relative effect on MSC and FFC, and (2) the strength of FFC as a driver of MSC. We expected FFC would be more driven by climate and forest conditions, while MSC would be more impacted by climate and soil conditions.
Results/Conclusions: Forest floor carbon showed a strong link to climatic conditions and litter quality as represented by the community weighted mean percent nitrogen per leaf mass. Mineral soil carbon was controlled predominantly by soil nutrient content of nitrogen and iron, with relatively small effects from climate, landscape drainage, and community weighted mean of wood density. In contrast to our expectations, the pathway between forest floor C and mineral soil C is poorly supported across the northern hardwoods with only 7.7% of the variation in mineral soil C explained by forest floor carbon. The perception of aboveground litter decomposition as a predominant route to stable SOC requires further study with particular focus on belowground plant traits, root-C allocation, and belowground decomposition.