Dynamics of organic matter accumulation and decomposition in the surface soil of forestry-drained peatland sites in Finland

We studied organic matter accumulation dynamics in peatland surface soil, using the root collar depth of tree-ring aged Scots pine seedlings for dating the base level of quantitative soil samples. The data consisted of 222 samples collected from 47 forestry-drained and four undrained locations. At the drained sites, the data indicated an average dry biomass accumulation of about 4 kg m−2 in samples representing the past 30 years. Despite great variance in the data, the results clearly indicate decreasing per annum accumulation values with increasing sample age, thus implying rapid decomposition of the fresh litter. Derived from the age-mass relationship we can estimate that about 95% of 1 year’s litter input will be decomposed during 30 years. High decomposition rate of the litter suggests that drained peatland forest soils do not act as a carbon sink. The average detritus accumulation values were somewhat higher on the undrained control sites than on the drained sites. Among the forestry-drained sites, the average accumulation was significantly lower in sites with timber volumes exceeding 200 m3 ha−1, as compared with sites with timber volumes <100 m3 ha−1, suggesting a connection between tree stock and litter decomposition rate.

► Litter accumulation of forestry-drained peatlands by root collar depth.
► Only 4 kg m2 of dry litter accumulated during the past 30 years on drained sites.
► About 95% of 1 year’s litter input will be decomposed during 30 years.