Submitted to: Canadian Journal of Forest Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/22/1997
Publication Date: N/A
Citation: Interpretive Summary: Accumulation of C in a forest soil is derived from litter fall and root input while losses are the result of microbial degradation of organic matter, eluviation, solution losses and erosion. In an old-growth forest, soil C is thought to be in dynamic equilibrium between accumulation and loss. As forest ecosystems mature they accumulate soil C to a maximum carrying potential, which is controlled by climate, topography, soil type and vegetation. Therefore, at equilibrium the amount of C added to the soil via vegetation is equal to the amount of C lost through organic matter degradation and other losses. Our data show that as forests mature, significantly more C in both the L, F and H layers and in organic material in the top 10 cm of mineral soil is stored in a more recalcitrant form. In old-growth forests, not only is there more C stored in the soil, but significantly more C is stored in a recalcitrant form (lignin) in young-growth forests. Forests soils have been estimated to contain approximately 60% of the C contained in terrestrial ecosystems. Greater percentages of recalcitrant compounds (lignin) in organic matter of old- and second- growth soils should result in slower organic matter decomposition and C turnover rates in the L, F and H layers and in the organic material in the 0-10 cm of mineral soils in forests throughout the temperate region.
Technical Abstract: The amount and type of carbon C in a forest soil reflects the past balance between C accumulation and loss. In an old-growth forest soil, C is thought to be in dynamic equilibrium between accumulations and losses. Disturbance upsets this equilibrium by altering the microclimate, the amount and type of vegetation growing on a site and properties that affect organic matter decomposition. We measured total C and forms of soil C in the L, F and H layers and in the light fraction of soil organic matter in the 0-10 cm of mineral soil in old-, second- and young-growth Douglas-fir soils in the Oregon Coast Range. Total C in L, F and H layers and in organic material in the top 10 cm of mineral soil in old-growth forests was higher than in young- or second-growth forests. Old-growth forests had a higher lignin concentration and lower concentrations of sugar, hemicellulose, and cellulose in the L, F and H layers and in the light fraction of organic material than second- or young-growth forests. Old-growth forests had greater amounts of FWO, sugar, cellulose and lignin, in the L, F and H layers and greater amounts of hemicellulose, cellulose and lignin in the light fraction of organic matter in the 0-10 cm of mineral soil than young- and second- growth forests. Concentrations of fats, waxes, and oils (FWO), sugar and tannin in the light fraction of organic matter in the 0-10 cm of mineral soil did not differ with forest age.