Processes affecting carbon storage in the forest floor and in downed woody debris

Many forests differ from other types of ecosystems, such as grasslands or rangelands, in that they develop a thick horizon of decaying organic matter, together with highly heterogeneous accumulations of woody debris, on the soil surface. Particularly in temperate and boreal forests, foliar, root, and woody litter accumulate in all stages of decomposition from fresh litter to material that is highly decayed and partly stabilized. As litter decays, organic carbon in the surface organic horizon has several fates: some is mineralized to CO₂ through biotic respiration, some is stabilized and remains in place to form a humus layer, and some is converted to soluble decomposition intermediates and transported via soil solution to deeper soil horizons. The characteristics of the surface organic horizon (O horizon), or forest floor, depend on temperature and rainfall regimes, litter production rates, litter quality, and soil microbial and animal activities. Litter quality is determined largely by the tree species present, which in turn depend on elevation, climate, and land-use history.