Stocks and dynamics of soil organic carbon and coarse woody debris in three managed and unmanaged temperate forests
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The effect of forest conservation on the organic carbon (C) stock of temperate forest soils is hardly investigated. Coarse woody debris (CWD) represents an important C reservoir in unmanaged forests and potential source of C input to soils. Here, we compared aboveground CWD and soil C stocks at the stand level of three unmanaged and three adjacent managed forests in different geological and climatic regions of Bavaria, Germany. CWD accumulated over 40–100 years and yielded C stocks of 11 Mg C ha−1 in the unmanaged spruce forest and 23 and 30 Mg C ha−1 in the two unmanaged beech–oak forests. C stocks of the organic layer were smaller in the beech–oak forests (8 and 19 Mg C ha−1) and greater in the spruce forest (36 Mg C ha−1) than the C stock of CWD. Elevated aboveground CWD stocks did not coincide with greater C stocks in the organic layers and the mineral soils of the unmanaged forests. However, radiocarbon signatures of the O e and O a horizons differed among unmanaged and managed beech–oak forests. We attributed these differences to partly faster turnover of organic C, stimulated by greater CWD input in the unmanaged forest. Alternatively, the slower turnover of organic C in the managed forests resulted from lower litter quality following thinning or different tree species composition. Radiocarbon signatures of water-extractable dissolved organic carbon (DOC) from the top mineral soils point to CWD as potent DOC source. Our results suggest that 40–100 years of forest protection is too short to generate significant changes in C stocks and radiocarbon signatures of forest soils at the stand level.
KeywordsForest management Forest conservation Carbon stock Coarse woody debris Forest soil Organic layer Radiocarbon Soil organic carbon
We thank Helga Hertel-Kolb, Uwe Hell, Petra Eckert and Oliver Beyer for their help in the field and with sample preparation. We express our gratitude to the members of the Central Analytical Department of the Bayreuth Centre of Ecology and Environmental Research (BayCEER) for chemical analysis, the forest rangers responsible for the investigated forests for providing forest records and additional information on the study sites and Alfred Schubert of the LWF in Freising for providing material and advice on soil sampling. The study was funded by the Bavarian Ministry for Nutrition, Agriculture and Forestry.
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